Tectonic evolution of the Malay Peninsula inferred from ... - UM Expert

Journal of Asian Earth Sciences 134 (2017) 130–149

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Tectonic evolution of the Malay Peninsula inferred from Jurassic to Cretaceous paleomagnetic results Yo-ichiro Otofuji a,⇑, Yuji T. Moriyama a, Maiko P. Arita a, Masanari Miyazaki a, Kosuke Tsumura a, Yutaka Yoshimura a, Mustaffa Kamal Shuib b, Masatoshi Sone b, Masako Miki a, Koji Uno c, Yutaka Wada d, Haider Zaman e a

Department of Earth and Planetary Sciences, Faculty of Science, Kobe University, Kobe 657-8501, Japan Department of Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia c Graduate School of Education, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan d Department of Earth Sciences, Nara University of Education, Nara, Japan e Department of Geology, Faculty of Science, Taibah University, Madinah 41477, Saudi Arabia b

a r t i c l e

i n f o

Article history: Received 17 June 2016 Received in revised form 7 October 2016 Accepted 13 October 2016 Available online 14 October 2016 Keywords: Paleomagnetism Jurassic to Cretaceous Red beds Malay Peninsula Indian continent Australian continent

a b s t r a c t A primary remanent magnetization is identified in the Jurassic-Cretaceous red bed sandstones of the Tembeling Group in Peninsular Malaysia. This high-temperature magnetic component is unblocked at 680–690 °C, revealing a clockwise deflected direction of Ds = 56.8°, Is = 31.6° (where ks = 8.5, a95 = 11.3° and N = 22) in stratigraphic coordinates. The primary origin of this component is ascertained by a positive fold test and a geomagnetic polarity reversal in the Kuala Wau section. Secondary remanent magnetizations are identified in the rocks of the Tembeling and Bertangga basins, which indicate a counterclockwise deflection in the geographic coordinates (Dg = 349.1°, Ig = 15.3° where kg = 11.8, a95 = 5.1°, N = 72). The comparison with the expected paleomagnetic directions from the 130 Ma and 40 Ma Eurasian poles indicates two-stages of tectonic movement in the southern Malay Peninsula: (1) a clockwise rotation of 61.1° ± 11.9° accompanied by a 13.3° ± 8.1° southward displacement after the Cretaceous; and (2) a subsequent counter-clockwise rotation of 18.5° ± 5.0° to the present day position. The first stage of rotation is ascribed to tectonic deformation caused by the indentation of India into Asia after 55 Ma, while the second stage is attributed to the collision of the Australian Plate with SE Asia after 30–20 Ma. The present paleomagnetic results from the Jurassic-Cretaceous Tembeling Group thus reveal impacts of both of these collisions on SE Asia in general and on Peninsular Malaysia in particular. Ó 2016 Elsevier Ltd. All rights reserved.

1. Introduction The India-Asia collision marks one of the most important tectonic episodes that occurred on the meso-Cenozoic Earth. This event gave rise tectonic deformation on Southeast (SE) Asia (Fig. 1). The three-decade-old ‘‘extrusion” model proposed by Tapponnier and colleagues (Tapponnier et al., 1982; Peltzer and Tapponnier, 1988; Replumaz and Tapponnier, 2003) has proved highly influential in explaining the subsequent regional-scale deformation pattern for the Asian continent. Based on analogue models, they envisaged that India’s indentation into Asia induced clockwise (CW) and the south-eastward displacement to mainland SE Asia and its offshore extension, ‘‘Sundaland” (Borneo, Java Sumatra) from the main part of the continent. It is clear from ⇑ Corresponding author. E-mail address: [email protected] (Y.-i. Otofuji). http://dx.doi.org/10.1016/j.jseaes.2016.10.007 1367-9120/Ó 2016 Elsevier Ltd. All rights reserved.

paleomagnetic and geological data that the near-field areas of Indochina have moved in the manner described by Tapponnier et al. (1982) (Fig. 1) e.g., CW rotation (Yang and Besse, 1993; Aihara et al., 2007; Tanaka et al., 2008; Takemoto et al., 2009; Otofuji et al., 2010, 2012; Kornfeld et al., 2014) and the southeastward displacement of SE Asia (Leloup et al., 1995; Ali et al., 2010; Sato et al., 2011; Cogné et al., 2013; Tsuchiyama et al., 2016). The southern part of Sundaland, however, does not fit this pattern. For instance, paleomagnetic declinations from Cenozoic rocks from Peninsular Malaysia, Borneo, western Sulawesi and Celebes Sea indicate counter-clockwise (CCW) (Fig. 1) rather than CW, rotations. (Haile et al., 1977; Haile, 1978; Sasajima et al., 1980; Schmidtke et al., 1990; Shibuya et al., 1991; Fuller et al., 1999; Richter et al., 1999). Moreover latitudinal motions are thought to be negligible (Fuller et al., 1999). Furthermore, Clift et al. (2008) suggest that a plate boundary may tectonically decouple mainland SE Asia from large portions of Sundaland.

Y.-i. Otofuji et al. / Journal of Asian Earth Sciences 134 (2017) 130–149

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Fig. 1. Structural sketch map, and tectonic subdivision of the modern Sunda block and surrounding regions (modified from Morley (2012), Hall (2012) and Metcalfe (2013)). Base map from the ETOPO2 Shuttle Radar Topography Mission (SRTM) image. The Sunda block (s.l.) consists mainly of the Indochina (IC), Sukhothai (SK), Shan-Thai (ST), East Malaya (EM), West Sumatra (WS), Southwest Borneo basement (SB), and Luconia (LC) blocks. Other blocks include the: South China (SC) and West Burma (WB). The faults or tectonic lines include the: Red River fault (RRF), East Vietnam Boundary fault (EVBF), Wang Chao fault (WF), Sagaing fault (SF), Three Pagodas fault (TPF), Ranong fault (RF), Khlong Marui fault (KF), Great Sumatran fault (GSF), Philippine fault (PF), and West Baram line (WBL). Half arrows indicate directions of strike-slip fault movement; white (or red) half arrows for ductile (or brittle) shear sense. Black arrows with dot ends indicate the observed declinations of the late Mesozoic–Cenozoic rocks in each area (Extended data Table 3); closed (or open) arrows indicate data from primary (or secondary) remanent magnetizations. Abbreviations attached to the arrows are based on locations of palaeomagnetic studies, as referred to in Table 3. T = study area. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

The aim of this study is therefore to deduce the location of this cryptic tectonic feature by identifying areas within the Malay Peninsula with distinctive palaeomagnetic histories (based on their vertical axis rotations and/or latitudinal motion histories). A CCW tectonic rotation of the Malay Peninsula is predicted by Richter et al. (1999), although their interpretation is based only on secondary magnetization found in rocks of the Jurassic-Cretaceous Tembeling Group from Peninsular Malaysia. Hence, a discovery of primary remanent magnetization from the area is required to confirm the predicted phenomenon of CCW rotation. 2. Geological setting SE Asia is a complex collage of continental fragments, consisting mainly of Indochina, Sukhothai and Sibumasu (including the Intha-

non zone) blocks from east to west (Metcalfe, 2011; Morley, 2012; Sone et al., 2012) (Fig. 1). These blocks accreted to the southeastern margin of the proto-Asian continent by the Late Triassic after breaking from Gondwanaland and drifting northward. In the present-day tectonic framework SE Asia is bounded by the Indian-Australian Plate to the west and the Philippine Sea Plate to the east. Peninsular Malaysia is divided into three north-south extended geological belts; the western, central and eastern belts (Fig. 2a). The central and eastern belts are regarded as parts of a single tectonic block (the East Malaya Block) derived from Gondwana in the Devonian. In contrast, the western belt forms part of the Sibumasu Block, which was also derived from Gondwana later in the Permian. The western belt and the East Malaya Block collided with each other along the Bentong-Raub suture zone in the Late Triassic (Ng et al., 2015).

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Fig. 2. (a) Tectonic subdivision of the Malay Peninsula. (b) Paleomagnetic sampling sites are marked by closed circles. Red-colored closed circles show locations where CW deflected declinations were observed. Magnetostratigraphic studies were conducted on the samples from the Kuala Tahan road and Kuala Wau sections. The numbered sampling sites refer to the site names (e.g. 34 = MY34). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

After the deposition of marine sediments in the Triassic (e.g., the Semantan Formation) the red bed clastic sediments (most importantly the Tembeling Group) were deposited in the Jurassic to Cretaceous (JK). These JK red beds are separated by an angular unconformity from older sequences in Peninsular Malaysia (Tjia, 1996; Abdullah, 2009). According to Khoo (1977), the basal part of the Tembeling Group is characterized by volcaniclastic sediments of the Kerum Formation (including lava and pyroclastics) and the upper part is dominated by red colored rocks such as the Manking Sandstone and Termus Shale. The distribution of red beds appears to be most common in the eastern half of the central belt (Fig. 2b). Voluminous sediments characterized by red, ferric-rich siliciclastics were deposited in the fluvial and lacustrine basins, including the Tembeling and Bertangga basins. These deposition centers are interpreted as having been developed as pull-apart depressions due to dextral strike-slip motion along the N-S trending faults (Tjia, 1996). Based on the occurrences of plant fossils (Gleichenoides pantiensis, Gleichenoides gagauensis, and Frenelopsis malaiana) and palynomorphs (Classopollis Classoides, Exesipollenite, Clavatipollennites, and Cycadopite), the Tembeling Group has been placed in the Jurassic to Early Cretaceous period (Abdullah, 2009). This group is interpreted as having undergone two phases of deformation in the Cretaceous and Eocene (Hutchison, 1993; Tjia, 1996), although the exact timings and mechanisms of such deformations remain unresolved (Morley, 2012). The final folding in the area probably developed during the Eocene phase of the dextral deformation.

