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Field relations, geochemistry, origin and emplacement of the Baltoro granite, Central Karakoram

Published online by Cambridge University Press:  03 November 2011

M. P. Searle ,
M. B. Crawford  and
A. J. Rex
M. P. Searle
Affiliation:
M. P. Searle, Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, U.K.
M. B. Crawford
Affiliation:
M. B. Crawford, A. J. Rex, Department of Geology,University of Leicester, Leicester LE1 7RH
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Abstract

The Miocene Baltoro granite forms a massive plutonic unit within the Karakoram batholith, and is composed of comagmatic monzogranites and leucogranites with a mineralogy consisting of quartz-K-feldspar-plagioclase-biotite ± muscovite ± garnet, with accessory sphene, zircon, monazite and opaques. Geochemically the Baltoro granites are mildly peraluminous, and show a calc-alkaline trend on trace-element normalised diagrams with high LIL/HFS element ratios and negative Nb, P and Ti anomalies. REE are strongly fractionated with little or no Eu anomaly. Leucogranites are depleted in most elements compared to monzogranites with notable exceptions being Rb, K and the HREEs. Initial 87Sr/86Sr ratios are 0·7072-0·7128, considerably lower than High Himalayan leucogranites (0·74-0·79), and are indicative of a lower continental crust source. The probable petrogenesis of the Baltoro granite involves dehydration melting of a biotite-rich pelite to produce a voluminous, hot, water-undersaturated magma which could then separate from its source and intrude through an already thickened and still hot crust. Fractional crystallisation of the monzogranites produced the leucogranites and a pegmatite dyke swarm. A suite of lamprophyre dykes including amphibolerich vogesites and biotite-rich minettes intrude the country rock, dominantly to the north, around the Baltoro granite. These calc-alkaline shoshonitic lamprophyres are volatile-rich mantle-derived melts intruded around the same time as the granite, indicating simultaneous melting of the mantle and lower crust beneath the Karakoram during the Miocene, approximately 30 Ma after the India-Asia collision which initially caused the crustal thickening. Intrusion of mantle melts provided heat to promote crustal melting and may have selectively contaminated the granite magma.

The Baltoro granite intrudes sillimanite gneisses with melt pods along the southern margin indicating temperatures above 700°C at the time of intrusion. Locally, internal fabrics and numerous aligned xenoliths along the southern margin in the Biafo glacier region indicate steep, southward-directed thrusting during emplacement. Along the northern contact, the Baltoro granite intrudes anchimetamorphic to greenschist facies metasedimentary rocks with an andalusite-bearing contact aureole. Northward-directed culmination collapse normal faulting during Miocene emplacement is inferred, in order to explain the P-T differences either side of the pluton. This also provided an extensional stress regime in the upper crust to accommodate the rising magma.

