Abstract:  Longgang volcanic area is located in Huinan and Jingyu County, Eastern Jilin Province, and is an important part of the Quaternary continental volcanic rock area on the continental margin of Northeast China. In order to further explore the genesis and tectonic significance of basaltic lava in the study area, based on field geological investigation, Rb-Sr isotopic dating, element geochemistry and whole rock Pb isotopic analysis were carried out. The experimental results show that: 1) The Rb-Sr isochron age of whole rocks, plagioclase and amphibole from seven trachybasalt lava samples is (1.81 ± 0.34) Ma (MSWD=0.17, n=7). 2) The values of Na2O + K2O in trachybasaltic lavas range from 6.44% to 6.65%, with high A/CNK (1.24-1.27) and Mg# (39.09-39.81) values. Compared with the primitive mantle, the trachybasaltic lavas significantly enriched in Rb, Ba, Sr and other large ion lithophile elements (LILE), enriched in light rare earth elements (LREE), weakly enriched high field strength elements (HFSE) such as Nb, Ta, Zr, Hf, U and Th, depleted heavy rare earth elements (HREE), with weak Eu anomalies (δEu=0.95-1.07) and weakly enriched in Pb. 3) The (87Sr/86Sr) i values in the studied rocks range from 0.705 074 to 0.705 206, and the ratios of 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb in the whole rocks are 17.984-18.329, 15.490-15.523 and 38.315-38.400, respectively. Combined with the recent research results and the existing understanding of regional tectonic evolution, it shows that the diagenetic age of basaltic lava is the Calabrian stage of the Early Pleistocene. The diagenetic magma is mainly formed by mantle-derived magma, with a small amount of young lower crust components added, showing the attributes of oceanic island basalts (OIB) or intraplate metasomatic basalt. In addition, the formation of trachybasaltic lava and its associated volcanic activity occurred in an extensional tectonic environment at about 1.81 Ma, which may be related to the roll-back after the subduction of the Pacific plate under the northeastern Eurasia continent.

Key words:  Rb-Sr dating, element geochemistry, Pb isotope, basaltic lava, Longgang volcanic area; , Jilin Province