飛騨外縁帯(特に青海-蓮華帯)及び上越帯に関する諸問題

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Fundamental features of the Hida Marginal Structural Belt: Though the Hida Marginal Structural Belt is distributed geographically surrounding the Hida Massif, it is a quite different tectonostratigraphic composite terrane distinctly separated the Hida Complex. The general geologic situation of the so-called Hida Marginal Structural Belt indicates that the Belt is a suture zone between the Hida Massif and the Mino Belt. The most remarkable features of the Hida Marginal Belt have been recognized as the existence of high-pressure type crystalline schists, early to middle Paleozoic strata including limestone masses, and serpentinite in large scale. However, recent radiometric studies have indicated that the ages of metamorphism have a wide range from 676 Ma to 310 Ma concerning the various tectonic blocks included in the serpentinite melanges. In addition to these results, the sedimentary paleoenvironments of various tectonic units composing the Marginal Belt were made up to more clear and also the igneous activities during Paleozoic time were elucidated by some researchers. All those results of studies strongly suggest that, in the present Marginal Belt, the different structural terranes from each other with respect to the original sedimentary environment and the metamorphic fields were juxtaposed and most of their mutual boundaries are faults or faults zone, most typically overthrusts from east to west. In other words, various products of sedimentation, igneous activitie sand metamorphism generated with in the different terranes such as continent, continental margin or island arc, trench and oceanic floor are mixed complicatedly in the present narrow belt. In this sense, the Marginal Belt is not simply a marginal part, but an independent mobile belt. Tectonic divisions of the Hida Marginal Structural Belt and of the Omi-Renge Belt: The Omi-Renge Belt is widest in the Marginal Belt and almost all tectonic units are well exposed. Its geologic map and tectonic division are shown in Figs. 2 and 3. The Omi-Renge Belt is divisible into five longitudinal subbelts (units). That from east to west are: (1) Outer sedimentary zone occupying the northeastern corner of the Belt and corresponding to the northern extremity of the Mino Belt, (2) Serpentinite nappe zone (eastward-thrusting body on the outer sedimentary zone), (3) Omi Limestone block overlying basaltic volcanics, (4) Outer serpentinite melange zone comprising various crystalline schists of high-pressure type and mid-Paleozoic strata as tectonic blocks, and (5) Inner melange zone characteristically composed of little or unmetamorphosed Paleozoic strata (olistostrome facies) intruded by late-Cretaceous acidic rocks. The Unazuki Metamorphic Zone is clearly separated from the Hida Complex by the Eboshiyama thrust from west to east. The mutual relationship between each zones including the Unazuki zone is schematically shown in Fig. 5. The tectonic division of the Hida Marginal Structural Belt is shown in Fig. 4. The Unazuki zone and the inner melange zone constitute the Hida marginal arc (continental marginal arc). Structural devision of the Joetsu Tectonic Belt: The geologic map based on the recent studies is shown in Fig. 6. The eastern limit of the Joetsu Tectonic Belt is defined by north-south ward fault displaced laterally by the E-W or NEE-SWW faults. The northern extension of the fault is still not clear. The Joetsu Tectonic Belt is divisible into two subzones: that is, the Katashina zone (B) composed of metabasalt, metagabbro-diorite complex and the Tanigawadake zone (A) characterized by the predominance of serpentinite and high-pressure type crystalline schists included originally as tectonic block in the former. The rocks of the Katashina zone belong to the ophiolitic suite, being correlatable to that of the Maizuru zone. The Upper Triassic, lower Jurassic and lower Cretaceous strata are presumably the relics of tectonic mixture before the intrusion of Cretaceous granites. St

飛騨外縁帯(特に青海-蓮華帯)及び上越帯に関する諸問題

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