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Peninsular Gneiss is a term coined to highlight the older gneissic complex of the metamorphics found all over the Indian Peninsula. This term was first fashioned by W.F.Smeeth of the Mysore Geological Department in 1916 based on the first scientific study of this rock exposure. The Geological Survey of India identified one of the best exposures of this rock mass, protruding high above the ground as a hillock (pictured), dated 2.5 to 3.4 billion years, in the Bangalore city in India at the famous Lalbagh gardens and declared it as a National Geological Monument to propagate the knowledge of the rock formation among the public, since Lalbagh is frequented by visitors from all over the world.〔(【引用サイトリンク】 title=Peninsular Gneiss )〕 It is also called the Lalbagh rock.〔(【引用サイトリンク】title= Lalbagh - Abounting with natural landmarks )〕 As general information, gneiss is a coarse-grained high grade metamorphic rock formed at high pressures and temperatures in which light and dark mineral constituents are segregated into visible bands.〔 ==Geology== (詳細はArchean gneisses and schists, which are the oldest rocks of the Indian Shield, constitute a considerable area of Peninsular India. The Dharwar (Super Group) and the Peninsular Gneissic Complex are the classified groups of the Precambrian rocks of India. The extent of the Archean system is depicted as the dominant system of South India in the pictured Geological Map of India. In most stratigraphic schemes, the peninsular gneisses are shown as the younger Archaean strata situated above the Sargur Group. Granitization of the older sedimentary–volcogenic sequence are reported as sources of the peninsular gneisses made up of polyphase migmatites, gneisses and granites ranging in composition from granodiorite to tonalite. The rocks of the Dharwar Group, which are mainly sedimentary in origin, occur in narrow elongated synclines resting on the gneisses found in Bellary district, Mysore and the Aravallis of Rajputana. The supracrustal rocks of the Dharwar Group of the southern Indian Peninsula, as depicted in the geological map of South India, have the Peninsular Gneiss as the basement rock formation, also stated to be the remobilized basement. Migmatization of pre-existing metasedimentary and meta–igneous rocks are considered the contributors to formation of the composite gneiss.〔〔(【引用サイトリンク】title= Structural evolution of the Peninsular Gneiss — an early Precambrian migmatitic complex from South India K. Naha, R. Srinivasan and S. Jayaram )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Peninsular Gneiss」の詳細全文を読む スポンサード リンク
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