中部地方中央構造線沿いに露出するマイロナイトの全岩主成分元素組成

概要

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The whole-rock major element composition of the mylonites in the Kashio shear zone along the Median Tectonic Line in the vicinity of Takato-Ichinose and Kashio, Nagano Prefecture were analysed by X-ray fluorescence spectrometry, together with those of the Hiji tonalites. The mylonites were tentatively classified into three types based on mesoscopic occurrences of feldspar porphyroclasts : porphyroclastic type, fine-porphyroclastic type and fine-grained type. The porphyroclastic type is characterized by coarse-grained feldspar porphyroclasts in a fine-grained matrix containing quartz, feldspar and phyllosilicate aggregates. The fine-porphyroclastic type seems to be well-deformed porphyroclastic mylonites, so that the size of feldspar porphyroclasts is smaller than that within the porphyroclastic type due to intense grain size reduction. The fine-grained type contains only a few feldspar porphyroclasts in a well-banded fine-grained matrix. There exists no systematic difference between the chemical compositions of these three types of mylonites. The SiO_2 contents range from 51 to 73 wt.%. Concentrations of TiO_2,FeO, MnO, MgO, K_2O and P_2O_5 Were proportioned to SiO_2 content but tend to be scattered at SiO_2 > 70 wt.%. The chemical compositions of the Hiji tonalites are indistinguishable from those of the mylonites, consistent with the idea that the Hiji tonalite is a source rock of the three types of mylonites.
静岡大学の論文