--> Dominant Role of Structural Inheritance in the Distribution of Faulted Sags, Erlian Basin, the Eastern Central Asian Orogenic Belt (NE China)

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Dominant Role of Structural Inheritance in the Distribution of Faulted Sags, Erlian Basin, the Eastern Central Asian Orogenic Belt (NE China)

Abstract

It has been widely accepted that structural inheritance acts as a dominant factor on tectonic evolution and structural deformation pattern of the lithosphere. However, some problems regarding tectonic inheritance control on extensional sedimentary basins developing on orogenic belts, still remain unsolved. Here we reported an example to illustrate how pre-existing structures control the distribution of faulted sags and hydrocarbon-bearing faulted sags within an extensional basin. Erlian Basin is an extensional basin superposed on the Eastern central Asian orogenic belt during Early Cretaceous, only consisting of 10 hydrocarbon-bearing faulted sags among numerous faulted sags. Based on geophysical and geological survey data, the distribution of these faulted sags, the characteristics of pre-existing structures in Erlian Basin, and their relationship are studied. Our results shows that 68 faulted sags in Erlian Basin can be grouped into South Sag Group and North Sag Group based on their orientations and affinity of sag-boundary faults. The two sag groups are separated by 3 uplifts, displaying a basin-range-like tectonic framework as a whole. The distribution of these faulted sags in Erlian Basin was strongly influenced by pre-existing structures, as these faulted sags developed along pre-existing deep faults; the sag groups were superimposed over the Hercynian synclinorium, while the uplifts had a genetic relationship with the Hercynian anticlinorium; and the rigid Xilinhot block separated the two sag groups. These results suggest that structural evolution of Erlian Basin during Early Cretaceous had a good inheritance from the pre-existing structures formed during orogenic period. Specifically, the pre-existing deep faults strongly weakened the lithosphere and localized strain, and had a priority in activity under extensional tectonic setting, which controlled the distribution and development of faulted sags. Similarly, the zone where a rheological property varies also has a significant influence on the distribution of faulted sags. In addition, our results also suggest that the faulted sags superimposed on pre-existing deep faults, the intersection of pre-existing deep faults and rigid block are the prospective hydrocarbon-rich zones that had experienced enough subsidence and then formed abundant high-quality source rocks during the basin evolution period.