Precambrian Research 103 (2000) 191 – 206
Proterozoic crustal evolution in the NW Himalaya (India)
as recorded by circa 1.80 Ga mafic and 1.84 Ga granitic
magmatism
Christine Miller
a,*, Urs Klo¨tzli
b, Wolfgang Frank
b, Martin Tho¨ni
b,
Bernhard Grasemann
baInstitut fu¨r Mineralogie und Petrographie,Uni6ersity of Innsbruck,Innrain 52,A-6020Innsbruck, Austria bInstitut fu¨r Geologie,Uni6ersity of Vienna,Althanstrasse 14,A-1090 Vienna, Austria
Received 6 July 1999; accepted 19 May 2000
Abstract
Single zircon dating of the Rampur metabasalts of the Larji – Kullu – Rampur window in the Lesser Himalayas
yielded an evaporation age of 1800913 Ma. The zircon age is considerably younger than the previously published
whole rock Sm – Nd age of 2510990 Ma, suggesting that the Sm – Nd age may be geologically meaningless and that
the Sm – Nd whole rock array may have resulted from mixing. In the NW Himalaya, there is also evidence for extensive silicic melt generation in the Paleoproterozoic. Zircons from a metarhyodacite in the Larji – Kullu – Rampur
window yielded an evaporation age of 1840916 Ma, which we interpret as the minimum age of magmatism. The
Main Central Thrust granitic mylonites are interpreted as the basement of the Neoproterozoic Haimanta Group metasediments. Together with the granitic rocks from the Lesser Himalaya, they were derived from pre-existing continental crust prior to 1.84 Ga. The Nd depleted mantle model ages are in the range of 2.6 – 2.4 Ga, suggesting a contribution of Archean crust. A recycled Archean component is also documented by a 2.9 Ga domain in one of the zircons. © 2000 Elsevier Science B.V. All rights reserved.
Keywords:NW Himalaya; Proterozoic magmatism; Geochronology; Geochemistry
www.elsevier.com/locate/precamres
1. Introduction
The Himalayan orogen is a product of the Cainozoic collision between India and Asia. In the course of this collision, the Higher Himalaya (HH) was thrusted southwards over the Lesser
Himalaya (LH) along the Main Central Thrust (MCT). Both, HH and LH are considered parts of the northern passive margin of India. Many studies have focussed on the Phanerozoic se-quences, but the provenance of the largely unfos-siliferous Proterozoic sediments in both units is less well understood (Frank et al., 1995; Parrish and Hodges, 1996). Data on the basement of
these Proterozoic supracrustal sequences and/or
* Corresponding author.
E-mail address:christine.miller@uibk.ac.at (C. Miller).
C.Miller et al./Precambrian Research103 (2000) 191 – 206 192
magmatic rocks are sparse and contradictory. Pre-vious Rb – Sr and Sm – Nd dating of LH granitic and mafic rocks yielded whole rock ages ranging from 2510 to 1220 Ma (Frank et al., 1977; Bhanot et al., 1982; Bhat and LeFort, 1992). Better con-straints on the age and provenance of the Protero-zoic supracrustal sequences, associated igneous suites and their basement, however, are essential for reconstructions of the relationship between HH and LH before the onset of the Himalayan orogeny.
We have sought to characterize the age and distribution of the Proterozoic igneous suites in the different units and we have used the Sm – Nd technique to compare their protolith characteris-tics. Another key objective of our study was to
determine zircon207Pb
/206Pb ages from a
metarhy-odacite and a metabasalt that are associated with clastic metasediments in the basal sedimentary succession (Rampur formation) of the LH. For the metabasalts, our new zircon data do not confirm the Archean Sm – Nd whole rock age in the literature. In addition, we present geochemical data on the Rampur metabasalts and on grani-toids from the LH and the MCT zone which provide constraints on their source characteristics and the crustal evolution of the former passive margin of northern India.
2. Regional geology
In the Himalaya of NW India three major tectonic units can be distinguished from south to
north (Gansser, 1964): (i) the Subhimalaya
Miocene – Pleistocene molasse deposits which are overthrusted along the Main Boundary Thrust by the (ii) LH, which consists primarily of Protero-zoic to Cambrian low-grade metasedimentary rocks, metagranitoids and metavolcanics. (iii) The HH, thrusted over the LH along the MCT, com-prises greenschist to amphibolite facies
Precam-brian to Cambrian metasediments (High
Himalaya Crystalline) and the Paleozoic to Meso-zoic Tethyan Zone (Fig. 1). Neogene nappe stack-ing of these major units, differential uplift and erosion have exposed the LH in two tectonic windows — the Kishtwar Window in the NW
(Fuchs, 1975; Sta¨ubli, 1988; Guntli, 1993) and the Larji – Kullu – Rampur Window (LKRW) in the SE (Auden, 1948; Berthelsen, 1951; Jhingran et al., 1952; Frank et al., 1973; Tho¨ni, 1977).
In the LKRW and in the Simla area two super-posed Proterozoic supracrustal sequences can be distinguished, each ending with redbeds and a shallow-water carbonate platform: (i) Rampur
(Chail)-Khaira-Shali and (ii) the younger,
Neoproterozoic Simla – Blaini – Krol sequences
(e.g. Frank et al., 1995). Stromatolites in the Shali Group carbonates at the top of the lower se-quence suggest a lower to mid-Riphean age (Ash-girei et al., 1975). The basal unit of this lower sequence is the Rampur formation (Jhingran et al., 1952), consisting of massive beds of white quartzarenites alternating with thin layers of seriz-ite and chlorseriz-ite schists, locally associated with metarhyolites and metabasaltic dikes and lava flows (Rampur metabasalts). Where preserved, sedimentary structures like cross bedding and rip-ple marks indicate a normal polarity for these series. At present, it is not clear whether the Rampur formation quartzites are unconformably overlying the Bandal granitoid complex (Srikantia and Bhargava, 1998) or whether the granitoids intrude these quartzites (Sharma, 1977). This im-portant issue can only be resolved through further studies. Rb – Sr whole rock data suggest a Pale-oproterozoic age for the Bandal granitoids (Frank et al., 1977) which are remarkably similar to the Jeori – Wangtu granitoid gneiss complex (JWGC, Fig. 1), except for the higher metamorphic grade of the latter.
The JWGC is an integral part of the LKRW (Bhargava, 1982; Srikantia and Bhargava, 1998) and consists of partly mylonitic augen gneisses (Wangtu gneiss), paragneisses, mica schists and minor concordant sheets of metabasites. It is characterized by an inverted metamorphic zona-tion (Vannay and Grasemann, 1998). Near Jhakri the JWGC is faulted along a W dipping thrust overlying the quartzites of the Rampur formation.
Preliminary 40Ar
/39Ar geochronology results
C.Miller et al./Precambrian Research103 (2000) 191 – 206 193
out-of-sequence thrust. The JWGC probably rep-resents the basement for the Rampur formation and has been faulted onto its own cover during the last few Ma along the above mentioned W directed out-of-sequence thrust (Vannay et al., 1999).
