Cumulate hornblendite enclaves in diorite–porphyrite intrusions from the Shuangyashan, Northeast China, and implications for the transition from lower crust to upper mantle in subduction setting

摘要: A suite of hornblendite (amphibole proportion ≥90%) enclaves were found in Late Cretaceous diorite–porphyrite stocks intruding the lower coal strata around Shuangyashan City, eastern Heilongjiang Province, Northeast China. The have similar mineralogy and may be divided into clinopyroxene-bearing clinopyroxene-free hornblendites both them show cumulate textures: pargasitic amphibole clinopyroxene are cumulus anorthitic plagioclase is intercumulus. accumulation might occurred magma chamber, minor enclosed was earlier crystallized, followed by a large amount amphibole, residual melt trapped between crystals finally formed intercumulus plagioclase. Probably, such crystallization process could produce layered cumulates: part dominated upper composed one. geochemistry imply hydrous basaltic parental enriched Rb, Ba, Th other large-ion lithophile elements. generation related to subduction Paleo-Pacific plate beneath Eurasian continent at that time. Estimated pressure, P-wave velocity, density for generally agreement with values local crust–mantle transition zone, suggesting these cumulates origin from crust mantle arc back-arc settings.