The Palaeoproterozoic Rift-Type Volcanism in Luliangshan Area, Shanxi Province, and Its Geological Significance

Abstract

The Paleoproterozoic Luliang Group(～2 300 Ma) and Yejishan Group (～2 100 Ma) in central Luliang Mountains of Shanxi Province mainly consist of detrital formation in the lower part and volcanic formation in the upper part. The volcanic formation is dominated by basic volcanics (basalt) with less acidic volcanics (rhyolites). The basalts in the area, which have low MgO and P 2O 5 content but contain abundant FeO *,K 2O+Na 2O and LREE,are similar to continental basalts. The acidic volcanics are characterized by high LIL and ΣREE values as well as large (La/Yb) N ratios. The sedimentary environment and geochemical characteristics of the volcanics indicate that the volcanic rocks of the Luliang Group and Yejishan Group were erupted in intracontinental or epicontinental rift type tectonic setting. The positive e Nd ( t DM ) value (～+3.0) suggests that the parental magma of the basalts in both group was derived from depleted mantle source, and the lower e Nd ( t FM ) value (about zero) shows that the parental magma was contaminated by continental materials. The existence of the Palaeoproterozoic rift-type volcamism implies that a considerable continental crust was formed in the North China Craton at the end of Archean.