卷 13, 编号 3 (2019)

Geological data and about 300 precision geochronological and geochemical determinations are analyzed to identify the Albian–Cenomanian continental-margin orogenic belt and simultaneous igneous province of Pacific Asia. The orogenic belt represents a newly formed region of continental lithosphere that resulted from the deformation of mainly Jurassic–Early Cretaceous epioceanic terranes. The igneous province is made up of volcanic and intrusive complexes of mostly Albian age, which are syn-orogenic within the belt and post-orogenic beyond it. The igneous rocks include A-, I-, and S-type granitoids; adakites; and VAB- and OIB-type basalts and their intrusive analogues. Both the orogenic belt and the igneous province were formed in a tectonic setting of a transform continental margin between 110 and 95 Ma. The interval of 103–97 Ma became the peak of orogenic and magmatic activity caused by upwelling of the hot asthenospheric mantle through destructed stagnant slabs of the pre-Albian subduction. The Albian–Cenomanian age of the large gold, copper, tungsten, tin, and other ore deposits argues in favor of recognition of the corresponding metallogenic province. The first age data (100–97 Ma) are reported for the granite from the Malmyzh deposit within the Sikhote-Alin Ridge.

The results of comprehensive (geological, geochemical, geochronological, and petro- and paleomagnetic) study of the Aptian–Albian rocks of the Kema Terrane and the northeastern Udyl segment of the Kiselevka–Manoma Terrane are presented. The obtained results suggest that the studied volcanogenic–terrigenous complexes of rocks formed in a suprasubduction zone at about the same time (early Albian, 110 Ma ago) at close latitudes but in different island arcs unequally distant from the continent: the complexes of the Kema Terrane at a latitude of 36° ± 6° N in the island arc close to the continent as evidenced by the petro–geochemical characteristics of the volcanites and the presence of ancient zircons in the sediments; and the rocks of the Udyl segment of the Kiselevka–Manoma Terrane at a latitude of 33° ± 5° N in an intraoceanic island arc separated from the volcanic arc of the Kema terrane by an interarc basin, which was wide and deep enough to avoid the influence of the continental source areas in the sediment accumulation zone of the Kiselevka–Manoma Terrane. Based on the conclusions, the geodynamic reconstruction is developed for the formation and history of motions of the studied rock complexes during the oceanic plate movement, their displacement along the transform margin, as well as post-accretionary movements at various distances to the current position with the following coordinates: Udyl 52° N, 140° E; Kema 45°–46° N, 136°–137° E.

The Itmurundy zone of the northern Balkhash area is a Pacific-type orogenic belt. It possesses a complex geological structure and hosts rocks of mantle, accretionary and post-orogenic associations. The volcanic and sedimentary rocks of the accretionary association belong to three suites: Itmurundy (O_1-2), Kazyk (O_2-3) and Tyuretai (O₃-S₁). The suites are separated by tectonic unconformities or faults of three orders: 1) large regional faults; 2) medium faults separating mantle and oceanic accreted rocks; 3) small faults separating packages consisting of oceanic sediments. The Itmurundy Fm. (O_1-2) is the most lithologically variable consisting of oceanic basalt, pelagic chert, hemipelagic siliceous mudstone and siltstone, and trench greywacke sandstone. The packages, each consisting of chert-siliceous mudstone, are separated from each other by 2^nd and 3^rd order faults of probably thrust nature, i.e. they are parts of duplex structures. The presence of duplex structures and the high degree of deformation of Itmurundy Fm. rocks are typical of accretionary complexes. The associations of volcanic and sedimentary rocks under study represent a full section of oceanic plate stratigraphy (OPS): basalt (MORB, OIB)—chert (pelagic)—siliceous mudstone, siltstone and shale (hemipelagic)—trench sandstones (greywacke). The structural position and the lithology of Itmurundy rocks accord well with the model of formation of accretionary complexes at Pacific-type convergent margins, in particular, those in the western Pacific.