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The Narryer Gneiss Terrane is a geological complex in Western Australia that is composed of a tectonically interleaved and polydeformed mixture of granite, mafic intrusions and metasedimentary rocks in excess of 3.3 billion years old, with the majority of the Narryer Gneiss Terrane in excess of 3.6 billion years old. The rocks have experienced multiple metamorphic events at amphibolite or granulite conditions, resulting in often complete destruction of original igneous or sedimentary (protolith) textures. Importantly, it contains the oldest known samples of the Earth's crust: samples of zircon from the Jack Hills portion of the Narryer Gneiss have been radiometrically dated at 4.4 billion years old, although the majority of zircon crystals are about 3.6-3.8 billion years old. The Narryer Gneiss Terrane is adjacent to the northernmost margin of the Yilgarn Craton and is abutted on the north by the Gascoyne Complex metasedimentary and metagranite orogen. The Narryer Gneiss Terrane also includes parts of the Yarlarweelor Gneiss which abuts to Nabberu Basin metamorphic sequences of the Bryah-Padbury Basins, where it is present as discontinuous slivers of metamorphic rocks, pelites, metaconglomerates and gneisses caught up within regional strike-slip oblique thrust faults. The Narryer Gneiss in this far-eastern region may form the basement to the 2.0-1.8 billion year old Proterozoic rocks, and the unconformity surface may be preserved within the thrust sheets. The Narryer Gneiss Terrane is divided into four major rock sequences (Myers 1990); the Dugel Gneiss, Meeberrie Gneiss, Manfred Complex, and unassigned polydeformed leucocratic gneisses and metasediments. ==Dugel Gneiss== The Dugel Gneiss is syenogranitic or monzogranitic in composition and this is interpreted as the protolith. The gneiss is leucocratic, with only minor amounts of biotite and muscovite. The rock exhibits variable intensity of metamorphic banding which may include grain size variations, and has a high degree of deformation around the margins, and preserves an amphibolite facies metamorphic assemblage. The gneiss is pervasively shot through with pegmatite veins. Within the low-strain zones, the Dugel Gneiss exists as a medium-grained leucocratic metagranite with phenocrysts of K-feldspar which has recrystallized into granulite facies. The rock is greasy-looking with annealed quartz and feldspar, and syn-granulite facies leucosomes cutting across metamorphic banding, and subsequently deformed by later metamorphism. The Dugel Gneiss is considered to be intruded into the older Meeberrie Gneiss, possibly as sheets or sills, but most contacts are overprinted by ductile metamorphic banding or mylonite zones. 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「Narryer Gneiss Terrane」の詳細全文を読む スポンサード リンク
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