STRUCTURAL AND SEISMIC EVIDENCE FOR INTRACONTINENTAL SUBDUCTION IN THE PETER THE 1ST RANGE, CENTRAL-ASIA

Citation
Mw. Hamburger et al., STRUCTURAL AND SEISMIC EVIDENCE FOR INTRACONTINENTAL SUBDUCTION IN THE PETER THE 1ST RANGE, CENTRAL-ASIA, Geological Society of America bulletin, 104(4), 1992, pp. 397-408
Citations number
68
Language
INGLESE
art.tipo
Article
ISSN journal
0016-7606
Volume
104
Issue
4
Year of publication
1992
Pages
397 - 408
Database
ISI
SICI code
0016-7606(1992)104:4<397:SASEFI>2.0.ZU;2-R
Abstract
This paper examines the stratigraphy, structure, and seismicity of the Peter the First Range, an actively deforming foreland basin in Soviet Tadjikistan. The range represents a highly deformed segment of a larg e intracontinental basin, the Tadjik Depression, which is being shorte ned in response to the Cenozoic convergence between two orogenic massi fs, the Pamir and the Tien Shan Ranges. The Late Jurassic to Paleogene stratigraphy of the Peter the First Range includes more than 2,000 m of shallow marine to nonmarine sediments deposited under relatively qu iescent conditions, close to sea level. In contrast, the correlative u nits of the northernmost Pamir, directly south of the Peter the First Range, show evidence of proximity to a major, uplifted source area to the south. These Mesozoic-early Cenozoic strata are overlain by thick sequences of alluvial sandstone and conglomeratic units that coarsen u pward through the Neogene and record the progressive uplift of the Pam ir. Shortening within the Peter the First Range is recorded by kilomet er-scale isoclinal, upright-to-over-turned folds, and imbricate, north -verging thrusts that emerge near the northern edge of the range and m ark the active tectonic boundary with the Tien Shan. Most of the defor mation appears to postdate the accumulation of the Mio-Pliocene molass e. The stratigraphy and structure of the region are best explained by a model of the Mesozoic Tadjik Depression as an intracontinental, fore land basin, developed in a back-arc position with respect to the activ e Andean or collisional orogens located in northern Afghanistan and th e Pamir. Seismicity in the region is dominated by earthquakes extendin g from the surface to approximately 12-km depth, apparently occurring within the deformed sediments of the Peter the First Range. A subhoriz ontal zone of relatively low activity at this depth may mark the locat ion of a basal detachment that underlies a structurally thickened sedi mentary section. This aseismic zone is in turn underlain by a south-di pping belt of seismicity that extends from about 17- to 35-km depth, a nd which can be traced updip to the seismogenic crystalline basement o f the Tien Shan range to the north. We interpret this south-dipping st ructure as a zone of intracontinental subduction that may be an updip continuation of the enigmatic, intermediate-depth Wadati-Beni-off Zone beneath the Pamir Range to the south.