Tectonic Affinity Of The Neoproterozoic-aged Imorona-itsindro Suite In Madagascar And Its Geological Significance

Madagascar occupied a central position within the East African Orogen. Tectonic affinity of the Neoproterozoic (-850-750 Ma) Imorona-Itsindro Suite throughout the Malagasy shield could provide important constraints on the paleogeography during the supercontinent transformation from Rodinia to Gondwana as well as implications for mineral resources exploration. In this doctoral dissertation, the following investigations have been undertaken:(1) as for the "mafic endmembers" of the Imorona-Itsindro Suite, a case study on the geology and geochemistry of the Ambatondrazaka gabbros has provided insights into their timing, petrogenesis, source region and tectonic affinity; (2) published geochemical data of the "felsic endmembers" of the Imorona-Itsindro Suite were compiled and processed to reevaluate their magma series, genetic type, source characteristics and tectonic affinity; (3) published U-Pb geochronological data of detrital zircons from the Neoproterozoic sedimentary basins were compiled and processed to reveal the regional tectonic setting from the view of sedimentary geology; (4) as for the "later" Ambalavao Suite (-580-510 Ma), a case study on the geology and geochemistry of the Ambatondrazaka granite dykes has provided a chance to discuss their magma nature, source region and deep processes, which could also constrain the tectonic affinity of the "early" Imorona-Itsindro Suite.Based on the above results, the main conclusions can be drawn as follows:(1) Neoproterozoic igneous rocks of the Imorona-Itsindro Suite in Madagascar were emplaced within a continental rifting setting (failed rift), and their intra-plate affinity can be well coordinated with the petrological and geochemical features of the Seychelles granitoids and the Malani Igneous Suite in northwest India;(2) Continental rifting during Neoproterozoic time indicates that Madagascar may be prospective for magmatic Cu-Ni±PGE, Ti-Fe±V, Cr and hydrothermal Sn-W mineral exploration; the Ti-Fe-V mineralization associated with the Ambatondrazaka gabbros probably resulted from trans-magmatic fluids;(3) Except for those igneous rocks in Madagascar, Seychelles and northwest India, Neoproterozoic rifting-related magmatism is also wildly recognized wthin the Southern Granulite Terrane of south India and Sri Lanka, the "deadline" of this rifting-related igneous activity may be ～750 Ma;(4) It is postulated that the Bemarivo terrane accreted to northern Madagascar at ～520 Ma may record the intra-oceanic subduction of the Mozambique Ocean, which initiate at ～750 Ma and is coincidently coeval with the timing of the first major break-up event of the supercontinent Rodinia;(5) Based on regional correlation, a rifting model rather than arc model is favored for Neoproterozoic igneous rocks in the South China, Indochina, and Lhasa blocks since most of their ages range from ～860 to 750 Ma; furthermore, these blocks may be not located on the peripheray of Rodinia.