In the NW Himalayas, the MCT zone consists of highly deformed mylonitic orthogneisses and paragneisses (i.e. metamorphic equivalents of the Haimanta Group metasediments) revealing an in-verted metamorphic gradient. This greenschist to amphibolite facies metamorphic sequence in the hanging wall is distinct from the footwall which comprises low-grade metamorphic Precambrian
sedimentary rocks of the LH along a brittle thrust zone. Field observations suggest that the pro-toliths of the mylonitic orthogneisses did not in-trude into the Haimanta Group, but rather represent the basement of these Proterozoic metasediments (Trivedi et al., 1984; Srivastava and Mitra, 1996; Grasemann et al., 1999). This interpretation is supported by the large lateral extent of the orthogneisses and the fact that they always have the same litho-tectonic position at the base of the Haimanta Group. The characteristic association of the MCT orthogneiss mylonites with carbonaceous-graphitic schists and phyllites has been assigned different names in different
C.Miller et al./Precambrian Research103 (2000) 191 – 206 194
Fig. 2. Zircons from (a) metabasalt HB65/96 and (b) metarhy-olite HF49/90, Larji – Kullu – Rampur window.
Bhuntar and Manikaran. These metabasalts have also been studied by Bhat and LeFort (1992). The original mineralogy and textures of these volcanic rocks have been destroyed by Tertiary deformation and greenschist facies metamorphism. The meta-morphic assemblage is Amp (ferri – potassian –
tschermakitic hornblende)+Bio [Mg/(Mg+Fe)
=0.47]+Plg (Ab80 – 82)+Qtz+sphene+ilmenite.
3.2. Geochronology of the Rampur metabasalts
Knowing the age of the Rampur metabasalts is of major importance for the stratigraphic correla-tions in the LH. Analysis of subtype S24 and S25 (Fig. 2a; Pupin and Turco, 1972) zircons from
metabasalt HB65/96 by the single grain
evapora-tion technique (Kober, 1987; Klo¨tzli, 1997)
yielded an age of 1800913 Ma (1 s) without
evidence of an older component (Table 1). This age is interpreted as dating magmatic zircon growth. However, if this zircon is inherited, this would represent a maximum crystallization age.
In contrast, Bhat and LeFort (1992) published
a whole rock Sm – Nd isochron age of 2510990
Ma (2 s), also from the Rampur metabasalts. In
addition, Bhat et al. (1998) studied the Sm – Nd systematics of the Garhwal and Bhowali mafic volcanic rocks of the Kumaun Lesser Himalaya and interpreted the composite whole rock Sm –
Nd reference line as indicating an age of 25109
80 Ma. Dating metabasaltic rocks by means of whole rock Sm – Nd isochrons, however, is highly problematic. Several published Sm – Nd isochrons on old mafic rocks have subsequently been shown by other methods to represent mixing arrays without any chronological meaning (e.g. Chauvel et al., 1985; Compston et al., 1986; Gruau et al., 1990).
Our zircon207Pb
/206Pb date implies that the 2.5 Ga age may be geologically meaningless and can-not be correlated with the magma-forming event. Depleted mantle Nd model ages for the Rampur metavolcanic rocks, including the data of Bhat and LeFort (1992), fall in the range 1.40 – 2.17 Ga (Table 2). These ages are younger than their Sm – Nd ‘isochron’ age, again indicating that the Archean age is not meaningful.
areas (e.g. Bajaura Nappe: Frank et al., 1973; Outer Granite Band: Bhatia and Kanwar, 1973; Baragaon Gneiss: Bhanot et al., 1978; Seawa Paragneiss: Sharma et al., 1973; Gahr-Manjrot Formation: Bassi, 1989). The age of the Precam-brian Haimanta Group metasediments is not well constrained, but several lines of evidence suggest a Neoproterozoic age (Frank et al., 1994; Draganits et al., 1998).
3. Lesser Himalaya: Rampur metabasalts
3.1. Petrography
C
.
Miller
et
al
.
/
Precambrian
Research
103
(2000)
191
–
206
195
Table 1
Single zircon evaporation data of metabasalt HB65/96 and of metarhyolite HF49/90, Larji–Kullu–Rampur window, NW Himalaya
No. of blocks Evaporation 207Pb/206Pb 1 SEc 1 SE (%)c 207Pb/206Pb 208Pb/206Pbb 1 SEb Th/Ue
Sample 1 SE 1 SEb
(radiogenic)b age (Ma)d
temperature (°C)a (Ma)b
HB65/96-A(S24,150mm,1:4,sl.turbid,colourless,no inclusions)
20 1254
1127Ac1 0.11156 0.00026 0.2 1825 4
4 1276 0.10960 0.00210
1127Ac2 1.9 1793 35
4 1296 0.11037 0.00078 0.7
1127Ac3 1806 13
0.11051 0.00081 0.7 1808 13
Mean
HB65/96-B(S25,100mm,1:3,sl.turbid,colourless)
10 1360 0.10936 0.00030
1127Bc1 0.3 1789 5
20 1383 0.11238 0.00022 0.2 1838 4 0.076 0.001 0.211
1127Bc2 0.002
6 1449 0.10790 0.00232 2.2
1127Bc3 1764 39 0.093 0.001 0.259 0.002
Mean 0.10988 0.00187 1.7 1797 31
HF49/90-A(J5,150mm,1:4,colourless)
1 1400 0.11329 0.00126 1.1
1053AC1 1853 20 0.1277 0.0021 0.352 0.006
1053AC3 10 1420 0.11264 0.00098 0.9 1842 16 0.1215 0.0008 0.335 0.002
1053AC5 10 1440 0.11313 0.00070 0.6 1850 11 0.1279 0.0009 0.353 0.003
11 1461 0.11487 0.00095 0.8
1053AC7 1878 15 0.1305 0.0022 0.359 0.006
10 1480 0.11293 0.00116 1.0 1845 19
1053AC9 0.1211 0.0018 0.334 0.005
0.11335 0.00089 0.8 1854 14
Mean
HF49/90-B(J5,120mm,1:5,colourless)
1053BC1 10 1301 0.11260 0.00841 7.5 1842 136 0.1118 0.0100 0.309 0.028
10 1340 0.11252 0.00205 1.8
1053BC2 1841 33 0.1084 0.0025 0.299 0.007
1053BC4 10 1461 0.11257 0.00111 1.0 1841 18 0.1114 0.0025 0.308 0.007
1053BC6 10 1380 0.11246 0.00143 1.3 1839 23 0.1138 0.0101 0.314 0.028
10 1400 0.11304 0.00614 5.4
1053BC8 1859 98 0.1170 0.0057 0.323 0.016
1053BC10 10 1420 0.11245 0.00446 4.0 1839 72 0.1354 0.0062 0.374 0.017
10 1440 0.11108 0.00455 4.1
1053BC12 1817 74 0.1443 0.0101 0.399 0.029
5 1460 0.11182 0.00156 1.4 1829
1053BC14 25 0.1541 0.0121 0.426 0.033
0.11232 0.00060 0.5 1837
Mean 10
HF49/90-C(J4,150mm,1:4,colourless,sl.turbid)
10 1340 0.11294 0.00563 5.0
1053CC1 1847 90 0.1319 0.0076 0.364 0.021
1053CC2 10 1380 0.11375 0.00262 2.3 1860 42 0.1288 0.0114 0.031 0.007
1053CC3 10 1400 0.11243 0.00229 2.0 1839 37 0.1206 0.0126 0.333 0.035
10 1400 0.11196 0.00236 2.1
1053CC4 1831 38 0.1208 0.0021 0.334 0.006
1053CC5 10 1420 0.11082 0.00304 2.7 1813 50 0.1151 0.0072 0.318 0.020
8 1420 0.11159 0.00165 1.5
1053CC6 1825 27 0.1186 0.0033 0.328 0.009
10 1440 0.10870 0.00825 7.6
1053CC7 1778 139 0.1188 0.0508 0.33 0.141
5 1440 0.11167 0.00156 1.4
C
.