3. Paleomagnetic sampling Paleomagnetic samples were collected during three field visits at different localities in the Tembeling and Bertangga basins, the central part of Peninsular Malaysia. After selecting the most suitable rock types for the paleomagnetic investigation during the first field trip in 2011, dark to red-colored sandstones were sampled from a wider area in 2013. Fig. 2b shows 90 sampling sites, which are distributed in an area extending from the upper Tembeling River north of Kuala Tahan (4.52°N, 102.51°E) to the Tekai River and to Maran and Kuala Wau in the south (3.48°N, 102.78°E). Except for the basal volcanic site of MY34, all of the collected samples are dark to red-colored sandstones. During the third field trip in 2014, we exclusively focused on the two localities (Fig. 2b) in which the CW deflected declinations were discovered at four sites in our reconnaissance studies. We selected two magnetostratigraphic sections for sampling; one along the Kuala Tahan road in the Tembeling Basin (4.23°N, 102.40°E) where 18 layers with 1110 m in total thickness were sampled (MY51, MY 50, MY71– MY87) and another one in front of the Kuala Wau school in the Bertangga Basin (3.48°N, 102.78°E) where 17 layers with183 m in total thickness were sampled (MY26, MY88–MY99, MK01, MY02). The bedding in the first section shows a structural dip of 26–79° eastward. The almost continuous strata of the second section with fine-grained lithology have a structural dip of 28–48° southwestward.


Up to 11 block samples oriented with the magnetic compass were collected from each site. No declination correction was conducted because the International Geomagnetic Reference Field (International Association of Geomagnetism and Aeronomy Working Group V-MOD, 2010) indicates an almost 0° declination in the study area. 4. Paleomagnetism 4.1. Laboratory procedures Cylindrical samples with a diameter of 2.5 cm were cored from each hand sample and cut into 2.2 cm long specimens in the laboratory. Natural remanent magnetizations (NRMs) of the selected specimens were measured in the magnetically shielded laboratory of Kyoto University, using a 2G Enterprises three-axis cryogenic magnetometer (model 760R). To monitor the chemical changes of the magnetic mineralogy during the thermal treatment, the magnetic susceptibility was measured after each heating step using a Bartington MS2 susceptibility meter. The specimens were subjected to progressive thermal demagnetization (ThD) in 13 heating steps up to 590 °C or in 18 steps up to a maximum of 690 °C using two custom-built thermal demagnetizers. The internal field for each instrument was less than 8 nT at a sampleheated position. The demagnetization data for each sample were plotted on orthogonal vector diagrams (Zijderveld, 1967) and equal-area projections. The paleomagnetic directions were determined by principal component analysis (Kirschvink, 1980). Sitemean and formation-mean directions were calculated using the statistics of Fisher (1953). 4.2. Thermal demagnetization results The samples of 90 sites from the Tembeling and Bertangga basins show initial NRM intensities in the range of 2.0 103 to 608 103 A/m (Table 1). The highest NRM intensity is observed in the basaltic samples of site MY34. When demagnetized by stepwise ThD, an abrupt decrease in the NRM intensities at 100 °C is observed in samples from 8 sites, indicating the presence of goethite (Table 1). After the removal of the goethite-related component, the thermal demagnetization behaviors of the samples was characterized using a number of magnetization components in NRM and the unblocking temperature (Tub) of the highest magnetic component. Three types of magnetic components (single, two and three NRM components) were identified in the samples (Figs. 3 and 4). The Tub in each sample is divided into three categories (I–III). The categories I, II, and III have a Tub between 580 °C and 620 °C, 620 °C and 670 °C, and 680 °C and 690 °C, respectively. The number of magnetization components and categories of the Tub are shown in Table 1 and in each demagnetization diagram (Figs. 3 and 4). The single NRM component is observed in seven sites. The samples of three sites are in category II (Fig. 4a, h), three sites consist of samples of categories II and III (Fig. 4‘), and the remaining site is of category III. In the case of the samples with two NRM components, the high-temperature component (HTC) appears after the lowtemperature component (LTC) is unblocked at 300–350 °C. Three sites are in the category I, 18 sites belong to the category II (Fig. 4b, c, f), 19 sites consist of samples of the categories II and III (Fig. 4e, g, i, k), and the remaining 9 sites are in category III (Figs. 3c and 4d). For sites with three components, the mediumtemperature component (MTC) appears above 300–350 °C before unblocking at 590 °C or 650–670 °C. The HTC follows. Samples of two sites are in category II. Two sites consist of samples in the categories II and III (Fig. 3a, b), while samples of the remaining 28 sites

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belong to the category III (Figs. 3d–j and 4j). NRM of the samples in category I is mainly carried by magnetite, whereas hematite is probably the carrier of NRM of the samples in the categories II and III. 4.3. The NRM directions Three NRM directions, corresponding to LTC, MTC and HTC, are recognized in the studied samples. The NRM directions of MTC and HTC carried by hematite are divided into two groups (Fig. 5). One, named the CW-deflected group, is characterized by CW-deflected declinations (Fig. 5a). The other, named the CCW-deflected group, is characterized by CCW-deflected declinations (Fig. 5b). 4.3.1. LTC magnetization The LTC is identified in 40 sites from the Tembeling Basin and 24 sites from the Bertangga Basin. After these site-mean directions are recalculated as values at the representative study area point (102.5°E, 4.0°N), a formation-mean direction in the geographic coordinate system is obtained as Dg = 355.7°, Ig = 10.0°, kg = 36.3, and a95 = 3.0° (N = 64) (Table 2), which is nearly parallel to the axial dipole field direction (D = 0°, I = 8.0°) in the study area. Fold tests of McElhinny (1964) and McFadden (1990) proved negative, indicating acquisition as VRM during the Brunhes chron. A Tub of 350 °C for the LTC could be attributed to the approximately one million years relaxation time of hematite (Pullaiah et al., 1975), during which a record of the axial geocentric dipole field was acquired at ambient temperatures. 4.3.2. CW-deflected group CW deflected declinations are identified in the HTC in the Kuala Tahan and Kuala Wau stratigraphic sections and at site MY34 (Figs. 3 and 5a). Almost all samples of the CW-deflected group belong to category III (Tub = 680–690 °C) besides samples from site MY34 (Tub = 620–680 °C) (Table 1). Reversed polarity directions are observed in the samples from site MY34 (Ds = 255.4°, Is = 22.0°, and a95 = 13.6°) and the Kuala Tahan road section, dual polarities are identified in the samples from the Kuala Wau section. The NRM directions in the Kuala Tahan road section are characterized by reversed polarity directions with large westerly deflected declinations (between 210.7° and 283.9°) with respect to the south throughout the magnetostratigraphic column (Fig. 6a). Only two successive layers reveal positive inclinations of Is = 25.7° and 19.0°. KY82 and KY81. The reversed polarity directions in the remaining 10 layers give a mean inclination of 17.6° ± 8.4°. The comparison with the positive inclinations from the two layers indicates a deviation of more than 43°. The HTC directions with normal inclination from two layers may be ascribed to an anomalous geomagnetic field direction at the time of the excursion. Excluding the data of geomagnetic excursion, the locality mean-direction after tilt correction (Ds = 248.3°, Is = 19.6°, ks = 8.4, a95 = 17.7°, N = 10) is obtained for the samples from the Kuala Tahan road section. The NRMs in the Kuala Wau section both exhibit CW deflected directions (Fig. 6b). One is easterly-deflected from the north with normal polarity and the other is westerly deflected from the south with reversed polarity. The polarity change from reverse to normal polarity occurs in stratigraphic order. Five of the studied layers (MY89-MY92) show reversed polarity directions, where the inclination varies between 12.5° and 51.7° and the declination ranges between 227.7° and 254.4°. A well-defined polarity change is observed in the strata between MY89 and MY99. In the zone of the polarity change (between MY93 and MY96), variable inclinations (e.g., MY93, MY95 and MY96) with large dispersion in the NRM directions are observed. The normal polarity direction is then observed from MY97 to MY26, where the inclination and declination vary between 25.4° and 59.5° and 11.2° and 33.4°,

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Table 1 Palaeomagnetic results of the Jurassic-Cretaceous red beds from the Tembeling Group. Sampling site

Latitude

Longitude

Number of components

Tub (°C)

Category

n

In situ

Tilt corrected

k

a95 (°)

Dec. (°)

Inc. (°)

Dec. (°)

