Neoarchean arc magmatism and Paleoproterozoic granulite‐facies metamorphism in the Bhavani Suture Zone, South India

Abstract

The Bhavani Suture Zone in the Southern Granulite Terrane marks the zone of amalgamation of the Neoarchean Nilgiri Block and the northwestern Madurai Block in southern India. Here, we report detailed petrological, geochemical, and geochronological data on the Mettupalayam mafic-ultramafic complex within this suture zone with a view to evaluate the tectonothermal history of the Bhavani Suture Zone and adjoining crustal blocks. The metamorphosed complex includes charnockite, hornblendebiotite gneiss, mafic granulite, amphibolite, garnet-bearing mafic granulite, and dioritic gneiss along with metamorphosed banded iron formation. The mafic granulite and the dioritic gneiss occur as concordant layers of varying thickness within the hornblendebiotite gneiss. The salient geochemical features of the mafic granulite and the dioritic gneiss including the enrichment of large-ion lithophile elements and depletion of highfield-strength elements suggest a subduction-related arc magmatic setting. However, the amphibolites show MORB-related affinity, suggesting its formation from a N-MORB-related source and their accretion together with the overlying banded iron formation. The peak metamorphic conditions of the garnet-bearing mafic granulite were estimated using conventional geothermobarometers as 800-820°C/8.5-9.2 kbar, which we further confirm through phase equilibrium modelling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 -Fe 2 O 3 (NCKFMASHTO) system. Magmatic zircons with high Th/U ratio from the amphibolite display a well-defined discordia with an upper intercept age of 2,600 ± 38 Ma. Zircon grains from the dioritic gneiss show weighted mean 206 Pb/ 207 Pb age of 2,524 ± 6 Ma from concordant zircon spots and a comparable upper intercept age of 2,562 ± 34 Ma from discordant zircon spots, indicating protolith emplacement related to Neoarchean arc magmatism as inferred from our geochemical data. The thin overgrowth rims around the magmatic zircon grains in the amphibolite yielded an upper intercept age of 2,520 ± 20 Ma, which is comparable with the protolith crystallization age of the dioritic gneiss. Slightly younger weighted mean 207 Pb/ 208 Pb ages of 2,463 ± 27 Ma (from dioritic gneiss) and 2,422 ± 30 Ma (from amphibolite) are also obtained from the metamorphic zircon rims. These ages are correlated to the timing of high-grade metamorphism associated with final collision of the Nilgiri Block and the northwestern Madurai Block. Similar Neoarchean-Paleoproterozoic magmatism and high-grade metamorphism were

Antiperthite and Mesoperthite Exsolution Textures in the Zhengjiapo BIF, Changyi Metallogenic Belt, North China Craton: Evidence of UHT Metamorphic Overprint

“…As mentioned above, iron mineralization is spatially and temporally related to orogenic events with extensive links from greenschist facies to amphibolite facies, even granulite facies metamorphism. For example, the BIF iron ore deposits in the Quadrilatero Ferrifero of Brazil underwent greenschist to amphibolite facies metamorphism [54]; several occurrences of magnetite-hematite ore from the Yilgarn Craton experienced lower greenschist to lower amphibolite facies metamorphism in [52,55]; banded iron formations in Um Nar, central eastern desert of Egypt, occur with intercalated greenschist facies metamorphic of volcaniclastic and epiclastic rocks in the ophiolitic-island arc system of the Arabo-Nubian [56] and around Mettupalayam within the Bhavani Suture Zone, South India granulite facies metamorphized BIF composed of magnetite and quartz occurs in association with meta-volcaniclastic rocks [57]. These Archean and Proterozoic BIF deposits are usually controlled by strike-slip fault zones or metamorphosed during different further orogenic processes [53].…”

“…The pyroxene-rich domains of pyroxenite were formed at 900-1000 • C/1-1.2 GPa, whereas the garnet and clinopyroxene-rich domains of garnet clinopyroxenite show similar UHT temperature (900-1000 • C) and higher pressures of ~1.8~2 GPa [58]. The tectonic model of oceanic plate subduction refers to an initiation by break-off of the oceanic plate along the southern flanks of the Dharwar Craton [57]. The BIF iron ore bodies in the Yinshan block of the NCC are interlayered with plagioclase amphibolite in the greenstone belt, and their formation is linked to seafloor volcanism and hydrothermal activity in a ridge subduction related slab window [60].…”

“…For example, in the late Neoarchean to early Paleoproterozoic Craton of the southern Indian Peninsula, there is a set of an arc-accretionary complex consisting of BIF, metasediment, metatuff, amphibolite, garnet-kyanite schist, metagabbro, pyroxenite, and charnockite. The pyroxene-rich domains of pyroxenite were after [47]) [12,14,15,[56][57][58]; (b) HT-UHT metamorphic records from the mafic and granitic granulites in the JLJB. All P-T trajectory data in Figure 5b were taken from the rocks in the Jingshan Group, while samples in this study were taken from the Fenzishan Group [71,[73][74][75][76][77].…”

“…Figure 5. (a) Evaluations of the P-T stability fields of represented metamorphic BIF in the worldafter[47])[12,14,15,[56][57][58]; (b) HT-UHT metamorphic records from the mafic and granitic granulites in the JLJB. All P-T trajectory data in Figure5bwere taken from the rocks in the Jingshan Group, while samples in this study were taken from the Fenzishan Group[71,[73][74][75][76][77].…”

Satellite data based abundance mapping of mafic and ultramafic rocks in Mettupalayam, Tamil Nadu, India

“…The study area belongs to the Nilgiri block of SGT and comprises charnockite, mafic and ultramafic rocks, and anorthosite (Uthup et al 2020).…”