Tourmaline occurs as a minor but important mineral in the alteration zc,ne of the Archean orogenic gold deposit of Guddadarangavanahalli （G.R.Halli） in the Chitradurga greenst^ne belt of the western Dharwar craton, ...Tourmaline occurs as a minor but important mineral in the alteration zc,ne of the Archean orogenic gold deposit of Guddadarangavanahalli （G.R.Halli） in the Chitradurga greenst^ne belt of the western Dharwar craton, southern India. It occurs in the distal alteration halo of the G.R.Halli golcl deposit as （a） clusters of very fine grained aggregates which form a minor constituent in the natrix of the altered metabasalt （AMB tourmaline） and （b） in quartz-carbonate veins （vein tourmaline）. ~[＇he vein tourmaline, based upon the association of specific carbonate minerals, is further grouped as （i） albite-tourmaline-ankerite-quartz veins （vein-1 tourmaline） and （ii） albite-tourmaline-calcite-quartz veins （vein-2 tourmaline）. Both the AMB tourmaline and the vein tourmalines （vein-I and vein-2） belong to the alkali group and are clas- sified under schorl-dravite series. Tourmalines occurring in the veins are zoned while the AMB tour- malines are unzoned. Mineral chemistry and discrimination diagrams 1eveal that cores and rims of the vein tourmalines are distinctly different. Core composition of the ve：n tourmalines is similar to the composition of the AMB tourmaline. The formation of the AMB tourmaline and cores of the vein tour- malines are proposed to be related to the regional D1 deformational event associated with the emplacement of the adjoining ca. 2.61 Ga Chitradurga granite whilst rims of the vein tourmalines vis-a- vis gold mineralization is spatially linked to the juvenile magmatic accretion （2.56-2.50 Ga） east of the studied area in the western part of the eastern Dharwar craton.展开更多
The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision...The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision front in the north with a modern trench-arc system in the Andaman Sea region in the south.Ophiolitic subunits in the Nagaland–Manipur Hill area in the Indo-Myanmar Ranges occur as blocks or thrust sheets within a mélange with a serpentinite or fine-grained greywacke matrix,and are spatially associated with eclogitic and blueschist rock assemblages.This ophiolitic mélange zone is tectonically sandwiched between an older(Triassic–Cretaceous)accretionary prism complex(Nimi Flysch)to the east and a younger(Late Cretaceous–Miocene)accretionary wedge(Disang Flysch)to the west.The Nagaland–Manipur Hill ophiolitic mélange is thus part of a progressively westward migrated subduction-accretion complex,and it represents a typical subduction channel mélange evolved during the fast subduction of the Neotethyan oceanic lithosphere beneath Asia–Sundaland.展开更多
The continued existence of an Eo-Paleoarchean proto-continent through Proterozoic times in the Aravalli Mountain Range is now widely accepted.The protocontinent’s growth culminated with the outpouring of~2.5 Ga old s...The continued existence of an Eo-Paleoarchean proto-continent through Proterozoic times in the Aravalli Mountain Range is now widely accepted.The protocontinent’s growth culminated with the outpouring of~2.5 Ga old silicic magma by the end of Neoarchean,which produced polyphase granites-gneisses,and migmatites of the‘Banded Gneissic Complex.’The polycyclic Proterozoic orogenic processes involved crustal thickening and thermal perturbations,which reconstituted its pristine character.展开更多
The Paleoproterozoic Debari supracrustals of the Aravalli Supergroup in the Bhukia area,Western India,host a possibly unique type of mesothermal gold-sulfide mineralization in ultrasodic albitite rocks along second ge...The Paleoproterozoic Debari supracrustals of the Aravalli Supergroup in the Bhukia area,Western India,host a possibly unique type of mesothermal gold-sulfide mineralization in ultrasodic albitite rocks along second generation deformation structures.展开更多