Miller
et
al
.
/
Precambrian
Research
103
(2000)
191
–
206
196
Table 1 (Continued)
Sample No. of blocks Evaporation 207Pb/206Pb 1 SEc 1 SE (%)c 207Pb/206Pb 1 SE 208Pb/206Pbb 1 SEb Th/Ue 1 SEb temperature (°C)a (radiogenic)b age (Ma)d (Ma)b
10 1460 0.11103 0.00162 1.5
1053CC10 1816 26 0.0953 0.0030 0.264 0.008
8 1480 0.10947 0.00316 2.9
1053CC12 1719 53 0.0775 0.0096 0.215 0.027
Mean (excl. C7, C12) 0.11202 0.00098 0.9 1832 16
HF49/90D(J4,130mm,1:3,colourless,sl.turbid)
1053DC1 10 1320 0.21539 0.00538 2.5 2947 40 0.4866 0.0353 1.214 0.085
10 1340 0.11414 0.00180 1.6
1053DC2 1866 29 0.1266 0.0082 0.349 0.022
1053DC3 5 1380 0.11147 0.00283 2.5 1824 46 0.1338 0.0076 0.370 0.021
0.11281
Mean (excl. C1) 0.00189 1.7 1845 30
0.11248 0.00100 0.9 1840 16
HF49/90
(mean of 4 grains)
aError on evaporation temperature is estimated to be910°C. bWeighted mean from indivial scan ratios.
cAll errors reported are 1 standard errors of the mean.
C
Sr and Nd isotopic data for Proterozoic igneous rocks from the NW Himalaya
Unita
LH LKRW, Sainj Metabasalt 1800 19
HF45/90 180 0.305 0.72763699 3.6 11.8 0.1844 0.5127793 5.4 2.00
LH LKRW, Rampur Metabasalt 1800 21 180 0.338 0.71695197 5.2 24.7 0.1273 0.5118793 1.0
HB65/96 1.40
LH LKRW, Rampur Metabasalt 1800
Rj25b 0.132 0.511859923 −0.3 2.12
Rj21b LH LKRW, Rampur Metabasalt 1800 0.377 0.71637949 0.134 0.511864917 −0.6 2.16
Rj15b LH LKRW, Rampur Metabasalt 1800 0.136 0.511885928 −0.7 2.17
LH LKRW, Rampur Metabasalt 1800 0.391
Rj2b 0.72803945 0.153 0.512191925 1.4 2.03
LH LKRW, Rampur Metabasalt 1800 0.189 0.72803927 4.7 1.51
Rn6b
Proterozoic felsic rocks
LH LKRW Leucogranite 1840 445
HF37/90 70 19.460 1.19248922
LH LKRW Granite 1840 243 501 1.412 0.7431199 10.3 66.4 0.094 0.51110498 −6.2
HF39/90 2.38
LH LKRW Leucogranite 1840 483 69 21.620
HF40/90 1.31165917
HF41/90 LH LKRW Granite 1840 309 330 2.735 0.7837092
LH LKRW Bio-granite 1840 212
HF42/90 152 4.105 0.8341198
LH LKRW Qtz-syenite 1840 309 201 4.519
HF43/90 0.84727936
HF46/90 LH LKRW Leucogranite 1840 348 62 16.970 1.1508098
HF48/90 LH LKRW Qtz-monzonite 1840 151 176 2.495 0.74302910
LH LKRW, Sainj Metarhyolite 1840 260 143 5.381
HF49/90 0.86610912 12.0 65.9 0.110 0.51131099 −5.9 2.44
HF35/92 LH JWGC, Wangtu Granitic gneiss 1860 298 72 3.083 0.7895896 LH JWGC, Wangtu Granitic gneiss 1860 296 139 12.460
HF36/92 1.0445098
HF102/90 LH KW, E Kishtwar Granitic gneiss 1840 352 130 8.018 0.93982910 HF103/90 LH KW, E Kishtwar Qtz-monzonite 1840 291 630 1.343 0.74238914
LH KW, E Kishtwar Granite 1840 282 357 2.313
HF106/90 0.76737911 7.1 39.1 0.109 0.51115197 −8.8 2.63
HF108/90 LH KW, E Kishtwar Granite 1840 274 257 3.120 0.8047697
LH KW, E Kishtwar Granitic gneiss 1840 372 100 11.148
HF110/90 1.0130296
LH KW, E Kishtwar Granite 1840 315 130 9.109
HF111/90 0.9502098
MCT Bajaura Granitic mylonite 1840 345 64 16.320
HF50/90 1.1452098 21.9 130.4 0.102 0.51121999 −5.8 2.40
MCT Bajaura Granitic mylonite 1840 227 98 6.860 0.9058295
HF52/90
MCT Bajaura Granitic mylonite 1840 180 56 9.440
HF54/90 0.8463096
HF37/92 MCT Baragaon Granitic mylonite 1840 276 108 7.510 0.88259914
HB52/96 MCT Luhri Granitic mylonite 1840 286 163 5.140 0.8498396
MCT Kotlu Granitic mylonite 1840 231 95 7.130
HB61/96 0.8448399
MCT Machad Granitic mylonite
HB66/96 1840 267 65 12.130 0.8890797
Paleozoic intrusi6es
HHC Mandi Bi–Ms granite 496
HF67/91c 3.7 14.9 0.149 0.51195499 2.41
HHC Jaspa Ms-granite 496
T41c 2.6 9.5 0.166 0.512020911 2.96
HHC Kaplas Bi–Ms granite 554 12.5
HF144/90c 75.4 0.099 0.51183696 1.58
aLH=Lesser Himalaya, MCT=Main Central thrust, HHC=High Himalaya Crystalline, LKRW=Larji–Kullu–Rampur Window, KW=Kishtwar Window, JWGC=Jeori–Wangtu gneiss complex. bData from Bhat and LeFort (1992, 1993).