Inc. (°)

8

269.2

44.2

255.4

22.0

17.5

13.6

III III III III III III III

6 7 6 3 7 7 7

171.7 207.2 288.8 302.9 304.9 223.1 316.1

45.0 57.9 64.3 63.6 56.6 48.8 69.3

210.7 229.2 274.7 282.2 283.9 238.0 280.2

1.5 14.8 21.2 22.6 16.5 10.3 25.7

16.4 23.7 30.7 16.2 68.8 148.9 24.0

17.0 12.7 12.3 31.7 7.3 5.0 12.6

690 690

III III

6 6

186.8 237.6

49.2 60.5

222.4 225.3

28.8 24.4

13.2 20.6

19.1 15.1

690 690 690 690

III III III III

8 5 7 8

226.4 269.5 296.2 236.7

14.3 31.3 27.9 47.8

225.1 269.5 282.0 238.8

19.0 25.7 10.8 21.9

10.3 10.4 19.2 13.2

18.1 24.9 14.1 17.3

10

242.6

62.9 248.3

19.6

7.4 8.4

19.1 17.7

(A) CW-deflected group [Kuala Tahan] MY34(lava)

04°300 53.900

102°300 44.5300

3

620–680

II, III

[Kuala Tahan road section] MY86 MY76 MY50 ⁄MY75 MY74 MY73 MY71

04°140 28.300 04°130 44.100 04°130 44.000 04°130 44.100 04°130 44.100 04°130 44.100 04°130 44.100

102°240 11.300 102°230 49.600 102°230 50.300 102°230 49.600 102°230 49.600 102°230 49.600 102°230 49.600

3 3 2 2 3 3 3

690 690 690 690 690 690 690

MY51 MY77

04°130 44.200 04°130 44.000

102°230 44.000 102°230 43.900

2 3

#MY81 #⁄MY82 MY83 MY84

04°130 45.300 04°130 47.300 04°130 48.900 04°130 45.300

102°230 40.900 102°230 39.500 102°230 35.200 102°230 33.400

3 3 3 3

Mean

04.23°

102.40°

[Kuala Wau section] MY26 MK02 MK01

03°280 54.200 03°280 54.000 03°280 54.000

102°470 00.700 102°470 00.900 102°470 00.900

2 3 3

690 690 690

III III III

6 7 7

37.8 24.7 32.1

5.0 0.3 3.0

28.8 18.1 20.3

42.6 25.4 35.9

58.8 80.1 21.6

8.8 6.8 13.3

MY99 MY98 MY97 ⁄MY96 ⁄MY95 MY94 ⁄MY93 MY92 MY66 MY91 MY90 ⁄MY89

03°280 56.600 03°280 56.600 03°280 56.600 03°280 56.600 03°280 56.600 03°280 57.700 03°280 57.700 03°280 57.700 03°280 57.500 03°280 57.700 03°280 58.100 03°280 58.100

102°470 06.000 102°470 06.000 102°470 06.000 102°470 06.000 102°470 06.000 102°470 07.000 102°470 07.000 102°470 07.000 102°470 07.100 102°470 07.000 102°470 07.400 102°470 07.400

3 3 3 3 3 3 3 3 3 3 3 3

680 690 680 680 690 690 690 690 690 690 680 680

III III III III III III III III III III III III

7 7 5 4 6 8 3 6 10 8 8 6

41.0 42.7 33.7 359.6 285.3 237.6 245.7 230.1 245.4 246.0 235.9 256.9

1.6 7.7 8.8 12.3 22.2 0.2 51.1 4.9 10.9 5.8 2.4 25.2

33.4 30.4 11.2 343.6 273.8 245.0 239.9 227.7 245.4 247.7 237.7 254.4

43.5 59.5 54.5 31.9 3.6 42.5 10.0 51.7 17.0 30.5 30.9 12.5

16.2 94.9 17.0 3.0 2.1 60.5 2.9 159.3 37.5 8.6 181.6 5.0

15.4 6.2 19.1 64.9 61.5 7.2 91.9 5.3 8.0 20.0 4.1 33.5

Mean

03.48°

102.78°

11

46.1

0.1 41.9

41.3

29.1 15.5

8.5 12.0

(B) CCW-deflected group [1] HTC with Tub of 620–690 (°C) [Tembeling Basin] MY19 MY17 MY18 MY33

04°310 04.100 04°310 04.000 04°310 04.000 04°300 49.600

102°290 14.900 102°290 14.100 102°290 14.100 102°300 43.900

2 1 2 2

590–690 620–670 680–690 650–670

II, III II III II

4 6 4 9

8.3 354.3 358.0 335.3

4.4 18.9 9.9 13.6

355.6 336.5 0.3 328.4

11.7 28.0 3.0 13.4

57.0 23.9 34.1 37.2

12.3 14.0 16.0 8.5

⁄MY31 MY37 MY38 MY36 MY35 MY05 MY06 MY40 MY14 ⁄MY39 MY07 MY13

04°300 20.100 04°260 42.400 04°260 42.400 04°260 39.200 04°260 37.100 04°250 55.900 04°250 55.400 04°250 53.300 04°250 53.300 04°250 51.000 04°250 05.400 04°240 35.000

102°310 54.000 102°270 58.400 102°270 58.400 102°280 02.300 102°280 04.800 102°230 04.600 102°230 02.700 102°270 43.300 102°270 44.100 102°270 49.200 102°230 40.900 102°260 05.900

2 2 2 2 1 2(G) 2 1 2(G) 2 2(G) 2

670–680 620–690 650–680 620–690 670–680 680–690 650–680 670–680 650 650–680 620–680 620–650

II, III II, III II, III II, III II, III III II, III II, III II II, III II, III II

5 7 9 8 6 5 4 9 4 11 6 5

25.0 2.6 348.7 343.7 330.1 330.5 317.3 341.1 2.5 305.1 351.0 1.3

16.1 9.3 5.9 24.8 25.3 28.1 27.1 4.0 2.0 36.0 5.1 6.4

353.4 12.2 353.7 351.5 277.2 339.4 316.6 333.1 344.6 5.3 341.4 0.7

37.9 39.4 40.3 45.8 41.5 10.6 25.5 31.3 52.2 25.9 23.5 3.4

2.6 11.5 156.3 82.2 32.3 56.0 203.4 142.4 63.1 4.3 21.5 284.4

71.2 18.6 4.1 6.1 12.0 10.3 6.5 4.3 11.7 25.0 14.8 4.4

MY47 MY48 MY46 MY49 MY45 MY44 MY43 MY41 MY42

04°160 23.900 04°160 07.700 04°150 34.200 04°140 34.500 04°140 26.500 04°140 24.200 04°110 03.200 04°100 36.200 04°100 21.400

102°220 47.4.00 102°240 46.800 102°230 28.7.00 102°240 11.800 102°250 22.000 102°250 21.400 102°320 00.300 102°330 33.200 102°330 19.100

2 2 2 2 2 2 2 1 2

670–690 650–680 680–690 650–680 670–690 670–680 650–690 680–690 680–690

II, III II, III III II, III II, III II, III II, III III III

11 7 8 6 8 7 9 8 8

327.1 22.1 313.9 332.2 341.9 333.1 336.1 0.2 17.1

18.4 9.7 36.5 15.1 6.4 14.3 34.4 1.0 23.3

314.5 36.6 322.4 354.9 355.7 347.4 330.5 352.5 30.0

14.5 43.9 3.8 12.6 12.4 49.8 20.1 8.3 3.1

67.2 14.0 12.0 74.7 160.1 125.2 277.4 165.0 118.1

5.6 16.7 16.6 7.8 4.4 5.4 3.1 4.3 5.1

MY56 MY59 MY60

03°570 19.400 03°570 16.800 03°570 16.800

102°260 35.900 102°260 30.900 102°260 30.900

1 2 2

620 620–650 670

II II II

6 7 7

1.3 359.8 348.3

2.8 10.6 17.9

357.7 2.5 1.0

9.6 4.5 8.7

273.9 61.5 83.0

4.1 7.8 6.7

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Y.-i. Otofuji et al. / Journal of Asian Earth Sciences 134 (2017) 130–149 Table 1 (continued) Sampling site

Latitude

Longitude

MY01 MY02 MY57 MY58 MY52 ⁄MY55

03°570 14.500 03°570 14.500 03°570 12.400 03°560 59.800 03°560 59.200 03°560 41.600

102°260 33.500 102°260 33.500 102°260 32.600 102°260 31.000 102°260 45.500 102°260 37.600

Mean

4.52°

102.49°

[Bertangga Basin] ⁄MY65(mud) ⁄MY65(sand) MY61 MY62 MY63 MY20 MY21 MY22 MY23 MY24 MY69 MY68 MY67 MY28 MK03 MK04

03°340 09.100 03°340 09.100 03°330 48.600 03°330 48.600 03°330 48.600 03°330 29.900 03°330 29.900 03°320 27.600 03°300 36.400 03°300 34.700 03°290 35.900 03°290 33.800 03°290 19.900 03°290 01.500 03°280 54.000 03°250 52.900

