Turkish Journal of Earth Sciences
Turkish J Earth Sci (2014) 23: 1-15 © TÜBİTAK doi:10.3906/yer-1302-12
http://journals.tubitak.gov.tr/earth/
Research Article
Source of the mineralizing fluids in ultramafic related magnesite in the Eskişehir area, northwest Turkey, along the İzmir–Ankara Suture: a stable isotope study 1,
2
Asuman KAHYA *, Mustafa KUŞCU Department of Geology, Aksaray University, Aksaray, Turkey 2 Department of Geology, Süleyman Demirel University, Isparta, Turkey 1
Received: 25.02.2013
Accepted: 15.08.2013
Published Online: 01.01.2014
Printed: 15.01.2014
Abstract: The Eskişehir magnesite deposits (Süleymaniye, Margı, and Tutluca) are located in the western part of the İzmir–Ankara Suture Zone, northwestern Turkey. These vein and stockwork type magnesite deposits, which occur along major and minor fault systems, are hosted by Alpine-type ultramafic rocks. The purpose of this study was to understand the origin of the hydrothermal waters responsible and the source of carbon dioxide, and to compare these deposits with similar magnesite occurrences in Turkey and elsewhere. Petrographic and XRD analyses indicate that magnesite was the major carbonate mineral formed. Deposits are predominantly micritic and locally microsparitic, but some also contain secondary calcite and dolomite. The δ13C (V-PDB) values of the Süleymaniye magnesites (–2.7‰ to –7.7‰), the Margı magnesites (–7.6‰ to –11.2‰), and the Tutluca magnesites (–8.7‰ to –10.4‰) indicate that sources of carbon may include atmospheric carbon, dissolved inorganic carbon, freshwater carbonate, and mantle derived CO2. The δ18O (SMOW) compositions of the magnesite range from 27.4‰ to 30.8‰ and show that the oxygen was derived from marine limestone and metamorphic rocks. The Süleymaniye magnesites have heavier carbon isotopic values than the others because of the greater contribution of mantle sourced CO2, while oxygen isotopic values were similar to those of other altered ultramafic related magnesites in Europe (Former Yugoslavia, Greece). The Margı and the Tutluca magnesite deposits have carbon and oxygen isotopic values similar to those of other ultramafic-related magnesite deposits. Based on isotopic data, we argue that the magnesite deposits in the Eskişehir area formed in a near surface environment at low pressure and temperature. The estimated temperature, using average δ18O values, suggests that magnesite was precipitated from water at 37 °C. Key words: Magnesite, stockwork, vein, Eskişehir, isotope geochemistry
1. Introduction There are several economic magnesite deposits in the western section of the İzmir–Ankara Suture Zone (IASZ). The host rocks are ultramafic Cretaceous ophiolitic units around Süleymaniye (Mihallıccık), Margı (Dağküplü), and Tutluca in the Eskişehir region (Figure 1) with characteristics of Supra Subduction Zone (SSZ) types. Magnesite mineralization is common in the Cretaceous ophiolities in the IAS zone. The Eskişehir area provides the main economic magnesite production in Turkey. The Tutluca magnesite deposits have been operated as open-pit quarries, but the magnesite deposits of Süleymaniye and Margı have become depleted. Magnesite mineralization in the study area is restricted to shallow depths because it fills in brittle fractures and cracks in serpentinites as veins and stockworks. The common serpentinite minerals are chrysotile, lizardite, and small amounts of antigorite, but these are pervasively altered with alteration accompanied by the formation of magnesite deposits. * Correspondence:
[email protected]
Typically the carbonation of magnesium silicate minerals (e.g., serpentinite, olivine) at temperatures below 200 °C is an exothermal process, involving the incorporation of CO2 into stable carbonate (Boschi et al., 2009). Serpentine may coexist with CO2-poor fluids, but it becomes unstable as the partial pressure of CO2 increases in the fluid phase, and at low temperatures (300 °C (e.g., Abu-Jaber and Kimberley, 1992; Zedef et al., 2000), 6. Volcanogenic sources (e.g., Illich, 1968; Zedef et al., 2000), and 7. Deep-seated sources (cf. Kruelen, 1980) or a combination of the above (e.g., Zedef et al., 2000). Numerous studies have used the δ18O and δ13C isotope ratios of magnesite to suggest the source of the fluids responsible for magnesite formation in Australia, Yugoslavia, Greece, and Turkey (e.g., Gartzos, 1980, 1990, 2004; Kralik et al., 1989; Jedrysek and Halas, 1990; Fallick et al., 1991; Abu Jaber and Kimberley, 1992a, 1992b; Brydie et al., 1993; Zedef et al., 2000; Schroll, 2002; Ece et al., 2005; Kuşcu and Cengiz, 2005). In this study, the δ13C values of the Süleymaniye stockwork magnesite deposits have a range between –2.70‰ and –7.7‰ V-PDB. The
