The Dabie Shan of eastern China is a ϳ200 kilometers wide mountain range with nearly 2 kilometers of relief and is an archetype of deep ultrahigh-pressure metamorphic rock exhumation. Despite its regional and petrologic importance, little is known about the low-temperature and post-orogenic evolution of the Dabie Shan. Here we present apatite and zircon (U-Th)/He (AHe and ZHe, respectively) and apatite fission-track (AFT) cooling ages from the Dabie Shan that constrain the patterns and history of exhumation over the last ϳ115 myr. On the scale of the whole orogen, ZHe and AHe ages are inversely correlated with mean elevation and are systematically younger in the core of the range. These cooling ages were converted to exhumation rates assuming steady-state erosion and accounting for topographic effects. These results indicate that, since the Eocene, flanks of the range have eroded at rates as low as 0.02 km/myr, while the range core has eroded at about 0.06 km/myr. Even in the core of the range, these recent exhumation rates are at least 10 to 20 times slower than those estimated for the initial stages of exhumation in the Triassic-Jurassic. In a 1.4 kilometer vertical transect in the core of the range, all ages are positively correlated with elevation, with ZHe ages increasing from 76 to 112 Ma, AFT from 44 to 70 Ma, and AHe from 24 to 43 Ma. We present a simple model for topographic correction of thermochronometric ages in vertical transects, using the admittance ratio (ratio of isotherm relief to topographic relief). Applied to the AHe age-elevation relationship, this yields Tertiary exhumation rates of 0.05 to 0.07 km/myr in the core of the Dabie Shan, in good agreement with regional exhumation rate patterns. Finally, age-elevation relationships for all three chronometers in the vertical transect are consistent with a constant exhumation rate of 0.06 ؎ 0.01 km/myr since the Cretaceous, with a possible modest increase in exhumation rates (as high as 0.2 km/myr) between 80 to 40 Ma. These data show no evidence for significant variations in exhumation rates over the last ϳ115 myr, as might be expected for decay of old topography or tectonic reactivation of old structures. introduction Collisional orogenies typically produce topographic and geophysical anomalies persisting several hundred million years. The post-orogenic evolution of mountain ranges and their responses to erosion and subsequent tectonic events provides insights to a variety of problems, including the deep crustal architecture of orogens, dynamics of lithospheric roots, and the erosional decay of topographic anomalies. Typically, the topographic and structural decay of an ancient mountain range is not monotonic, and

No abstract

No abstract

Fission-track, (U-Th)/He thermochronology, and cooling properties indicate that the southern Daba arcuate zone (SDBAZ) underwent a distinctive phase of rapid cooling in 153-100 Ma at a rate of 1.44-1.90°C/Ma. This rapid uplifting strongly contrasts with (1) the previous, rapid foreland subsidence during Early to Middle Jurassic in response to late-orogenic compression from the Qinling belt, (2) the succeeding long, slow cooling phase and relative thermal stability that occurred during the 100-45 Ma period. This rapid cooling event in the SDBAZ parallels those experienced by two adjacent upheavals of Huangling (HLUZ) and Hannan-Micang (HMUZ), with cooling rates of 2.22-3.17°C/Ma for the HLUZ in 160-126 Ma, 4.91°C/Ma for the southern HMUZ in 150-125 Ma, as well as 2.11°C/Ma for the northern HMUZ in 150-105 Ma. Comparing thermal histories among the SDBAZ, the HLUZ, the HMUZ, and the Wudang metamorphic zone (WDMZ), we infer that the Daba arcuate structural belt formed in 153-100 Ma. The combined dating data support a correlation with a low-angle arcuate south-thrusting of the Qinling orogen triggered by northward convergence of the Yangtze Craton, contemporaneously encountering rigid basement obstructions from the HLUZ and the HMUZ, respectively. Both the SDBAZ and neighboring domains additionally underwent a comparatively fast cooling and uplift since about 45 Ma.

Drilling has revealed suites of magnesian granite and diorite emplaced in Early Jurassic time (198–195 Ma) and an arc‐related low‐temperature (678 to 696°C) magmatism in NE South China Sea. These rocks have 87Sr/86Sri (0.705494 to 0.706623) and εNdt (−0.9 to +2.2) as evidence of evolved mantle‐derived magmas, coupled with enriched fluid‐mobile elements Cs to K and Pb implying involvement of subduction‐zone fluids. Another Early Jurassic granodiorite (zircon U‐Pb 187 Ma) drilled from the SW East China Sea, a magnesian high‐K calc alkaline, is comparably confined to a range of low‐temperature (~675°C) arc‐related granite, characterized by enrichment of fluid‐mobile elements and Nb‐Ta depletion. Its Sr‐Nd isotopes (87Sr/86Sri = 0.705200, εNdt = 1.1) suggest a product of evolved mantle‐derived melts. Together with detrital igneous zircons from Paleocene sequences, these observations reveal an Early Jurassic arc‐related low‐temperature (600 to 740°C) magmatism in the SW East China Sea. These arc‐related granitoids, along with those from SE Taiwan, could define an Early Jurassic NE‐SW trending Dongsha‐Talun‐Yandang magmatic arc zone along the East Asian continental margin paired with Jurassic accretionary complexes from SW Japan, East Taiwan to the West Philippines. This arc‐subduction complex assembly was associated with oblique subduction of the paleo‐Pacific slab beneath Eurasia, presumably responsible for Early Jurassic lithospheric extension in south China block.