102°420 41.500 102°420 41.500 102°460 04.600 102°460 04.600 102°460 04.600 102°410 51.100 102°410 51.100 102°370 31.600 102°420 48.000 102°420 59.900 102°440 19.100 102°440 23.500 102°460 29.600 102°510 08.500 102°470 00.900 102°450 44.700

Mean

03.56°

102.77°

[2] MTC with Tub of 650–670 (°C) [Kuala Tahan-Jerantut road section] MY86 MY87 MY76 ⁄MY50 MY75 MY74 MY73 ⁄MY72 MY71 MY80 MY79 ⁄MY51 MY78 MY77 MY81 MY82 MY83 MY84

04°140 28.300 04°140 23.000 04°130 44.100 04°130 44.000 04°130 44.100 04°130 44.100 04°130 44.100 04°130 44.100 04°130 44.100 04°130 44.000 04°130 44.000 04°130 44.200 04°130 44.000 04°130 44.000 04°130 45.300 04°130 47.300 04°130 48.900 04°130 45.300

102°240 11.300 102°240 09.700 102°230 49.600 102°230 50.300 102°230 49.600 102°230 49.600 102°230 49.600 102°230 49.600 102°230 49.600 102°230 43.900 102°230 43.900 102°230 44.000 102°230 43.900 102°230 43.900 102°230 40.900 102°230 39.500 102°230 35.200 102°230 33.400

Mean

04.23°

102.40°


Tub (°C)

2(G) 3(G) 2 2 2 2

620 620–650 650 650 650–680 650–670

2 3 2 3 2 3 2 1(G) 2(G) 2(G) 2 1 3 2 3 2

2

3 2 2 2

620–670 620–670 670–680 690 650–690 680 670 670 670 670–680 620–650 670–680 670–690 670–690 690 690

670 650 660 650 650 650 650 670 650 660 670 670 670 660 660 650 660 670

Category

II II II II II, III II

II II II, III III II, III III II II II II, III II II, III II, III II, III III III

II

III II II II

n

In situ

k

a95 (°)

5.4 3.2 7.6 4.3 9.5 15.2

51.3 31.5 35.3 65.4 67.1 8.4

13.0 13.9 10.3 7.5 9.4 28.1

348.8

13.6

16.7 7.9

6.5 9.8

330.1 313.7 5.5 356.4 13.7 329.5 339.0 6.4 7.1 0.3 354.3 347.2 16.7 183.8 341.5 293.4

18.2 36.1 20.8 26.5 20.4 13.3 17.4 9.0 3.4 0.0 40.4 28.3 30.5 19.9 13.4 77.1

5.0 6.9 81.6 20.8 38.0 56.3 230.2 125.9 39.6 180.9 152.3 366.0 9.4 121.5 44.7 79.9

45.7 27.4 5.7 13.5 9.9 16.5 6.1 6.0 19.8 5.0 4.9 2.9 16.7 11.2 8.4 6.2

354.6

22.2

5.3 4.2

19.1 24.0

359.9 11.6 1.5 342.1 11.1 4.6 7.2 9.2 14.6 3.4 10.7 326.9 0.5 11.9 8.9 12.3 31.5 8.9

13.5 30.9 3.4 8.6 22.5 18.1 18.6 7.9 21.6 31.6 11.5 1.8 7.9 24.6 20.5 23.7 17.2 23.9

46.1 123.1 320.6 10.0 141.2 33.5 52.4 8.0 197.3 101.0 10.6 10.3 156.1 83.5 21.8 119.9 14.7 28.6

8.2 6.9 3.4 20.1 4.7 10.6 8.4 20.8 4.3 6 19.4 21.9 4.8 6.6 12.1 7.0 14.9 11.5

9.2

16.7

20.6 28.5

8.6 7.3

Tilt corrected

Dec. (°)

Inc. (°)

Dec. (°)

Inc. (°)

4 5 7 7 5 5

350.3 352.9 345.1 357.0 344.8 343.1

8.0 3.1 6.3 13.9 14.5 0.2

357 356.9 352.5 1.8 350.1 349.5

31

348.5

11.8

4 6 9 7 7 3 4 6 3 6 7 8 10 3 8 8

332.3 325.2 355.5 344.7 3.0 327.7 335.4 3.8 7.1 359.5 349.1 348.3 9.9 183.3 351.7 18.7

4.6 17.3 20.5 21.7 23.8 0.1 6.5 6.0 2.9 2.9 6.2 4.6 13.2 4.1 9.3 16.5

14

354.2

11.2

8 5 7 7 8 7 7 8 7 7 7 6 7 7 8 5 8 7

334.1 326.5 352.2 339.3 349.2 346.1 349.5 353.3 347.8 343.1 353.1 336.5 351.2 353.2 351.8 25.1 22.8 355.3

16.9 26.5 17.0 1.5 26.9 22.8 22.3 22.0 31.2 27.3 26.2 24.1 17.9 23.5 22.1 1.7 58.1 36.4

15

351.2

25.5

[Kuala Wau section] MK02 MK01

03°280 54.000 03°280 54.000

102°470 00.900 102°470 00.900

660 660

7 8

2.1 358.8

13.5 16.6

349.1 341.3

24.2 24.2

48.5 24.8

8.8 11.4

⁄MY99 MY98 MY97 MY96 MY95 MY94 MY93 MY92 MY66 ⁄MY91 MY90 ⁄MY89 MY88

03°280 56.600 03°280 56.600 03°280 56.600 03°280 56.600 03°280 56.600 03°280 57.700 03°280 57.700 03°280 57.700 03°280 57.500 03°280 57.700 03°280 58.100 03°280 58.100 03°280 58.100

102°470 06.000 102°470 06.000 102°470 06.000 102°470 06.000 102°470 06.000 102°470 07.000 102°470 07.000 102°470 07.000 102°470 07.100 102°470 07.000 102°470 07.400 102°470 07.400 102°470 07.400

660 650 650 650 650 660 660 650 650 650 650 650 670

8 7 6 8 7 7 7 8 10 8 8 6 8

1.1 1.0 3.8 344.3 354.7 326.8 346.2 327.7 297.9 327.9 323.0 303.6 341.9

21.0 20.5 13.2 20.0 17.4 13.8 11.9 17.3 19.4 24.7 11.7 13.5 13.6

336.6 328.0 338.7 325.0 326.2 310.9 331.8 313.6 293.8 311.7 315 297.8 329.7

36.4 40.7 35.1 27.5 52.1 23.0 26.2 14.5 1.5 21.2 14.2 1.7 25.8

4.2 17.3 46.2 32.0 21.5 12.3 17.3 35.1 16.5 3.2 54.8 3.8 13.2

30.6 14.9 10.0 9.9 13.3 17.9 14.9 9.5 12.3 37.4 7.5 39.7 15.9

03.48°

102.78°

12

342.7

16.6 324.7

26.5

17.7 18.3

10.6 10.4

5.0

19.5

40.6

14.6

(C) Magnetite component (Tub < 590 °C) [Tembeling Basin] MY12(HTC) 04°240 35.200

102°260 06.700

2

2

590–620

II

I

4

1.2

4.7

(continued on next page)

136


Table 1 (continued) Sampling site

Latitude

Longitude

MY45(MTC) MY53(HTC)

04°140 26.500 03°560 36.800

102°250 22.000 102°260 39.500

[Bertangga basin] ⁄MY64(HTC) ⁄MY20(MTC)

03°340 37.400 03°330 29.900

102°460 03.900 102°410 51.100

Mean


2 2

Tub (°C)

590 530–590 530–590 590

Category

I I

n

In situ

k

a95 (°)

9.2 0.8

198.8 22.5

3.9 16.5

349.4 1.6

10.6 12.2

6.8 5.3

25.0 32.2

10.5

3.3

22.5 27.6

26.6 23.9

Tilt corrected

Dec. (°)

Inc. (°)

Dec. (°)

Inc. (°)

8 5

350.2 10.4

22.5 4.2

13.8 12.3

7 3

336.9 357.9

20.9 8.6

3 3

0.9

6.9

(A) CW-deflected group; sites from the Kuala Tahan, Kuala Tahan road section and Kuala Wau section. (B) CCW-deflected group; sites with [1] HTC with Tub of 620 °C and 690 °C, and [2] MTC with Tub of 650 °C and 670 °C, (C) Magnetite component (Tub < 590 °C); sites with magnetite component. n: number of samples measured for directions. (G) Observed Goethite. Tub: unblocking temperature of the highest temperature component. Category: Tubs are categorized into I, II and III (see text). D and I refer to declination and inclination, respectively. k is the Fisherian precision parameter and a95 is the radius of the cone at the 95% confidence level with respect to the mean direction (Fisher, 1953). Italic: Data with pound (#) (MY81 and MY82) indicate records of geomagnetic excursion. Because of the large dispersion in directions (a95 > 20°) data with asterisk (*) are not used for further calculation together with data of excursions.

Fig. 3. Zijderveld plots of the CW-deflected group samples after thermal demagnetization. Open (solid) symbols indicate projection onto the vertical (horizontal) plane. All directions are plotted in geographic coordinates. Sample name is described by site name and sample number (for example in (a) MY34-1: MY34 is the site name and l is the sample number). Number of magnetization components in NRM and categories are shown under a sample name (e.g. (3, II)).


