Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of south China

Abstract

In order to better constrain the paleogeographic evolution of south China we measured Sm‐Nd and Rb‐Sr isotopic compositions for 23 Mesozoic granites that crop out throughout the area. Tightly grouped neodymium depleted mantle model ages (1.4 ± 0.3 Ga) suggest the region is underlain by relatively homogeneous Proterozoic crust and fail to define crustal provinces. Neither the isotopic nor geologic data suggest that a Mesozoic suture exists. However, granites possessing anomalously high Sm (>8 ppm) and Nd (>45 ppm) concentrations, relatively high initial epsilon neodymium (−4 to −8), and high but variable initial 87Sr/86Sr (0.759 to 0.713) form a northeast trending zone that coincides with two prominent Mesozoic basins. Southeast of the zone lie the majority of Mesozoic intrusives and Upper Triassic to Lower Cretaceous extensional basins found in south China. Mesozoic paleomagnetic poles are well clustered northwest of the zone. Pre‐Cretaceous poles southeast of it are discordant with respect to those from the northwest. The only recognized tectonostratigraphic terrane in south China lies southeast of the zone. The terrane is bordered by a northeast trending sinistral fault that was active in the Mesozoic. Other faults in south China have similar attitudes, ages, and sense of shear. Together, the observations suggest that the Mesozoic tectonic regime in south China consisted of strike‐slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults. The zone, defined by the granites enriched in Nd and Sm, demarcates displaced terranes to the southeast from relatively stable land to the northwest.

Zircon U–Pb, molybdenite Re–Os and muscovite Ar–Ar isotopic dating of the Xitian W–Sn polymetallic deposit, eastern Hunan Province, South China and its geological significance

“…However, the tectonic regime responsible for the Yanshanian magmatism and related W-Sn mineralization is still debated. Gilder et al (1996) identified the NNE-trending Shi-Hang granite belt, characterized by low T DM (neodymium depleted mantle model age) values and relatively high ε Nd values in central South China, and attributed it to the coeval processes of lithospheric extension and crust-mantle interaction. Mao et al (1998) proposed the mantle plume model to explain the extensive polymetallic mineralization and associated granites in the Mesozoic of South China.…”

“…(1) The NNE-trending Shi-Hang (from Shiwandashan in the west to Hangzhou in the east) high-Ɛ Nd granite belt in the interior of South China (Gilder et al, 1996;Hong et al, 2002;Mao et al, 2013a;Zhou et al, 2015), where the Xitian deposit lies, is probably a Neoproterozoic suture zone between the YZB and CAB. The flat subduction of the Paleo-Pacific plate beneath the SCB in Mesozoic might have terminated beneath the belt, where there existed contemporaneous bimodal magmatism, diagnostic of the continental arc to intra-arc rift setting due to slab rollback (Jiang et al, 2009 and references therein); (2) The Early Yanshanian granitic magmatism took place only in the Nanling region, with a southeastward-younging trend, in comparison with the distribution of the Late Yanshanian (140-90 Ma) volcanic and intrusive rocks near to the coast (Gilder et al, 1991;Chen and Jahn, 1998;Zhou and Li, 2000;Sun et al, 2003;Wang et al, 2005;Li et al, 2006;Li and Li, 2007;Li et al, 2007a).…”

Geochronological and geochemical constraints on the petrogenesis of Middle Paleozoic (Kwangsian) massive granites in the eastern South China Block

“…The Jiangshan-Shaoxing Fault may represent an important boundary fault between the Yangtze and Cathaysia Blocks (e.g., Wang et al, , 2005Wang et al, , 2008Zhang and Wang, 2007). Such a conclusion is also supported by some other geological observations, for example,: (1) the Jiangshan-Shaoxing Fault is closely associated with the Shi-Hang or Gan-Hang zone (commonly recognized in Chinese literature), which is characterized by zonal geophysical and geochemical anomalies as well as important multi-metal mineralization (along the Shi-Hang and Gan-Hang zone, many Mesozoic A-and I-type granites and volcanic rocks with higher ε Nd (t) values are usually accompanied by giant oredeposits with Sn-polymetallic and U mineralization) (e.g., Qin, 1991;Gilder et al, 1996;Chen and Jahn, 1998;Yuan et al, 1989;Hunan BGMR, 1988;Jiang et al, 2008;Yang et al, 2011;Zhao et al, 2010;Jiang et al, 2006;; (2) the Moho depth suddenly changes from 34-36 km in the west to 30-32 km to the east of the JiangshanShaoxing Fault (Zhang and Wang, 2007); and (3) the Sr-Nd-Pb isotopic compositions of the Jurassic mafic rocks are characterized by an EM1 reservoir to the west but by EM2 + DMM reservoir to the east of the Fault (e.g., Dai et al, 2008;Wang et al, , 2005Wang et al, , 2008. However, the tectonic nature of the Jiangshan-Shaoxing Fault during the Kwangsian period remains controversial.…”

Early Cretaceous potassic volcanic rocks in the Jiangnan Orogenic Belt, East China: Crustal melting in response to subduction of the Pacific–Izanagi ridge?

“…The Mesozoic geology of SE China, including the JOB and LYRB, is characterized by extensive Jurassic to Cretaceous igneous rocks consisting predominantly of granites and felsic volcanic rocks of potassic affinity generated in an extensional environment (e.g., Gilder et al, 1991Gilder et al, , 1996. As discussed above, the P-T and compositional conditions for generation of the Tianmushan potassic magmas include: (1) high-K crustal source; (2) a thinned crust; and (3) a high thermal gradient resulting from upwelling asthenosphere.…”

“…1b), is one of the most important Mesozoic metallogenic-and magmaticbelts in eastern China (Gilder et al, 1991(Gilder et al, , 1996Chen and Jahn, 1998). Most of the Mesozoic igneous rocks of the JOB show high-K calc-alkaline to shoshonitic affinities with relatively high Nd concentrations and more radiogenic Nd (typical ε Nd (t) between − 8 and − 4) than those felsic igneous rocks from the adjacent areas (typical ε Nd (t) between −15 and −12) (Gilder et al, 1996). In this paper, we present high-precision zircon U-Pb ages and Hf isotopic compositions and whole-rock geochemical data from an Early Cretaceous felsic potassic volcanic suite from the Tianmushan basin in the eastern JOB.…”