This paper reports on the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating of zircon and on the field emission electron probe microanalyzer (FE-EPMA) U-Th-Pb dating of monazite from pelitic granulites and the surrounding Itoshima granodiorite from the Mt. Ukidake area, Sefuri Mountains, northern Kyushu. Zircons from the Itoshima granodiorite give an age of Ma. Metamorphic domains within zircons from pelitic granulites yield a slightly older age of Ma, which is consistent with ages of-Ma obtained from analysis of monazite by U-Th-Pb dating using FE-EPMA. Analysis of inherited domains within zircons from the pelitic granulite gives a narrow range of ages from to Ma, with a youngest age of Ma. These ages are comparable with those of the Renge metamorphic rocks in north Kyushu, although the age and conditions of metamorphism at Renge are significantly different from the granulites analyzed here. Metamorphic ages for the granulites are nearly identical to the reheating age of the Higo metamorphic rocks in central Kyushu, as well as the main metamorphic age of the Ryoke metamorphic rocks in southwest Japan. However, the age distributions of detrital zircons from the Mt. Ukidake area are different from those of the Higo and Ryoke metamorphic rocks, implying a different provenance for each metamorphic rock unit.

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.

We revised the stratigraphy of the Hitachi metamorphic district, based on supplementary U-Pb SHRIMP zircon ages and a review of the geochronological data available for this district. Early to late Cambrian formations and intrusives are grouped into the Cambrian Hitachi volcano-plutonic complex, which consists of the Akazawa Formation, the Tamadare Formation, meta-granites and meta-porphyry. Post-Silurian mica gneiss that occurs near the Tamadare Formation is newly defined as the Takizawa Formation, distinct from the Tamadare Formation. The Daioin and Ayukawa formations are early Carboniferous and early Permian in age, respectively. The contact between the Hitachi volcano-plutonic complex and the Daioin Formation is marked by a prolonged hiatus. There are no geochronological data available for the Omika Formation.Zircon U-Pb age data of the Nishidohira Formation indicate deposition during the Early Cretaceous. The Nishidohira Formation was intruded by Ma granitoids and was metamorphosed during -Ma under conditions of the amphibolite facies, kyanite-sillimanite zone. Sedimentation, metamorphism and exhumation, and intrusion of granitic magma in the terrain of the Nishidohira Formation occurred over a short period of time during the Cretaceous. A similar rapid metamorphism and exhumation is also recorded in the Takanuki metamorphic rocks of the Abukuma Belt.We reconstructed the basement of the Northeast Japan Arc for the period before the opening of the Japan Sea, assuming that the Median Tectonic Line had a linear trend from the Southwest Japan Arc to the Northeast Japan Arc during the Paleogene. After the reconstruction, the Paleozoic Hitachi Formations and the Abukuma Belt move closer to the Jiamusi and Khanka blocks of Northeast China. This result indicates that the Cambrian Hitachi volcano-plutonic complex was originally marginal part of the North China Block.