137

Fig. 4. Zijderveld plots of the CCW-deflected group samples after thermal demagnetization. Open (solid) symbols indicate projection onto the vertical (horizontal) plane. All directions are plotted in geographic coordinates. See figure caption 3 for further explanation about the sample names.

respectively. Based on the data with CW-deflected directions, the locality mean-direction is calculated after tilt correction; Ds = 221.9°, Is = 41.3, ks = 15.5, a95 = 12.0°, N = 11) for the Kuala Wau section. When the HTC site-mean directions of the CW-deflected group from three localities are recalculated at the representative study area point (102.5°E, 4.0°N), a combined formation-mean direction at 102.5°E, 4.0°N is calculated. Data with a95 larger than 20° are excluded from calculation of the formation-mean. The mean direction is Dg = 52.1°, Ig = 29.6°, kg = 4.5, a95 = 16.4°, N = 22) in geographic coordinates and Ds = 56.8°, Is = 31.6°, ks = 8.5, and a95 = 11.3° in stratigraphic coordinates. (Fig. 5a and Table 2). The McFadden (1990) fold test reveals positive results at the 95% confidence limit, where 8.996 and 1.582 are obtained for parameter n1 in geographic and stratigraphic coordinates, respectively. A critical value of 5.460 is calculated for parameter nc at the 95% confidence level. The positive fold test suggests a pre-folding origin for the HTC of the CW deflected group in the study area. The primary origin is ascertained by recording the polarity change in the Kuala Wau section 4.3.3. CCW-deflected group The CCW deflected declinations are observed in MTC with the Tub between 650 °C and 670 °C before tilt correction (Fig 5b). A similar

direction is also identified in samples with the single component and HTC before tilt correction. The samples belong to categories II or III (Tub = 620–690 °C) (Fig. 4). The site-mean directions with a95 < 19.8° are reliable. Because nearly identical formation-mean directions are obtained before tilt correction (Table 2) for the HTC and MTC-related NRMs at the representative point (102.5°E, 4.0°N), 72 site-mean directions were used to calculate a combined formation-mean direction (Dg = 349.1°, Ig = 15.3°, kg = 11.8, and a95 = 5.1° in geographic coordinates and Ds = 350.5°, Is = 18.9°, ks = 7.1, and a95 = 6.8° in stratigraphic coordinates) for the CCW deflected group (Fig. 5b). With the application of the tilt correction, the precision parameter (k) decreases from 11.8 to 7.1, indicating a negative fold test (McElhinny, 1964; McFadden, 1990). The values of 0.047 in geographic coordinates and 33.18 in stratigraphic coordinates are obtained for the n1 parameter, whereas a critical value of 9.870 is calculated for the nc parameter at the 95% confidence level. It is, therefore, concluded that this CCW-deflected component postdates folding and is a secondary NRM. 4.3.4. Magnetite related component The NRM component related to magnetite (category I) is identified only at 5 sites. We determine it as secondarily acquired because its mean direction is nearly parallel to the one obtained from the LTC.

138


Fig. 5. Equal-area projection of the paleomagnetic directions. (a) The site-mean directions (before and after tilt correction) with a 95% confidence limit for CW-deflected sites. Solid (open) symbols indicate projections on the lower (upper) hemisphere. Formation mean directions are shown by black stars along with ovals of the 95% confidence limit. The yellow square and blue triangle are the geocentric dipole direction and the present geomagnetic field direction (IGRF) in the study area, respectively. (b) The site-mean directions (before and after tilt correction) with the 95% confidence limit for the CCW-deflected sites. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

5. Rock magnetism The progressive acquisition of isothermal remanent magnetization (IRM) was performed on selected samples up to a maximum field of 2.7 T using a 2G Enterprises 2G660 Pulse magnetizer. The

same samples were then subjected to back-field IRM up to 1000 mT. The IRMs were measured using a Natsuhara Giken SMM-85 spinner magnetometer. Thermal demagnetization of the composite IRMs (2.7 T, 0.4 T and 0.12 T) was carried out to identify Tub spectra in one sample from each site (Lowrie, 1990).

139

Y.-i. Otofuji et al. / Journal of Asian Earth Sciences 134 (2017) 130–149 Table 2 Formation mean directions. Sampling site

Latitude

Longitude

(1) CW-deflected group HTC with Tub of 680–690 (°C) Mean 04.0° 102.5°

N

22

In situ

Tilt corrected

Dec. (°)

Inc. (°)

52.1

29.6

Dec. (°)

56.8 (2) CCW-deflected group [1] HTC with Tub of 620–690 (°C) Mean 04.0° 102.5°

350.1

04.0°

102.5°

Fold test

Lat. (°N)

31.6

4.5 8.5

16.4 11.3

16.6

10.3 6.2

7.0 9.3

22.6

18.4 9.2

6.7 9.7

18.9

11.8 7.1

5.1 6.8

Positive n1(geographic) = 8.996 n1(stratigraphic) = 1.582 nc = 5.460

VGP Long. (°E)

A95 (°)

34.0

173.1

11.3

79.8

22.5

6.5

75.5

45.5

6.4

78.4

33.3

4.7

Inc. (°)

11.2

Negative 27

347.3

21.9 350.6

[1] +[2] Mean

a95 (°)

Negative 45

350.4 [2] MTC with Tub of 650–670 (°C) Mean 04.0° 102.5°

k

72

349.1

15.3 350.5

Negative n1(geographic) = 0.047 n1(stratigraphic) = 33.18 nc = 9.870

(1) CW-deflected group and (2) CCW-deflected group. N: number of sites. See Table 1 for all other explanations.

Fig. 6. Magnetostratigraphic results from the Kuala Tahan road and Kuala Wau sections. Declinations and inclinations with 95 per cent confidence limit are displayed as per their levels in the sections. Sequential locations of the sampling sites are shown in the adjacent stratigraphic succession. Normal polarity, reversed polarity and excursion are marked by black, white and gray colors, respectively.

Thermo-magnetic analyses were conducted on selected samples in air using an automatic recording horizontal thermomagnetic balance at Kyoto University (with a magnetic field of 0.85 T). As is evident from the IRM acquisition and thermal demagnetization of the composite IRM curves (Fig. 7), the HTC of category III in the CW-deflected group is dominantly determined by hematite. The IRM acquisition curves indicate no saturation up to a maximum field of 2.7T, and their representative back-field demagnetization curves show remanence coercivity in the range between 400 and 1000 mT, indicating the presence of high-coercivity magnetic minerals (hematite or goethite). The presence of hematite is also indicated by Tub of 680–690 °C in the hard coercivity IRM component. The thermo-magnetic analysis reveals a Curie temperature

of 670 °C, confirming the presence of hematite in the studied samples (Fig. 9a). The HTC in the CCW-deflected group samples consisting of categories II and III is also determined by hematite (Fig. 8). A Tub range of 620–690 °C in the hard coercively IRM fraction suggests the presence of hematite (Fig. 8). Except for a few samples that show a Curie temperature of 670 °C (Fig. 9c), most samples show a Curie temperature between 620 °C and 650 °C (Fig. 9b, d). The presence of magnetite is suspected in several samples from MY20 and MY34, as is evident from a Tub of 580 °C in the soft coercivity fraction (0.12 T) of the composite IRMs (Fig. 7a). The inflection at 580 °C in the thermo-magnetic curve (Fig. 9d) confirms the presence of magnetite.

140


Fig. 7. Rock magnetic results of the CW-deflected samples, in which primary remanent magnetization is detected. Curves in the first row indicate the IRM acquisition by the applied DC field. Curves in the second row indicate thermal demagnetization of the composite IRMs imparted in the DC fields of 2.7 T, 0.4 T and 0.12 T along three perpendicular axes.

To identify the occurrence and texture of iron oxides in the CW deflected samples microscopic observations under reflected light were conducted on polished thin sections using a Nikon optical microscope. Sub-angular to rounded hematite grains up to 100 lm in size were identified. These detrital hematite grains, which are either homogeneous (specular hematite) grains or show densely crowded exsolution lamellae (martite), are distributed throughout the studied samples (Fig. 10). The grains reveal distinctive reflection pleochroism under the cross-polarized light, diagnostic of an ilmenite–hematite solid solution series. In addition,

pigmentary hematite is also observed as a reddish matrix around the detrital grains. 6. Discussion 6.1. Paleomagnetic directions in the Tembeling Group Primary NRM with CW-deflected rather than CCW-deflected declination was discovered at 22 sites of the Tembeling Group. The primary origin of this component is ascertained through


141

Fig. 8. Rock magnetic results of the CCW-deflected samples, in which secondary remanent magnetization is observed. Curves in the first row indicate the IRM acquisition by the applied DC field. Curves in the second row indicate thermal demagnetization of the composite IRMs imparted in the DC fields of 2.7 T, 0.4 T and 0.12 T along three perpendicular axes.

reliable thermal demagnetization results, a positive fold test and a record of polarity change in the Kuala Wau section. A tilt corrected formation-mean of Ds = 56.8°, Is = 31.6°, ks = 8.5, and a95 = 11.3° (N = 22) is calculated from the CW deflected sites (Fig. 5), which we consider as a characteristic remanent direction for the Jurassic-Cretaceous Tembeling Group.

