Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and 40Ar/39Ar Thermochronology

Tectonics - Tập 20 Số 5 - Trang 729-747 - 2001
Laurent Godin1, Randall R. Parrish2, Richard L. Brown3, K. V. Hodges4
1University of Oxford.
2School of Earth and Environmental Sciences
3Carleton University
4Massachusetts Institute of Technology,

Tóm tắt

New and published U‐Pb geochronology and 40Ar/39Ar thermochronology from footwall and hanging wall rocks of a segment of the South Tibetan detachment system exposed in the Annapurna area of central Nepal Himalaya bring additional constraints on the timing of metamorphism, crustal thickening, and normal faulting resulting in exhumation of the Himalayan metamorphic core. Early Oligocene crustal thickening led to Eohimalayan kyanite‐grade metamorphism between 35 Ma and 32 Ma. The resulting thermal event affected the Early Ordovician augen gneiss (Formation III) and produced kyanite‐bearing leucosomes in the upper part of the metamorphic core. This event is linked with underthrusting of the Greater Himalayan metamorphic sequence below the Tethyan sedimentary sequence and the growth of an Oligocene fan structure that has thickened the Tethyan sedimentary sequence to 25 km, thus provoking kyanite‐grade melting at deeper structural levels. Early Paleozoic monazite and zircon populations indicate that part of the metamorphism affecting the Himalayan metamorphic core could be pre‐Cenozoic. Regional correlations indicate that the Annapurna detachment was active during early Miocene time. A weakly deformed leucogranitic dike intruding into the immediate hanging wall yielded reversely discordant monazite ages between 23 and 22.5 Ma, which suggest that the ductile strain in the Annapurna detachment zone terminated at ca. 22 Ma. On the basis of a 40Ar/39Ar muscovite age, renewed southwest verging deformation (D4) is interpreted to occur at ca. 18 Ma. Rapid exhumation resulting from extensional faulting cooled the entire metamorphic core through the muscovite Ar closure temperature (330°–430°C) between 15 and 13 Ma. Muscovites from the immediate hanging wall of the Annapurna detachment yielded slightly younger ages, between 13 and 11 Ma, testifying to late hydrothermal activity in the Annapurna detachment zone that could be linked with the initiation of brittle faulting associated with the late Neogene Thakkhola graben system.

Từ khóa


Tài liệu tham khảo

10.1130/0016-7606(2000)112<467:ICOTSR>2.0.CO;2

10.1016/S0012-821X(99)00209-5

10.1029/JB083iB10p04975

Bodenhausen J. W. A., 1971, On the geology of the upper Kali Gandaki valley, Nepalese Himalayas, Proc. Ser. I, Akad. Wetenschappen, 74, 526

Bodenhausen J. W. A. T.deBooy C. G.Egeler H. J.Nijhuis On the geology of central west Nepal: A preliminary note Int. Geol. Cong. Rep. Sess. 22nd XI 101 1964.

Bordet P., 1971, Recherches Géologiques dans l'Himalaya du Népal: Région de la Thakkhola

10.2113/gssgfbull.S7-XVIII.6.1377

Brown R. L., 1993, Himalayan Tectonics, Geol. Soc. Spec. Publ., 461

10.1139/e86-111

Burchfiel B. C. Chen Zhiliang K. V.Hodges Liu Yuping L. H.Royden Deng Changrong Xu Jiene The South Tibetan Detachment System Himalaya Orogen: Extension Contemporaneous With and Parallel to Shortening in a Collisional Mountain Belt Spec. Pap. Geol. Soc. Am. 269 41 1992.

10.1038/311219a0

Caby R., 1983, Le grand chevauchement central himalayen: Nouvelles données sur le métamorphisme inverse à la base de la Dalle du Tibet, Rev. Géogr. Phys. Géol Dyn., 24, 89

Cebula G. T., 1986, The Fish Canyon Tuff, a potential standard for the 40Ar/39Ar and fission‐track methods, Terra Cognita, 6, 139

Colchen M., 1981, Zagros‐Hindu Kush‐Himalaya Geodynamic Evolution, Geodyn. Ser.

Colchen M., 1986, Recherches Géologiques dans l'Himalaya du Népal: Annapurna‐Manaslu‐Ganesh Himal

10.1130/0016-7606(1996)108<1594:OPAOPE>2.3.CO;2

Coleman M. E. The tectonic evolution of the central Himalaya Marsyandi valley Nepal Ph.D thesis 221 pp. Mass. Inst. of Technol. Cambridge 1996b.

