期刊
GEOSCIENCE FRONTIERS
卷 13, 期 1, 页码 -出版社
CHINA UNIV GEOSCIENCES, BEIJING
DOI: 10.1016/j.gsf.2021.101260
关键词
Mafic-ultramafic layered intrusion; Ultrahigh-temperature metamorphism; Zircon and monazite geochronology; Central Madurai Block; Southern Granulite Terrane
资金
- Foreign Expert grants
- China University of Geo-sciences (Beijing)
The study reports the discovery of a dismembered layered mafic-ultramafic intrusion associated with Mg-Al granulites in the Madurai Block of the Southern Granulite Terrane. The rock types and mineral compositions were analyzed to determine the metamorphic conditions and geological ages, and the intrusion was correlated to a Paleoproterozoic suprasubduction zone setting.
The Madurai Block in the Southern Granulite Terrane (SGT) of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly. This block is composed of three sub-blocks: the Neoarchean Northern Madurai block, Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block. The margins of these blocks are well-known for the occurrence of ultrahigh-temperature (UHT) granulite facies rocks mostly represented by Mg-Al metasediments. Here we report a dismembered layered mafic-ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block. The major rock types of the layered intrusion include spinel orthopyroxenite, garnet-bearing gabbro, gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture. The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel, cordierite and orthopyroxene. The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions. Conventional thermobarometry yields near-peak metamorphic conditions of 9.5-10 kbar pressure and a minimum temperature of 980 degrees C. We computed P-T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases, which yield temperature above 1000 degrees C. FMAS petrogenetic grid, Al-in-orthopyroxene isopleth, conventional thermobarometry and calculated pseudosection reveal a clockwise pressure-temperature (P-T) path and near isothermal decompression. The U-Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca. 2.0 Ga and the metamorphic overgrowths yield weighted 206Pb/238U mean ages ca. 520 Ma. Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded 206Pb/238U weighted mean ages of ca. 532 Ma and 523 Ma marking the timing of metamorphism. We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting, defining the Ganguvarpatti area as part of a collisional suture assembling the Northern and Central Madurai Blocks. The Paleoproterozoic magmatism and late Neoproterozoic-Cambrian UHT metamorphism can be linked to the tectonics of the Columbia and Gondwana supercontinents. (c) 2021 China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).
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