This primary NRM is probably carried by specular hematite (Fig. 10). During the stepwise demagnetization of NRM and IRM, a Tub of 680–690 °C was observed (Fig. 4). However, the thermomagnetic analysis reveals a Curie temperature of 670 °C for the same rock samples. Previous studies (Lee et al., 1996; Cox et al., 2005; Tan et al., 2007; Jiang et al., 2015) have reported two types

142


Fig. 9. Strong field thermo-magnetic analysis of the selected samples in an air environment. (a) Samples with primary remanent magnetization (CW-deflected group). (b, c, d) Samples with secondary remanent magnetization (CCW-deflected group). Red and blue lines indicate heating and cooling curves, respectively. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

of hematite with NRM components in the red sandstones, a lowtemperature component with a Tub between 610 °C and 660 °C and a high-temperature component with a Tub between 680 °C and 690 °C. They recognized the high-temperature component as a primary NRM. Although no differentiation has been made between the specularite and pigment-related NRMs through Curie temperature analysis, Dunlop and Ozdemir (1997) have attributed the lower Tub to the hematite pigment because Tub is a strong function of grain size. In our case, the microscopic observations confirm the presence of specular hematite along with martite in the CW deflected group (Fig. 9). Specular hematite is thus considered as a carrier of primary NRM in the CW deflected group, which is attributed to detrital remanent magnetization (Liu et al., 2011; Kodama, 2012). A secondary NRM was also identified in rocks of the Tembeling Group (Fig. 5). This component, which we recognized as the MTC in both the magnetostratigraphic sections, unblocks between 650 °C and 670 °C prior to the appearance of primary NRM (Fig. 3). In addition, a secondary NRM was identified in HTCs at the 45 sites of categories II and/or III with a wide range of Tub (620–690 °C) and low Curie temperature (620–670 °C). Recent studies (Liu et al., 2011; Kodama, 2012) attributed the low-temperature component in the authigenically formed pigment hematite to secondary chemical remanent magnetization (CRM). Hence, the observed Tub of 620–670 °C in the MTC and HTC of our samples is probably due to fine-grained hematite particles (pigments) of chemical origin. However, the carrier of secondary NRM with Tub of 680–690 °C (category III) in the HTC remains enigmatic. Because samples of category II or III coexist at 22 sites in the CCW-deflected group (Table 1), pigments can grow to larger particles (Geissman and Harlan, 2002; Park et al., 2003). We recognize that the issue of secondary NRM in hematite remains to be properly resolved. Detection of the CCW-deflected

direction (Dg = 349.1°, Ig = 15.3°, kg = 11.8, a95 = 5.1°, N = 72) in the secondary NRM of the Tembeling Group should be considered as a step into that direction. Although large in magnitude, an almost similar trend of direction (D = 325.5° and I = 28.1°, a95 = 8.8°, N = 13) has been reported by Richter et al. (1999) from Peninsular Malaysia. 6.2. CW and CCW tectonic rotation in the Malay Peninsula We attribute the CW- and CCW-deflected declinations of the Tembeling Group to tectonic movement in the area. The CW deflected direction, carrying a complete set of polarity change from normal to reverse polarity, is recorded in a thick sedimentary sequence. Dual polarities are also reported in the CCW deflected direction of Peninsular Malaysia in Richter et al. (1999). These facts indicate that both the CW and CCW deflected declinations can be ascribed to a tectonically related rather than a short-term phenomenon associated with an anomalous geomagnetic field. The CW tectonic rotation of the Tembeling Group occurred prior to the CCW rotation because these events are recorded in the primary and secondary magnetizations, respectively. According to previous studies (Tjia, 1996; Morley, 2012) the Tembeling Group underwent two phases of folding (during the Late Cretaceous and Eocene), suggesting the post-Eocene as a time of CCW rotation in the study area. According to the present paleomagnetic results (D 57°), the CW rotated zone extends from Peninsular Malaysia to the southern Peninsular Thailand. The CW rotated area extends locally from the upper Tembeling River (04°310 N, 102°100 E), via the Kuala Tahan road section (04°140 N, 102°240 E) to the Kuala Wau area (03°290 N, 102°470 E), and covers a more than 120-km-long strip in the Central Belt. As previously reported by Richter et al. (1999), the CW deflected declinations (residing in the secondary magnetization)


(a) MY73-4

143

a95 = 12.7°, N = 13 in geographic coordinates). The CW rotation in the southern Malay Peninsula was, therefore, followed by CCW rotational movement at a later stage. 6.3. Paleoposition of the southern Malay Peninsula inferred from paleomagnetism

(b) MY94-5

Fig. 10. Reflected light photomicrograph of the selected samples (CW-deflected group). (a) Homogenous specular hematite grain in the sample from site MY73. (b) Martite grain with dense exsolution lamellae in the sample from site MY94.

have also been distributed in the Triassic Main-Range granites and the Permo-Triassic Chunping Limestone of the Western Belt. A geographical distribution of the CW deflected declination can thus be extended up to the Ranong-Klong Marui fault zone in southern Thailand, the hinge of the Malay Peninsula (Fig. 1). Northeasterly deflected declination (D = 31.1°) is observed for the primary magnetization reported from the Middle to Late Jurassic Khlong Min and Lam Thap formations of the Trang Syncline (Yamashita et al., 2011). No evidence of CW deflected declination is reported from the northern limb (Fig. 1) in Peninsular Thailand. We thus conclude that the entire southern part of the Malay Peninsula from Johor in the south to the Ranong-Klong Marui fault in the north underwent a CW tectonic rotation. Thus, the southern Malay Peninsula belongs to the CW-rotated region in SE Asia. The CCW tectonic rotation also occurred in the entire southern Malay Peninsula. The present study reveals the occurrence of CCW deflected declinations in the Tembeling (04°140 N, 102°240 E) and Bertangga (03°290 N, 102°470 E) basins. Richter et al. (1999) also reported CCW deflected declinations from the central and eastern belts of Peninsular Malaysia. A secondarily acquired CCW declination is also reported near the hinge of the Malay Peninsula (Fig. 1). As mentioned by Yamashita et al. (2011), the Jurassic Khlong Min and Lam Thap formations in the Trang area also shows a CCW deflected secondary magnetization (Dg = 342.8°, Ig = 22.3°,

A quantitative paleoposition was estimated for the southern Malay Peninsula using paleomagnetic data (Fig. 11). Assuming that a secondary magnetization with CCW deflected declination was acquired by rocks of the Tembeling Group after folding in the Eocene, we compared the CCW-deflectred direction and the expected declination calculated from the 40 Ma European reference pole (Besse and Courtillot, 2002). We have chosen Europe instead of NE Asia because SE Asia (consisting of Shan-Thai, Indochina, and Malay Peninsula) moved independently from NE Asia after experiencing a CW rotation and southward displacement (Tanaka et al., 2008; Tsuchiyama et al., 2016). The similarity between the observed and expected paleolatitudes of the Malay Peninsula (7.8° ± 2.7° N and 8.3°N, respectively) indicates no significant latitudinal displacement after the acquisition of secondary magnetization (Fig. 11a). The comparison with the expected declination, however, indicates a CCW rotation of 18.5° ± 5.0° for the southern Malay Peninsula without any further southward displacement. The paleoposition and magnitude of CW rotation for Peninsular Malaysia are estimated with respect to the 130 Ma European reference pole (Besse and Courtillot, 2002). The observed inclination places the southern Malay Peninsula within a small paleolatitudinal circle of 17.1° ± 7.8° N of the reference pole (Fig. 11b). When compared with the expected paleolatitude (3.8° ± 2.2° N), a southward displacement of 13.3° ± 8.1° is predicted for the Malay Peninsula after the Cretaceous. It should be noted that the inclination flattening in red beds does not affect the conclusion of the southward displacement but may increase amount of the displacement, in the order of 1–2° in terms of latitudes (Cogné, 2013). The magnitude of the CW rotation is estimated as follows: Initially, the corrected declination value before the CCW rotation is evaluated as 75.3° by adding the magnitude of the CCW rotation (18.5°) to the declination of the primary remanent magnetization (56.8°), and then it is compared with the expected direction (Dexp = 14.2° ± 2.2°). The magnitude of the CW rotation reaches up to 61.1° ± 11.9°. This information suggests that the southern Malay Peninsula experienced a southward displacement of more than 5° along with a CW rotation of 61°. We conclude that the tectonic deformation of the southern Malay Peninsula occurred in two stages (Fig. 11). The rocks of the Tembeling Group acquired remanent magnetization at 17°N paleolatitude from the Jurassic to Cretaceous. Thereafter, the area experienced a 13° southward displacement and reached close to its present day position in the Paleogene. Before or during this displacement the Malaya Peninsula also experienced a CW rotation of more than 60°. After the Eocene-Oligocene, the area rotated CCW by approximately 19° to its present position. 6.4. Tectonic model for the southern Malay Peninsula As shown in Fig. 12, CW rotation accompanied with southward displacement is attributed to tectonic deformation caused by the Eocene (55 Ma) collision of India with Asia (Leech et al., 2005; Zhu et al., 2005; Najman et al., 2010). This is a common regional tectonic phenomenon observed in the Shan-Thai and Indochina blocks (Fig. 1). While CW rotation is recorded in paleomagnetism in these blocks (Fig. 1; Table 3), southward displacement of 400–1050 km is estimated from geological offset across the Red River Fault zone (Leloup et al., 1995; Ali et al.,

