Genesis of the Late Archean granitoids of the northern part of the Dharwar foreland (Dharwar Craton), south India – Insights from field, crystal size distribution, thermobarometry, microgeochemical and bulk-rock geochemical studies

• Published in: Chemie der Erde Vol. 81; no. 1; p. 125688
• Main Authors: Boraiaha, Chandan K., Ugarkar, Annappa G., Padhi, Jayant K., Chandan, Rashmi, Kallapur, Mallappa V.
• Format: Journal Article
• Language: English
• Published: Elsevier GmbH 01.04.2021
• Subjects: Crustal evolution; CSD; Dharwad granitoids; Dharwar Foreland; Magma chamber processes; Dharwad granitoids; Magma chamber processes; CSD; Dharwar Foreland; Crustal evolution
• ISSN: 0009-2819; 1611-5864
• DOI: 10.1016/j.chemer.2020.125688

•First report of younger granitoids (<2.61 Ga) from the northern part of the Shimoga greenstone belt.•Magma-mixing and subsequent equilibrium crystallization played a significant role in the granitoid genesis.•The relative age of granitoids coincides with the final stages of cratonization in the Dharwar Craton. An intrusive granitoid pluton into TTG-Dharwar Supergroup greenstone sequence is being reported for the first time from the Dharwar Foreland region. Based on field and petrographic characteristics, these granitoids are classified as - quartz-monzodiorites and granites. Occasional mafic bodies of dioritic-granodioritic composition with size ranging from small microgranular magmatic enclaves to bodies of several centimeters are common in these granitoids. The granitoids are devoid of any crystal-plastic fabric as well as high-strain characteristics. The textural (CSD) studies indicate that the quartz-monzodiorites are derived from magma mixing whereas the granites are derived from equilibrium crystallization of the magma derived from the reworking of quartz-monzodiorites. The P-T estimates indicate that the quartz-monzodiorites were crystallized at higher temperature (>950 °C) and pressure (3.09–4.36 kbar) conditions in a reducing environment at mid-crustal levels. However, the granites indicate lower temperature (<750 °C) and pressure (0.89–1.88 kbar) conditions of crystallization in an oxidizing environment at shallow-crustal levels. The bulk rock chemical characteristics indicate that the quartz-monzodiorites were derived from the melt generated by the mixing of two melts - a melt derived from the differentiation of sanukitoids senso lato (s.l.) and a melt derived from the partial melting of TTG. On the other hand, reworking of the hot crystallizing quartz-monzodiorite due to its rapid upliftment to shallow crustal levels resulted in a decompression melting which gave rise to granitic melts. The relative age of the Dharwad granitoids is estimated to be ∼2580–2560 Ma and unlike the other older granitoids (> 2.61 Ga) reported from the northern part of the Shimoga greenstone belt, the studied granitoids marks the final stage of cratonization in the Foreland region.