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
5«
5«
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