Keywords

Batholithcrust-mantle interactioncrustal meltinggeochemistryisotope datalamprophyreleucogranitemetamorphic aureolemicroprobe datamonzogranite
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 83 , Issue 3 , 1992 , pp. 519 - 538
Copyright
Copyright © Royal Society of Edinburgh 1992

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References

Allègre, C. J. & Othman, B. D. 1980. Nd-Sr isotopic relationships in granitoid rocks and continental crust development: a chemical approach to orogenesis. NATURE 286, 335–42.CrossRefGoogle Scholar
Asif Khan, M., Qasim Jan, M., Windley, B. F., Tarney, J. & Thirlwall, M. F. 1989. The Chilas mafic-ultramafic igneous complex; The root of the Kohistan island arc in the Himalaya of northern Pakistan. GEOL SOC AM, SPEC PAP 232, 75–94.Google Scholar
Burchfiel, C. & Royden, L. 1985. N-S extension under the convergent Himalayan regime. GEOLOGY 13, 679–82.2.0.CO;2>CrossRefGoogle Scholar
Burchfiel, B. C., Molnar, P., Ziyun, Z., K'uangyi, L., Shuji, W., Minmin, H. & Sutter, J. 1989. Geology of the Ulugh Muztagh area, northern Tibet. EARTH PLANET SCI LETT 94, 57–70.CrossRefGoogle Scholar
Burg, J. P., Brunel, M., Gapais, D., Chen, G. M. & Liu, G. H. 1984. Deformation of leucogranites of the crystalline Main Central thrust sheet in southern Tibet (China). J STRUCT GEOL 6, 535–42.CrossRefGoogle Scholar
Coulon, C., Maluski, H., Bollinger, C. & Wang, S. 1986. Mesozoic and Cenozoic volcanic rocks of central and southern Tibet. 39Ar-40 Ar dating, petrological characteristics and geodynamical significance. EARTH PLANET SCI LETT 79, 281–302.CrossRefGoogle Scholar
Clemens, J. D. & Vielzeuf, D. 1987. Constraints on melting and magma production in the crust. EARTH PLANET SCI LETT 86, 287–306.CrossRefGoogle Scholar
Cuney, M., LeFort, P. & Zhixiang, W. 1984. Uranium and thorium geochemistry and mineralogy in the Manaslu leucogranite (Nepal Himalaya). In Geology of Granites and Their Metallogenic Relations, 853–73. Proc. International symposium Nanjing University, China.Google Scholar
Debon, F. & LeFort, P. 1982. A chemical mineralogical classification of common plutonic rocks and associations. TRANS R SOC EDINBURGH EARTH SCI 73, 135–49.CrossRefGoogle Scholar
Debon, F., Zimmerman, J. L. & Betrand, J. M. 1986. Le granite du Baltoro (batholite axial due Karakoram, nord Pakistan): une intrusion subalcaline d'age Miocène Superieur. C. R. ACAD SCI 303, 463–8.Google Scholar
Deng, W. 1978. A preliminary study on the petrology and petrochemistry of the Quaternary volcanic rocks of northern Tibet autonomous region (in Chinese). ACTA GEOL SINICA 52, 148–62.Google Scholar
Deniel, C., Vidal, Ph., Fernandez, A., LeFort, P. and Peucat, J. J. 1987. Isotopic study of the Manaslu granite (Himalaya, Nepal): inferences on the age and source of Himalayan leucogranites. CONTRIB MINERAL PETROL 96, 78–92.CrossRefGoogle Scholar
De Paolo, D. J. 1981. A neodymium and strontium isotopic study of the Mesozoic calc-alkaline granite batholiths of the Sierra Nevada and Peninsula Ranges, California: J GEOPHYS RES 86, 10470–88.CrossRefGoogle Scholar
Desio, A. 1964. Geological tentative map of the western Karakoram. Institute of Geology, University of Milan.Google Scholar
Desio, A. & Zanettin, B. 1970. Geology of the Baltoro Basin. Leiden: E. J. Brill.CrossRefGoogle Scholar
