Zircon standard data. Stenian–Tonian arc magmatism in west–central Madagascar: the genesis of the Dabolava Suite
Archibald Donnelly B.Collins Alan S.Foden John D.Payne Justin L.Macey Paul H.Holden PeterThéodore Razakamanana
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The Neoproterozoic metasedimentary successions and igneous suites in the central Korean Peninsula provide important insights into the tectonic evolution of East Asia. Here we report detailed detrital zircon UPb age data from the Neoproterozoic metasedimentary successions as well as geochemical data on the early Neoproterozoic rift-related plutonic rocks. Our results together with the available data from the central Korean Peninsula, lead to the following inferences. (1) Regional sedimentation in the early Neoproterozoic (ca. 1000–920 Ma) as a result of the late Paleoproterozoic to early Neoproterozoic intracratonic rifting. (2) Arc magmatism in the southern periphery of the central Korean Peninsula in the early Neoproterozoic (ca. 913–895 Ma and ca. 865–770 Ma). (3) Back-arc magmatism in the inland area of the central Korean Peninsula in the early Neoproterozoic (ca. 888–852 Ma). (4) Magmatism and sedimentation in the early Neoproterozoic (ca. 765–720 Ma) due to early Neoproterozoic back-arc and intracratonic rifting. The early-Neoproterozoic geological and tectonic events in the central Korean Peninsula correlate with those in the southeastern part of the North China Craton. The spatial and temporal similarities and discrepancies in the early Neoproterozoic geological records of the Sino-Korean continent mark the tectonic evolution within a continental inland (the southeastern part of the North China Craton) and a continental margin (the central Korean Peninsula).
Peninsula
Continental arc
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The southern Midyan terrane is a composite Tonian to Ediacaran tectonostratigraphic crustal block in the northern Arabian Shield that prior to Red Sea opening was contiguous with coeval rocks in the Eastern Desert of Egypt and Sinai. Ion microprobe (sensitive high-resolution ion microprobe [SHRIMP]) dating of 12 rock samples described here and the results of other dating programmes establish a clear timeframe for depositional, intrusive, and structural events in the region and provide a chronology of tectonism in this part of the Arabian-Nubian Shield. Deposition of Zaam and Bayda group volcanosedimentary rocks and emplacement of mafic-ultramafic complexes and TTG-type diorite, tonalite, and granodiorite denote formation of the Tonian (780–715 Ma) Zaam arc and fore-arc ophiolite above a possible west-dipping subduction system in the southern part of the Midyan terrane. Convergence with the Hijaz terrane farther south and obduction of ophiolite nappes resulted by ~700 Ma in development of the Yanbu suture. Ongoing or a new subduction system led to a ~705–660 Ma Cryogenian pulse of magmatism represented by I-type calc-alkaline diorite, granodiorite, and granite that have volcanic-arc and syn-collisional granite affinities. This was followed, after a brief end-Cryogenian hiatus, by a 635–~570 Ma period of Ediacaran magmatism marked by monzogranite, syenogranite, and minor gabbro and diorite. These rocks are reported to have within-plate to volcanic-arc and syncollision chemical characteristics but their precise tectonic setting is uncertain. Structurally, the intrusions are diapiric and were evidently emplaced in an extensional regime consistent with an overlap between intrusion and Najd faulting associated, at this time, with transpressional collision and northward extension through much of the ANS. Terminal magmatism in the southern Midyan terrane postdated cessation of Najd faulting at ~575 Ma and resulted in the emplacement of undeformed within-plate A-type alkali-feldspar granites and mafic (lamprophyre) and felsic dikes.
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Volcanic arc
Island arc
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Abstract: U–Pb ion microprobe investigations of zircons from gneisses, granites and migmatites of the pre-Devonian Smerenburgfjorden and Richarddalen Complexes constrain the tectonic evolution and origin of Svalbard's Northwestern Terrane. Field relationships combined with U–Pb age data indicate that a late Meso- to Neoproterozoic metapelitic protolith was intruded by Tonian ( c . 960 Ma) granitoids and suggest that the entire Northwestern Terrane is underlain by early Neoproterozoic granitoids intruding older metasediments. Both rock types were later involved in Caledonian deformation, with subsequent migmatization and granite genesis at c . 435–420 Ma. Ages of inherited zircons in granites and migmatites reflect anatexis of this late Meso- to Neoproterozoic protolith, with zircon xenocrysts ranging in age from c . 1030 to 1820 Ma. Pronounced lithological, geochronological and tectonothermal similarities to NE Svalbard (Nordaustlandet) and the Krummedal supracrustal sequence of East Greenland suggest a strong correlation between Svalbard and East Greenland prior to Caledonian orogenesis. Supplementary material: Ion microprobe analytical methods, data table and zircon descriptions are available at http://www.geolsoc.org.uk/SUP18326 .
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Abstract The Neoproterozoic East African Orogen reflects closure of the Mozambique Ocean and collision of the Congo and Dharwar cratons. This palaeogeographical change and its environmental consequences are poorly understood, but new detrital zircon ages from Madagascar and published data from elsewhere provide evidence for multiple ocean basins and two‐stage collision. We propose that central Madagascar rifted from the Congo Craton and crossed a Palaeomozambique Ocean to collide with the Dharwar Craton at c. 700 Ma, opening a Neomozambique Ocean in its wake. Closure of the Neomozambique Ocean at c. 600 Ma juxtaposed the Congo and Dharwar cratons and resulted in prolonged collisional orogenesis concluding at c. 500 Ma.
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Oceanic basin
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Abstract Madagascar hosts several Paleoproterozoic sedimentary sequences that are key to unraveling the geodynamic evolution of past supercontinents on Earth. New detrital zircon U–Pb and Hf data, and a substantial new database of ∼15,000 analyses are used here to compare and contrast sedimentary sequences in Madagascar, Africa, and India. The Itremo Group in central Madagascar, the Sahantaha Group in northern Madagascar, the Maha Group in eastern Madagascar, and the Ambatolampy Group in central Madagascar have indistinguishable age and isotopic characteristics. These samples have maximum depositional ages >1700 Ma, with major zircon age peaks at c. 2500 Ma, c. 2000 Ma, and c. 1850 Ma. We name this the Greater Itremo Basin, which covered a vast area of Madagascar in the late Paleoproterozoic. These samples are also compared with those from the Tanzania and the Congo cratons of Africa, and the Dharwar Craton and Southern Granulite Terrane of India. We show that the Greater Itremo Basin and sedimentary sequences in the Tanzania Craton of Africa are correlatives. These also tentatively correlate with sedimentary protoliths in the Southern Granulite Terrane of India, which together formed a major intra‐Nuna/Columbia sedimentary basin that we name the Itremo‐Muva‐Pandyan Basin. A new Paleoproterozoic plate tectonic configuration is proposed where central Madagascar is contiguous with the Tanzania Craton to the west and the Southern Granulite Terrane to the east. This model strongly supports an ancient Proterozoic origin for central Madagascar and a position adjacent to the Tanzania Craton of East Africa.
Rodinia
Supercontinent
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