C.Miller et al./Precambrian Research103 (2000) 191 – 206 198
3.3. Geochemistry of the Rampur metabasalts
Major, trace element and rare earth element (REE) data of four metabasic rocks from the Rampur – Jhakri section and Sainj are given in Table 3. The analyzed samples are
quartz-tholei-itic in composition. In addition to high SiO2 and
relatively low MgO, the major element composi-tion is characterized by high FeO*. The
Mg-num-bers range between 29 and 55 [Mg-number=
Mg/(Mg+Fe2+
), setting Fe3+
/Fe2+
=0.15]. The
chondrite-normalized REE patterns are shown in Fig. 3(a). All samples plot within the field
previ-ously reported for the Rampur metavolcanic rocks (Bhat and LeFort, 1992). The three evolved
samples from Jhakri are LREE enriched (LaN/
YbN=4.9 – 5.4) with relatively flat HREE
pat-terns at approximately 17 times chondrite and
small negative Eu anomalies (Eu/Eu*=0.86 –
0.94), quite similar to samples Rj15, Rj21 and Rj25 from the same section analyzed by Bhat and LeFort (1992). In contrast, the more primitive
metabasalt HF45/90 from Sainj has lower REE
contents, a lower LaN/YbN ratio of 2.3 and does
not possess a depletion in Eu. Another illustration of the trace element signature is given by the primitive mantle normalized diagram (Fig. 3b). Apart from the greater spread for the more in-compatible elements, this diagram shows negative Ta, Nb, Sr and P anomalies for the samples from Jakri. The distinct negative Nb anomaly is also seen in the sample from Sainj and in the meta-basalts analyzed by Bhat and LeFort (1992). Sr and Nd isotopic data are given in Table 2 and in Bhat and LeFort (1992, 1993). Accepting a 1.8 Ga
eruption age, our samples yielded initial oNd
val-ues of +5.4 and +1.0, the samples analyzed by
Bhat and LeFort (1992) range from +4.7 to
−0.7. Only four Sr isotopic data exist so far.
Calculated with an age of 1.8 Ga, our initial 87Sr
/86Sr ratios range from 0.7082 to 0.7197, those
reported by Bhat and LeFort (1993) range from 0.7066 to 0.7179.
3.4. Petrogenesis of the Rampur metabasalts
The low Mg-numbers of the Rampur meta-basalts clearly indicate that they could not have been in equilibrium with mantle olivine. Even the least evolved sample in terms of incompatible elements has a much lower Mg-number (55) and Ni content (125 ppm) than expected for
un-modified primary basalts. MgO/FeO*, a monitor
of ferromagnesian silicate fractionation, ranges from 0.61 to 0.21. The development of small negative Eu anomalies in the more evolved sam-ples is consistent with fractionation of plagioclase. The primitive mantle normalized patterns of the Rampur metabasalts (Fig. 3b) resemble those ob-served in other Proterozoic mafic dikes (Tarney, 1992) and in many continental flood basalts
C
Major (wt%), trace element and REE (ppm) concentrations of Rampur metabasalts and granitic rocks from the Larji–Kullu–Rampur and Kishtwar windows, the Jeori–Wangtu gneiss complex and the MCT zone, NW Himalaya
HF45/90 HB65/96 HB33/97 HB34/97 HF49/90 HF39/90 HF46/90
Sample no.: HF102/90 HF106/90 HF35/92 HF37/92 HF50/90
Metabasalt Metabasalt Metabasalt Metabasalt Metarhyolite
Lithology Granite Granite Granite Granite Granite Mylonite Mylonite
Unit LKRW LKRW LKRW LKRW LKRW LKRW LKRW KW KW JWGC MCT MCT
Sainj W Jakri W Jakri W Jakri Sainj Sainj
Location Sainj E Kishtwar E Kishtwar Wangtu Baragaon Bajaura
49.7 51.6 50.1 53.5 68.2 68.5
SiO2 71.3 69.4 68.2 74.6 66.8 74.5
1.4 1.5 2.6 1.8 0.6 0.5
TiO2 0.3 0.4 0.4 0.2 0.2 0.2
13.6 13.7 11.3 12.1 13.7 14.8
Al2O3 14.4 15.4 14.1 13.4 14.4 11.7
99.5 99.5 100.3 100.8 98.6 99.5
Total 98.7 98.8 98.6 99.5 99.7 99.0
n.d. n.d. 200 180 962 1273 891 1446 1247 680 470 2620
F
180 180 144 191 140 498
Sr 64 128 355 72 108 63
0.31 0.46 0.57 0.53 0.50 0.16 0.18
Tm 0.04 0.25 0.36 0.54 1.03
1.7 2.9 3.6 3.5 2.9 1.0
Yb 1.1 0.04 1.3 2.5 3.7 6.5
C.Miller et al./Precambrian Research103 (2000) 191 – 206 200
Fig. 4.oNd versus 1/Nd diagram at the time of eruption (1.8 Ga) with fractional crystallization (FC) and AFC (DePaolo, 1981) trends for the metabasic rocks from the LKRW (includ-ing samples analyzed by Bhat and LeFort, 1992). The AFC vectors represent fractional crystallization of metabasalt Rn6 with assimiliation of granitoid HF50/90 (r=0.3). Note that this is not a unique solution, just a possible explanation for the crustal contamination model.
high initial87Sr
/86Sr ratios that are far outside the variation range of the mantle trend.
Essentially two options are available for the introduction of a crustal component: either (i) magmas were derived from the mantle and be-came contaminated during ascent through the crust (crustal-level contamination) or (ii) recycling of older crust (mantle source contamination). The evidence at the moment is far from clear-cut although the correlation between Nd content and
o(t)Nd (Fig. 4) would be consistent with
increas-ing degrees of contamination of the least evolved mafic lavas by LREE-enriched crust such as the
Proterozoic granitoids. The correlation (R=0.93)
between 1/Nd and 143Nd
/144Nd in the Rampur
metabasalts also indicates that the 2.5 Ga Sm – Nd array (Bhat and LeFort, 1992) is an artifact of mixing between depleted mantle melts generated at 1.8 Ga and an older enriched lithospheric component.
