| Abstrakt: |
We present field, petrographic and mineral compositions of biotite, amphibole, and feldspars from Neoarchean Nizamabad granites from the northeastern part of the Eastern Dharwar Craton, southern India. These granites are classified as hornblende biotite granite (HBG), biotite granite (BTG), monzogranite (MG), and microgranular enclaves (ME) hosted in HBG and BTG. The temperature estimates using amphibole and biotite thermometry exhibit similar results, with higher temperatures for HBG (818 to 859 ±22°C) and ME (800 to 855 ±22°C), and slightly lower temperatures for BTG and MG (829 to 830 ±12°C and 820 to 829 ±12°C). Based on barometry, HBG amphiboles crystallized at pressures between 363 and 448 ±60 MPa (avg. PHBG = 398 MPa), whereas the MEs crystallized at pressures between 313 and 438 ±60 MPa (avg. PME = 386 MPa). The estimated pressures suggest that these granites crystallized at depths of 14–15 km, corresponding to the upper to mid-continental crust. The amphibole compositions reveal that these granites crystallized from a water-rich magma, with >5 wt.% H2O and evolved under high oxidizing conditions NNO + 2 (Nickel–Nickel–Oxide), corresponding to magnetite (oxidized) series granites. The amphibole and biotite compositions suggest a crust-mantle mixed source for HBG, ME, and BTG, while the MG is purely crustal derived. The water-rich and highly oxidizing conditions of the parental magmas rule out a lower crustal granulitic source for the Nizamabad granites. The amphibole and biotite compositions suggest their crystallization from calc-alkaline parental magma in a subduction setting at high oxygen fugacity (fO2) conditions. This study infers the role of convergent margin tectonics in the emplacement of these granites, and their compositional variability is attributed to crust–mantle interactions in this domain of the Eastern Dharwar Craton. Research Highlights: The granitoids from the NE part of the Eastern Dharwar Craton are characterized as hornblende biotite granites (HBG), biotite granites (BTG), monzogranite (MG), and mafic enclave (ME). Estimated pressures suggest that these granites crystallized at depths of 14 to 15 km, corresponding to the upper to mid-continental crust. The water-rich (> 5 wt.% H2O content) and high oxidizing conditions (NNO+2) of HBG, BTG, and ME corresponds to magnetite (oxidized) series granites. The amphibole and biotite compositions from the Nizamabad granites suggest the crust-mantle mixed source for HBG, ME, and BTG, while the MG are purely crustal derived. The compositions of these granites suggest their crystallization from calc-alkaline parental magma in subduction settings at high oxygen fugacity (fO2) conditions. The study infers the role of convergent margin tectonics in the emplacement of compositionally variable granitoids in the NE part of the Eastern Dharwar Craton. [ABSTRACT FROM AUTHOR] |
