资源环境科技发展态势分析平台

The sedimentary record of the Paleoproterozoic Aravalli Supergroup in northwest India provides evidence for a progression from passive margin to active margin and back to passive margin that can be linked to the Precambrian crustal evolution of peninsular India. U-Pb detrital zircon age data from elastic sedimentary rocks constrain the depositional age of the Aravalli Supergroup to within the ca. 2.4-1.6 Ga age bracket. The 3.3-2.9 and 2.5 Ga basement granitoids of the Banded Gneiss Complex have been identified as the source rocks for the Delwara Formation from the Lower Aravalli Supergroup. The Delwara sandstones show enrichment of Zr and depletion of Ti and Sc, indicating a passive-margin depositional environment. Immature sandstones of the Middle Aravalli Udaipur Formation incorporate detritus from ca. 1.97-1.79 Ga magmatic arc rocks (characterized by zircon epsilon(Hf(t)) values varying from +6.1 to -7.8) and continental basement (ca. 2.5 Ga). Tectonic discrimination characteristics of Middle Aravalli sandstones, such as K2O/Na2O-SiO2, TiO2-Fe2O3, La-Th-Sc, and Th-Sc-Zr/10, suggest a continental arc setting, in agreement with their average modal composition of Q(23)F(27)L(50) (where Q is quartz, F is feldspar, and L is lithics), which indicates a proximal source and transitional arc setting. The stratigraphically higher Bowa Formation of the Middle Aravalli Supergroup received additional detritus from 1.78 to 1.72 Ga extension-related magmatic arc rocks, and these strata are characterized by zircons with subchondritic epsilon(Hf(t)) values, suggesting a back-arc setting, in agreement with tectonic discrimination plots. The Upper Aravalli Debari sandstones are dominated by 1.87-1.65 Ga detritus. Their high maturity (average: Q(92)F(4)L(4)) and geochemical features are consistent with a passive-margin setting. Integration of the lithostratigraphic relationships and compositional data suggests that the rocks of Aravalli Supergroup archive the record for the development of early Paleoproterozoic passive-margin platform sedimentation, followed by a transition to continental arc and subsequently to an evolved rift-basin-passive-margin setting.