Geochemistry of the Jingpohu Holocene basaltic rocks, Hellongjiang province, and discussion on their deep processes.

Holocene basaltic rocks of the Jingpohu area are located in the "Crater For est" and "Frog Pool" areas at the northwest Jingpohu Lake. Although there i s only 15km between two areas, there is a difference in petrology between t hem: alkaline olivine basalt without any magacrsts in the "Crater Forest", and leucite tephrite with kaersutitet phlogopite and anorthoclasite megacry sts in the "Frog Pool". The studies on their geochemical characteristics sh ow that leucite tephrite has higher contents of Al2O3, Na2O, K2O, more enri chment in LREE and LILE, and lower contents of MgO, CaO, lower Mg-# values and Na/K ratioes than alkaline olivine basalt, although both of them belong to sodic alkaline basalt. In contrast, their xenoliths have inverse geoche mical characteristics. Disproof calculation shows that the great difference in petrology and geochemistry was not resulted from the various degrees of partial melting of the same source. Based on their Sr, Nd and Pb isotopic data, this paper proposes that the activity of the mantle plume during 6800 0 to 3490 years ago led to the different degrees of "metasomatism", which m ade the extreme mantle source heterogeneities beneath the Jingpohu area. Le ucite tephrite was derived from the more enriched mantle source with lower degree of partial melting of mantle source than alkaline olivine basalt.