Geochemistry and origin of dolerite blocks in serpentinite in the Kurosegawa Belt of the Shima Peninsula, Mie Prefecture, Southwest Japan

Abstract

Dolerite occurs as blocks within serpentinite in the Kurosegawa Belt, located between the Northern and Southern Chichibu belts on Shima Peninsula, Mie Prefecture, Southwest Japan. On the peninsula, this dolerite is considered as a significant component of the Kurosegawa Paleozoic Rocks that define the Kurosegawa Belt. However, dolerite itself is not necessarily the component because it also appears, to a minor extent, in Jurassic accretionary complexes distributed across the Northern and Southern Chichibu belts, with a previous work having associated the dolerite with the Jurassic accretionary complexes of the Chichibu Belt on the basis of geochemistry and structural relationships. Whole-rock geochemical analyses were conducted on dolerite within the serpentinite in the Shima Peninsula to determine its origin. The dolerite has a geochemical signature consistent with islandarc tholeiite, according to geochemical discrimination diagrams and trace-element spider-diagrams normalized to N-MORB and chondrite. This feature suggests that the dolerite is not an oceanic component within the Jurassic accretionary complexes. On the basis of the geochemistry of the mafic Kurosegawa Paleozoic Rocks in other areas, the dolerite within the serpentinite on the Shima Peninsula is inferred to be correlative with one of the Kurosegawa Paleozoic Rocks. The dolerite might also be associated with the Mitaki Igneous Rocks in the Kurosegawa Belt in Shikoku, Southwest Japan.