Main Features of Kuril-Kamchatka Deep-Sea Trench Tectonics and Geologic Development: ABSTRACT

Abstract

The upper crust structure of the Kuril-Kamchatka deep-sea trench and continental slope is a system of horst-anticlinorial uplifts of the acoustic basement and separating them partially are compensated graben-synclinorial troughs stretching in the northeastern direction according to the trench general trend. From dredging data the acoustic basement rock associations of the horst-anticlinorial uplifts of the trench continental slope are pre-Neogene (Late Cretaceous and older) complexes of the deformed geosynclinal volcanogenic and sedimentary deposits broken by gabbroids, granodiorites, and granitoids. Graben-synclinal troughs are filled with sedimentary deposits mainly of the Neogene-Quaternary ages, the thickness of which in some basins exceeds 1.8 mi (3 km). The oceanic slope of the trench is composed of the sedimentary End_Page 968------------------------------ layer with thickness of about 300 to 990 ft (100 to 300 m), lying on the second layer of the oceanic crust. According to the dredging, the acoustic basement roof on the marginal oceanic swell (Hokkaido Rise) is mainly composed of metamorphosed basalts and it seems to include the sedimentary rock intercalation. From the whole rock K-Ar data, the period of intensive basaltic volcanism on the Hokkaido Rise is from Cretaceous to Paleogene. Crustal faults along the Kuril-Kamchatka and Aleutian trenches can be characterized as normal faults, especially for the oceanic side, which points out their development in crustal tension conditions. The faults transversal to the trenches are mainly established from magnetic data. The anomalous magnetic field is subdivided generally in two regions in which the trend of anomalies varies from the subparallel (in the southern part of trench) to the subtransversal to the trench (in the northern part). A vast region next to the oceanic plate adjacent to the crustal and northeast parts of the Kuril-Kamchatka trench is characterized by the absence of linear magnetic anomalies which can be associated with the structure and movement of the subducted plate. End_of_Article - Last_Page 969------------