Carboniferous and Triassic eclogites in the western Dabie Mountains, east‐central China: evidence for protracted convergence of the North and South China Blocks

Abstract

SHRIMP U-Pb dating and laser ablation ICP-MS trace element analyses of zircon from four eclogite samples from the north-western Dabie Mountains, central China, provide evidence for two eclogite facies metamorphic events. Three samples from the Huwan shear zone yield indistinguishable late Carboniferous metamorphic ages of 312 ± 5, 307 ± 4 and 311 ± 17 Ma, with a mean age of 309 ± 3 Ma. One sample from the Hong'an Group, 1 km south of the shear zone yields a late Triassic age of 232 ± 10 Ma, similar to the age of ultra-high pressure (UHP) metamorphism in the east Qinling-Dabie orogenic belt. REE and other trace element compositions of the zircon from two of the Huwan samples indicate metamorphic zircon growth in the presence of garnet but not plagioclase, namely in the eclogite facies, an interpretation supported by the presence of garnet, omphacite and phengite inclusions. Zircon also grew during later retrogression. Zircon cores from the Huwan shear zone have Ordovician to Devonian (440-350 Ma) ages, flat to steep heavy-REE patterns, negative Eu anomalies, and in some cases plagioclase inclusions, indicative of derivation from North China Block igneous and low pressure metamorphic source rocks. Cores from Hong'an Group zircon are Neoproterozoic (780-610 Ma), consistent with derivation from the South China Block. In the western Dabie Mountains, the first stage of the collision between the North and South China Blocks took place in the Carboniferous along a suture north of the Huwan shear zone. The major Triassic continent-continent collision occurred along a suture at the southern boundary of the shear zone. The first collision produced local eclogite facies metamorphism in the Huwan shear zone. The second produced widespread eclogite facies metamorphism throughout the Dabie Mountains-Sulu terrane and a lower grade overprint in the shear zone.

Indosinian isotope ages of plutons and deposits in southwestern Miaoershan-Yuechengling, northeastern Guangxi and implications on Indosinian mineralization in South China

“…The well-developed oscillatory zoning and complete crystal forms of the group 2 zircon grains (Nos. 1, 9, 13, 16, 17, 20, 22, 24 and 25, also in Figure 4, sample Y-21), together with their relatively high Th/U (0.1-1.5) also indicate they are magmatic rather than metamorphic in origin [35][36][37]. The group 2 zircon grains also lack overgrowth rims which are often observed around residual zircon grains that have suffered from magmatism.…”

Diachroneity of continental subduction and exhumation: Constraints from the Permian-Triassic HP metamorphic terrane in the Tongbai orogen, central China

“…The conclusion is supported by the following two facts. (1) The garnet-whole rock Lu-Hf and Sm-Nd isochron ages of the oceanic-type eclogites from Xiongdian and adjacent area in the Hong'an orogen are concentrated to 271-252 Ma [26][27][28][29], which are later than the metamorphic zircon U-Pb ages of ~315 Ma obtained for the same eclogites [27,[30][31][32]. This suggests that these Carboniferous oceanic-type eclogites may have been reworked by continental subduction during the Late Permian.…”

Single-grain detrital muscovite Rb-Sr isotopic composition as an indicator of provenance for the Carboniferous sedimentary rocks in northern Dabie, China

“…However, Paleozoic highpressure metamorphic rocks were rarely reported in the Qinling-Dabie orogenic belt. Eclogites found in the Dabie ultrahigh-pressure metamorphic terrane mostly give Early Mesozoic ages, except for those exposed in the western Dabie region that were dated at about 310 Ma (Sun et al, 2002b). Therefore, we propose that the Middle Paleozoic detrital phengites found in the Carboniferous sedimentary sequences originated from high-pressure metamorphic rocks of the southern margin of the North China block (or the North Qinling terrane), that formed during the closure of the Proto-Tethyan Qinling ocean and subsequent collision of the North and South Qinling terranes prior to the Carboniferous ( Fig.…”