Mantle Petrology and Geochemistry Beneath the

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nature and evolution of the mantle beneath this region. .... mantle beneath the CPR. We discuss mantle ...... deformed and subsequently recrystallized man-.
/11.Wooti.oo,.l GeoiaJIT R~ Vol. :~. 1994, pp. 328-358. C.opyrigh1 0 1994 b"y V. H. Winslon & Son, lnr. All rights reserv...J.

Mantle Petrology and Geochemistry Beneath the Nograd-Gomor Volcanic Field, Carpathian-Pannonian Region CSA BA SZABb I

Department of Petrology and Geochemistry, EOtvOs University, Budapest, Hungary, MUzeum Krt. 4/ A, H-1088 AND LAWRENCE

A.

TAYWR

Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996

Abstract Neogene to Quaternary alkali basalts within the N6gr8d-GOmOr Volcanic Field (NGVF) contain abundant mafic and ultramafic xenoliths and megacrysts, yielding insight into the nature and evolution of the mantle beneath this region. The Cr-diopside suite of ultramafic nodules has been classified by texture, mineralogy, and chemistry into two groups: Group 1spinel lherzolite and spinel websterite, with protogranular to porphyroclastic or equigranular textures and small amounts of pargasitic amphibole; and Group 2-dunite and spine! lherzolite, with "secondary" recrystallized textures and minute amounts of phlogopite. Cr-diopside-rich veinlets occur in Groups 1 and 2, forming composite xenoliths. Calculated bulk-rock compositions and most mineral compositions vary distinctly with texture. "Secondary" recrystallized xenoliths (Group 2) are depleted in "basaltic" major elements, which decrease gradually through equigranular-textured xenoliths towards protogranular to porphyroclastic xenoliths. Nevertheless, within Group 1, amphibole-bearing equigranular and protogranular-to-porphyroclastic xenoliths cannot be distinguished by rare-earth element (REE) contents. Their unfractionated REE patterns and the formation of amphibole can be attributed to modal metasomatism. However, anhydrous xenoliths from Group 1, showing a negative correlation between "basaltic" major and rare-earth elements, are indicative of the effects of cryptic metasomatism. This might be controlled by percolation of metasomatizing melts (Navan and Stolper, 1987; Bodinier et al., 1990) or by a small amount of metasomatizing agents near the vein conduit (Nielson et al., 1993). Principal features of Group 2 xenoliths, such as "secondary" recrystallized textures, clinopyroxenite veins, high-F-content phlogopite, and depletion in "basaltic" major elements, reflect complex mantle events, including modal and cryptic metasomatism. Although the lithospheric mantle beneath the NGVF has been considerably modified, the nature of this upper mantle is consistent with existence of a subducted slab. This subducted slab was the possible source of the metasomatic agents.

Introduction INSIGHT INTO the nature and evolution of the mantle can be provided by petrologic and geochemical studies of mantle xenoliths occurring in alkali basalts and kimberlites. Neogene-toQuaternary alkali basalts and their pyroclastic deposits are distributed widely within the Carpathian-Pannonian Region (CPR) of Eastern Europe. They have entrained many ultramafic and mafic nodules and a great variety of mafic 1Also

Department of Geological Sciences, University of Tennessee, Knoxville, TN 37996. Present address: Department of Geological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.

002Q.6814/94/56/328-31 SI0.00

and feldspar megacrysts. Numerous well-known localities from the Transdanubian Volcanic Region (TVR) (Embey-lsztin et al., 1989) are extremely rich in xenolithic material and have been studied in detail previously (e.g., Kurat et al., 1980; Embey-lsztin et al., 1989; Szabo and Vaselli, 1989; Downes et al., 1992). Furthermore, Vaselli et al. (in press) have just completed an extensive geochemical study of ultramafic xenoliths in alkali basalts of the Persany Moun,tains, Eastern Transylvania. The present paper is the first general overview of the petrology and geochemistry of representative ultramafic xenolith suites in alkali basalt and basanite flows, dated at 6.4 to 1.3 m. y. 328

329

N6GRAD-G0M0R VOLCANIC FIELD

,,. . DfNPY

SLOVAKIA

, -~ , -·

.. L-~_...::;:....__,.~~-====--1

NTB

... ,...

06,NFL~

D

.

~TK -.~ '

\.

HUNGARY __...

N

0

t

5

0

Andesite

l

Alkali Basalt

D Cr-Diopside Suite c::, Al-Augite Suite

0

'

"~

\



..

Crustal Xenoliths

IOKm

• I



\.





