The Protoliths of the Xiarihamu Eclogites from the Western Part of East Kunlun and Continent/Arc-Continent Collision

Xiarihamu eclogites occur as lenses in the Proterozoic Jinshuikou Group at the western part of East Kunlun. The eclogites have SiO2 content varying from 47.4% to 50.78% and Mg# values from 40 to 62, implying that protoliths of the eclogites were highly fractionated mafic rocks and suggesting that they belong to tholeiite series. This study divides the Xiarihamu eclogites into two groups in the light of Nb contents, Nb-enriched eclogites (Nb>7×10-6) and normal eclogites (Nb-6). The Nb-enriched eclogites are characterized by low SiO2, MgO, Al2O3 and high FeOt, TiO2. The chondrite-normalized REE patterns of the Nb-enriched eclogites display OIB patterns consistent with Paleozoic Nb-enriched basalts (NEB) and Seki island arc basalts. In additional, the primitive mantle-normalized trace elements spider diagrams have weakly negative anomalies of Nb, Ta, Ti, consistent with Paleozoic Nb-enriched basalts (NEB). The normal eclogites (Nb-6) are characterized by low FeOt, TiO2 and high SiO2, MgO, Al2O3. The REE patterns of normal eclogites display E-MORB patterns; the spider diagrams show weakly negative anomalies of Nb, Ta, P and positive anomalies of U, Sr, consistent with continental back arc basin basalt (BABB) like Okinawa BABB. ΕNd(0) and ΕNd(t=571Ma) isotopic contents of the Nb-enriched eclogites are 0~4.55 and -0.88~7.26 and those of the normal eclogites are 2.2~5.19, 3.17~6.22, both plotted into the field of HP-UHP belts of Caledonian orogeny and Sulu-Dabie orogeny. Trace element diagrams also show that the samples have been assimilated and contaminated. Therefore, the protoliths of the Xiarihamu eclogites could be interpreted to be derived from intracontinental BABB with the origin reconstructed by subduction-related crust and assimilation-contamination during magmatism. According to the published age data, it can be concluded that high-pressure metamorphic event in the North Kunlun terrane occurred in the Late Ordovician-Silurian and the Xiarihamu eclogite is probably the result of metamorphism owing to an arc-continent collision during closure of the back-arc basin. © 2018, Science Press. All right reserved.