Extreme mantle heterogeneity beneath the Jingpohu area, northeastern China- Geochemical evidence of holocene Basaltic Rock

Holocene basaltic rocks of the Jingpohu area are located in the "Crater For est" and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrolo gical characteristics are very different: alkaline olivine basalt without a ny megacrysts in the former and leucite tephrite with Ti-amphibole, phlogop ite and anorthoclasite megacrysts in the latter. On the basis of their geoc hemical characteristics, the two types of basaltic rocks should belong to w eakly sodian alkaline basalts. But leucite tephrite is characterized by hig her Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LR EE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg-# values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which sugg ests that the mantle beneath the Jingpohu area was homogeneous before under going some geological processes about 3490 years ago. As the activity of th e mantle plume led to different degrees of metasomatism, extreme mantle sou rce heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enr iched mantle source region and resulted from strong metasomatism.