Crustal exhumation and indications for Snowball Earth in the East African Orogen: North Ethiopia and East Eritrea

M. Beyth*, D. Avigad, H. U. Wetzel, A. Matthews, S. M. Berhe

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

43 Scopus citations

Abstract

The northeast Ethiopian plateau is composed of a low-grade metamorphic complex which includes the Tsaliet Metavolcanics overlain by the NE-trending upright folded metasediments of the Tambien Group including a thick stromatolitic carbonate sequence. High-grade metasediments and orthogneisses structurally underlie this unit in the Red Sea Lowlands of east Eritrea. In east Eritrea, the low-grade Bizen Domain metasediments and metavolcanics structurally overlie the Ghedem Domain high-grade rocks with a subhorizontal moderately W-dipping transition zone of tectonic origin. Field studies augmented by remote sensing analysis of Modular Optoelectronic Multispectral Stereo Scanner on Priroda (MOMS-2P) images are used to outline the structure, stratigraphy and geomorphology and the continuation of the Negash Synclinorium with adjacent structures up to the Bizen Domain in east Eritrea. The protolith age of the low- and high-grade rocks is around 850 and 800 Ma, respectively. Peak metamorphic conditions in the high-grade metasediments reached 700 °C and up to 12 kbar (depth of ∼40 km) at ∼650 Ma. This indicates that an elevated mountain belt with a very thick crust existed in Eritrea during the evolution of the East African Orogen (EAO). Rapid exhumation of the high-grade metamorphic rocks occurred between 640 and 545 Ma involving extension along a tectonic transition zone. The transition zone is a ductile detachment overprinted by brittle low-angle faulting. Although partly pertaining to a Tertiary deformation related to the opening of the Red Sea, we suggest that this low-angle zone was a detachment surface in the Neoproterozoic that accommodated extension during orogenic collapse to restore normal crustal thickness which was thickened due to collision between East and West Gondwana. The sedimentary rocks of the Tambien Group in north Ethiopia and the Bizen Domain in east Eritrea (stromatolitic limestone, stromatolitic dolostone, polymict conglomerate-diamictites), their stratigraphy and age of deposition suggest association with "Snowball Earth". Light δ13C (-6.74 and -6.88‰) were measured for the stromatolitic dolostone and algal mat of the Bizen Domain which are characteristic for cap-carbonates associated with Snowball Earth.

Original languageAmerican English
Pages (from-to)187-201
Number of pages15
JournalPrecambrian Research
Volume123
Issue number2-4
DOIs
StatePublished - 10 Jun 2003

Bibliographical note

Funding Information:
Alem Kibreab, Head Department of Mines, Eritrea, enabled us to carry out this study. This work was also supported by the German Israel Foundation which supports German Israel cooperation and by the Geological Survey of Israel. The field work was supported by the Israel Ministry for Foreign Affairs. We also thank A. Varshavsky for helping with data reduction and Avner Ayalon for carrying out the isotopic measurements. We would like to acknowledged the constructive comments by R. Stern, M. Abdelsalam, R. Greiling, W. Ghebreab, E. Abd-El-Motaal, T. Kuskey and anonymous reviewer.

Keywords

  • East African Orogen
  • Eritrea
  • Ethiopia
  • Exhumation
  • Extensional tectonics
  • Low-angle fault
  • Neoproterozoic
  • Orogenic collapse
  • Remote sensing
  • Snowball Earth

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