TY - JOUR
T1 - U-Pb zircon geochronology of the eastern part of the Southern Ethiopian Shield
AU - Stern, R. J.
AU - Ali, Kamal A.
AU - Abdelsalam, Mohamed G.
AU - Wilde, Simon A.
AU - Zhou, Qin
N1 - Funding Information:
We dedicate this study to the memory of Dr. Lulu Tsige. Lulu who worked extensively in the SES, and helped MGA collect the samples in 2005. He passed away on September 5, 2011 of cancer in Addis Ababa at the age of 45. This work was supported by NSF-OISE grant #0804749 and a Blaustein-Cox fellowship at Stanford University to RJS and a post-doctoral fellowship from Curtin University in Perth, Australia to KAA. The SHRIMP II facility in Perth is operated jointly by Curtin University, the University of Western Australia and the Geological Survey of Western Australia, with support from the Australian Research Council. The manuscript was greatly improved following the constructive criticism of J. Jacobs, editor P. Cawood, and two anonymous reviewers. This is UTD Geosciences contribution number #1226, TIGeR publication #400, and Missouri S&T Geology and Geophysics Program contribution #41.
PY - 2012/6
Y1 - 2012/6
N2 - The Southern Ethiopian Shield (SES) in the central East African Orogen lies at the junction of Neoproterozoic (880-550. Ma) largely greenschist-facies juvenile crust of the Arabian-Nubian Shield in the north and more metamorphosed and remobilized older crust of the Mozambique Belt to the south. The SES exposes a polycyclic sialic gneissic basement (represented by the Alghe Terrane in this study) with interleaved ophiolitic-volcano-sedimentary (Kenticha, Megado, and Bulbul) terranes. U-Pb zircon SHRIMP and LA-ICP-MS dating of 8 igneous and metamorphic intermediate and felsic bodies in the eastern SES yield Neoproterozoic crystallization ages: 847. ±. 11, 855. ±. 14, 732. ±. 5, 665. ±. 8, 657. ±. 6, 560. ±. 8, and 548. ±. 8. Ma. From these and previously published ages, we infer 4 principal magmatic episodes: 840-890. Ma (Late-Tonian-Early Cryogenian), 790-700. Ma (Cryogenian), ~660. Ma (Moyale Event), and Pan-African (630-500. Ma; Ediacaro-Cambrian). Neoproterozoic zircon xenocrysts (941, 884, 880, 863, 762, 716 and 712. Ma) confirm the dominance of Neoproterozoic crust in the study area. One sample of undeformed granite from the Alghae Terrane has abundant Archean zircons and may be a ~550. Ma melt of ~2.5. Ga crust, demonstrating for the first time that Archean crust or sediments with abundant Archean zircons exists in the SES. In spite of ~300 million years of Neoproterozoic igneous activity, we see no evidence of systematic compositional evolution in SES igneous rocks from early low-K suites to late high-K suites. Ediacaran deformation and magmatism of the SES reflects Late Tonian and Cryogenian formation of mostly juvenile crust that was subsequently deformed and chemically modified as a result of collision between large fragments of East and West Gondwana. Terminal collision began at ~630. Ma and caused crustal thickening, melting, uplift, erosion, orogenic collapse, and tectonic escape over a broad region of the East African Orogen, including up to ~25. km of erosion of SES crust. Plate convergence was likely continuous from ~630. Ma, forming major N-S structures. Deformation stopped at ~550. Ma and was followed by exhumation between ~ 530 and 500. Ma.
AB - The Southern Ethiopian Shield (SES) in the central East African Orogen lies at the junction of Neoproterozoic (880-550. Ma) largely greenschist-facies juvenile crust of the Arabian-Nubian Shield in the north and more metamorphosed and remobilized older crust of the Mozambique Belt to the south. The SES exposes a polycyclic sialic gneissic basement (represented by the Alghe Terrane in this study) with interleaved ophiolitic-volcano-sedimentary (Kenticha, Megado, and Bulbul) terranes. U-Pb zircon SHRIMP and LA-ICP-MS dating of 8 igneous and metamorphic intermediate and felsic bodies in the eastern SES yield Neoproterozoic crystallization ages: 847. ±. 11, 855. ±. 14, 732. ±. 5, 665. ±. 8, 657. ±. 6, 560. ±. 8, and 548. ±. 8. Ma. From these and previously published ages, we infer 4 principal magmatic episodes: 840-890. Ma (Late-Tonian-Early Cryogenian), 790-700. Ma (Cryogenian), ~660. Ma (Moyale Event), and Pan-African (630-500. Ma; Ediacaro-Cambrian). Neoproterozoic zircon xenocrysts (941, 884, 880, 863, 762, 716 and 712. Ma) confirm the dominance of Neoproterozoic crust in the study area. One sample of undeformed granite from the Alghae Terrane has abundant Archean zircons and may be a ~550. Ma melt of ~2.5. Ga crust, demonstrating for the first time that Archean crust or sediments with abundant Archean zircons exists in the SES. In spite of ~300 million years of Neoproterozoic igneous activity, we see no evidence of systematic compositional evolution in SES igneous rocks from early low-K suites to late high-K suites. Ediacaran deformation and magmatism of the SES reflects Late Tonian and Cryogenian formation of mostly juvenile crust that was subsequently deformed and chemically modified as a result of collision between large fragments of East and West Gondwana. Terminal collision began at ~630. Ma and caused crustal thickening, melting, uplift, erosion, orogenic collapse, and tectonic escape over a broad region of the East African Orogen, including up to ~25. km of erosion of SES crust. Plate convergence was likely continuous from ~630. Ma, forming major N-S structures. Deformation stopped at ~550. Ma and was followed by exhumation between ~ 530 and 500. Ma.
KW - East African Orogen
KW - Ethiopia
KW - Neoproterozoic
KW - Pan-African
KW - U-Pb zircon geochronology
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U2 - 10.1016/j.precamres.2012.02.008
DO - 10.1016/j.precamres.2012.02.008
M3 - Article
AN - SCOPUS:84860637015
SN - 0301-9268
VL - 206-207
SP - 159
EP - 167
JO - Precambrian Research
JF - Precambrian Research
ER -