Introduction Geology of the Indian subcontinent is not only diverse and interesting but also has been studied for a long period.Reflection of a rich geoscientific heritage may be illustrated by a couple of lesser know...Introduction Geology of the Indian subcontinent is not only diverse and interesting but also has been studied for a long period.Reflection of a rich geoscientific heritage may be illustrated by a couple of lesser known early or first“discoveries/descriptions”from the Indian subcontinent.Heinrich(1966)in his book“The Geology of Carbonatites”mentions that the first description of carbonatite was provided from India by Bose(1884)as quoted below(italics and bold for emphasis).展开更多
文摘Tourmaline occurs as a minor but important mineral in the alteration zc,ne of the Archean orogenic gold deposit of Guddadarangavanahalli （G.R.Halli） in the Chitradurga greenst^ne belt of the western Dharwar craton, southern India. It occurs in the distal alteration halo of the G.R.Halli golcl deposit as （a） clusters of very fine grained aggregates which form a minor constituent in the natrix of the altered metabasalt （AMB tourmaline） and （b） in quartz-carbonate veins （vein tourmaline）. ~[＇he vein tourmaline, based upon the association of specific carbonate minerals, is further grouped as （i） albite-tourmaline-ankerite-quartz veins （vein-1 tourmaline） and （ii） albite-tourmaline-calcite-quartz veins （vein-2 tourmaline）. Both the AMB tourmaline and the vein tourmalines （vein-I and vein-2） belong to the alkali group and are clas- sified under schorl-dravite series. Tourmalines occurring in the veins are zoned while the AMB tour- malines are unzoned. Mineral chemistry and discrimination diagrams 1eveal that cores and rims of the vein tourmalines are distinctly different. Core composition of the ve：n tourmalines is similar to the composition of the AMB tourmaline. The formation of the AMB tourmaline and cores of the vein tour- malines are proposed to be related to the regional D1 deformational event associated with the emplacement of the adjoining ca. 2.61 Ga Chitradurga granite whilst rims of the vein tourmalines vis-a- vis gold mineralization is spatially linked to the juvenile magmatic accretion （2.56-2.50 Ga） east of the studied area in the western part of the eastern Dharwar craton.
文摘The Nagaland–Manipur Hill ophiolite belt in NE India represents the southern extension of the Neotethyan Yarlung-Zhangbo suture zone in Southern Tibet,and connects this on-land exposure of the late Mesozoic collision front in the north with a modern trench-arc system in the Andaman Sea region in the south.Ophiolitic subunits in the Nagaland–Manipur Hill area in the Indo-Myanmar Ranges occur as blocks or thrust sheets within a mélange with a serpentinite or fine-grained greywacke matrix,and are spatially associated with eclogitic and blueschist rock assemblages.This ophiolitic mélange zone is tectonically sandwiched between an older(Triassic–Cretaceous)accretionary prism complex(Nimi Flysch)to the east and a younger(Late Cretaceous–Miocene)accretionary wedge(Disang Flysch)to the west.The Nagaland–Manipur Hill ophiolitic mélange is thus part of a progressively westward migrated subduction-accretion complex,and it represents a typical subduction channel mélange evolved during the fast subduction of the Neotethyan oceanic lithosphere beneath Asia–Sundaland.
文摘The continued existence of an Eo-Paleoarchean proto-continent through Proterozoic times in the Aravalli Mountain Range is now widely accepted.The protocontinent’s growth culminated with the outpouring of~2.5 Ga old silicic magma by the end of Neoarchean,which produced polyphase granites-gneisses,and migmatites of the‘Banded Gneissic Complex.’The polycyclic Proterozoic orogenic processes involved crustal thickening and thermal perturbations,which reconstituted its pristine character.
文摘The Paleoproterozoic Debari supracrustals of the Aravalli Supergroup in the Bhukia area,Western India,host a possibly unique type of mesothermal gold-sulfide mineralization in ultrasodic albitite rocks along second generation deformation structures.
文摘Introduction Geology of the Indian subcontinent is not only diverse and interesting but also has been studied for a long period.Reflection of a rich geoscientific heritage may be illustrated by a couple of lesser known early or first“discoveries/descriptions”from the Indian subcontinent.Heinrich(1966)in his book“The Geology of Carbonatites”mentions that the first description of carbonatite was provided from India by Bose(1884)as quoted below(italics and bold for emphasis).
