Abstract:

Based on field geological survey, petrogeochemical analysis and ¹⁴C dating by high precision accelerator mass spectrometry, the Cenozoic volcanism in the Mock River region of central Daxing’anling has been studied. It’s proved that there happened active volcanisms in the Cenozoic period in Mock River region, which covered over 80 km² area and erupted in the strombolian style. The earliest volcanism started in the Late Pleistocene period and experienced four eruption cycles. There was a shortterm intermittent between the first and second eruption cycles. The volcanic rock resulted from the Cenozoic volcanism in the Mock River region belongs to the high K calcalkaline olivine basalt, and characterized by low silicon (SiO₂ content between 46.16% and 51.44%, the average is 48.66%), high Mg (MgO content between 10.08% and 13.79%, the average is 10.36%), high K(K₂O content between 1.25% and 2.31%, the average is 1.53%), high Ti(TiO₂ content between 1.80% and 2.69%, the average is 2.30%). Integrated data above with those in adjacent regions, some conclusions can be drawn as followings. Firstly, the Cenozoic volcanic rock in this area belongs to the OIB basalt derived from the reactivating deep fault under the extensional tectonic environment. Secondly, little or no crust-derived material was contaminated during the magma ascending. In addition, there happened fractional crystallization of olivine and clinopyroxene instead of plagioclase feldspar crystallization differentiation.

Key words: volcanoes, geochemistry, Late Pleistocene period, age of ¹⁴C, volcanism