4. Lesser Himalaya and MCT zone: felsic magmatic rocks
4.1. Geochronology of felsic igneous rocks
Frank et al. (1977) published a Rb – Sr whole
age of 1840970 Ma (2 s) based on four granitic
WR samples from Bandal and Sainj (LKRW), documenting the existence of Proterozoic acid magmatism in the Himalayas. Our 24 granitic samples from the Kishtwar Window, LKRW, JWGC and the MCT orthogneiss mylonites (Table 2) also plot on this regression, suggesting the widespread presence of Paleoproterozoic felsic plutons in the LH and in the MCT zone, in agreement with radiometric evidence in the litera-ture. In the JWGC, the Wangtu granitoid gave a
U – Pb zircon age of 1866910 Ma (Singh et al.,
1994), and Rb – Sr whole rock ages of 2025986
Ma (Kwatra et al., 1986) and 1866964
(Ramesh-war et al., 1995). The MCT mylonitic or-thogneisses yielded a Rb – Sr whole rock age of
1865960 Ma (Trivedi et al., 1984). Although
Rb – Sr systematics do not resolve the Proterozoic magmatic activity in detail due to the possibility of open-system behavior in such complex terrains
(CFB). Ti/V ratios in the range of 20 – 50 are also
consistent with an origin similar to CFB (Sher-vais, 1982), i.e. moderately high degrees of partial melting of shallow mantle and fractionation pro-cesses under reducing conditions. The trace ele-ment characteristics of the Rampur samples are clearly different from those typical of ocean island basalts (OIB; Fig. 3b), but they share some chem-ical features (high large ion lithophile elements,
low TiO2 and negative Ta – Nb anomalies) with
subduction zone magmas. Whereas the trough at Sr is probably a consequence of low-pressure plagioclase fractionation as indicated by the nega-tive Eu anomalies, the neganega-tive Nb – Ta anomaly could reflect the existence of a residual Nb – Ta phase during the partial melting process in the mantle (e.g. Foley and Wheller, 1990). Alterna-tively, the Nb – Ta anomaly could be a conse-quence of crustal contamination. A continental crustal signature is indeed suggested by several geochemical parameters such as the distinctly low
Ce/Pb (4.4 – 11.9) ratios relative to OIB and
N-MORB, and the combination of high Th/Yb
(0.4 – 1.5) ratios with low Ta/Yb (:0.2). In
C.Miller et al./Precambrian Research103 (2000) 191 – 206 201
it is striking that in the Lesser Himalaya we did not find any evidence for the Early Paleozoic magmatic event that is widespread in the HH Crystalline (e.g. LeFort et al., 1986).
Metarhyodacite HF49/90 is associated with the
basal metasediments of the Rampur formation in
which K-feldspar forms conspicuous ovoid phe-nocrysts. Quartz phenocrysts are blue, frequently embayed and may show signs of incipient dy-namic recrystallization. Together with
bookshelf-type plagioclase porphyroclasts the quartz
phenocrysts are set in a sheared groundmass of fine-grained feldspar, biotite and quartz. Zircons (Fig. 2b) plot in subtype fields J4 and J5 in the typologic zircon classification diagram (Pupin and Turco, 1972). Four zircons were analyzed by the single zircon evaporation technique (Kober, 1987; Klo¨tzli, 1997). They yielded a well defined age of
1840916 Ma (1 s; Table 1), which we interpret
as the age of magmatism. One of the zircons also
preserved evidence of an earlier (\2.9 Ga) event,
surprisingly in the low temperature steps.
4.2. Geochemistry and implications for granitoid petrogenesis
Forty four samples (Lesser Himalaya and MCT granitic mylonites) are characterized by high lev-els of K2O (4.4 – 6.0 wt%) throughout the SiO2 range from 62 to 75 wt% (Table 3). For the
majority of samples Al2O3/(Na2O+K2O+CaO)
is 1.1 to 1.4 and normative corundum is \1%.
All analyzed samples are preferentially enriched in
LREE (LaN/YbN=12.4 – 42.1) and show
pro-nounced negative Eu anomalies (Eu/Eu*=0.16 –
0.65). On a multi-element variation diagram (Fig. 5), they are characterized by negative Ba, Nb, Sr, P and Ti anomalies and by relatively high levels of Rb, Th and U. Table 2 presents the Sr and Nd isotopic characteristics of the Proterozoic granitic
rocks. 87Sr/86Sr initial ratios are generally high
(0.711 – 0.721). The initialoNd values are negative
and range from −5.8 to −8.8.
Most of the granitic rocks from the LH and the MCT zone are peraluminous. Some are even S-type, based on the criteria proposed by Chappell and White (1974). Some granitoids have elevated
concentrations of high-field strength (HFS)
cations which suggest that they are A-type (Fig. 6). However, diagnostic mineralogical features are absent and isotopic compositions are far too evolved for these rocks to be included in the A-type granitoid group. Their high trace element abundances are probably due to entrainment of
C.Miller et al./Precambrian Research103 (2000) 191 – 206 202
Fig. 6. Rb versus (Nb+Y) plot for granitic rocks from the Larji – Kullu – Rampur window (LKRW), Kishtwar window (KW), MCT zone and Jeori – Wangtu Granitic Gneiss complex (JWGC), NW Himalaya. Field boundaries from Pearce et al. (1984). COLG=collisional granites, VAG=volcanic arc granites, WPG=within-plate granites, ORG=oceanic ridge granites.
5. Lithostratigraphic and paleogeographic correlations
It has been suggested (Parrish and Hodges, 1996; Whittington et al., 1999) that the lithologi-cal sequences of the HH Crystalline and LH can be identified along strike of the Himalayan orogen on the basis of their distinct Nd model ages and that the MCT marks a terrane boundary. Accord-ing to WhittAccord-ington et al. (1999), the HH is charac-terized by depleted mantle model ages in the range of 1.2 – 2.0 Ga and distinct from the LH where Nd model ages range from 2.3 – 3.4 Ga. Our Sm – Nd data (Table 2) suggest that this could merely reflect an inadequate database. The analyzed Paleoproterozoic LH granitic rocks and the MCT orthogneiss mylonite have model ages ranging between 2.4 and 2.6 Ga. However, in the NW Himalaya, the Paleozoic granites within the HH Crystalline (Fig. 1) yield model ages ranging from 1.6 to 2.9 Ga (Table 2 and unpublished data) and thus overlap data reported for the LH and the MCT zone.
The tholeiitic composition of the Rampur meta-basalts indicates a lherzolitic source and relatively high degrees of partial melting. In addition, the
lack of a residual garnet signature (Ce/Yb:9)
suggests shallow depth of melting and, possibly, passive crustal extension. The tectonic setting of the Rampur metabasalts remains ambiguous, but at present there is no clear geochemical evidence for the involvement of plume material in their petrogenesis. The suggestion by Bhat et al. (1998) that they were generated above the center of an Archean mantle plume is based on the interpreta-tion of an apparently erroneous Sm – Nd isochron age. It fails to explain the absence of a plume signature in the basalt trace element chemistry, the absence of komatiites in the LH and the low MgO – high Na2O chemical composition of these mafic volcanic rocks. According to White and McKenzie (1989), central plumes of rising mantle are characterized by abnormally high tempera-tures. As the potential asthenosphere temperature is increased up to 1480°C, the percentage of MgO increases systematically from about 10 to 18%, and the percentage of Na2O simultaneously decreases.
