Timing the Initiation of Extension Along the Shanxi Rift, China, With Implications for the Cenozoic Tectonics of Asia
Abstract
The Shanxi rift accommodates east-west extension along the eastern margin of the Ordos block in the North China craton. Previous workers have assumed a Paleogene initiation age for the southern part of the Shanxi rift, because Paleogene sediments occur in the graben basin. However, these sediments also occur along the rift shoulder in the footwalls of major rift-bounding faults, implying Paleogene sediments may be pre-rift. The central and northern parts of the Shanxi rift contain only Neogene sediments, suggesting a Neogene initiation age. Three hypotheses for the timing of rift initiation are proposed: (1) the Shanxi rift initiated in the Paleogene, (2) the rift initiated in the Neogene, and (3) the southern part of the Shanxi rift initiated first in the Paleogene, and subsequent rifting propagated to the north in the Neogene. These hypotheses are being tested by (i) (U-Th) He dating of apatite and (ii) fission track dating of apatite and zircon from east-west transects across graben-bounding normal faults along the Shanxi rift. East-west extension is active across east Asia, occurring in the Himalaya, Tibet, along the northwest and east margins of the Ordos Block, the Hangay extensional system, and in the Lake Baikal region. These systems may be induced by a common dynamic cause because they share the same extension direction. Genetic relations among these systems can be tested by determining (1) kinematic relationships and (2) timing of rifting. To the south the Shanxi rift terminates at the left-slip Qinling fault, which may connect with the left-slip Kunlun fault to the west via a large contractional step-over structure. Both faults are important structures accommodating the Indo-Asian collision in the past 10 m.y. The Kunlun fault marks the northern boundary of active north-trending rifts in Tibet. If the Kunlun fault does kinematically connect with the Qinling fault, these relationships suggest a dynamic link between active east-west extension in Tibet and in North China. However, it is widely assumed that east-west extensional structures in the Himalaya and Tibet, which initiated between 18 and 8 Ma, result from gravitational collapse and indicate when the Tibetan Plateau achieved its maximum elevation. The results of this study will test the validity this hypothesis, and the possible dynamic connection between east-west extension in Tibet and in North China.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.T61A1225W
- Keywords:
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- 8107 Continental neotectonics;
- 8109 Continental tectonics: extensional (0905);
- 9320 Asia;
- 9604 Cenozoic