207-14 Lithospheric Structure of the Neoproterozoic Ad Damm and Fatima Fault Zones, Arabian Shield: Implications for the On-Land Continuation of a Red Sea Transform Fault

Session: Honoring the Late Professor Mohamed Abdelsalam: Outstanding Researcher, Generous Colleague, Legendary Mentor, and Ambassador for the Geosciences In Africa

Presenting Author:

Authors:

Abstract:

This work uses Bouguer gravity anomalies from the World Gravity Model 2012 (WGM2012) to image the lithospheric structure beneath the Neoproterozoic Ad Damm and Fatima Fault Zones in the western part of the Arabian Shield, on the eastern margin of the Neogene–Quaternary Red Sea Rift. The Ad Damm Fault Zone separates the Neoproterozoic Asir Terrane to the southeast from the Jeddah Terrane to the northwest, while the Fatima Fault Zone crops out within the Jeddah Terrane. The Ad Damm Fault Zone is interpreted as an on-land continuation of the transform fault that separates the southern seafloor spreading segment of the Red Sea from the more advanced continental rift segment to the north. A Bouguer gravity anomaly map and a series of NW–SE-trending two-dimensional (2D) forward gravity models are used to investigate the lithospheric structure across the Ad Damm and Fatima fault zones. Results show that the northeastern part of the Ad Damm Fault Zone is marked by a steep gravity gradient. The Jeddah Terrane, located northwest of the fault, exhibits relatively high Bouguer gravity anomalies reaching approximately +70 mGal, while the Asir Terrane to the southeast shows lower values, reaching around –15 mGal. In contrast, the Fatima Fault Zone is associated with a gravity high anomaly of ~110 mGal. On average, the crustal thickness between the Ad Damm and Fatima fault zones is estimated at ~30 km, with the upper crust averaging ~10 km. In some locations, relatively thicker crust is observed beneath the Ad Damm Fault Zone, and a thicker (~35 km) total crust with a thinner (<8 km) upper crust is found between the Ad Damm and Fatima fault zones. Overall, the thickness of the sub-continental lithospheric mantle (SCLM) in the study area is ~60 km. These results suggest that lithospheric stretching associated with the opening of the Red Sea caused significant uniform thinning of the SCLM, while crustal thickness varies between ~25–35 km. It further shows that the Fatima Fault Zone, which crops out in the middle of the Jeddah Terrane, lies above a relatively shallower Moho than the Ad Damm Fault Zone, highlighting the influence of lithospheric pre-existing structures and their respective rheological behavior on the rate of crustal stretching.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.