Zircon SHRIMP U-Pb Dating of the Tourmalinites from Boron-bearing Series of Borate Deposits in Eastern Liaoning and its Geological Implications

摘要

This paper focused on the zircon sensitive high resolution ion micro-probeU-Pb geochronology of the tourmalinites from boron-bearing series of borate deposits in Eastern Liaoning.The zircons commonly have core-rim structures,most cores show oscillatory zoning in cathodoluminescence and plane polarized light images,suggesting a magmatic detrital origin.Ages of the magmatic detrital zircons from the hyalotourmalite samples(N13) and(N14) are 2175±5Ma and 2171±9Ma,respectively.Moreover,metamorphic zircon from the sample(N13) shows an age of 1906±4Ma.Zircon core and rim from the hyalotourmalite sample(N02) record ages of 2171±6Ma and 1889±62Ma,which are explained as indicating the formation and metamorphic ages.Combined with the geological and geochemical studies,it can be concluded that the tourmalinites are formed during sedimentary exhalative mineralizations in the mid-Paleoproterozoic(～2170Ma) and underwent the metamorphism in the late-Paleoproterozoic(～1900Ma).The tourmalinites are the products of submarine acid volcanism in the extension rifting phase of the Liaoji Paleoproterozoic Rift,the rock-forming materials of which are derived from the mantle sources with recycling crustal contamination.The emergence of tourmalinites not only indicates the mid-Paleoproterozoic tectonic-magmatic processes,but also provides impetus,heat and material sources for the mineralization of borate deposits in Eastern Liaoning.