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Permian age of orogenic thickening and crustal melting in the Garm Block, South Tien Shan, Tajikistan

Konopelko D, Klemd R, Mamadjanov Y, Hegner E, Knorsch M, Fidaev D, Kern M, Sergeev S (2015)

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Publication Language: English

Publication Type: Journal article

Publication year: 2015

Journal

Book Volume: 113

Pages Range: 711-727

Journal Issue: 2

DOI: 10.1016/j.jseaes.2015.09.004

Abstract

In this paper we present new data for the metamorphic Garm Block (150 × 40 km) that was traditionally shown on regional maps as fragment of a Precambrian basement. The Garm Block comprises migmatized gneisses and schists for some of which peak metamorphic conditions (600–660 °C at 7–9 kbar) characteristic for medium P/T series metamorphic belts were determined. U–Pb ages of overgrown rims of zircon grains and newly grown magmatic zircon grains from four migmatitic samples indicate that melting occurred during peak metamorphic conditions between 299 and 290 Ma. Thus the Garm Block is the first Early Permian regional metamorphic terrane established in the southern part of the Central Asian Orogenic Belt. A crosscutting granite intrusion yields a concordia age of 290 Ma identical to the age of metamorphism and similar to ages of post-collisional intrusions elsewhere in the Tien Shan. Detrital zircon grains from the Garm samples yield an age spectrum with major peaks at 700–550 Ma and 1150–700 Ma, and smaller ones at ca. 2.7–2.4 Ga and 3.5–3.3 Ga. The youngest grains define an Ediacarian maximum depositional age of the sedimentary protoliths. The presence of Grenvillian ages of 1150–800 Ma, which are characteristic for the Tarim Craton, and the lack of ca. 1.6–1.2 Ga ages, characteristic for the Northern Tien Shan, suggest an origin of the Precambrian zircon grains from southern continental blocks similar to the Tarim Craton. Six granitoid samples yield negative εNd values of −10.6 to −3.7 consistent with the reworking of crustal material with 1.8–1.1 Ga average crustal residence times and the formation of the South Tien Shan belt on a continental basement with Paleoproterozoic or older crust. The Garm Block formed as a consequence of lithospheric thickening during the Late Carboniferous collision of two continental blocks that created the South Tien Shan fold belt. Lateral crustal melt flow coupled with extension may have resulted in exhumation of the Permian metamorphic rocks.

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APA:

Konopelko, D., Klemd, R., Mamadjanov, Y., Hegner, E., Knorsch, M., Fidaev, D.,... Sergeev, S. (2015). Permian age of orogenic thickening and crustal melting in the Garm Block, South Tien Shan, Tajikistan. Journal of Asian Earth Sciences, 113(2), 711-727. https://dx.doi.org/10.1016/j.jseaes.2015.09.004

MLA:

Konopelko, Dmitry, et al. "Permian age of orogenic thickening and crustal melting in the Garm Block, South Tien Shan, Tajikistan." Journal of Asian Earth Sciences 113.2 (2015): 711-727.

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