144


Fig. 11. Paleo-position and paleo-attitude of the southern Malay Peninsula at times when secondary and primary remanent magnetizations were acquired. Closed (open) arrows indicate declinations of the primary (secondary) remanent magnetizations obtained from Jurassic-Cretaceous rocks. (a) Secondary magnetization: The Malay Peninsula was located at 7.8° N palaeo-latitude, forming a small circle around the 40 Ma European pole (Besse and Courtillot, 2002). The circled area is a zone of the 95% confidence limit in terms of paleo-latitude. The arrow of the paleomagnetic direction is almost parallel to the paleo-meridian. (b) Primary magnetization: The Malay Peninsula was located at 17.1° N paleo-latitude, forming a small circle around the 130 Ma European pole (Besse and Courtillot, 2002).

2010) as well as from paleomagnetic investigations. The southern Malay Peninsula is probably part of a larger East Asian territory where extrusion tectonics occurred (Tapponnier et al., 1982). The CW tectonic rotation also occurred in the Sukhothai Terrane, which was originally an old island arc of the Indochina Block (Sone et al., 2012). The Nan area in Thailand, which belongs to the Sukhotai Terrane, experienced a CW rotation of 13° and a southward displacement of 16.2° ± 13.5° (Aihara et al., 2007). The Cardamom Mountains in south Cambodia, which have been described as a southern extension of the Sukhotai Terrane (Sone et al., 2012), also experienced CW rotation of 33° and southward displacement of 6.0° ± 3.5° (Tsuchiyama et al., 2016). Because the Central Belt of the Malay Peninsula is recognized as an extension of the Sukhothai Terrane (Metcalfe, 2011; Morley, 2012), it seems reasonable to predict that the southern Malay Peninsula was rotated CW and was displaced southward together with the Shan-Thai and Indochina blocks. Geological reconstructions based on seismic tomography also indicate the CW rotation along with southward displacement of the Indochina and Malay peninsulas (Replumaz et al., 2004, 2014). The CCW rotation of the Malay Peninsula can be attributed to the second phase of collisions that significantly affected southern Sundaland (including Borneo, western Sulawesi, and the Celebes Sea). The CCW-deflected declinations (D = 270–320°) have been observed in Jurassic to early Miocene rocks of southern Sundaland (Haile et al., 1977; Haile, 1978; Sasajima et al., 1980; Schmidtke et al., 1990; Shibuya et al., 1991; Richter et al., 1999; Fuller et al., 1999). Fuller et al. (1999) assigned a middle Miocene age to the CCW rotation in the area. The characteristic tectonic features of such rotation in southern Sundaland are probably induced by the collision of the Australian Plate with SE Asia. According to geological and geophysical observations from the region (Lee and Lawver, 1995; Charlton, 2000; Hall, 2002, 2012; Pubellier et al., 2003;

Smyth et al., 2007; Hutchison, 2010) the northern tip (the Sula Spur) of Australia started colliding with Sundaland at 25 Ma (Oligocene to early Miocene). The timing of the CCW rotation in southern Sundaland and southern Malay Peninsula must be contemporaneous to this second phase of collision. We illustrate reconstructions showing Cenozoic two-stage tectonic movements of Sundaland (Fig. 12(B)). In late Jurassic–Cretaceous times, the Malay Peninsula was located at 17°N, and much of Sundaland was still in the interior of proto-Eurasia. First, the whole Sundaland migrated as an extruded continental block due to the collision and following the indentation of India to southern Eurasia since the early Eocene. The Malay Peninsula was rotated 61° CW and concurrently or subsequently displaced more than 580 km in distance to the current position before the beginning of the Miocene (Fig. 12(b)). It may have been subjected to southward displacement until 17 Ma together with the Shan-Thai and Indochina blocks (Wang et al., 1998; Gilley et al., 2003). Second, the Malay Peninsula was subjected to a CCW rotation of 19° during the Miocene. This, together with Borneo (CCW rotation of 50°), occurred as a consequence of the Australia–Sunda collision, accompanying the Philippine Sea spreading and northerly migration of the Philippine–Indonesian archipelagos next to Borneo. These collisional deformations resulted in stretching and Lshaped bending of the current Sunda block (Fig. 12d). This may be partly owed to the fact that much of Sundaland has high surface heat flow, that is, a hot, thin or weak lithosphere (Currie and Hyndman, 2006).

7. Conclusions The nature of remanent magnetization in the JurassicCretaceous red sandstones from the Tembeling Group (Peninsular


145

Fig. 12. Reconstructions showing multi-stage (late Mesozoic–Present-day) tectonic motions of the Malay Peninsula and the whole Sunda block (demarcated by a thick yellow line). A thick brown line demarcates the Australian continental crust. The longitudinal placement of each block is arbitrary. Arrows with dot ends indicate declinations of primary (block) and secondary (open) magnetization from the late Jurassic–Cretaceous rocks of Peninsular Malaysia. (A) Late Jurassic–early Cretaceous times. The Malay Peninsula was located at 17° N paleolatitude. (B) 55–25 Myr BP (Tectonic Phase 1). The Malay Peninsula has migrated southward more than 5.2° (13.3° ± 8.1°) in latitude (equivalent to >580 km in distance) to the area close to the current position due to extrusion tectonics induced by the 55 Ma collision and subsequent penetration of India into Eurasia. It experienced a CW rotation of 61° before or during the displacement. Indochina also rotated 37° CW and displaced 7° southward in latitude. The southward displacement may have lasted until 17 Ma. (C) 25–10 Myr BP (Tectonic Phase 2). Since the northern tip of the Australian continent collided with the southern margin of Sundaland approximately 25 Myr ago, the Malay Peninsula underwent a CCW rotation of 19° to the current position. Borneo also rotated CCW 50°. (D) Presentday configuration of the stretched and L-shaped Sunda block. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

99.4 99.4 99.4

8.38 8.1 7.5

2.5 2.8–5.1 1.4 4.0 4.0

East Malaya Block Peninsular Malaysia Segamat (basalt flow) Kuantan (diolite dike) Singapore (diolite dike) Tembelin (red beds)(Primary) (T) Tembelin (red beds)(secondary)(T)

102.8 103.2–103.5 104.0 102.5 102.5

96.5 98.7 99.7

101.0

20.7 16.8 13.5

19.2

Sukothai Terrane Nan (N)

108.3 103.1

105.0–109.4

106.0

102.5–104.1

103.8 103.4 103.9 102.4 105.4 105.5 103.0 103.0 102.5–104.1

101.1 101.1 100.5 100.4 100.5 100.9 101.0 100.9 101.0 101.2 101.9

Long. (°E)

Sibumasu Terrane Thailand Kalaw (K) Mae Sot (MS) Ratchaburi (R) Peninsular Thailand Thung-Yai Red beds NorthTrang syncline (NT) West Trang syncline (WT)

11.7 11.6

10.4– 12.9

Da Lat (D) Koah Kong (KK)

Southern tip Da Lat

Muan Phin (MP)

Muan Sakon Nakhon

18.5 18.3 18.2 18.1 16.7 16.5 16.5 16.5 16.5– 17.2 16.5– 17.2 16.5

24.1 24.1 23.6 23.4 23.4 23.4 23.0 22.8 22.4 21.9 21.6

Shan-Thai Block Simao Basin Zhengyuan Zhengyuan Jinggu Jinggu Jinggu Jinggu Pu’er (P) Zhengwan Dadugang Menlun Phong Saly (PS)

Indochina Block Khorato Basin Borikhanxay (B) Borikhanxay Amphoe Bung Kuan (A) Vientiane (V) Khammounane + Savannaket Savannaket (SV) Nam Nao (NN) Nam Nao Muan Sakon Nakhon (SN)

Lat. (°N)

Locality name

Table 3 Jurassic to Cretaeous Paleomagnetic results available from SE Asia.