HFSE-rich restite phases from crustal source rocks during partial melting. The observed REE distributions and the negative Sr and Eu anoma-lies indicate fractionation by mineral phases con-taining these elements at some stage in the evolution of the source or of the magma (e.g. residual plagioclase combined with plagioclase fractionation). These compositional features, the
range in initial 87
Sr/86
Sr ratios and the negative
initial oNd values (Table 2) clearly point to a
major role of older continental crust in the forma-tion of these granitoids. The depleted mantle model ages (Table 2) suggest a contribution of Archean crust. A recycled Archean component is
also documented by the\2.9 Ga domain detected
C.Miller et al./Precambrian Research103 (2000) 191 – 206 203
In the NW Himalaya, a period of silicic volcan-ism and granite emplacement occurred around 1.86 – 1.84 Ga. These Paleoproterozoic granitoids are not restricted to the LH tectonic windows. From S of Kishtwar to Nepal, they form a nearly continuous zone of mylonites and augengneisses at the base of the MCT. The geochemical and isotopic similarities between the MCT mylonites and the Lesser Himalaya granitic rocks are consis-tent with the notion that the MCT cuts down-sec-tion into the hanging-wall. The considerable areal
extent and the range in initial87
Sr/86
Sr and initial
o (Nd) of the Paleoproterozoic granitoids clearly
suggest processes of large-scale reworking of sialic crust. The geochemical data (Fig. 6) apparently rule out subduction-related magmatism, but can-not distinguish between (i) anatexis of existing crust during a period of syn- to post-collisional crustal thickening; (ii) crustal melting in a post-collisional extensional regime or (iii) melting in response to post-collisional lithospheric delamina-tion and mafic underplating. As there is no clear evidence for collision-related crustal thickening
and/or deformation, an alternative thermal cause
for crustal melting must be found. An attractive mechanism has been proposed by Sandiford et al. (1998). Their thermal-isostatic model predicts sig-nificant crustal melting as a consequence of burial of basement sequences enriched in heat producing elements during thermal subsidence.
Proterozoic rocks are also present in the Ar-avalli domain south of the Himalayas. Unfortu-nately, possible connections are not only obscured by the alluvium of the intervening Indo-Gangetic plain but also by the fact that an unknown amount of Proterozoic material has been de-stroyed in the Himalayan orogeny. Available geochronological data suggest that several periods of acid magmatism have affected the Aravalli domain between c. 3.3 and 0.8 Ga (e.g. Tobisch et al., 1994; Wiedenbeck et al., 1996). In addition, a Paleoproterozoic (c. 2.5 – 2.4 Ga) mafic magmatic event is recorded at the base of the Aravalli Supergroup (e.g. Verma and Greiling, 1995). These lavas are LREE enriched and range from magnesian komatiites to Fe-rich tholeiites. They have been interpreted as products of the interac-tion of a deep mantle plume with subcontinental
lithosphere (Ahmad and Tarney, 1994). The avail-able data, however, are still too sparse and too imprecise to allow any firm assessment of the continuation of the LH into the northwestern part of the Indian shield. Still, it is interesting to note that the NE – SW trending Aravalli mountain range is characterized by a complex history of multiple tectonic events (e.g. Verma and Greiling, 1995) that affected both, the sialic Archean bament and the Proterozoic sedibamentary cover se-quences (Aravalli and Delhi Supergroups). In contrast, there is no evidence for a distinct post-depositional deformation and metamorphic re-crystallization in the Proterozoic domains of the LH prior to the Himalayan orogeny and no evi-dence for the Early Paleozoic granitic magmatism that is widespread in the HH Crystalline. This is illustrated by the U – Pb data for the Wangtu
granitoid: an upper concordia intercept of 18669
10 Ma was obtained from the regression of five bulk zircon fractions (Singh et al., 1994), whereas
the lower intercept of 48928 Ma suggests
Ter-tiary Pb loss or zircon overgrowth.
6. Conclusions
Our data on metagranitic, metabasic and metasedimentary rocks from the LH, the MCT zone and the HH in NW India lead to the
follow-ing conclusions: (1) 207Pb
/206Pb single zircon ages
of 1800913 Ma for the Rampur metabasaltic
rocks suggest that the previously published Sm – Nd whole-rock isochron age of 2.5 Ga is geologi-cally meaningless. (2) The Rampur metabasalts are quartz-normative tholeiites with trace ele-ments typical of continental tholeiites. Few, if any, represent primary magmas. Rather, they have been affected by extensive fractionation and, likely, crustal assimilation processes. (3) A period of silicic volcanism and granite emplacement oc-curred around 1.86 – 1.84 Ga. (4) Nd model ages for these peraluminous granitic rocks extend to 2.63 Ga, indicating recycling of older crust and Early Proterozoic to Late Archean sources. (5)
Recycling of an Archean component (\2.9 Ga)
C.Miller et al./Precambrian Research103 (2000) 191 – 206 204
study provides information about the timing, pet-rogenesis and spatial distribution of Proterozoic magmatic activity in the NW Himalaya, further studies are necessary to establish a comprehensive time scale, especially for the evolution of the
basement (JWGC) of the Proterozoic
supracrustals in the NW Himalaya.
Acknowledgements
Field studies were financed by the Fonds zur
Fo¨rderung der wissenschaftlichen Forschung
(FWF), projects P7499-GEO and P11765-GEO. We thank Monika Jelenc (Vienna) for her help with Sr isotope analyses, and J. Kramers and M. Wiedenbeck for their careful and constructive reviews.
Appendix A
A.1. Analytical techniques
Major elements, F, Cl, Sc and Ga were deter-mined on powder pellets by X-ray fluorescence using standard methods. Other trace elements and rare earth elements (REE) were determined by inductively coupled plasma mass spectrometry (ICP-MS) at the Centre de Recherches Pe´t-rographiques et Ge´ochimiques (Vandoeuvre-le`s-Nancy, France).
Mineral composition data were obtained with an ARL SEMQ electron microprobe by
energy-and/or wavelength-dispersive spectrometry at the
University of Innsbruck. The accelerating voltage was 15 kV and sample current 20 nA. Natural and synthetic standards were used for calibration.
Single zircon evaporation dating followed
modified procedures originally described by
Kober (1987). Full details of our technique are given by Klo¨tzli (1997). Reported ages and errors are propagated weighted mean values calculated
from at least 20 measured207Pb
/206Pb ratios. For
all evaluated evaporation steps, 206Pb
/204Pb was
\50 000, thus no common Pb correction was
applied. All errors reported are 1 standard errors of the mean (approx. 68% confidence limit).
Nd and Sm concentrations were determined by
isotope dilution, using a mixed 147Sm –150Nd
spike, or by ICP-MS for some whole rock samples and run as metals on a Finnigan MAT 262 multi-collector mass spectrometer. Nd was ionized using a Re double filament. Within-run isotope
frac-tionation was corrected for146Nd/144Nd=0.7219.