England, P. C. & Thompson, A. 1986. Some thermal and tectonic models for crustal melting in continental collision zones. In Coward, M. P. & Ries, A. (eds) Collision Tectonics, 83–94. Geological Society London, Special Publication 19.Google Scholar
Gromet, L. P. & Silver, L. T. 1983. R.E.E. distributions among minerals in a granodiorite and their petrogenic implications. GEOCHIM COSMOCHIM ACTA 47, 925–39.CrossRefGoogle Scholar
Harris, N. B. W., Pearce, J. A. & Tindle, A. G. 1986. Geochemical characteristics of collision zone magmatism. In Coward, M. P. & Ries, A. (eds), Collision Tectonics, 67–81. Geological Society, London Special Publication 19.Google Scholar
Hawkesworth, C. J. & Norry, M. J. 1983. Continental Basalts and Mantle Xenoliths. Cheshire: Shiva Publications.Google Scholar
Henderson, P. 1984. General geochemical properties and abundances of rare-earth elements. In Henderson, P. (ed.) Rare-earth Element Geochemistry, 1–29. Barking: Elsevier.Google Scholar
Herren, E. 1987. Zanskar Shear Zone: Northeast-southwest extension within the Higher Himalayas (Ladakh, India). GEOLOGY 15, 409–13.2.0.CO;2>CrossRefGoogle Scholar
Hodges, K. V., Hubbard, M. S. & Silverberg, D. S. 1988a. Metamorphic constraints on the thermal evolution of the central Himalayan orogen. PHILOS TRANS SOC LONDON A326, 257–80.Google Scholar
Hodges, K. V., LeFort, P. & Pêcher, A. 1988b. Possible thermal buffering by crustal anatexis in collisional orogens: Thermobarometric evidence from the Nepalese Himalaya. GEOLOGY 16, 707–10.2.3.CO;2>CrossRefGoogle Scholar
Huppart, H. E. & Sparks, R. S. J. 1988. The generation of granitic magmas by intrusion of basalt into continental crust. J PETROL 29, 599–624.CrossRefGoogle Scholar
Jacobssen, S. B. & Wasserburg, G. J. 1980. Sm-Nd isotopic evolution of chondrites. EARTH PLANET SCI LETT 50, 149–55.CrossRefGoogle Scholar
Jaupart, C. & Provost, A. 1985. Heat focussing, granite genesis and inverted metamorphic gradients in continental collision zones. EARTH PLANET SCI LETT 73, 385–97.CrossRefGoogle Scholar
LeFort, P. 1975. Himalayas: The collided range, present knowledge of the continental arc. AM J SCI 155A, 1–44.Google Scholar
LeFort, P. 1981. Manaslu leucogranite: A collisional signature of the Himalaya, a model for its genesis and emplacement. J GEOPHYS RES 86, 10, 545–68.Google Scholar
LeFort, P. 1986. Metamorphism and magmatism of the Himalaya. In Coward, M. P. & Ries, A. C. (eds) Collision Tectonics, 159–72. Geological Society of London Special Publication 19.Google Scholar
LeFort, P., Cuney, M., Deniel, C., France-Lanord, C., Sheppard, S. M. F., Upreti, B. N. & Vidal, P. 1987. Generation of the Himalayan leucogranites. Tectonophysics 134, 39–57.CrossRefGoogle Scholar
Marsh, N. G., Saunders, A. D., Tarney, T. & Dick, H. J. B. 1979. Geochemistry of basalts from the Shikoku and Daito basins, DSDP Leg 58. In Vries Klein, G. de & Kobayashi, K. et al. (eds) Initial Reports of the Deep Sea Drilling Project 49, 657–91. Washington DC.Google Scholar
McKenna, L. W. & Walker, J. D. 1990. Geochemistry of crustally derived leucocratic igneous rocks from the Ulugh Muztagh area, northern Tibet and their implications for the formation of the Tibetan Plateau. J GEOPHYS RES 95, 21, 483–502.Google Scholar
Miller, C. F. 1985. Are strongly peraluminous magmas derived from pelitic sedimentary sources? J GEOL 93, 673–89.CrossRefGoogle Scholar
