Eclogite-Glaucophane Schist Complexes of the USSR and Their Bearing on the Genesis of Blueschist Terranes
Published:January 01, 1975
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N. L. DOBRETSOV, V. S. SOBOLEV, 1975. "Eclogite-Glaucophane Schist Complexes of the USSR and Their Bearing on the Genesis of Blueschist Terranes", Contributions to the Geology of the Bering Sea Basin and Adjacent Regions, R. B. Forbes
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USSR eclogite-glaucophane schist complexes are located in the northwestern circum-Pacific, Ural-Tien-Shan and Altai-Sayan regions.
The Kamuikotan-Susunai belt of Hokkaido and Sakhalin is believed to be a northern continuation of the Mesozoic Sanbagawa belt of Honshu and Kyushu. The Penjina belt of Koryakia is among the more ancient blueschist terranes (40K/40Ar ages of 300 to 350 m.y.). It is characterized by a rather simple structural style, weakly schistose fabrics, and jadeite-lawsonite-bearing rocks that grade into typical greenschist.
In the Ural-Tien-Shan belt, glaucophane schist and eclogites are confined to the Main Ural and Kan-Atbashy fault zones, and the two belts are of similar structure and age. The age of metamorphism is either Riphean (1,000 to 1,100 m.y.) or Ordovician-Silurian (380 to 450 m.y.). Although the facies relations vary at different localities, the rocks from this belt frequently contain glaucophane, jadeite with quartz, and eclogitic assemblages. The Ural-Tien-Shan terranes conclusively prove that schist containing glaucophane, lawsonite, and jadeite is not restricted to the relatively young (post-Paleozoic) metamorphic belts, as suggested by various authors, and that the genesis of intracontinental blueschist belts is more compatible with trough or rift systems than with typical subduction zones of oceanic plates.
Laboratory data on gaseous-fluid inclusions, solid state metamorphic reactions, and field relations lead us to conclude that the high pressures associated with blueschist facies metamorphism are related to high fluid or “autoclave” overpressures generated by water released by dehydration reactions.
Our work on the crystal chemistry of amphiboles reinforces the existence of intermediate Na-Ca amphiboles. We propose the name “barroisite” for intermediate Na-Ca amphiboles of the glaucophane-hornblende series and the name “winchite” for members in the glaucophane-actinolite series.
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Contributions to the Geology of the Bering Sea Basin and Adjacent Regions
- Altai Russian Federation
- Commonwealth of Independent States
- glaucophane schist
- metamorphic rocks
- P-T conditions
- Russian Federation
- Russian Republic
- Sakhalin Russian Federation
- Siberian fold belt
- Altai Russian Republic
- Sakhalin Russian Republic