All errors quoted in Table 2 correspond to 2
standard errors of the mean. The 143Nd/144Nd
ratio for the La Jolla international standard
dur-ing the course of this investigation was
0.51184698 (35 runs). Errors for the147
Sm/144 Nd
ratio are91%, or smaller, based on iterative
sam-ple analysis and spike recalibration. The following model parameters were used for the calculation of
depleted mantle (DM) ages: 147Sm
/144Nd
=0.222,
143Nd
/144Nd
=0.513114 (Michard et al., 1985). A
linear evolution of the Nd isotope composition of the DM is assumed throughout geological time,
oNd values are calculated relative to CHUR. Sr
and Rb concentrations were determined using a VG Micromass MM 30 and Ta filaments. Through the course of this study the value for the
NBS 987 Sr standard was 0.7101191. Maximum
errors for 87
Rb/86
Sr ratios are estimated to be9
1%.
A.2. Location of sample HB65/96 (Rampur metabasalt)
The majority of samples investigated by Bhat and LeFort (1992), including the five samples used in constructing their Sm – Nd whole rock isochron, were taken along their section 1, the Sutlej valley between Rampur and Jhakri. Sam-pling along this section is only possible along the Sutlej river and along road-cuts. Metabasalt
HB65/96 was collected 2 km W Jhakri along the
Rampur – Jhakri section 1 at a road cut in the
second bend E of the village Jakho (N 31° 27% E
77° 31% on the map 1: 50.000, sheet E53/11,
pub-lished by the Government of India, 1973).
References
C.Miller et al./Precambrian Research103 (2000) 191 – 206 205
Ashgirei, G.D., Sinha, A.K., Raben, M.E., Dimitrenko, O.B., 1975. New findings on the geology of Lower Himalaya, Himachal Pradesh, India. Chayanica Geol. 1, 143 – 151. Auden, J.B., 1948. Some new limestone and dolomite
occur-rences in Northern India. Indian Miner. 2, 77 – 91. Bassi, U.K., 1989. Delineation of Vaikrita Thrust in Mandi
and Kulu districts, Himachal Pradesh. Rec. Geol. Surv. India 122, 19 – 20.
Berthelsen, A., 1951. A geological section through the Hi-malaya. Medd. Dansk. Geol. Foren. 12, 102 – 104. Bhanot, V.B., Kwatra, A.K., Pandey, B.K., 1978. Rb/Sr whole
rock age for the Chail Series of Northwestern Himalaya. J. Geol. Soc. India 19, 224 – 225.
Bhanot, V.B., Bhandari, A.K., Singh, V., Kansal, A.K., 1982. Precambrian (1220 m. y.) Rb – Sr whole rock isochron age for Bandal granite, Kulu Himalaya, Himachal Pradesh. Geol. Surv. India Misc. Publ. 41, 272 – 277.
Bhargava, O.N., 1982. The tectonic windows of the Lesser Himalaya. Himal. Geol. 10, 135 – 155.
Bhat, M.I., LeFort, P., 1992. Sm – Nd age and petrogenesis of Rampur metavolcanic rocks, NW Himalayas: Late Archean relics in the Himalaya belt. Precam. Res. 56, 191 – 210.
Bhat, M.I., LeFort, P., 1993. Nd-isotopic study of the Late archean comtinental tholeiites, NW Lesser Himalayas: a case of ocean island basalt source for continental tholeiites. J. Himal. Geol. 4, 1 – 13.
Bhat, M.I., Claesson, S., Dubey, A.K., Pande, K., 1998. Sm – Nd age of the Garhwal – Bhowali volcanics, western Himalayas: vestiges of Late Archean Rampur flood basalt province of the northern Indian craton. Precam. Res. 87, 217 – 231.
Bhatia, G.S., Kanwar, R.C., 1973. Mylonitization in outer Granite Band of Dalhousie, Himachal Pradesh. Himal. Geol. 3, 103 – 115.
Boynton, W.V., 1984. Cosmochemistry of the rare earth ele-ments: meteorite studies. In: Henderson, P. (Ed.), Rare Earth Element Geochemistry. Elsevier, Amsterdam, pp. 63 – 114.
Chappell, B.W., White, A.J.R., 1974. Two contrasting granite types. Pacific. Geol. 8, 173 – 174.
Chauvel, C., Dupre´, B., Jenner, G.A., 1985. The Sm – Nd age of Kambalda volcanics is 500 Ma too old!. Earth Planet Sci. Lett. 74, 315 – 324.
Compston, W., Williams, I.S., Campbell, I.H., Gresham, J.J., 1986. Zircon xenocrysts from the Kambalda volcanics: age constraints and direct evidence for older continental crust below the Kambalda – Norseman greenstones. Earth Planet Sci. Lett. 76, 299 – 311.
DePaolo, D.J., 1981. Trace element and isotopic effects of combined wallrock assimilation and fractional crystallisa-tion. Earth Planet Sci. Lett. 53, 189 – 202.
Draganits, E., Grasemann, B., Frank, W., Miller, Ch., Wies-mayr, G., 1998. The sedimentary protoliths of the HHC in the Chamba – Lahaul area, NW Himalayas, India. 13th Himalaya-Karakoram-Tibet Workshop, Peshawar, Ab-stract Vol., 58 – 59.
Foley, S.F., Wheller, G.E., 1990. Parallels in the origin of the geochemical signatures of island arc volcanics and connental potassic igneous rocks: The role of residual ti-tanates. Chem. Geol. 85, 1 – 18.
Frank, W., Hoinkes, G., Miller, Ch., Purtscheller, F., Richter, W., Tho¨ni, M., 1973. Relations between metamorphism and orogeny in a typical section of the Indian Himalayas. Tschermaks Min. Petr. Mitt. 20, 303 – 332.
Frank, W., Tho¨ni, M., Purtscheller, F., 1977. Geology and petrography of Kulu-south Lahul area. In: Himalayas. Science de la Terre, CNRS, Paris, 268, 147 – 172. Frank, W., Miller, Ch., Grasemann, B., Tho¨ni, M., 1994. The
Haimanta – Simla Slate/Krol Belt sedimentary megacycle (paleogeographic setting and provenance of sediments). Ninth Himalaya-Karakoram-Tibet Workshop, Kath-mandu, Abstract Vol., 46 – 48.
Frank, W., Grasemann, B., Guntli, P., Miller, Ch., 1995. Geological map of the Kishtwar-Chamba-Kulu region (NW Himalayas, India). Jb. Geol. B.-A. 138, 299 – 308. Fuchs, G. 1975. Contribution to the Geology of the
North-Western Himalayas. Abh. Geol. B.-A. 32, 59 pp. Gansser, A., 1964. Geology of the Himalayas, Interscience,
London, 289 pp.
Grasemann, B., Fritz, H., Vannay, J.-C., 1999. Quantitative kinematic flow analysis from the Main Central Thrust Zone (NW Himalaya India): implications for a decelerat-ing strain path and the extrusion of orogenic wedges. J. Struct. Geol. 21, 837 – 853.
Gruau, G., Chauvel, C., Jahn, B.M., 1990. Anomalous Sm – Nd ages for the early Archean Onverwacht Group vol-canics. Contrib. Miner. Petrol. 104, 27 – 34.
