U‐Pb Zircon Ages of Granitoid Rocks in the North Dabie Complex, Eastern Dabie Shan, China

Multichronometric Evidence for an In Situ Origin of the Ultrahigh‐Pressure Metamorphic Terrane of Dabieshan, China

“…3a). This age is in agreement with the U-Pb concordia upper intercept ages of 700-800 Ma previously obtained on zircons from gneisses (Ames et al 1993;Rowley et al 1997;Xue et al 1997;Hacker et al 1998). The Th/U ratios of gneiss zircon on either core or rim fall within the range, which is identical 1.0 ‫ע‬ 0.4 within error to the observed Th/U ratios in the zircon cores analyzed by Rowley et al (1997), which implies that they have an igneous origin.…”

“…Our U-Pb data on zircon from the country rock do not emphasize the Triassic UHPM age as did eclogitic zircons. Up to now, only zircons from the Shima and Wumiao eclogite host gneisses, which present extreme metamorphic conditions (pressure up to 41 kbars), recorded the 220-210-Ma event (Ames et al 1993;Rowley et al 1997;Xue et al 1997;Hacker et al 1998). The lack of a record of ∼220-Ma ages in the gneissic zircons may simply be an artifact of sampling, or it may indicate the inability of zircons to accrete new rims during retrograde metamorphism due to a lack of suitable fluids.…”

“…These observations add to the ongoing controversy regarding the exotic/tectonic emplacement or in situ origin of the coesite-bearing metamorphic rocks. Previous combined structural, petrographic, and geochronological studies on UHPM rocks from two main localities (Shima and Wumiao) have suggested an in situ origin of the coesite-bearing eclogites with their associated host gneisses Xue et al 1997;Hacker et al 1998). To examine whether such an in situ relationship is more widespread than these two localities, we undertook a detailed and precise geochronological study on other well-known coesite-bearing eclo-gites and associated host gneisses from the Bixiling Complex and the Shuanghe UHPM sheet.…”

Diverse P–T paths of the northern Dabie complex in central China and its reworking in the early Cretaceous

“…Besides the above mentioned abundant Triassic ages, a number of early Cretaceous magmatic and metamorphic ages have also been reported, supporting the notion that a widespread magmatic intrusion and overprinted HT/UHT metamorphic event in the NDC occurred in early Cretaceous ( 130 Ma) accompanied by extensive (Xue et al, 1997;Hacker et al, 1998Hacker et al, , 2000Bryant et al, 2004;Xie et al, 2006), for the mafic to ultramafic rocks and granitoids (Zhao et al, 2005, and of 120-130 Ma obtained using different methods (RbSr, Sm-Nd and Ar-Ar) for the mafic-ultramafic rocks (Jahn et al, 1999), all indicate that the massive granitoids and maficultramafic rocks were nearly synchronously emplaced in the early Cretaceous. Whereas an Sm-Nd isochron age of 136 ± 18 Ma for a mafic granulite from Huilanshan (Hou et al, 2005), a zircon U-Pb age of 128 ± 2 Ma for a gneiss (Xie et al, 2006), and zircon U-Pb ages of 130 Ma for a tonalitic gneiss (Liu et al, 2007b) and 126 ± 4 Ma to 131 ± 36 Ma for granitic gneisses (Zhao et al, 2008), together with zircon U-Pb ages of 145 ± 2 Ma to 120 ± 2 Ma for the migmatites , suggest that the NDC underwent an intense overprinting HT/UHT granulite facies metamorphism and migmatitization in the early Cretaceous ( 130 Ma).…”

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

“…Although recent studies have shown that the North and South China (Yangtze) blocks likely underwent similar thermal events in the early Precambrian, especially in late Archean and early Proterozoic (e.g., Zheng et al, 2006;Zhang et al, 2006), they have had different thermal histories during Late Proterozoic and Early Paleozoic times. During the Late Proterozoic, the evolution of the Yangtze block was associated with magmatic-metamorphic events especially along the northern and western margins (e.g., Chen et al, 2003a, b;Rowley et al, 1997;Xue et al, 1997;Hacker et al, 1998). The southern margin of the North China block, in turn, was characterized by Early Paleozoic magmatism and metamorphism (e.g., Kröner et al, 1993;Zhai et al, 1998;Zhang, 1999, 2000).…”