10.2475/ajs.298.7.553

10.1038/374049a0

10.1029/98TC02777

10.1038/333760a0

10.1016/0377-0273(90)90010-D

10.1126/science.288.5465.497

10.1007/BF00375529

10.1098/rsta.1988.0135

10.1016/0016-7037(77)90184-3

Fuchs G., 1977, The geology of the Kamali and Dolpo regions, western Nepal, Jahrb. Geol. Bundesanst., Austria, 120, 165

Gansser A., 1964, Geology of the Himalayas

Godin L. Tectonic evolution of the Tethyan sedimentary sequence in the Annapurna area central Nepal Himalaya Ph.D. thesis 219 pp. Carleton Univ. Ottawa 1999.

10.1130/0091-7613(1999)027<0151:BFITCO>2.3.CO;2

10.1130/0-8137-2328-0.199

Gradstein F. M., 1992, The Mesozoic continental margin of central Nepal, Geol. Jahrb., 77, 3

10.1144/GSL.SP.1993.074.01.28

10.1130/0091-7613(1994)022<0559:NCOTAO>2.3.CO;2

10.1029/94TC01611

10.1016/0012-821X(95)00091-P

10.1093/petroj/40.1.3

10.1029/TC007i003p00583

10.1098/rsta.1988.0087

10.1130/0091-7613(1988)016<0707:PTBBCA>2.3.CO;2

10.1126/science.258.5087.1466

10.1007/BF00286839

10.1029/96TC01791

10.1029/TC008i004p00865

Hurtado J., 1998, The South Tibetan system in the Kali Gandaki valley, Annapurna Himalaya, north central Nepal: A synthesis of structural geology and neotectonics (abstract), Geol. Soc. Am. Abstr. Programs, 30, A‐269

10.1111/j.1525-1314.1992.tb00095.x

10.1016/0012-821X(85)90086-X

10.1016/0016-7037(82)90165-X

Le Fort P., 1975, Himalayas: The collided range: Present knowledge of the continental arc, Am. J. Sci., 275, 1

10.1029/JB086iB11p10545

Le Fort P., 1986, The 500 Ma magmatic event in Alpine southeast Asia, a thermal event at Gondwana scale, Sci. Terre Mem., 47, 191

10.1016/0040-1951(87)90248-4

10.2113/gssgfbull.S7-XXVI.1.129

McDougall I., 1988, Geochronology and Thermochronology by the 40Ar/39Ar Method

10.1016/0012-821X(94)90185-6

Nazarchuk J. H. Structure and geochronology of the Greater Himalaya Kali Gandaki region west‐central Nepal M.Sc. thesis 157 pp. Carleton Univ. Ottawa 1993.

10.1017/S0016756800023190

10.1139/e90-152

10.1130/0016-7606(1996)108<0904:ICOTAA>2.3.CO;2

Parrish R. R., 1987, Synthesis and purification of 205Pb for U‐Pb geochronology, Chem. Geol., 66, 103

10.1130/0091-7613(1989)017<1076:UPAOTB>2.3.CO;2

Parrish R. R. J. C.Roddick W. D.Loveridge R. W.Sullivan Uranium‐lead analytical techniques at the Geological Survey of Canada Radiogenic Age and Isotopic StudiesPap. Geol. Surv. Can. 87‐2 3–7 1987.

Parrish R. R., 1997, 12th Himalaya‐Karakoram‐Tibet Workshop: Abstract Volume, 71

10.1038/311615a0

Pêcher A., 1977, Himalaya‐Sciences de la Terre, Colloq. Int. CNRS, 301

10.1111/j.1525-1314.1989.tb00573.x

10.1130/0091-7613(1994)022<0783:IOAART>2.3.CO;2

10.1016/0016-7037(87)90261-4

10.1016/0012-821X(80)90181-8

10.1086/516018

10.1016/0012-821X(84)90114-6

10.1016/0012-821X(86)90130-5

10.1029/92TC00213

10.1029/91TC01011

10.1029/JB085iB11p06174

10.1016/0191-8141(86)90037-4

10.1111/j.1525-1314.1989.tb00579.x

10.1130/0016-7606(1987)98<678:TCOTAT>2.0.CO;2

10.1098/rsta.1988.0082

10.1093/petrology/37.4.733

10.1029/93TC01130

10.1016/0012-821X(75)90088-6

10.1016/0012-821X(77)90060-7

Swapp S. M., 1991, Inverted metamorphism within the Tibetan slab of Bhutan: Evidence for a tectonically transported heat‐source, Can. Mineral., 29, 1019

10.1046/j.1525-1314.1996.00426.x

10.1130/0091-7613(1993)021<0371:MMFTTO>2.3.CO;2

10.1016/S0012-821X(68)80059-7

Thông tin
Thông tin xuất bản

Tectonics

Tập 20 Số 5

729-747

Thông tin tác giả