岩石鉱物科学 43, 71 99, 2014 九州・黒瀬川構造帯における古生代花崗岩類および 関連火成岩類の LA ICP MS ジルコン U Pb 年代 LA ICP MS zircon U Pb geochronology of Paleozoic granitic rocks and related igneous rocks from the Kurosegawa tectonic belt in Kyushu, Southwest JapanThe Yatsushiro area in Kyushu Island, southwest Japan, forms the western tip of the Kurosegawa tectonic belt. This area is underlain by a serpentinite melange with complicated tectonic block assemblage of granitic rocks, high temperature (HT) type metagabbro (Grt Cpx granulite, Grt amphibolite and Cpx bearing amphibolite), and high pressure (HP) type metagabbro (Jd Gln rock and Gln bearing metagabbro). The granitic rocks and the gabbros are the protoliths of the HT type metagabbro (HT gabbro), and supposed to be derived from volcanic arc at an active continental margin based on their major, trace, and rare earth element (REE) chemistry, while geochemistry of the gabbro protoliths of the HP type metagabbro (HP gabbro) indicates mid oceanic ridge basalt (MORB) like precursors. The laser ablation inductively coupled plasma mass spectrometry (LA ICP MS) zircon U Pb dating of the granitic rocks and the HT gabbro gave the Ordovician magmatic ages (~ 450 Ma). On the other hand, the HP gabbro showed the igneous age of the Late Cambrian (~ 490 Ma). Similar rock suites collected from the Kurosegawa tectonic belt in Shikoku and in the Kii peninsula have the same chemical and age a‹nities according to their rock types. These results indicate the strong geological and tectonic similarities within the Kurosegawa tectonic belt. The similar assemblage is present in the South Kitakami belt suggesting similarities in their origin.
Special Issue``Japanese granites and tectonics'' PrefaceGranitic continental crust is a unique feature of the Earth and, as such, the origin and growth of granitic continental crust is a major focus of research in the earth sciences. This special issue focuses on petrochemistry and isotope petrology, geology petrography of granites, U Pb zircon geochronology, K Ar geochronology, crust mantle structure beneath Northeast Japan, and evolution of the continental crust. These topics provide usuful information on petrogenesis and tectonic evolution of the arc crust of the Japanese Islands.
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