K-Ar Ages and Geochemistry of the Late-Cenozoic volcanic Rocks in Keluo, Heilongjiang Province

TLDR: In this paper, a suite of chrysolites with the inject twin were found under a microscope firstly in the world, including various crystal stock with the fourling and the six-ling.

Abstract: Fifteen volcanic rock samples and one mantle xenolith sample which were collected from 8 volcanos and other places have been studied systematically, including petrogra-phic investigation, K-Ar dating, major and trace element and REE analysis as well as O, Sr and Nd isotope determination. The chrysolites with the inject twin are found under a microscope firstly in the world, including various crystal stock with the fourling and the six-ling. The chemical compositions show that it is a suite of magma wth a characterized SiO2-unsaturated, high aboundent of K and Mg and poor Ca as well as by much rich incompatible elements, REE (ΣREE=321-1002 ppm, (La/Lu)a= 42.5-76.4) and mantle compatible element also. The values of δ18O (5.8-8.7%0) are a little higher than that of the primary mantle while the isotope compositions of Sr and Nd fell in quadrant Ⅳ along the mantle array extension and closed to the origin of the coordinates on Sr-Nd diogram, it appeared as a primary mantle. K-Ar apparent age of volcanic rocks range from 0.03Ma to 2.98Ma, majority of them belong to Late-Pleistocene. An apparent age of the xenolith is about 70Ma while the oldest basalt is from 93.3Ma to 95.5Ma. The trend analysis suggest that there is a still posibility of eruption. The comparative experiment of dating between the conventional sample and after pick out of olivine sample implied that the dated ages of the Late-Cenozoic olivine-basalts distributed in northeast and east China may be older than the real values.