KAHYA and KUŞCU / Turkish J Earth Sci Table 2. Isotopic composition of magnesite in Turkey and elsewhere. Sample and location
δ13C (‰)
δ18O (‰)
Description
Reference
Salda Lake
0.2–4.7
30.6–37.3
Hydromagnesite
Zedef et al. 2000
Akgöl Hydromagnesite
0.1–0.7
28.2–27.9
Dry lake sediment
Zedef et al. 2000
Pamukkale
5.3–6.2
19.3–23.0
Travertine calcite
Zedef et al. 2000
Kocabas
–0.2–5.2
19.5–24.7
Travertine calcite
Zedef et al. 2000
Hırsızdere
–0.3–4.4
21.6–25.9
Bedded magnesite
Zedef et al. 2000
Helvacıbaba
–7.5–(–8.0)
24.9–25.3
Detrital magnesite
Zedef et al. 2000
Helvacıbaba
–7.0–(–7.6)
25.3–27.0
Bedded dolomite
Zedef et al. 2000
W. Helvacıbaba
–10.1–(–11.9)
26.4–27.3
Stockwork magnesite
Zedef et al. 2000
E. Helvacıbaba
–10.3–(–13.8)
26.6–27.3
Stockwork magnesite
Zedef et al. 2000
Helvacıbaba
–10.0–(–10.8)
27.3–29.0
Stockwork magnesite
Zedef et al. 2000
Koyakcı Tepe
–11.8–(–14.3)
25.9–27.7
Vein stockwork magnesite
Zedef et al. 2000
Arapömer Deresi
–0.4–1.4
27.0–27.7
Stockwork magnesite
Zedef et al. 2000
Salda Lake
1.6–2.4
29.8–30.9
Cretaceous limestone
Zedef et al. 2000
N. Evia (Greece)
–8.6 – (–13.3)
25.4–30.1
Vein and stockwork magnesite
(Gartzos, 1990)
Lesvos (Greece)
–12.5 – (–3.9)
24.0–27.7
Vein and stockwork magnesite
(Gartzos, 1990)
Chalkidiki (Greece)
–14.3–(–14.8)
27.4–28.6
Vein and stockwork magnesite
(Gartzos, 1990)
Madenli
–10.1–(–11.4)
26.8–28.1
Vein and stockwork magnesite
Kuscu et al. 2005
Salda
4.4–4.9
36.4–38.2
Hydromagnesite
Kuscu et al. 2005
Asağıtırtar Margı Nemli
7.8–8.8 –10.1–(–13.7) –9.1–(–10.8)
26.9–32.4 25.6–28.3 26.1–27.8
Huntite Stockwork type Magnesite Stockwork type magnesite
Kuscu et al. 2005 Ece et al. 2005
Süleymaniye
–2.70–(–7.7)
27.4–29.4
Vein and stockwork magnesite
This study
Margı
–7.6–(–11.2)
27.8–30.8
Vein and stockwork magnesite
This study
Tutluca
–8.7–(–10.6)
27.2–29.2
Vein and stockwork magnesite
This study
Margı deposits are characterized by δ13C values of –7.6‰ and –11.2‰ V-PDB and the Tutluca deposits similar δ13C values from –8.7‰ to –10.6‰ V-PDB. These values are appropriate for deep-seated or mantle sources of CO2 (ranging from –4‰ to –8‰ V-PDB; Denies, 1980) and indicate derivation from the decarboxylation of organicrich sediments buried beneath the obducted ultramafic rocks, with some contribution from the thermal decarbonation of limestone (Fallick et al., 1991; Zedef et al., 2000; Ece et al., 2005). Temperature is the most important factor that controls oxygen isotope fractionation. Hence, the temperature of the water can be calculated using the following equation (Aharon, 1988): 103 Inα = δ18Om – δ18Ow = A (106T–2) + B In this equation, 103 Inα is the per mil (‰) fractionation between magnesite (m) and water (w), T is the temperature in degrees Kelvin, A and B are constant (A
Ece et al. 2005
= 3.53 and B = –3.58 for magnesite from Aharon (1988)). The estimated temperature of water from which stockwork magnesite has been precipitated is ~37.9 °C, according to average δ18O values in the areas studied. The average δ18Om value is 28.6‰ V-SMOW (n = 20) and the assumed δ18Ow is 5‰ V-SMOW (from Zedef et al. (2000)). According to this, we can say that magnesite formed from low and moderate-temperature water under surface or nearsurface conditions. In the present study areas, ophiolites are the remnants of the Neotethys ocean that closed during the late Triassic–Early Cretaceous. The ultramafic rocks were emplaced during the Late Triassic to Early Jurassic. The area was later subject to tectonic movements that produced faulting and fracturing. However, in addition, the Margı-Taycılar, Tutluca, and Süleymaniye areas were also influenced by volcanic activity in the Mesozoic, Eocene, and Miocene periods, respectively. The isotopic data indicate that meteoric water percolated through
11
KAHYA and KUŞCU / Turkish J Earth Sci
N
S
Kyzyl T.