••





..

·.,.J.; •.





..

06,

DC::, 0_.. NBN ~

'

Fie. I. Simplified map of the N6gr3.d-GOmOr Volcanic Field (NGVF), showing distribution of the xenoliths, and the principal locals, using the text: NPY = Patakalja-Podrecany; NMS = Mask6falva-Maskova; NFL= Fiilek-Fil'akovo-KercsiktetO; NTB = Terbeled-Terbel'ovce; NTK= FU:lek Kov.icsi-Fil'avske Kovace~ NME = Medves Plateau-EresztvCny; NMM = Medves Plateau-Magyarb.inya; NBN =88.rna-Nagykii

"

330

C. SZABO AND L. TAYLOR

TABLE 1. Modal Proportions of the NGVF Xenoliths and Equilibrium Temperatures 1 and Oxygen Fugacity2 Site

Rock type:'

OI

NBNIO NMS09 NMS\6 NMSJO

Jh, Jh, Jh,

wh•

62 62 61 26

NBN25 NBN27 1 NBN30 NBN54

Jh, Jh, Jh, \h, Jh, Jh, Jh, Jh, Jh, Jh, Jh, Jh, amplhz

73 76 75 75 71 65 75 81 78 67 66 68 23

14 15 16 15 19 20 13 II 13 19 19 16

Jh, dunite dunite dunite Jh,

80 88 91 96 78

9 4 4

NMEI3 NMEIS NME19 NME23 NMM02 NTB03 NFLIO

NFLIS NFL\ F'

NBN\5 NBN22 NBN23 1 NBN3\

NBNSI

Op
mit-rc>graphs showing cllfftri"lll h•Alural t ypes of pcrilfil"ed IJy amphibole. I. Equig.r•nu· l 11 r•l e~1 u red lhcnolite with a Cr·diop$iJe .. nch vtin (NRN.27); deple1ion in chnopyroJ:e1\e (light gr:Jy &rnir1,S) i11 notable

ad1ac,.111 10 vein.

335

N6GRAD-G0M0R VOLCANIC FIELD

3. Average Microprobe Analyses of Orthopyroxenes

TABLE

Sample: Texture:

"' Si0 2 1i0 2 Al 20:1

Cr 20:1

MgO

c,o

MnO

NBNIO

NMS09

Porph

15

Porph 15

54.6 (2)1 0.11 (2)

54.5 (2) 0.13 (\)

4.76 0.38 32.4 0.99

4.59 0.39 32.7 0.77 0.14

(20) (3) (4) (9)

NMSIO Porph 17

NMS16 Porph

NBN25

NBN27

NBN30

Equi

17

12

Equi 19

Equi 18

54.4 (2)

55.0 (2)

O.ll (1) 4.61 (11)

0.12 (1)

55.4 (1) O.IO (I)

4.49 (16)

3.79 (4)

0.32 (3)

0.33 (2)

32.9 (1) 0.72 (2) 0.14 (I)

33.5 (I)

6.27 (5) 0.09 (l)

0.08 (2) 31.7 (1) 0.65 (2) 0.16 (I) 8.05 (6) 0.09 (I)

6.32 (5) 0.10 (I)

6.19 (3) 0.06 (I)

100.17

(22) (5) (2) (3)

(2)

0.67 (I)

Fe0 2 Na20

0.13 (I) 6.38 (7) 0.12 (9)

To1al

99.87

99.58

99.85

100.11

Si TI Al

N•

1.891 0.002 0.194 0.010 1.673 0.036 0.003 0.184 0.008

1.892 0.003 0.187 0.010 1.693 0.028 0.004 0.181 0.006

1.896 0.002 0.189 0.002 1.647 0.024 0.004 0.234 0.005

l.897 0.003 0.182 0.008 1.694 0.026 0.003 0.182 0.006

1.909 0.002 0.154 0.009 1.720 0.024 0.003 0.178 0.004

Total

4.001

4.004

4.003

4.001

mg#

0.90

0.90

0.88

0.90

0.13 (2)

NBN54 Equi

NMEI3

NMEl8

NME19

Equi

Equi

Equi

14

22

9

19

55.2 0.09 3.76 0.36 33.1 0.68

(2) 56.0 (2) 55.5 (2) (I) 0.03 (I) 0.08 (I) (20) 2.51 (12) 3.97 (14) (5) 0.47 (7) 0.40 (6) (2) 33.8 (2) 33.5 (2) (2) 0.72 (2) 0.67 (2) 0.14 (I) 0.14 (2) 0.1 l (2) 6.32 (6) 5.81 (6) 5.92 (7) 0.04 (I) 0.05 (I) 0.07 (I) 99.59

