Cenozoic Tectonics of the Western Arabia Plate Related to Harrat Magmatism near Al Madīnah, Kingdom of Saudi Arabia

Professional Paper 1862-B
Jointly published with the Saudi Geological Survey [as Saudi Geological Survey Special Report SGS–SP–2021–1]
By:  and 



Sprawling volcanic fields, or harrats, in western Saudi Arabia have been emplaced during the past 30 million years following effusions of flood basalts in Ethiopia and Yemen. Although broadly associated with volcanism in three rift valleys (Red Sea, Gulf of Aden, and East African Rift Zone) radiating from the Afar depression, harrat abundance on the Arabian Peninsula indicates that volcanism is distinct from processes that opened the Red Sea and drive its magmatism. Harrats primarily lie unconformably on the Arabian Shield and locally on Paleozoic platform deposits, but several are conformable upon or interbedded with Paleogene supracrustal strata. Harrats erupted from linear chains of vents; some are oriented parallel to the Red Sea (N. 30° W.), but most trend northerly or north-northeasterly. Harrats consist mainly of weakly alkalic basalts and lesser amounts of their differentiation products, but some contain strongly alkalic rocks such as basanites and phonolites. Early harrats predate initial opening of the Red Sea 24–20 million years ago (Ma) and uplift of its flank 20–11 Ma, but younger harrats postdate the uplift and are larger and more abundant. Seismic studies identify substantially thinned continental lithosphere beneath the most voluminous harrats, but little crustal thinning is apparent at the surface, an indication that the lithosphere was eroded from below. The combination of plume impingement, rift valley formation, and erosion of the lithosphere beneath the Arabian Shield since 30 Ma indicates that the Afar plume thermally weakened the region, enabling the Arabia Plate to separate from the Africa Plate along the Red Sea and Gulf of Aden. The plume also thinned interior parts of the newly formed Arabia Plate, not just its margins, promoting mantle melting and volcanism.

Suggested Citation

Calvert, A.T., and Sisson, T.W., 2023, Cenozoic tectonics of the western Arabia Plate related to harrat magmatism near Al Madīnah, Kingdom of Saudi Arabia, chap. B of Sisson, T.W., Calvert, A.T., and Mooney, W.D., eds., Active volcanism on the Arabian Shield—Geology, volcanology, and geophysics of northern Harrat Rahat and vicinity, Kingdom of Saudi Arabia: U.S. Geological Survey Professional Paper 1862 [also released as Saudi Geological Survey Special Report SGS–SP–2021–1], 28 p., https://doi.org/10.3133/pp1862B.

ISSN: 2330-7102 (online)

ISSN: 1044-9612 (print)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Importance and Complexities of Red Sea Tectonics
  • Characteristics of Arabian Peninsula Harrats
  • Geologic Setting
  • New 40Ar/39Ar Constraints on Structures in and Adjacent to Harrat Rahat
  • Oligocene to Present Plate Tectonic Model
  • Red Sea Pure-Shear versus Simple-Shear Tectonic Models
  • Discussion and Summary
  • Acknowledgments
  • References Cited
  • Appendix 1. 40Ar/39Ar Analysis Results
Publication type Report
Publication Subtype USGS Numbered Series
Title Cenozoic tectonics of the western Arabia Plate related to harrat magmatism near Al Madīnah, Kingdom of Saudi Arabia
Series title Professional Paper
Series number 1862
Chapter B
DOI 10.3133/pp1862B
Year Published 2023
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Geology, Minerals, Energy, and Geophysics Science Center, Volcano Science Center
Description v, 28 p.
Country Kingdom of Saudi Arabia
Online Only (Y/N) N
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details