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The Ongole domain in the SW part of the Eastern Ghats Belt represents a Palaeoproterozoic granulite terrain and is mainly composed of a suite of charnockites and enderbites within which metapelitic granulites and basic granulites occur as enclaves. Geochemical data suggest that the intrusive metaigneous rocks (mafic granulites and charnoenderbites) possess trace and REE compositions that are typical of magmatic arcs. They are subalkaline, enriched in LREE and LILE and depleted in HREE and HFSE like Nb and Ta. The metapelitic granulites are FeAl rich hercynitequartz bearing rocks showing reaction textures indicating two separate metamorphic events. An initial MPHT event (spinelquartz, >900°C at 6.57.0 kbar) was followed by a MTHP event (grossularrich Grt2 overgrowth, OpxKySil symplectite ca. 700°C at 9 kbar).
Zircon from charnockites shows oscillatoryzoned magmatic cores with broad metamorphic rims. LAICPMS dating revealed concordant magmatic intrusion ages between 1760 – 1710 Ma and a concordant metamorphic age between 1620 – 1600 Ma. In addition, synmetamorphic intrusive enderbites showing magmatic and metamorphic ages of ca. 1600 Ma is present. Metamorphic rims of zircons from metapelites show concordant ages between 1620 1600 Ma, complying with the metamorphic age from charnockites.
In contrast, texturally controlled in situ EMP monazite dating of two chemically distinct monazite generations in metapelites revealed two metamorphic events separated by 6080 Ma. Small, rounded, unzoned monazite grains that are armored within porphyroblastic garnet show older ages of ca. 1620 Ma. The larger, patchy zoned matrix monazite and inclusions in Grt2 show younger ages of ca. 1540 Ma, only occasionally preserving older cores.
In summary, the presented geochemical, petrological and geochronological evidence suggest that the Ongole domain was formed as a magmatic arc near the Indian continent during the Palaeoproterozoic (ca. 17501700 Ma). Subsequently, it experienced UHT metamorphism accompanied by synmetamorphic intrusions during the late Palaeoproterozoic (ca. 1600 Ma), most likely due to magmatic underplating. This was followed by a crustal thickening event 6080 Ma later during early Mesoproterozoic (ca. 1540 Ma) due to the attachment of the Ongole magmatic arc with the Indian craton
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