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On the basement of the northwest sector of the Pacific Belt

Publication Date
DOI: 10.1016/0040-1951(70)90002-8
  • Earth Science


Abstract The northwest sector of the Pacific Belt is generally considered as a structure formed on Precambrian basement (platform) with whose disintegration and extermination the foundation of the regenerated geosynclinal system of the northwest sector of the belt was associated. The metamorphic complexes, outcropping in various structural zones of the northwest sector of the belt were in most cases interpreted as relict Precambrian massifs, left from disrupted and basificated basement of the platform. Modern data on the geology of the metamorphic complexes show that the metamorphosed strata in the northwest sector of the Pacific Belt are of various ages. Their structural role in Precambrian, Paleozoic, Mesozoic and Cenozoic zones of the northwest belt sector is also various: some form massifs of early consolidation or lie within the cores of anticlinoria; others are connected with zones of deep-seated fractures. Also the metamorphic rocks are situated at the contacts of granitic massifs with enclosing deposits, dated as Paleozoic and Mesozoic. These circumstances allow the conclusion that the structure of the northwest sector of the Pacific Belt is orthogeosynclinal, and elementary paleogeographic structural zones of the northwest sector of the geosynclinal systems were formed at different periods between the Upper Archean and Cenozoic, as is indicated by the outcrops of different-aged metamorphic complexes commonly coinciding, within the elementary structural zones, with the oldest parts of these zones. An epicratonic, ensialic nature of the geosynclinal system of the sector of the Pacific Belt, therefore, is at present not confirmed by the analysis of composition, structure and structural peculiarities of the metamorphic complexes of the sector. It seems most probable, to consider the geosynclinal systems of this belt, in analogy with recent geosynclines, as orthogeosynclines, that were laid on a sima base i.e., as geosynclines of ensimatic type. Geological analysis of the metamorphic complexes shows the impossibility of using rock metamorphism as criteria of age and particularly as criteria of the period of their geosynclinal accumulation. And therefore the presently available means of stratigraphic unification of the metamorphic strata of the various structural zones of the region are unreasonable.

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