Protolith origin of eclogites from the North Qaidam UHP metamorphic Belt, NW China: Implications for the breakup of the Rodinia supercontinent

The North Qaidam ultrahigh-pressure metamorphic belt (NQUB) is distinguished by the widespread distribution of eclogites. However, the protolith nature of these eclogites remains controversial. This study reports new zircon LA-ICP-MS U-Pb ages and whole-rock geochemistry as well as Sr-Nd isotopic data on the Yuka and Dulan eclogites in the NQUB. Zircon U-Pb dating results of these eclogites indicate that the protolith and metamorphic ages are 831-809 Ma and 439-433 Ma. Based on distinct geochemical features, the samples can be classified into high-Ti/Y type (Group 1) and low-Ti/Y type (Group 2 and Group 3). The Group 1 eclogite protoliths are geochemically similar to oceanic island basalts (OIB) and likely originated from garnet-spinel peridotite mantle sources. The protoliths of Group 2 eclogites have a similar mantle source to those of the Group 1 protoliths, but experienced a higher degree of fractional crystallization and crustal contamination. The Group 3 eclogites have N-MORB-like affinity, and may be derived from shallower mantle sources in the spinel stability field. The dif-ferences in mantle sources of enriched (Group 1 and Group 2) and depleted (Group 3) eclogite protoliths can be ascribed to varying extents of mixing between enriched plume and depleted MORB-type mantle components at various melting depths. Our results suggest that the Neoproterozoic protoliths of eclogites in the NQUB belonged to a part of widespread Neoproterozoic rift-related mafic magmatism in the Altun-Qilian-Kunlun Orogenic Belt. These rocks could be the products of mantle plume activities that caused the breakup of Rodinia. Most Neo-proterozoic mafic rocks in the NQUB experienced early Paleozoic HP/UHP metamorphism.

Automated summary

The North Qaidam ultrahigh-pressure metamorphic belt (NQUB) is characterized by the widespread occurrence of eclogites, the protolith nature of which is still a matter of debate. This study presents new zircon LA-ICP-MS U-Pb ages, whole-rock geochemistry, and Sr-Nd isotopic data for the Yuka and Dulan eclogites in the NQUB. The zircon U-Pb dating results indicate protolith and metamorphic ages of 831-809 Ma and 439-433 Ma, respectively. Based on distinct geochemical characteristics, the samples can be classified into high-Ti/Y type (Group 1) and low-Ti/Y type (Group 2 and Group 3) eclogites. The Group 1 eclogite protoliths show geochemical similarities with oceanic island basalts and likely originate from garnet-spinel peridotite mantle sources.