54.7 (I) 0.14 (I) (I) (IO) 4.35 (5) (3) 0.39 (2) 31.8 (2) (I) 0.74 (2) 0.86 (2) 0.15 (1) 0.17 (\) 7.35 (6) 6.22 (7) 0.05 (1) 0.07 (I) 55.2 (I)

0.03 3.48 0.44 33.6

54.8 (1) 0.06 (1) 4.03 (5) 0.44 (3) (I)

33.0 0.76 0.14 6.08

(2) (I) (6)

0.08 (I)

99.53

100.20

99.91

99.63

99.29

1.912 0.002 0.153 0.009 1.711 0.025 0.003 0.183 0.002

1.938 0.000 0.102 0.012 I.747 0.026 0.004 0.168 0.003

1.910 0.002 0.161 0.011 1.718 0.025 0.003 0.170 0.005

1.910 0.000 0.142 0.012 l.733 0.027 0.004 0.180 0.003

1.903 0.003 0.178 0.010 1.648 0.032 0.005 0.213 0.004

1.903 0.001 0.165 0.012 1.712 0.028 0.003 0.176 0.005

4.003

4.000

4.000

4.005

4.011

3.996

4.005

0.91

0.90

0.91

0.91

0.91

0.89

0.91

Cations based on 6 oxygens

c. Mg

c. M" Fo

1The number in parentheses represents the one 5igma precision of replicate analyses as expressed by the least digit cited. 2Total iron expres5ed as FeO. :iorthopyroxenes occur only as inclusions in olivines. Abbreviations: See Table 2.

.

6

>

5 -

IP

'

.

'

'

~ .. ••·~::·

-

Cl

~ ~

l!b.

4 -

~

M

0

N

3

:cc

Cl

PrPo



Equi

2 - 6 0 1

53.5



• ••• •

-



-

..... ~Lot.: t.t 6

Re cry





-

Ct>OO

Amplhz

'

'

'

54.5

55.5

56.5

Si02 (wt%) Fie. 3. Si0 2 vs. Al 20 3 for orthopyroxenes in Cr-diopside series from the NGVF. Legend: PrPo protogranular to porphyroclastic; Equi = equigranular; Recry = "secondary" recrystallized.

335

NXRAD-GiJMiJR VOLCANIC FJELD

TABLE 3. Average Microprobe Analyses of Orthopyroxenes NMS09

NMSIO

NMSl6

NBN25

NBN27

NBN30

NBN54

Porph 15

Porph 17

Porph

Equi 12

Equi 19

Equi 18

Equi

NME13 Equi

NME18 Equi

14

22

9

54.5 (2) 0.13 (I) 4.59 (22)

54.4 (2) 0.11 (I)

55.0 (2) 0.12 (I)

Na20

54.6 (2) 1 0.11 (2) 4.76 (20) 0.38 (3) 32.4 (4) 0.99 (9) 0.13 (I) 6.38 (7) 0.12 (9)

Total

99.87

99.58

s;

No

1.891 0.002 0.194 0.010 1.673 0.036 0.003 0.184 0.008

Total

mg#

Sample: Texture:

NBNIO Porph 15

"' SiO~

Ti02

Al 20.1 Cr 20,1

MgO

c.o MnO re0~

0.39 32.7 0.77 0.14 6.27 O.o9

4.61 0.08 31.7 0.65 0.16 8.05 0,09

(5) (2) (3) (2) (5) (I)

(11) (2) (1) (2) (1) (6) (I)

17

55.4 0.10 3.79 0.33 33.5 0.67 0.13

4.49 (16) 0.32 (3) 32.9 (I) 0.72 (2)

0.14 (I) 6.32 (5)

(1) (I) (4) (2) (1) (1) (2)

55.2 0.09 3.76 0.36

0.06 (I)

99.85

100.11

100.17

1.892 0.003 0.187 0.010 1.693 0.028 0.004 0.181 0.006

1.896 0.002 0.189 0.002 1.647 0.024 0.004 0.234 0.005

I.897 0.003 0.182 0.008 1.694 0.026 0.003 0.182 0.006

1.909 0.002 0.154 0.009 1.720 0.024 0.003 0.178 0.004

4.001

4.004

4.003

4.001

0.90

0.90

0.88

0.90

56.0 0.03 2.51 0.47 33.8 0.72 0.14 5.81 0.05

33.l (2) 0.68 0.14 6.32 0.04

6.19 (3)

