Newer Dolerite dykes, Jharkhand, India: a case study of magma generation, differentiation and metasomatism in a subduction zone setting

The NE-SW, NW-SE and E-W trending Proterozoic Newer Dolerite dykes around Chaibasa, Jharkhand, India are found to intrude Singhbhum Granites of late Archean age. Clouded plagioclase, bastitised orthopyroxene and uralitized clinopyroxene, magnetite-ilmenite, quartz-feldspar granophyric intergrowth are the characteristic minerals present in the dolerite dykes which assign a low grade metamorphosed character to the dolerite. Both olivine normative and quartz normative varieties are observed in this suite of dykes. These dolerites have been classified into two groups on the basis of REE distribution patterns: one with LREE (Light Rare Earth Element) enriched pattern (Group I) and the other with flat REE pattern (Group II). A significant positive correlation among trace elements Nb, Zr, La, Ce for Group I dykes suggest variable…