1�� ��esearch Center of Palaeontology �� Stratigraphy��Jilin University��Changchun 130026��China; 2�� The Inner Mongolia Autonomous ��egion Geological Exploration Fund Management Center��Hohhot 010020��China; 3�� Geological Party No. 1��Bureau of Geology and Mineral ��esources of Xinjiang��Changji 831100��Xinjiang��China

Chronological and geochemical data on the Mesozoic Longjiang stage volcanic rocks indicate that the rhyolite from the lower part of the Longjiang Formation formed in 120 ±1. 3 Ma and andesite from the upper part of the Longjiang Formation formed in 110. 7 ±1. 2 Ma�� It implies that the Longjiang Formation formed from two vol- canic events during an interval of about 10 Ma��and these two volcanic events could be compared with other related Early Cretaceous volcanic events of Northeast China�� The rock assemblages of Longjiang Formation are composed mainly of rhyolites and andesites��belonging to chemically calc- alkaline to high- K calc- alkaline series�� The ��EE patterns demonstrated L��EE enrichment and H��EE depletion��with weak negative Eu anomalies�� The volcanic rocks of Longjiang Formation were strongly enriched in large ion lithophile elements (LILE) such as K����b��U and Th��with depletion in high field strength elements ( HFSE) such as Nb��Ta and Ti�� Combined with geochem- ical characteristics and previous researches��the authors propose that the Early Cretaceous volcanic rocks in Xinsh- eng area��northern Heilongjiang were derived from partial melting of lower crust and were related to a post- orogenic extensional environment induced by the subduction of paleo- Pacific Plate to Eurasian Plate��