ソ連カムチャツカ半島東北部オリュートル地域の深成岩類
1992 年 87 巻 1 号 p. 1-11
詳細
1992 年 87 巻 1 号 p. 1-11
Geology and petrology of three plutons (the Epilchik, Machevna and Tigil) in the southern Olyutor Range of Northeastern Kamchatka (USSR) are briefly summarized in this paper. The Upper Cretaceous volcano-sedimentary rocks in the range consititute a prolongation of the submarine Shirshov ridge, that separates the Aleutian passive back arc basin from the Komandorsky basin. Many ultramafic and mafic to intermediate plutons of Paleogene age are distributed in the Upper Cretaceous rocks.
The Epilchik ultramafic pluton shows a concentric structure: the dunitic core passes progressively into wehrlite and clinopyroxenite of the rim, and into a discontinous margin of gabbro. The common presence of diopside and chromian spinel and the absence of orthopyroxene in the ultramafic pluton are characteristics recognized universally in Alaskan-type ultramafic complexes.
The Machevna pluton comprises North and South plutons. The two plutons are both zoned, with gabbroic rim and quartz dioritic core, accompanied by a small amount of clinopyroxenite. The northeastern contact of the North Machevna pluton is characterized by a complicated zone of gabbro and basalt, both the rocks have metamophosed to the amphibolite facies, presumably by synshear, hydrothermal fluid infiltration. The Tigil pluton is composed mainly of gabbro and quartz gabbro. The constituent rocks of the Machevna and Tigil plutons are characterized by low abundances in Ti, Zr and Rb, and by high magnetic susceptibility (30-200×10-3SI unit). These features are similar to those of plutonic rocks formed in intraoceanic island arcs, such as the Aleutian arc and Papua New Guinea etc..
The constituent rocks of the three plutons and their country rocks have suffered pervasive low-grade metamorphism, commonly up to the greenschist facies. To clarify the petrogeneses of three plutons in detail, further studies from both sides of igneous and metamorphic petrology are wanted.
