Significance of high-grade metasediments from the Neoproterozoic basement of Eritrea

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doi: 10.1016/S0301-9268(97)00040-5
Authors:Beyth, Michael; Stern, Robert J.; Matthews, Alan
Author Affiliations:Primary:
Geological Survey of Israel, Jerusalem, Israel
University of Texas at Dallas, Richardson, TX, United States
Hebrew University of Jerusalem, Jerusalem, Israel
Volume Title:Precambrian Research
Source:Precambrian Research, 86(1-2), p.45-58. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1997
Note:In English. 39 refs.; illus., incl. 4 tables, sketch maps
Summary:High grade orthogneiss, amphibolitic dykes and paraschist to migmatites were studied in the Red Sea Lowlands of eastern Eritrea. Chemical data and a mineral assemblage of kyanite, staurolite, almandine garnet, biotite and quartz indicate that the schists were formed by metamorphism of pelitic metasediments derived by sub aerial weathering, deposited in a marine environment. Thermobarometry based on element partitioning between coexisting minerals of schist, orthogneiss and amphibolite shows that peak metamorphic conditions were ca 700°C and 8-10 kbar. An overall clockwise P-T loop is suggested by the thermobarometry results, and is consistent with a collision setting. The Eritrean high-grade metasediments can be correlated with similar rocks in Arabia this defines a sedimentary basin that was at least 400 km from north to south. Low initial 87Sr/86Sr (0.7014-0.7028) and εNd(800Ma) of +2.5 to +4.7 along with a mean TDM model age of 1.05 Ga indicates that juvenile Neoproterozoic crustal sources controlled the sedimentation of the pelites, and permits negligible involvement of older crustal sources. Rb/Sr geochronology suggests an age of ca 650 Ma for thermal resetting, consistent with a model whereby plate collision between east and west Gondwanaland was responsible for the metamorphism and exhumation. These metasediments reflect the transition between the northern and southern sectors of the East African Orogen, containing the juvenile isotopic signature similar to rocks of the Arabian-Nubian Shield but a chemical composition and metamorphic grade that are indistinguishable from assemblages characteristic of the Mozambique Belt.
Subsections:Metamorphism: regional, dynamic
Subjects:Alkaline earth metals; Amphibolites; Basement; Chemical composition; Dikes; Electron probe data; Geochemistry; Gneisses; Gondwana; Grade; High-grade metamorphism; Intrusions; Isotope ratios; Isotopes; Major elements; Metals; Metamorphic rocks; Metamorphism; Metasedimentary rocks; Migmatites; Mineral assemblages; Nd-144/Nd-143; Neodymium; Neoproterozoic; Orthogneiss; P-T conditions; Partitioning; Petrography; Precambrian; Proterozoic; Rare earths; Sr-87/Sr-86; Stable isotopes; Strontium; Thin sections; Trace elements; Upper Precambrian; Whole rock; X-ray diffraction data; Africa; Arabian Peninsula; Arabian Shield; Asia; East Africa; Eritrea; Mozambique Belt; Nubian Shield; Red Sea region
Coordinates:N163000 N180000 E0420000 E0400000
Abstract Numbers:99M/2251
Record ID:1998031889
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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