The Cretaceous Okhotsk-Chukotka Volcanic Belt (NE Russia): Geology, geochronology, magma output rates, and implications on the genesis of silicic LIPs

摘要

The Cretaceous Okhotsk-Chukotka volcanic belt (OCVB) is a prominent subduction-related magmatic province, having the remarkably high proportion of silicic rocks (ca. 53% of the present-day crop area, and presumably over 70% of the total volcanic volume). Its estimated total extrusive volume ranges between 5.5×10~5 km~3 (the most conservative estimate) and over 10~6 km~3. This article presents a brief outline of the geology of OCVB, yet poorly described in international scientific literature, and results of a geochronological study on the northern part of the volcanic belt. On the base of new and published U-Pb and ~(40)Ar/~(39)Ar age determinations, a new chronological model is proposed. Our study indicates that the activity of the volcanic belt was highly discontinuous and comprised at least five main episodes at 106-98 Ma, 94-91 Ma, 89-87 Ma, 85.5-84 Ma, and 82-79 Ma. The new data allow a semi-quantitative estimate of the volcanic output rate for the observed part of the OCVB (area and volume approximately 10~5 km~2 and 2.5×10~5 km~3, respectively). The average extrusion rate for the entire lifetime of the volcanic belt ranges between 1.6 and 3.6×10~(-5)km~3yr~(-1) km~(-1), depending on the assumed average thickness of the volcanic pile; the optimal value is 2.6×10~(-5) km~3yr~(-1) km~(-1) Despite imprecise, such estimates infer the time-averaged volcanic productivity of the OCVB is similar to that of silicic LIPs and most active recent subduction-related volcanic areas of the Earth. However, the most extensive volcanic flare-ups at 89-87 and 85.5-84 Ma had higher rates of over 9.0 ×10~(-5) km~3yr~(-1)km~(-1). The main volumetric, temporal and compositional parameters of the OCVB are similar to those of silicic LIPs. This gives ground for discussion about the geodynamic setting of the latters, because the widely accepted definition of a LIP implies a strictly intraplate environment. Considering the genesis of the OCVB and other large provinces of silicic volcanism, we propose that residual thermal energy preserved in the continental crust after a previous major magmatic event may have been one of major reasons for high proportion of felsic rocks in a volcanic pile. In this scenario, underplating of mantle-derived basalts causes fast and extensive melting of still hot continental crust and generation of voluminous silicic magmas.