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GEOREF RECORD

Tectonic evolution of the northeastern Pamir; constraints from the northern portion of the Cenozoic Kongur Shan extensional system, western China

Alexander C. Robinson, An Yin, Craig E. Manning, T. Mark Harrison, Zhang Shuanhong and Wang Xiaofeng
Tectonic evolution of the northeastern Pamir; constraints from the northern portion of the Cenozoic Kongur Shan extensional system, western China
Geological Society of America Bulletin (August 2004) 116 (7-8): 953-973

Abstract

The late Cenozoic Kongur Shan extensional system lies along the northeastern margin of the Pamir at the western end of the Himalayan-Tibetan Orogen, accommodating east-west extension in the Pamir. At the northern end of the extensional system, the Kongur Shan normal fault juxtaposes medium- to high-grade metamorphic rocks in both its hanging wall and footwall, which record several Mesozoic to Cenozoic tectonic events. Schists within the hanging wall preserve a Buchan metamorphic sequence, dated as Late Triassic to Early Jurassic (230-200 Ma) from monazite inclusions in garnet. Metamorphic ages overlap with U-Pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the Paleo-Tethys ocean. The northern portion of the footwall of the extensional system exposes an upper-amphibolite-facies unit ( approximately 650 degrees C, 8 kbar), which structurally overlies a low-grade metagraywacke unit. The high-grade unit records late Early Cretaceous crustal thickening at ca. 125-110 Ma, followed by emplacement over the low-grade metagray-wacke along a north-northeast-directed thrust prior to ca. 100 Ma. Together these results indicate significant Middle Cretaceous crustal thickening and shortening in the northern Pamir prior to the Indo-Asian collision. A third late Miocene (ca. 9 Ma) amphibolite-facies metamorphic event ( approximately 650-700 degrees C, 8 kbar) is recorded in footwall gneisses of the Kongur Shan Massif. North of the Kongur Shan Massif, rapid cooling in the footwall beginning at 7-8 Ma is interpreted to date the initiation of exhumation along the Kongur Shan normal fault. A minimum of 34 km of east-west extension is inferred along the Kongur Shan Massif based on the magnitude of exhumation since the late Miocene ( approximately 29 km) and the present dip of the Kongur Shan normal fault ( approximately 40 degrees ). Field observations and interpretation of satellite images along the southernmost segment of the Kongur Shan extensional system indicate that the magnitude of late Cenozoic east-west extension decreases significantly toward the south. This observation is inconsistent with models in which east-west extension in the Pamir is driven by northward propagation of the right-slip Karakoram Fault, suggesting instead that extension is driven by vertical extrusion due to topographic collapse, radial thrusting along the Main Pamir Thrust, or oroclinal bending of the entire Pamir region.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 116
Serial Issue: 7-8
Title: Tectonic evolution of the northeastern Pamir; constraints from the northern portion of the Cenozoic Kongur Shan extensional system, western China
Affiliation: University of California at Los Angeles, Department of Earth and Space Sciences, Los Angeles, CA, United States
Pages: 953-973
Published: 200408
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 95
Accession Number: 2004-057850
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2004107
Illustration Description: illus. incl. block diags., sects., 2 tables, geol. sketch maps
N36°00'00" - N39°30'00", E73°00'00" - E77°00'00"
Secondary Affiliation: Chinese Academy of Geological Sciences, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200417
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