K2-Tpal K2-T(?) K(?) J3-K1 J3-K1

J3-K2 J2-K2 Post-K

J-K J1-J2 J1-J2

J1–3

K J3-K1

K

J (K1)

K1

J3-K1 K2 K2 k1 K1 K2 K1 J3 K2

K1-2 K1-2 J2 K1 K2 K2 K1-2 K1 K1 K2 J3-K1

Age

4 34 (15) 22 72

1(23) 9 13

13 12 19

11

21 11

21

17

4

18 16 14 10 8 12 10 10 8

7 4 10 – 7 8 25 11 12 6 19

N(n)

Redbeds Redbeds

Redbeds Redbeds Redbeds

Redbeds Redbeds Redbeds

Ryolite, Ryolite tuff, granite,silt Redbeds Redbeds

Redbeds

Redbeds

Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds

Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds Redbeds

In situ In situ In situ Positive Negative

Positive In situ

Positive Positive Positive

Positive

Positive Inconclusive

None

syn-folding at K1

Positive

Positive Positive Inconclusive Positive Positive Positive Inconclusive Inconclusive Inconclusive

Positive Positive Inconclusive Inconclusive Positive Inconclusive Positive Positive Positive Positive Positive

Fold test

306.0 332.8 340.7 56.8 349.1

32.6 31.1 342.8

44.7 359.8 348.5

32.2

11.4 43.4

14.5

30.8

31.8

41.8 21.2 31.8 25.9 28.8 27.7 28.1 26.6 31.4

61.8 144.2 83.3 84.4 115.8 79.4 59.9 51.8 64.1 33.2 29.8

37.3 36.6 18.5 31.6 15.3

18.8 12.2 22.3

23.4 31.4 24.7

33.3

35.4 31.9

33.3

39.9

38.3

46.6 37.1 28.7 37.4 45.7 38.0 40.5 37.7 27.1

46.1 49.4 36.8 39.6 36.0 43.3 45.2 47.9 48.1 30.9 32.7

Inc. (°)

Observed direction Dec. (°)

9.5 5.4 5.4 11.3 5.1

3.9 13.9 12.7

6.1 5.0 10.5

12.2

1.7 3.6

6.3

3.0

5.7

8.0 7.7 3.5 10.2 5.0 4.1 2.4 2.6 9.4

8.1 6.4 5.4 17.8 6.3 9.1 5.1 6.9 7.3 8.2 9.1

a95 (°)

Richter et al. (1999) Richter et al. (1999) Richter et al. (1999) This study This study

Bhongsuwan and Ponathong (2002) Yamashita et al. (2011) Yamashita et al. (2011)

Richter and Fuller (1996) Yang et al. (1995) Fujiwara et al. (2014)

Aihara et al. (2007)

Otofuji et al. (2012) Tsuchiyama et al. (2016)

Chi and Dorobek (2004)

Takemoto et al. (2009)

Charusiri et al. (2006)

Takemoto et al. (2009) Singsoupho et al. (2014) Charusiri et al. (2006) Singsoupho et al. (2014) Singsoupho et al. (2014) Singsoupho et al. (2014) Yang and Besse (1993) Yang and Besse (1993) Charusiri et al. (2006)

Tanaka et al. (2008) Tanaka et al. (2008) Huang and Opdyke (1993) Chen et al. (1995) Chen et al. (1995) Huang and Opdyke (1993) Sato et al. (2007) Kondo et al. (2012) Kondo et al. (2012) Tong et al. (2013) Takemoto et al. (2009)

Reference

146 Y.-i. Otofuji et al. / Journal of Asian Earth Sciences 134 (2017) 130–149

9 2(8) Tpal-Lower M J3-K1 5.0 S 4.75S East Sulawesi Biru (B) Dera Valley

120.2 119.7

6(48) 5(36) 2(17) 2(15) 3(21) 37(37) 1(5) K J-K J3-K1 J3-K2 J3 K K 5.7 1.4 1.4 1.2–1.5 1.1 1.5 S 1.2–1.4 S Southern part of the Sundaland Borneo Telupid (T) Bau Limestone Formation (Bau) Bau Limestone Formation(Penrissen) Bau-Lund Rd. (Padawan F.) (P) Kedadan Formation W. Kalimantan-Schwaner Mtns. W. Kalimantan-Schwaner Mtns.

117.1 110.2 110.2 109.9–110.3 110.4 110.0 110.0

13 7 4 J3-K1 Tru P 101.8–103.0 99.8–102.4 104.2 3.5 3.0–6.4 1.4–1.7 Tembelin (red beds)(secondary) Main range Granite Permian silicic igneous rocks

Lat. and Long. refer to latitude and longitude, respectively. The ages are as follows: P is Permian, Tru is Upper Triassic, J is Jurassic, J1 is Lower Jurassic, J2 is Middle Jurassic, J3 is Upper Jurassic; K is Cretaceous, K1 is Lower Cretaceous, K2 is Upper Cretaceous, T is Tertiary, Tpal is Paleogene and M is Miocene. N(n) is the number of sites (samples) used for paleomagnetic calculations. Dec. and Inc. refer to declination and inclination, respectively. a95 is the radius of the cone at the 95% confidence level with respect the mean direction.

Sasajima et al. (1980) Haile (1978) In situ

19.6 7.2 1.3 5.0 315.2 325.0

Schmidtke et al. (1990) Schmidtke et al. (1990) Schmidtke et al. (1990) Schmidtke et al. (1990) Schmidtke et al. (1990) Haile et al. (1977) Haile et al. (1977) 27.4 14.1 5.3 7.1 22.7 7.8 24.5 9.1 11.5 8.6 16.0 2.1 0.3 5.6 313.3 301.6 272.0 267.9 311.1 311.7 280.1 After In situ Positive Positive After In situ In situ

8.8 12.4 28.1 50.0 5 to 39 325.5 42.5 26–66 Negative In situ In situ

Inc. (°) Dec. (°)

N(n) Lat. (°N) Locality name

Table 3 (continued)

Long. (°E)

Age

Redbeds

Fold test

Observed direction

a95 (°)

Reference

Richter et al. (1999) Richter et al. (1999) Richter et al. (1999)


147

Malaysia) was examined by paleomagnetic and magnetostratigraphic studies. (1) Thermal demagnetization at 680–690 °C identified the CW deflected NRM direction of 22 sampling sites from the Tembeling and Bertangga basins. The primary origin of this direction (Ds = 56.8° and Is = 31.6°, a95 = 11.3°, N = 22) is confirmed by a positive fold test and a geomagnetic polarity reversal in the Kuala Wau section. (2) The studied samples contain a record of secondary magnetization, which is characterized by a mean CCW deflected direction (Dg = 349.1°, Ig = 15.3°, a95 = 5.1°, N = 72). (3) After the acquisition of primary remanent magnetization during the JurassicCretaceous at 17.1° ± 7.8° N the Malaya Peninsula underwent a southward displacement of 13.3° ± 8.1° to reach the present position in the Paleogene. After experiencing a CW rotation of 61.1° ± 11.9° in the Paleogene, the study area rotated CCW by 18.5° ± 5.0° without any latitudinal displacement. (4) Records of both CW and CCW tectonic rotations indicate that the Malaya Peninsula was affected by two different phases of collisions, the collision of India with Asia at an earlier stage and the collision of Australia with Asia at a later stage, respectively.

Acknowledgements Some of the statistical analyses were conducted using the computing programs of Cogné (2003). The authors would like to thank Professor Naoto Ishikawa (Kyoto University) for providing his laboratory facilities. We also thank Katsuya P. Fujiwara, Ryutaro J. Ichihashi, Weilisi and Kazuya Okayama for their help during the sampling trips. The useful suggestions from Eiichi Sato are acknowledged. We thank A.J. Barber and B. Huang for comments, and J. Ali for very careful and useful reviews. This research work was partly supported by Grant-in-aid (Nos. 18403012, 22403012) from the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) as well as the University of Malaya High Impact Research grant (UM.C/625/1/ HIR/140). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jseaes.2016.10. 007. References Abdullah, N.T., 2009. Mesozoic stratigraphy. In: Hutchison, C.S., Tan, D.N.K. (Eds.), Geology of Peninsular Malaysia. University of Malaya and Geological Society of Malaysia, Kuala Lumpur, pp. 87–131. Aihara, K., Takemoto, K., Zaman, H., Inokuchi, H., Miura, D., Surinkum, A., Paiyarom, A., Phajuy, B., Chantraprasert, S., Panjasawatwong, Y., Wongpornchai, P., Otofuji, Y., 2007. Internal deformation of the Shan-Thai block inferred from paleomagnetism of Jurassic sedimentary rocks in Northern Thailand. J. Asian Earth Sci. 30, 530–541. Ali, J.R., Fitton, J.G., Herzberg, C., 2010. Emeishan large igneous province (SW China) and the mantleplume up-doming hypothesis. J. Geol. Soc. 167, 953–959. Besse, J., Courtillot, V., 2002. Apparent and true polar wander and the geometry of the geomagnetic field over the last 200 Myr. J. Geophys. Res. 107 (B11), 2300. http://dx.doi.org/10.1029/2000JB000050. Bhongsuwan, T., Ponathong, P., 2002. Magnetic characterization of the Thung-Yai redbed of Nakhon Si Thammarat Province, southern Thailand, and magnetic relationship with the Khorat redbed. Sci. Asia 28, 277–290. Charlton, T.R., 2000. Tertiary evolution of the Eastern Indonesia Collision Complex. J. Asian Earth Sci. 18, 603–631. Charusiri, P., Imsamut, S., Zhuang, Z., Ampaiwan, T., Xu, X., 2006. Paleomagnetism of the earliest Cretaceous to early late Cretaceous sandstones, Khorat Group,

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