ИСТИНА

Among the largest volcanic areas of the Earth, having the extrusive volume of > 105 km3 (sometimes > 106 km3), and known as "Large Igneous Provinces" (LIPs), some provinces are dominated by silicic volcanic rocks. For such a specific case, S.E.Bryan with co-authors [1] suggested the term "silicic LIP", or SLIP. The recently published overviews [1, 2] mention only four Phanerozoic SLIPs, which are located in the present-day Australia, Argentina, Chile, and Mexico. However, at least six more Phanerozoic volcanic provinces of Central and Eastern Asia also fit the volumetric criteria of a SLIP: (1) Kazakhstan belt of Northern and Central Kazakhstan (400-365 Ma), (2) Balkhash-Ili belt of Southern and Central Kazakhstan (335-248 Ma), (3) Great Xing'an province of NE China (163-113 Ma), (4) SE China belt (178-85 Ma), (5) Okhotsk-Chukotka belt of NE Russia (106-75 Ma), and (6) Eastern Sikhote-Alin' belt of SE Russia (97-60 Ma). All SLIPs are superposed on the relatively young continental crust of Phanerozoic foldbelts and accreted margins. The time gap between the SLIP formation and the previous major magmatic event usually does not exceed 15 m.y., whereas most of mafic LIPs were formed in intracratonic settings, after a calm period of over 200 m.y. [2]. Compositionally, mafic and intermediate volcanic rocks of SLIPs combine features of both subduction-related and intraplate magmas. Major element compositions of crust-derived silicic rocks are quite similar, because they approach the ternary granite minimum, but trace element contents may reveal significant variations, resulted from the heterogeneity of crustal protolith and/or from the crystal fractionation process. The consideration of SLIPs in one group with mafic LIPs implies their formation in intraplate environments [1]. But at least four of six Asian volcanic belts listed above are thought to be Andean-type provinces, directly related with the subduction process. This infers the SLIPs represent a geodynamically distinct class of volcanic provinces. The thermal history of the crust is suggested to be important, yet still underestimated factor controlling their formation.