Petrology, geochemistry and geochronology of the meta-mafic rocks in the North Sulu ultrahigh-pressure belt: Implications for their petrogenetic diversity and complex tectonic evolution

作者：Liu, Lishuang^*; Liu, Fulai^*; Liu, Pinghua; Wang, Wei; Ji, Lei; Wang, Fang; Cai, Jia

来源：Precambrian Research, 2018, 316: 127-154.

DOI：10.1016/j.precamres.2018.08.002

• UHP and non-UHP meta-mafic rocks
• Geochemistry
• Zircon U-Pb dating
• Tectonic melange zone
• North Sulu UHP belt
• Jiaobei Terrane

The ultrahigh-pressure (UHP) eclogite and country rocks of the North Sulu UHP metamorphic belt have traditionally been considered the products of the deep subduction of the Yangtze Block (YB) beneath the North China Block (NCB). However, widely distributed non-UHP meta-mafic rocks, appearing as irregular lenses and thin layers together with UHP eclogite in the Haiyangsuo-Wuji-Weihai area along the northwestern margin of the North Sulu UHP belt, prompted investigation of the petrogenetic diversity and complex tectonic evolution of these rocks. The UHP index mineral assemblage of garnet + omphacite + rutile +/- phengite +/- coesite is common in the matrix of UHP and retrograde eclogites, or as inclusions preserved in metamorphic zircons indicating UHP metamorphism. In contrast with previous studies, herein high-pressure and medium-pressure (HP MP) granulite facies index mineral assemblage of garnet + clinopyroxene + plagioclase + quartz +/- orthopyroxene + ilmenite was commonly identified in the matrix of non-UHP mafic granulites and amphibolites, indicating that these rocks underwent HP MP granulite facies metamorphism rather than UHP metamorphism. The whole-rock geochemical data revealed multiple origins for the UHP and retrograde eclogites with protoliths derived from heterogeneous mantle or lower upper crust sources with weak fractional crystallization. In contrast, the protolith of the non-UHP meta-mafic rocks may have derived from a depleted or primitive mantle origin source with varying degrees of crustal contamination during emplacement. The UHP and retrograde eclogites exhibited Neoproterozoic (803-760 Ma) protolith ages and underwent UHP eclogite facies metamorphism in the Middle Triassic (233-225 Ma) with subsequent Late Triassic (219-210 Ma) amphibolite facies retrogression. In contrast, the non-UHP meta-mafic rocks exhibited older Paleoproterozoic ( > 1944 Ma) protolith ages. The two distinct metamorphic events that occurred in the Paleoproterozoic (1944-1825 Ma) and Middle Late Triassic (226-201 Ma) are related to the Paleoproterozoic Jiao-Liao-Ji orogeny and the Triassic collisional event between the YB and NCB, respectively. A combined study of petrography, whole-rock geochemistry and zircon U-Pb ages revealed that the UHP and retrograde eclogites show a close affinity to the Neoproterozoic continental crust on the northern margin of YB, whereas the non-UHP meta-mafic rocks show a close affinity to the Paleoproterozoic Jiaobei Terrane. Both the UHP and non-UHP meta-mafic rocks, together with their country rocks form an approximately 200 km long melange zone rather than a single UHP belt, which extends from the Haiyangsuo through the Wuji to the Weihai area along the northwestern margin of the North Sulu UHP belt.

• 出版日期2018-10
• 单位中国地质科学院