The origin of the ultramafic rocks of the Tulu Dimtu Belt, western Ethiopia-do they represent remnants of the Mozambique Ocean?

Blades, Morgan L. and Foden, John and Collins, Alan S. and Alemu, Tadesse and Woldetinsae, Girma (2019) The origin of the ultramafic rocks of the Tulu Dimtu Belt, western Ethiopia-do they represent remnants of the Mozambique Ocean? Geological Magazine, 156 (1). pp. 62-82. ISSN 14695081

Abstract

The East African Orogen contains a series of high-strain zones that formed as Gondwana amalgamated. The Tulu Dimtu shear belt is one of these N-S structures within the Barka-Tulu Dimtu zone in western Ethiopia, and contains ultramafic bodies of equivocal origin. Identifying the petrogenetic origin of these enigmatic rocks provides evidence for the geodynamic significance of these shear zones. Owing to their altered state, these ultramafic rocks' well-preserved chrome spinels provide the only reliable evidence for their source and tectonic affiliation. Chrome spinels have high Cr2O3 (30.04-68.76 wt ), while recalculated Fe2O3 (< 2 ) and TiO2 (0.01-0.51 ) values are low. The Cr# (molar Cr3+/Cr3+ + Al2+) and Mg# (Mg2+/Mg2+ + Fe2+) have averages of 0.88 and 0.22, respectively. Based on olivine-spinel equilibria, the calculated fO2 values (FMQ +3.03) for the dunites reveal a highly oxidized environment. This spinel chemistry (high Cr# > 0.6 and low Ti) supports a supra-subduction origin, with an oxidized mantle source more refractory than depleted MORB mantle (DMM). These spinel compositions indicate that some ultramafic bodies in western Ethiopia, including those from Daleti, Tulu and Dimtu, are serpentinized peridotites emplaced as obducted ophiolite complexes. By contrast, the ultramafic rocks from the Yubdo locality have a different spinel chemistry, with strong affiliation with igneous spinels formed in Alaskan-style mafic intrusions. These collective results suggest that regardless of their origin as supra-subduction ophiolites or as Alaskan-type intrusions, these spinels were formed on a convergent-subduction margin.

Item Type:	Article
Identification Number:	10.1017/S0016756817000802
Uncontrolled Keywords:	Alaskan-type intrusion,Western Ethiopian Shield,chrome spinel,ophiolite
Depositing User:	maria
Date Deposited:	10 Jun 2024 03:43
Last Modified:	10 Jun 2024 03:43
URI:	http://repository.ub.ac.id/id/eprint/220651

Text The_origin_of_the_ultramafic_rocks_of_the_Tulu_Dimtu_Belt_western_Ethiopia_do_they_represent_remnant.pdf Download (2MB)

Actions (login required)

View Item