Enclaves in granitoids of north of Jonnagiri schist belt,Kurnool district,Andhra Pradesh: Evidence of magma mixing and mingling |
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| Authors: | Mansoor Ahmad |
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| Institution: | (1) Department of Geological Engineering, Selcuk University, Konya, 42075, Turkey;(2) Department of Mining Engineering, Selcuk University, Konya, 42075, Turkey |
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| Abstract: | Calc-alkaline, metaluminous granitoids in the north of Jonnagiri schist belt (JSB) are associated with abundant mafic rocks
as enclave. The enclaves represent xenoliths of the basement, mafic magmatic enclaves (MME) and synplutonic mafic dykes. The
MME are mostly ellipsoidal and cuspate shape having lobate margin and diffuse contact with the host granitoids. Sharp and
crenulated contacts between isolated MME and host granitoids are infrequent. The MME are fine-grained, slightly dark and enriched
in mafic minerals compare to the host granitoids. MME exhibits evidences of physical interaction (mingling) at outcrop scale
and restricted hybridization at crystal scale of mafic and felsic magmas. The textures like quartz ocelli, sphene (titanite)
ocelli, acicular apatite inclusion zone in feldspars and K-feldspar megacrysts in MME, megacrysts across the contact of MME
and host and mafic clots constitute textural assemblages suggestive of magma mingling and mixing recorded in the granitoids
of the study area. The quartz ocelli are most likely xenocrysts introduced from the felsic magma. Fast cooling of mafic magma
resulted in the growth of prismatic apatite and heterogeneous nucleation of titanite over hornblende in MME. Chemical transfer
from felsic magma to MME forming magma envisage enrichment of silica, alkalis and P in MME. The MME show low positive Eu anomalies
whereas hybrid and host granitoids display moderate negative Eu-anomalies. Synplutonic mafic dyke injected at late stage of
crystallising host felsic magma, display back veining and necking along its length. The variable shape, dimensions, texture
and composition of MME, probably are controlled by the evolving nature and kinematics of interacting magmas. |
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