The pre-break-up position of Haag Nunataks within Gondwana: possible correlatives in Natal and Donning Maud Land
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The Llano Orogenic Belt along the present southern margin of Laurentia, regarded as continuation of the Grenvillian Orogen along the eastern Laurentian margin and exposed in basement uplifts in central and western Texas, records an ∼300‐m.yr. history of orogenesis culminating in arc‐continent and continent‐continent collision between ∼1150 and 1120 Ma and continuing until ∼980 Ma. The shape of the orogen and kinematics of the contractional deformation along the belt, together with the high‐P metamorphic conditions attained, indicate that a previously unidentified craton served as an indentor. It is paleomagnetically acceptable for the Kalahari Craton of southern Africa to have been opposed to this margin and within ∼1500 km of present‐day central Texas at ∼1100 Ma. Moreover, the Kalahari Craton is the correct size, and the structural and metamorphic evolution of the 1200–950 Ma Namaqua‐Natal Orogenic Belt that wraps around its present southern margin is compatible with that craton having been the indentor. The ocean basin that closed between the Laurentia and Kalahari Cratons would have been comparable to the present Pacific, with island arc/terrane accretion occurring during the Mesoproterozoic along opposing active convergent margins. The coeval 1.1 Ga Keeweenawan and Umkondo magmatic provinces of Laurentia and Kalahari, respectively, are associated with rifts at a high angle to the Llano and Namaqua Orogens. The rifts are interpreted as the result of collision‐generated extensional stresses within the two cratons. The voluminous mafic igneous rocks in both provinces, however, may reflect contemporaneous plume activity. Our reconstruction for 1.1 Ga provides a testable model for the Llano Orogenic Belt of Texas and the Namaqua Orogenic Belt of southwestern Africa as opposite sides of a Himalayan‐type collisional orogen, with the Natal Belt of southeastern Africa and the originally continuous Maudheim Belt of East Antarctica as a related Indonesian‐type ocean‐continent convergence zone. This reconstruction leads to a refinement of the paleogeography of Rodinia, with the Kalahari Craton in a position isolated from both the East Antarctic and Rio de la Plata Cratons by oceanic lithosphere. It also provides the first model for the assembly of that hypothetical early Neoproterozoic supercontinent. At least four separate cratonic entities appear to have collided along three discrete segments of the apparently anastomosing global network of "Grenvillian" orogens: the type‐Grenville Belt of eastern North America and counterparts in South America, the Llano‐Namaqua Belt, and the Eastern Ghats‐Albany/Fraser Belt of India‐East Antarctica and Australia. Over the remarkably short interval of ∼200 m.yr., this first‐order composite collisional event resulted in the amalgamation of most of Earth's continental lithosphere and defined the close of the Mesoproterozoic Era.
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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.
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The about 500 km long coastal stretch of central Dronning Maud Land (DML), East Antarctica, is critical for understanding both Gondwana and Rodinia assembly. In common Gondwana reconstructions central DML lies at the potential southern extension of the Mozambique Belt. We report the first extensive geochronological study of magmatic and metamorphic rocks from the area. These new U‐Pb SHRIMP zircon and Sm‐Nd‐data of rocks sampled during the German international GeoMaud 1995/96 expedition indicate that the oldest rocks in central DML are Mesoproterozoic in age. The crystallization ages of metavolcanic rocks were determined at c. 1130 Ma. Syn‐tectonic granite sheets and plutons give ages of c. 1080 Ma, contemporaneous with metamorphic zircon growth at granulite facies conditions. An anorthosite intrusion and a charnockite are dated at c. 600 Ma. Subsequent metamorphism is recorded for at least two different episodes at c. 570–550 Ma and between 530 to 515 Ma. The latter metamorphic event reached granulite facies and is associated with the syn‐tectonic intrusion of a granodiorite body at Conradgebirge. Initial ϵNd,t‐values of the U‐Pb dated rocks with crystallization ages around 1.1 Ga range from c. +7 to –4. These values suggest that their magmatic precursors represent variable mixtures of a primitive mantle‐derived and continental crust component generated within a mature island arc. Initial Nd isotope data of Cambrian meta‐igneous rocks are indistinguishable from the Grenville‐age rocks, probably representing partial melts of the Grenville‐age basement. The occurrence of Pan‐African syn‐tectonic granitoids is unique in DML. The structure and shape of this body indicates that the main structural ENE‐WSW trend of the region is Pan‐African in age and not older, as previously assumed. Some major late ductile sinistral shear zones occuring in the study area fit well in the overall sinistral transpressional setting of the Mozambique Belt. Thus, central DML very probably represents the southern continuation of the Mozambique Belt into East Antarctica.
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Comparative geology suggests that the continents adjacent to northern, western, southern, and eastern Laurentia in the Late Proterozoic were Siberia, Australia-Antarctica, southern Africa, and Amazonia-Baltica, respectively. Late Proterozoic fragmentation of the supercontinent centered on Laurentia would then have been followed by rapid fan-like collapse of the (present) southern continents and eventual consolidation of East and West Gondwanaland. In this scenario, a pole of rotation near the Weddell Sea would explain the observed dominance of wrench tectonics in (present) east-west trending Pan-African mobile belts and subduction-accretion tectonics in north-south trending belts. In the process of fragmentation, rifts originating in the interior of the Late Proterozoic supercontinent became the external margins of Paleozoic Gondwanaland; exterior margins of the Late Proterozoic supercontinent became landlocked within the interior of Gondwanaland.
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