Molnar, P. 1984. Structure and tectonics of the Himalaya: constraints and implications of geophysical data. ANNU REV EARTH PLANET SCI 12, 489–518.CrossRefGoogle Scholar
Norin, E. 1946. Geological Explorations in Western Tibet. In “Reports from the Scientific expedition to the northwestern provinces of China under the leadership of Dr Sven Hedin”, Publ 29 (III) Geology 7, Trycheri Aktiebolaget, Thule, 205p., Stockholm.Google Scholar
Parrish, R. R. & Tirrul, R. 1989. U-Pb age of the Baltoro granite, northwest Himalaya, and implications for monazite U-Pb systematics. Geology 17, 1076–9.2.3.CO;2>CrossRefGoogle Scholar
Pearce, J. A. & Houjon, Mei 1988. Volcanic rocks of the 1985 Geotraverse. Lhasa to Golmud. PHILOS TRANS R SOC LONDON A327, 169–201.Google Scholar
Pearce, J. A., Harris, N. B. W. & Tindle, A. G. 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. J PETROL 25, 956–83.CrossRefGoogle Scholar
Pinet, C. & Jaupart, C. 1987. A thermal model for the distribution in space and time of the Himalayan granites. EARTH PLANET SCI LETT 84, 87–99.CrossRefGoogle Scholar
Pitcher, W. 1983. Granite type and tectonic environment. In: Hsu, K. (ed.) Mountain Building Processes, 19–40, London: Academic PressGoogle Scholar
Pognante, U. 1990. Shoshonitic and ultrapotassic post-collisional dykes from northern Karakoram (Sinkiang, China). LITHOS 26, 305–16.CrossRefGoogle Scholar
Potts, P. J., Williams, Thorpe O., Isaacs, M. & Wright, D. W. 1985. High precision instrumental neutron-activation analysis of geological samples employing simultaneous counting with both planar and coaxial detectors. CHEM GEOL 48, 145–55.CrossRefGoogle Scholar
Rex, A. J., Searle, M. P., Tirrul, R., Crawford, M. B., Prior, D. J., Rex, D. C. & Barnicoat, A. 1988. The geochemical and tectonic evolution of the central Karakoram, North Pakistan. PHILOS TRANS SOC LONDON A326, 229–55.Google Scholar
Rogers, N. W., Hawkesworth, C. J., Parker, R. J. & Marsh, J. S. 1985. The geochemistry of potassic lavas from Vulsini, central Italy, and implications for mantle enrichment processes beneath the Roman region. CONTRIB MINERAL PETROL 90, 244–57.CrossRefGoogle Scholar
Saunders, A. D., Rogers, G., Marriner, F. G., Terrel, D. J. & Verma, S. P. 1987. Geochemistry of Cenozoic volcanic rocks Baja California, Mexico: implications for the petrogenesis of post-subduction magmas. J VOLCANOL GEOTHERM RES 32, 223–46.CrossRefGoogle Scholar
Scaillet, B., France-Lanord, C. and LeFort, P. 1990. Badrinath-Gangotri plutons (Garhwal, India): petrological and geochemical evidence for fractionation processes in a High Himalayan leucogranite. J VOLCANOL GEOTHERM RES 44, 163–88.CrossRefGoogle Scholar
Schärer, U. 1984. The effect of initial 230Th disequilibration on U-Pb ages: the Makalu case. EARTH PLANET SCI LETT 67, 191–204.CrossRefGoogle Scholar
Schärer, U., Xu, R. H. & Allegre, C. J. 1986. U-(Th)-Pb systematics and ages of Himalayan leucogranites, south Tibet. EARTH PLANET SCI LETT 77, 35–48.CrossRefGoogle Scholar
Schärer, U., Copeland, P., Harrison, T. M. & Searle, M. P. 1990. Age, cooling history and origin of post-collisional leucogranites in the Karakoram batholith; a multi-system isotope study N. Pakistan; J GEOL 98, 233–51.CrossRefGoogle Scholar
Searle, M. P. 1986. Structural evolution and sequence of thrusting in the High Himalayan, Tibetan-Tethys and Indus suture zones of Zanskar and Ladakh, western Himalaya. J STRUCT GEOL 8, 923–36.CrossRefGoogle Scholar