0.10 (\)

(2) (I) (20) (5) (2) (I) (6) (I)

99.59

(2) (I) (12) (7) (2) (2) (2) (6) (I)

55.5 0.08 3.97 0.40 33.5 0.67 0.11 5_92 0-07

(2) (I) (14) (6) (2) (2) (2) (7) (I)

55.2 0.03 3.48 0.44 33.6 0.74

(I) (1) (JO) (3) (I) (2) 0.15 (I) 6.22 (7) 0.05 (1)

54.7 (\)

0.14 (\) 4.35 (5) 0.39 (2) 31.8 (2) 0.86 (2)

0.17 (I) 7.35 (6) 0.07 (I)

NMEl9 Equi 19

54.8 (I) 0.06 (I) 4.03 (5) 0.44 (3) 33.0 (I) 0.76 0.14 6.08 0.08

(2) (I) (6) (I)

99.53

100.20

99.91

99.63

99.29

1.912 0.002 0.153 0.009 l.711 0.025 0.003 0.183 0.002

1.938 0.000 0.102 0.012 1.747 0.026 0.004 0.168 0.003

1.910 0.002 0.161 0.011 1.718 0.025 0.003 0.170 0.005

1.910 0.000 0.142 0.012 1.733 0.027 0.004 0.180 0.003

1.903 0.003 0.178 0.010 1.648 0.032 0.005 0.213 0.004

1.903 0.001 0.165 0.012 1.712 0.028 0.003 0.176 0.005

4.003

4.000

4.000

4.005

4.0ll

3.996

4.005

0.91

0.90

0.91

0.91

0.91

0.89

0.91

Cations based on 6 oxygens

T; Al

c, Mg

c,

Mn f,

1The number in parentheses represents the one sigma precision of replicate analyses 115 expressed by the least digit ciled. ''Total iron expressed as FeO. ·10rthopyroxenes occur only as inclusions in olivines. Abbreviations: See Table 2.

D~{}~

-

Ill

4 '"

' 3 - D

• 2 - .A

o 1

PrPo Equi

. .••• •

Recry

•• ··~ ::·.

• 6 a 6

!. ~AA: A 'tlf'I "!*ft~ ......... 6

A



-



-

Amplhz

L-~~~~~-...... ·~~~~~-...... ·~~~~~--'''-~--'

53.5

54.5

55.5

56.5

Si02 (wt%) FIG. 3. Si0 2 vs. Al 2 0 3 for orthopyroxenes in Cr-diopside series from the NGVF. Legend: PrPo = protogranular to porphyroclastic; Equi = equigranular; Recry ="secondary" recrystallized.

336

C. SZAB6 AND L. TAYLOR

TABLE

Sample: Texture:

"' SiO~

Ti0 2 Al 10-1 Cr~0-1

MgO

c.o

NME23 Equi 17

NMM02 Equi 13

NT803 Equi 5

55.6 0.08 3.43 0.50 33.4

55.9 0.05 3.57 0.42 32.6

55.3 0.o7 4.13 0.42 33.4 0.77 0.11 6.08 0.06

0.81 0.15 6.33 0.06

M"O Fe02 Na~O

3. (continued) Average Microprobe Analyses of Orthopyroxenes

(I)

(I) (3) (2) (l) (2) (2) (5) (l)

(2) (I) (12) (2) (2)

0.74 (I) 0.15 (I) 6.66 (7) 0.08 (I)

NFLlO Equi

NFLIS l-4ui

NFLJP Equi

NBNl5 Sec

NBN22

NBN23





NBN5l Se
x 0.2

0

co

--

c

PrPo



Equi

A

Re cry

+

Vein

.....

:!.6

40

1

50

' I o.812

~

0 30

50

I 0.756

• •• •eo .

6

45

.

0.1

0.0 30

40

c

0.2 0~

! 0"' i=

"'

CJ

. 6

45

• ot,8

0 2

o• '9.0

.6

c

-

c

0.0 30

c

~ 0 3 ~

c

0.4

~

. 40 .

35

4

~ 0.3 0

z"'"'

.

0 30 5

.

0

• •

"'

0.840

~

'if!.

c c::i

4

~eries from lhe NGVF Correlation coefficienls (r-!) are shown in insets. For an explanation of abbreviations, see Figure :l.

50

347

NOCRAD-GiJMOR VOLCANIC FIELD

TABLE

8.

