T116 Time Machine: Earth’s Deep-Time Geography—Data, Reconstructions, Challenges (Posters)

Monday, 16 October 2023
8:00 AM - 5:30 PM
Hall B

ESTIMATING UNKNOWN HYPEREXTENDED CONTINENTAL CRUST IN SOUTH AMERICA AND AFRICA DURING THE SOUTH ATLANTIC EXPANSION

Paper number: T116-13
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

This research focuses on estimating the unknown hyperextended continental crust between South America and Africa, formed during the expansion of the South Atlantic Ocean. A paleogeographic reconstruction has been conducted between the orogenic belts of SW Gondwana in SE Brazil-Uruguay and SW Africa, considering the continental crust stretched under the passive margin basins. Regional seismic surveys, gravimetry, and magnetometry data were used to investigate the crustal-scale structures of shields, terranes, and stretched crust in the South Atlantic Ocean. In addition, geological and isotope geochemistry data were integrated to define the terranes with significant properties. The region's complex geological events, including compressive, extensional, and transcurrent processes, pose challenges in reconstructing the paleogeography prior to forming the West Gondwana Supercontinent. The configuration of the cratonic cores resulted from the collision of the Rio de la Plata Craton (RLPC) with the Congo and Kalahari cratons, resembling the layout observed in Southeast Asia. This collision led to the development of numerous thrust-and-fold belts and strike-slip belts, which separate older continental fragments. The study sheds light on quantifying the hyperextended continental crust beneath South America and Africa during the South Atlantic Ocean expansion. Integrating regional seismic surveys, gravimetry, and magnetometry data with geological and isotope geochemistry data has enabled defining terranes with significant properties. However, reconstructing the paleogeography before the formation of the West Gondwana Supercontinent is complex due to the extensive geological events in the region. The presence of passive margin basins and the Atlantic Ocean prevents the extension of cratonic and mobile belts from onshore to offshore areas. The continental crust under the Atlantic Ocean now spans up to 450 km in length. By restoring the stretched margin, it is estimated that 200 to 300 km of unknown crust were not considered in the reconstruction of the SW Gondwana Supercontinent at 160 Ma before the breakup of South America and Africa. Our findings offer valuable insights into the geological evolution of this intriguing region and provide new perspectives for reconstructing hyperextended passive margins and understanding Precambrian terrane evolution.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-394451

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