Searle, M. P. 1991. Geology and Tectonics of the Karakoram Mountains. Chichester: John Wiley and Sons. (With Geological map of the Central Karakoram, scale 1:250,000.)Google Scholar
Searle, M. P. & Fryer, B. J. 1986. Garnet, tourmaline and muscovite-bearing leucogranites, gneisses and migmatites of the Higher Himalaya from Zanskar, Kulu, Lahoul and Kashmir. In Coward, M. P. & Ries, A. C. (eds) Collision Tectonics, 185–201. Geological Society of London Special Publication 19.Google Scholar
Searle, M. P. & Rex, A. J. 1989. Thermal Model for the Zanskar Himalaya, J METAMORPH GEOL 7, 127–34.CrossRefGoogle Scholar
Searle, M. P. & Tirrul, R. 1991. Structural and thermal evolution of the Karakoram crust. J GEOL SOC LONDON 148, 65–82.CrossRefGoogle Scholar
Searle, M. P., Rex, A. J., Tirrul, R., Windley, B. F., St Onge, M. & Hoffman, P. 1986. A geological profile across the Baltoro Karakoram Range, N. Pakistan. UNIV PESHAWAR GEOL BULL 19, 1–12.Google Scholar
Searle, M. P., Windley, B. F., Coward, M. P., Cooper, D. J. W., Rex, A. J., Rex, D.,Tingdong, Li, Xuchang, Xiao,Jan, M. Q., Thakur, V. C. & Kumar, S. 1987. The closing of Tethys and the tectonics of the Himalayas. BULL GEOL SOC AM 98, 678–701.2.0.CO;2>CrossRefGoogle Scholar
Searle, M. P., Cooper, D. J. W. & Rex, A. J. 1988. Collision tectonics of the Ladakh-Zanskar Himalaya. PHILOS TRANS R SOC LONDON A326, 117–50.Google Scholar
Searle, M. P., Rex, A. J., Tirrul, R., Rex, D. C., Barnicoat, A. & Windley, B. F. 1989. Metamorphic, magmatic and tectonic evolution of the Central Karakoram in the Biafo-Baltoro-Hushe regions of N. Pakistan. GEOL SOC AM, SPEC PAP 232, 47–73.Google Scholar
Searle, M. P., Parrish, R. R., Tirrul, R. & Rex, D. C. 1990. Age of crystallisation and cooling of the K2 gneiss in the Baltoro Karakoram. J GEOL SOC LONDON 147, 603–6.CrossRefGoogle Scholar
Srimal, N. 1986. India-Asia collision: implications from the geology of the eastern Karakoram. GEOLOGY 14, 523–7.2.0.CO;2>CrossRefGoogle Scholar
Tarney, J., Saunders, A. D., Weaver, S. D., Donellan, N. C. B. & Hendry, G. L. 1979. Minor element chemistry of Leg 49, North Atlantic Ocean. In Luyendyk, B. P., Cann, J. R. et al. (eds) Initial Reports of the Deep Sea Drilling Project 49, 657–91 Washington DC.Google Scholar
Taylor, S. R. & McLennan, S. M. 1981. The composition and evolution of the continental crust: rare-earth evidence from sedimentary rocks. PHILOS TRANS SOC LONDON A301, 381.Google Scholar
Taylor, S. R. & McLennan, S. M. 1985. The Continental Crust: It's Composition and Evolution. Oxford: Blackwell Scientific Publishers.Google Scholar
Vidal, P., Cocherie, A. & LeFort, P. 1982. Geochemical investigations of the origin of the Manaslu leucogranite (Himalaya, Nepal). GEOCHIM COSMOCHIM ACTA 46, 2279–92.CrossRefGoogle Scholar
Vielzeuf, D. & Holloway, J. R. 1988. Experimental determinations of the fluid-absent melting relations in the pelitic system: consequences for crustal differentiation. CONTRIB MINERAL PETROL 19, 111–31.Google Scholar
White, A. J. R. & Chappell, B. W. 1977. Ultrametamorphism and granitoid genesis. TECTONOPHYSICS 43, 7–22.CrossRefGoogle Scholar
Wyllie, P. J., Huang, C. R., Stern, C. R. & Maaloe, S. 1976. Granitic magmas: possible and impossible sources, water contents and crystallization sequences. CAN J EARTH SCI 13, 1007–19.CrossRefGoogle Scholar