INA Analyses' of Trace Elements in Peridotite Xenoliths

NMS09 Porph Amp

NMS16 Porph Amp

NBN25

15.4 2210 99 1970 100 nd nd nd

15.4 2280 103 2040 59 nd nd nd 0.24

13.9 2320 103 2330 64 21 2.6 0.20 0.19

12.6 2760 105 2370 70 nd nd nd 0.16

0.15

nd

0.05

nd 69

0.07

33

0.17 30

0.63 1.64 nd 0.34

0.45 1.98 nd 0.34

0.36

0.82

1.07 nd 0.27

0.131

0.143

0.115

Lu

nd 0.390 0.056

0.116 0.460 0.068

nd 0.240 0.036

2.16 nd 0.24 0.085 0.054 0.290 0.042

Ni/Co Ni!C.r [L./YbJN

19.9 0.89 I.IO

19.8 0.90 0.66

22.7 1.00 1.02

22.6 0.86 1.92

Sample: Texlure:

Mode 2 : So Cc Cn Ni Zn

Ba Rb c~

Hf

r.

Th Au

I..

c, Nd Sm Eu Tb Yb

0.18 0.09 nd 34

Equi Amp

NMEl9 Equi Amp

NFLIO Equi Amp

NFL15 Equi Amp

15.7

13.2

2250 106 2200 89 nd nd nd 0.18 nd nd 67

2120 IOI 2120 104 24

0.67 J.88 nd 0.29 0.121 0.079 0.380

0.054

20.7 0.98 J.20

NME23

NBN22

Equi

NBN30 Equi Anhydrous Anhydrous

s" Phi

NBN23

Cr-DV

nd 0.19 nd nd 18

6.0 1240 111 2590 BO nd nd nd 0.09 nd 0.06 22

4.8 2430 108 2100 128 43 10.6 0.43 0.IS

5.9 2970 132 2550 125 53 9.5 0.33

0.11 0.57

0.II 0.68 28

0.97 2.25 nd 0.38

0.30 1.09 nd 0.098

l.34 3.47 1.60

0.149

0.037

nd 0.300 0.054

nd 0.102

0.086 nd 0.162

0.166

2.18 4.90 3.00 0.65 0.25 nd 0.340

0.011

0.019

0.024

0.054

23.4 2.09 2.00

19.4 0.86 5.52

19.3 0.86

16.4 0.19 4.36

0.26

21.0 0.94

1.81

16

0.25

0.13

2.55 5.80

1.90 0.40 0.094 nd

10.45

36.3

4400 50

820 nd 40 3.7 nd 0.27 nd 0.37 12

1

Ppm and ppb for Au.

2Mode notation: Cr-DV

100

=Cr-diopside-rich vein; Amp= amphibole present; Phi= phlogopite presenL



Fig. 8. REE distribu1ion for prologranular to porphyrodastic (NMS09 and NMS16) and equigranular (NFLIO, NFLIS, NME23, NBN25, and NME19) Cr-diopside xenoli1hs from the NGVF compared to amphihole-bearing Crdiopside series from Victoria, Australia (dashed field) (Frey and Green, 1974) and Rhenish Massif, Germany (dotted field) (Stosch and Seek, 1980). REE values are normalized lo Cl chondrite (McDonough and Frey, 1989); values in inserted plot are normalized to primitive mantle (Sun and McDonough, 1989).

348

C. SZABO AND L. TAYLOR

50 -

13-Cs Rb Ba Th Nb Ta K La Ce Pb Nd P Sr Sm Hf Eu TiYYb

10

1

e NBN23 Vein

o NBN22



Geromino (Menzies et al., 1985)

o Rhenish Massif (Witt-Eickschen et al., 1993)

+ NBN30 0.1 La Ce

Nd

Sm Eu

Tb

Yb Lu

Fig. 9. REE distribution for "secondary" recrystallized (NBN22) and equigranular (NBN30) xenoliths and mantle Vf'in (NBN23 Vein) of C.r-diopside xenoli1hs from the NGVF compared to mantle veins from Geromino, soutliwPslern United Stales (Menzies el al., 1985), and from the Rhenish Massif (Witt-Eickschen et al., 1993). REE values are normalized to Cl ehondrite (McDonough and Frey, 1989); values in inserted plot are normalized to primitivP mantle (Sun and McDonough, 1989).

Type 1. With the exception of NBN30, the Group-I xenoliths (protogranular to porphyroclastic NMS09 and NMSl6 and equigranular NBN25, NFLIO, NFLIS, and NMEl9) containing amphibole ( 0

-1

c

PrPo Equi

-2

• 6

Recry