CO2
Hamam Hill
Arykaya Hill
CO2
L L
L L
Mg ++
Porsuk River
. . . .. . . O
O
???
CO2
Organic C
O
O
Meteoric water
+ + +
CO2
Without scale
Serpentinite
Metadetritikler
Marl-clay
Limestone
.. .. . . . .. . .. .. O
O
O
O
O
a)
L L
L
+ + +
Listvenite
L
Alluvium
O
Magmatic
Conglomeratesandstone
Thrust Fault
Magnesite mineralization
O
NE
SW CO2 Mjdet
v
B v
v v
Np1
++
CO2
Mg
Somdiken gneiss
Conglomeratesandstone
Np1
Smr
Mg
Mg
Meteoric Meteoric water water
Sgn
CO2
Organic C
???
Of
Organic C
Sgn
Mg
B
Meteoric water
Sgn
Np1
Np5
CO2
without scale
Somdiken marble
Mjdet
Metadetritics
Limestone
Np5
v v B v v
Peridotites
Of
Diabase dike
Magnesite mineralization
Thrust fault
Fault
b) NW
SE CO 2
CO 2 «yplak Hill
V PlB V V
Ism
Meteoric water CO
CO2
2
Organic C.
Ism
V
PlB V
İnönü Blueschist
Tof
Imr
Imr
İnönü Marble
V
Basalt
Mg
CO2
Thrust Fault
Mg
Tof
Mg
Meteoric water Mg
.0 Peridotites
0
Ply .
.
0
.
0
0
0 0 .
. Ply 0
0 .
.
without scale
ConglomerateSandstone
Magnesite mineralization
c) Figure 10. Model of the formation of magnesite in the study areas (a: Süleymaniye, b: Margı, c: Tutluca).
12
.
0
.
KAHYA and KUŞCU / Turkish J Earth Sci faults and fractures in both the ultramafic rocks and organic-rich sediments. The water dissolved Mg+2, Ca+2, OH–1, and Si+4 from the ultramafic rocks, taking them into solution. Carbon was derived from organic-rich sediments by decarboxylation of organic material, but also from dissolution of limestones. Volcanic activity may have been an additional source of CO2, augmenting the dissolution of limestone and decarboxylation with additional heat. These resulting solutions ascended, becoming more alkaline with pH > 11 (Ece et al., 2005; Kadir et al., 2013). As saturation increased, magnesite precipitated in fractures and cracks within near-surface ultramafic rocks. The oxygen isotope compositions of magnesites from the Eskişehir deposits range from 27.2‰ to 30.8‰, with carbon isotope compositions varying from –2.7‰ to –11.2‰. Similar compositions have been reported from similar vein and stockwork deposits from Turkey (Koyakcı Tepe; Helvacibaba, Nemli, and Margı), Poland, former Yugoslavia, and Greece (North Evia and Chalkidiki). All these deposits have similar isotopic compositions, suggesting that they formed under similar conditions. In the study area, magnesite occurs within cracks and fractures in ultramafic units that provide the source of the magnesium required. The deposits are commonly cryptocrystalline and consist of dense micrite and microsparite. The isotopic values of the Süleymaniye magnesite deposits suggest that CO2 was released during the decarbonation of limestone in the Karkin Formation, which is overthrust by the ophiolites. The Sömdiken marble provided the source of CO2 in the Margı magnesite deposits and İnönü marble the source of CO2 in the Tutluca magnesite (Figure 10a, b, c). Another potential CO2 source in the Süleymaniye and
Margı magnesite deposits is younger limestone units in the Porsuk Formation. Slightly higher δ13C values in these (–2.7‰, –11.2‰ V-PDB) may reflect mantle-derived CO2. Mesozoic volcanism may have influenced the formation of the Margi magnesite deposits, whereas Eocene volcanism at some distance from the Süleymaniye deposits reflected in a hot water source in the Hamamdere area may further support hydrothermal effects. In some way, Miocene volcanism is present in the Tutluca area and may have influenced magnesite deposition. We cannot exclude the contribution of meteoric water. Descending meteoric water may be heated and mixed with ascending CO2-bearing solutions. The formation of ultramafichosted magnesite deposits requires the interaction of CO2rich fluids and ultramafic rocks. Magnesium is released by serpentinization of the ultramafic rocks and during weathering. Serpentinization is thought to have taken place during obduction. At relatively low temperatures (
