Date of Award:

5-2003

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Bradley D. Ritts

Committee

Bradley D. Ritts

Abstract

Lower Cretaceous basins associated with the Hohhot detachment in the Daqing Shan of Inner Mongolia, China, allow us to better understand the tectonic evolution of extensional basins formed in association with detachment faulting and metamorphic core complex formation. The six basins, informally named N1, N2, S1, S2, S3, and S4, are located in different structural settings, or depozones, throughout the detachment-metamorphic core complex setting, and although all basins are consistent with previously proposed models for supradetachment basin sedimentation, second-order variability in sedimentary style is exerted by these distinct structural settings. The basins are composed of coarse, predominantly footwall derived, conglomerate deposited by mass-wasting and alluvial fan processes. Paleocurrent direction is generally southerly, indicating transverse transport away from the bounding detachment fault.

Two of the basins, N2 and S3, provide us with an understanding of the temporal evolution of supradetachment basins in the upper plate of a metamorphic core complex. These basins were joined in their early stages, but were later separated as extensional unroofing exhumed the lower plate of the core complex and folded the master detachment fault, causing it to propagate a new splay to the surface. Continued extension was accommodated on this new splay, allowing for continued deposition of Lower Cretaceous strata above the detachment fault on the southern flank of the Daqing Shan antiform. Another basin, S2, displays the same stratigraphy and records a similar evolution, but we speculate that it formed separately in a primary corrugation of the master detachment fault. The only unit exposed in basin S4, located near the eastern end of the detachment, is the uppermost unit. Paleocurrent and provenance data are similar to other basins. Thus, it strongly resembles the other basins in spite of the magnitude of extension. Basin S1 is located in an intra-hanging wall setting and resembles the other basins with the exception of a centrally located fine-grained interval. Basin N1 was filled by similar depositional processes, but the proportions of fill that these processes are responsible for is variable in comparison to the other Lower Cretaceous basins in the Daqing Shan. This study establishes that the basins described are all of similar geometry and depositional style, and that supradetachment basins of this style may occur in various positions within a detachment-metamorphic core complex setting, regardless of proximity to the exhumed metamorphic core and magnitude of extension.

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