Abstract:In the arc (basin)-back area of the Yidun arc belt in the north segment of the Sanjiang tectonic zone, southwestern China, there occurs a post-orogenic granite belt extending for more than 300 km in NNW direction. It strides across two different tectonic units of the arc (basin)-back area and the subduction area, and is accompanied by extensive Ag-Sn polymetallic mineralizations. More than ten granite bodies have very similar geochemical characteristics: high SiO 2 (73.8~76.3 wt%) and K 2 O+Na 2 O (7.16~8.41 %), and low Al 2 O 3 (11.9~13.6 %), CaO (0.46~1.54 %) and MgO (0.16~0.61 %), as well as high enrichment of Nb, Ta, Ga and Y, and strong depletion of Sr and Eu. Most of these features are peculiar to A-type granite. Rb-Sr and 40 Ar/ 39 Ar isotopic dating results indicate that the formation ages of the granites decrease from 103.7 Ma of the north end to 75.2 Ma near the south end, and that the magmatism became younger from north to south. The tectonic environment analysis clearly reveals that they were formed in post-orogenic within-plate extension settings. The magma genesis was controlled by a united crustal extension regime after the arc-continent collision. The granites have low ε Nd values ranging from -4.96 to -8.40, whereas the ε Sr values vary greatly ranging from -31.7 to 296, reflecting that the source composition transited from mantle -differentiated igneous rocks in the north to basement -dominated metamorphosed sedimentary rocks in the south. Under high temperature and water-absent conditions, the anatexes of the crustal rocks made a great amount of plagioclase separated from melts and left in magma sources. Through this mechanism, the post-orogenic granites took geochemical characteristics such as low Al 2 O 3 and CaO, and strong depletion of Sr and Eu.

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Surface-upwelling longwave radiation (LWUP) is an important component of the surface radiation budget. Under the general framework of the hybrid method, the linear models and the multivariate adaptive regression spline (MARS) models are developed to estimate the 750 m instantaneous clear-sky LWUP from the top-of-atmosphere (TOA) radiance of the Visible Infrared Imaging Radiometer Suite (VIIRS) channels M14, M15, and M16. Comprehensive radiative transfer simulations are conducted to generate a huge amount of representative samples, from which the linear model and the MARS model are derived. The two models developed are validated by the field measurements collected from seven sites in the Surface Radiation Budget Network (SURFRAD). The bias and root-mean-square error (RMSE) of the linear models are −4.59 W/m 2 and 16.15 W/m 2 , whereas those of the MARS models are −5.23 W/m 2 and 16.38 W/m 2 , respectively. The linear models are preferable for the production of the operational LWUP product due to its higher computational efficiency and acceptable accuracy. The LWUP estimated by the linear models developed from VIIRS is compared to that retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS). They agree well with each other with bias and RMSE of −0.15 W/m 2 and 25.24 W/m 2 respectively. This is the first time that the hybrid method has been applied to globally estimate clear-sky LWUP from VIIRS data. The good performance of the developed hybrid method and consistency between VIIRS LWUP and MODIS LWUP indicate that the hybrid method is promising for producing the long-term high spatial resolution environmental data record (EDR) of LWUP.