Original paper

Petrogenetic relationships between jadeitite and associated high-pressure and low-temperature metamorphic rocks in worldwide jadeitite localities: a review

Tsujimori, Tatsuki; Harlow, George E.

Abstract

Jadeitite-bearing serpentinite-matrix mélange is distributed in the Caribbean (Guatemala, Cuba, and Dominican Republic), circum-Pacific (Japan, Western USA, and Papua New Guinea), Alpine-Himalayan (Italy, Iran, Greece, and Myanmar), and Caledonian (Russia and Kazakhstan) orogenic belts, and always contains high-pressure, low-temperature (HP-LT) metamorphic rocks. There are also jadeitite xenoliths in kimberlitic pipes in the Colorado Plateau (USA). The oldest occurrences of jadeitite are Early Paleozoic in Japan, Russia, and Kazakhstan, suggesting subduction-zone thermal structures evolved the necessary high pressure/temperature conditions for jadeitite formation since Early Paleozoic; the youngest occurrence is a xenolith from the Colorado Plateau. Major occurrences consist principally of fluid precipitates (P-type) that infiltrated the mantle wedge; fewer occurrences document metasomatic replacement (R-type) of plagiogranite, metagabbro and eclogite, and both types may be possible in the same occurrence or system. The P-T conditions for jadeitite formation can be extended beyond the previously argued limits of blueschist-facies conditions. Some jadeitite formed at epidote amphibolite and others at eclogite facies conditions. Available geochronological data of both jadeitite and associated HP-LT rock show temporal discrepancies between jadeitite formation and HP-LT metamorphism at some localities. The close association between older jadeitite and younger HP-LT rock in a single mélange complex implies different histories for the subduction channel and jadeitite-bearing mélange. Jadeitite-bearing serpentinite mélange can stay at the mantle wedge for a considerable time and, as a result, experience multiple fluid-infiltration events. The subduction channel can occasionally incorporate overlying serpentinized mantle wedge material due to tectonic erosion. With time, the disrupted mantle wedge containing jadeitite veins is mixed with younger blueschists, exhumed eclogites and various fragments of suprasubduction-zone lithologies. Consequently, recrystallization and re-precipitation of jadeitite are reactivated along a slab-mantle wedge interface. All these possible scenarios and their combinations yield a complicated petrological record in jadeitite. With further investigation, the rock association of jadeitite-HP-LT metamorphic rocks-serpentinite has the potential to yield a greater understanding of subduction channels and overlying mantle wedge.

Keywords

jadeititeblueschisteclogitehp-lt metamorphismserpentinite mÉlangefluid precipitationmetasomatic replacement