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Zircon U-Pb geochronology and Nd isotope systematics of the Abas terrane, Yemen: Implications for Neoproterozoic crust reworking events
Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
Stockholm University, Faculty of Science, Department of Geological Sciences.
Stockholm University, Faculty of Science, Department of Geological Sciences. Swedish Museum of Natural History, Sweden.
Number of Authors: 4
2015 (English)In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 267, 106-120 p.Article in journal (Refereed) Published
Abstract [en]

High-spatial-resolution secondary-ion mass spectrometry (SIMS) U-Pb zircon ages, whole-rock Nd isotopic and geochemical data are reported for granites and granitic gneisses from a traverse across the Abas terrane, Yemen, a part of the Precambrian basement of southern Arabian Peninsula. SIMS U-Pb dating identifies two magmatic episodes, the first at c. 790-725 Ma represented by granitic gneisses, the second clearly post-tectonic at c. 625-590 Ma. The oldest sample in the post-tectonic group is slightly deformed while younger samples are undeformed indicating that penetrative deformation ceased at c. 625 Ma in the Abas region. Whole-rock(Nd)(t) values between -11 and +0.8, Nd model ages of 1.70-1.13 Ga indicate a significant contribution of evolved continental material in the genesis of the Abas granitoids, unlike most of the juvenile Arabian-Nubian Shield (ANS), although there are few inherited zircons. Secular variation in epsilon(Nd)(t)reflects a change in magma source with increasing juvenile magma and diminishing crustal input during post-tectonic (625-590 Ma) magmatism. The combination of subduction zone chemistry, absence of older rocks, paucity of inherited zircons, evolved Nd isotopic signatures and the I-type characteristics of the samples suggest that assimilation occurred at depth.

Place, publisher, year, edition, pages
2015. Vol. 267, 106-120 p.
Keyword [en]
Precambrian crustal evolution, Arabian Shield, Yemen, U-Pb zircon, Post-tectonic magmatism, Nd isotopes
National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
URN: urn:nbn:se:su:diva-120897DOI: 10.1016/j.precamres.2015.05.037ISI: 000359874800006OAI: oai:DiVA.org:su-120897DiVA: diva2:859874
Available from: 2015-10-09 Created: 2015-09-18 Last updated: 2017-08-10Bibliographically approved
In thesis
1. Crustal evolution of the Arabian–Nubian Shield: Insights from zircon geochronology and Nd–Hf–O isotopes
Open this publication in new window or tab >>Crustal evolution of the Arabian–Nubian Shield: Insights from zircon geochronology and Nd–Hf–O isotopes
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Arabian–Nubian Shield (ANS) represents a major site of juvenile Neoproterozoic crustal addition on Earth and documents Neoproterozoic tectonics bracketed by two supercontinent cycles, namely the fragmentation of Rodinia and the amalgamation of Gondwana. There is general consensus that the ANS formed by juvenile magmatic arc accretion and subsequent shield–wide post–tectonic magmatism. However, detailed understanding about the timing of events and the nature of magma sources in parts of the shield are lacking. To date, there are no isotopic data from the Paleozoic sedimentary sequences of the ANS, except those from the northern part. New zircon U–Pb, δ18O and whole–rock Nd isotopes are presented for plutonic rocks from the eastern Ethiopia, Yemen and southernmost Arabian Shield in Saudi Arabia. This thesis also presents the first combined in situ zircon U–Pb–O–Hf isotope data on the Cambrian–Ordovician sandstones of the Arabian Shield. The results are used to elucidate the crustal evolution of these parts of the ANS and to evaluate terrane correlations. Specifically, the nature of crustal growth, i.e., relative proportions of juvenile magmatic additions vs. crustal reworking, nature of the magma source and mechanism of crust formation (plume material vs. subduction zone enrichment) and understanding the provenance of the Cambrian–Ordovician sandstone sequences were important research questions addressed.

The results from Paper I suggest that the eastern Ethiopian Precambrian basement is dominated by reworking of pre-Neoproterozoic supracrustal material unlike contemporaneous rocks in the remaining parts of Ethiopia— indicating the presence of two distinct lithospheric blocks of contrasting isotopic compositions in Ethiopia. Metamorphic age distributions suggest that the eastern Ethiopian block was amalgamated with the juvenile Western Ethiopian Shield during ca. 580–550 Ma. Importantly, the suture between them may represent the northern continuation of a major suture identified further south in Africa along which Gondwana amalgamated. Similarly, the Abas terrane in Yemen (Paper II) is dominated by reworking of pre–Neoproterozoic crust and shows age and isotopic compositions that are inconsistent with the Afif terrane of Saudi Arabia, precluding correlation between the two regions. The trace element systematics of plutonic rocks from the southernmost Arabian Shield (paper III) point to enrichment due to subduction component, bear no evidence of a plume component, and are consistent with the adakite-like chemistry of some of the subduction–related plutonic samples. This reinforces the notion that the shield grew through juvenile magmatic arc additions. The combined zircon U–Pb–O–Hf data of the Cambrian–Ordovician sandstones (Paper IV) indicate their derivation from both the adjacent juvenile ANS and the more southerly crustal blocks that are dominated by reworking of pre–Neoproterozoic crust. The remarkable similarity in age spectra and homogeneity of Cambrian sandstones deposited across the northern margin of Gondwana point to continental–scale sediment mixing and dispersal regulated by the supercontinent cycle.

Place, publisher, year, edition, pages
Stockholm: Department of Geological Sciences, Stockholm University, 2017. 27 p.
Series
Meddelanden från Stockholms universitets institution för geologiska vetenskaper, 367
Keyword
Gondwana, Arabian–Nubian Shield, Azania, zircon U–Pb–O–Hf isotopes, Nd isotopes, Cambrian Sandstones, juvenile, pre–Neoproterozoic, reworking
National Category
Earth and Related Environmental Sciences
Research subject
Geology
Identifiers
urn:nbn:se:su:diva-145479 (URN)978-91-7649-938-2 (ISBN)978-91-7649-939-9 (ISBN)
Public defence
2017-09-20, De Geersalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-08-28 Created: 2017-08-06 Last updated: 2017-08-28Bibliographically approved

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