Research Article| August 01, 2004 Himalayan-type indenter-escape tectonics model for the southern part of the late Neoproterozoic–early Paleozoic East African– Antarctic orogen Joachim Jacobs; Joachim Jacobs 1University of Bremen, FB Geowissenschaften, PF 330440, 28334 Bremen, Germany Search for other works by this author on: GSW Google Scholar Robert J. Thomas Robert J. Thomas 2British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK Search for other works by this author on: GSW Google Scholar Author and Article Information Joachim Jacobs 1University of Bremen, FB Geowissenschaften, PF 330440, 28334 Bremen, Germany Robert J. Thomas 2British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK Publisher: Geological Society of America Received: 30 Jan 2004 Revision Received: 04 Apr 2004 Accepted: 07 Apr 2004 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2004) 32 (8): 721–724. https://doi.org/10.1130/G20516.1 Article history Received: 30 Jan 2004 Revision Received: 04 Apr 2004 Accepted: 07 Apr 2004 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Joachim Jacobs, Robert J. Thomas; Himalayan-type indenter-escape tectonics model for the southern part of the late Neoproterozoic–early Paleozoic East African– Antarctic orogen. Geology 2004;; 32 (8): 721–724. doi: https://doi.org/10.1130/G20516.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The East African–Antarctic orogen is one of the largest orogenic belts on the planet. It resulted from the collision of various parts of proto–East and West Gondwana during late Neoproterozoic–early Paleozoic time (between 650 and 500 Ma). We propose that the southern part of this Himalayan-type orogen can be interpreted in terms of a lateral-escape tectonic model. Modern Gondwana reconstructions show that the southern part of the East African– Antarctic orogen can best be reassembled when a number of microplates (the Falkland, Ellsworth-Haag, and Filchner blocks) are positioned between southern Africa and East Antarctica. This microplate assemblage is unusual. The microplates probably represent shear-zone–bounded blocks, produced by tectonic translation during lateral escape, similar to those currently evolving in Southeast Asia. One of the escape-related shear zones is exposed as the 20-km-wide Heimefront transpression zone in western Dronning Maud Land. Coats Land, a crustal block within the orogen, probably represents a block of older crust that was not subjected to tectonometamorphic reworking ca. 500 Ma by lateral tectonic escape. The southern part of the orogen is also typified by very large volumes of late-tectonic A2-type granitoids, intruded ca. 530–490 Ma, probably as a consequence of delamination of the orogenic root and the subsequent influx of hot asthenospheric mantle during tectonic escape. Erosional unroofing of the orogen is documented by the remnants of originally massive areas covered by Cambrian– Ordovician molasse-type sedimentary rocks throughout Africa, Arabia, and Antarctica, testifying to the past extent and size of this largest of orogens. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Whole-rock major and trace element geochemical and Rb–Sr/Sm–Nd isotopic data are presented for the Mesoproterozoic (∼1.0 Ga) metamorphic and igneous rocks of the Cape Meredith Complex, West Falkland. The data indicate that the oldest rocks, the ∼1.1 Ga supracrustal gneisses of the Big Cape Formation, which form three petrographic and geochemical groups (mafic amphibolite, quartz–plagioclase–biotite–hornblende intermediate gneiss and acid gneiss), probably represent a juvenile calc-alkaline, basalt–andesite–rhyolite volcanic sequence, with epsilon (εNdT) values and Nd T DM ages of ∼+3 to +6 and ∼1100 to 1400 Ma respectively. It is argued on geochemical grounds that these metavolcanics were extruded in an island-arc at around 1120 Ma. The Big Cape Formation was intruded by granitoids during and after a collisional orogenic event at around 1090 Ma. The oldest, foliated, (G1) granodiorite was emplaced as thin sheets at approximately 1090 to 1070 Ma and is characterized by εNd values of ∼+1.5 to 4 (T DM = ∼1200 to 1400 Ma), showing its juvenile nature. The ∼1070 Ma (G2) syntectonic granitoid gneisses and ∼1000 Ma G3 post-tectonic granites also exhibit juvenile characteristics (ε Nd = ∼0 to +5 and T DM = 2200 to 1200 Ma, respectively). The granitoids show a time-composition evolution from Na-rich (G1) granodiorite to potassic, high-High Field Strength Element granites (G3). The geochemical and isotopic characteristics and geological evolution of the Cape Meredith Complex is comparable with that of the adjacent Gondwana crustal blocks in Natal (SE Africa) and Dronning Maud Land (East Antarctica), supporting models that demonstrate these areas evolved in a contiguous, juvenile arc environment prior to, and during, a major orogenic event at ∼1.1 Ga. These events were associated with the birth of the Rodinian supercontinent. The three areas remained juxtaposed during Rodinia break-up and were subsequently incorporated into Gondwana in the same relative positions.
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