Guntli, P.,1993. Geologie und Tektonik des Higher und Lesser Himalaya im Gebiet von Kishtwar, SE Kashmir (NW Indien). Ph.D. thesis, ETH 10211, Zu¨rich.
Jhingran, A.G., Kohli, G., Shukla, B.N., 1952. Geological notes on the traverse to the Spiti-valley (Punjab). Jointly with 3rd Royal Danish Expedition to Central Asia 1950. Geol. Surv. India (unpublished report).
Klo¨tzli, U.S., 1997. Zircon evaporation TIMS: Method and procedures. Analyst 122, 1239 – 1248.
Kober, B., 1987. Single-zircon evaporation combined with Pb+ emitter bedding for 207Pb/206Pb-age investigations using thermal ion mass spectrometry, and applications to zirconology. Contrib. Miner. Petrol. 96, 63 – 71.
Kwatra, S.K., Bhanot, V.B., Kakar, R.K., Kansal, A.K., 1986. Rb – Sr radiometric ages of the Wangtu Gneissic Complex, Kinnaur district, Higher Himachal Himalaya. Bull. Indian Geol. Assoc. 19, 127 – 130.
LeFort, P., Debon, F., Peˆcher, A., Sonet, J., Vidal, P., 1986. The 500 Ma magmatic event in Alpine southern Asia, a thermal episode at Gondwana scale. Sciences de la Terre. Me´moire (Nancy) 47, 191 – 209.
C.Miller et al./Precambrian Research103 (2000) 191 – 206 206
Michard, A., Gurriet, P., Soudant, M., Albarede, F., 1985. Nd isotopes in French Phanerozoic shales: external vs. internal aspects of crustal evolution. Geochim. Cosmochim. Acta 49, 601 – 610.
Parrish, R.R., Hodges, K.V., 1996. Isotopic constraints on the age and provenance of the Lesser and Greater Himalayan sequences, Nepalese Himalaya. Geol. Soc. Am. Bull. 108, 904 – 911.
Pearce, J.A., Harris, N.B.W., Tindle, A.G., 1984. Trace ele-ment discrimination diagrams for the tectonic interpreta-tion of granitic rocks. J. Petrol. 25, 956 – 983.
Pupin, J.P., Turco, G., 1972. Une typologie originale du zircon accessoire. Bull. Soc. Fr. Miner. Cristallogr. 95, 348 – 359. Rameshwar, R.D., Sharma, K.K., Gopalan, K., 1995. Grani-toid rocks of Wangtu Gneissic Complex, Himachal Pradesh: an example of insitu fractional crystallization and volatile action. J. Geol. Soc. India 46, 5 – 14.
Sandiford, M., Hand, M., McLaren, S., 1998. High geother-mal gradient metamorphism during thergeother-mal subsidence. Earth Planet Sci. Lett. 163, 149 – 165.
Sharma, V.P., 1977. Geology of the Kulu-Rampur Belt, Hi-machal Pradesh. Mem. Geol. Surv. India 106, 235 – 407. Sharma, V.P., Chaturvedi, R.K., Sundaram, R., 1973. An
account of the stratigraphy and structure of Doda-Bhadar-wah-Basanthgarh region. Seminar on Geodynamics of the Himalayan Region, NGRI Hyderabad, 110 – 121. Shervais, J.W., 1982. Ti – V plots and the origin of modern and
ophiolitic lavas. Earth Planet Sci. Lett. 59, 101 – 118. Singh, S., Claesson, S., Jain, A.K., Sjoberg, H., Gee, D.G.,
Manickavasagam, R.M., Andreasson, P.G., 1994. Geo-chemistry of the Proterozoic peraluminous granitoids from the Higher Himalayan Crystalline (HHC) and Jutogh nappe, NW Himalaya, Himachal Pradesh, India. J. Nepal Geol. Soc. 10, 125.
Srikantia, S.V., Bhargava, O.N., 1998. Geology of Himachal Pradesh. Geol Soc. India, Bangalore, 406 pp.
Srivastava, P., Mitra, G., 1996. Deformation mechanism and inverted thermal profile in the North Almora Thrust my-lonite zone, Kumaon Lesser Himalaya, India. J. Struct. Geol. 18, 27 – 39.
Sta¨ubli, A., 1988. Metamorphose und Deformation im Bereich der zentralen Hauptu¨berschiebung (MCT), (Kishtwar Fen-ster, NW Himalaya). Ph.D. thesis, ETH 8573, Zu¨rich.
Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D. and Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geol. Soc. Spec. Publ. 42, pp. 313 – 345.
Tarney, J., 1992. Geochemistry and significance of mafic dyke swarms in the Proterozoic. In: Condie, K.C. (Ed.), Proterozoic Crustal Evolution. Developments in Precam-brian Geology 10. Elsevier, Amsterdam, pp. 151 – 179. Tho¨ni, M., 1977. Geology, structural evolution and
metamor-phic zoning in the Kullu valley (Himachal Himalayas, India) with special reference to the reversed metamor-phism. Mitt. Ges. Geologie- und. Bergbaustud. O8sterr. 24, 125 – 187.
Tobisch, O.T., Collerson, K.D., Bhattacharyya, T., Mukho-padhyay, D., 1994. Structural relationships and Sr – Nd isotope systematics of polymetamorphic granitic gneisses and granitic rocks from central Rajasthan, India: implica-tions for the evolution of the Aravalli craton. Precam. Res. 65, 319 – 339.
Trivedi, J.R., Gopalan, K., Valdiya, K.S., 1984. Rb – Sr ages of granitic rocks within the Lesser Himalayan nappes, Kumaun, India. J. Geol. Soc. India 26, 641 – 654. Vannay, J.-C., Grasemann, B., 1998. Himalayan inverted
metamorphism in the High Himalaya of Kinnaur (NW India): petrography versus thermobarometry. Schweiz Miner. Petrogr. Mitt. 78, 107 – 132.
Vannay, J.-C., Sharp, Z.D., Grasemann, B., 1999. Himalayan inverted metamorphism constrained by oxygen isotope thermometry. Contrib. Miner. Petrol. 137, 90 – 101. Verma, P.K., Greiling, R.O., 1995. Tectonic evolution of the
Aravalli orogen (NW India): an inverted Proterozoic rift? Geol. Rundsch. 84, 683 – 696.
White, R., McKenzie, D., 1989. Magmatism at rift zones: the generation of volcanic continental margins and flood basalts. J. Geophys. Res. 94, 7685 – 7729.
Whittington, A., Foster, G., Harris, N., Vance, D., Ayres, M., 1999. Lithostratigraphic correlations in the western Hi-malaya — An isotopic approach. Geology 27, 585 – 588. Wiedenbeck, M., Goswami, J.N., Roy, A.B., 1996.
Stabiliza-tion of the Aravalli craton of northwestern India at 2.5 Ga: an ion microprobe zircon study. Chem. Geol. 129, 325 – 340.
