The West-central sedimentary basin is one of the important areas for oil-gas exploration in Taiwan.Based on the data of oil wells and gravity surveys,the Kriging insertion equations and the depth-density empirical formula,the authors calculated the 3-D density structure and residual density structure of the sedimentary strata of the study area.Moreover,according to the Poisson equation and the FEM,the authors also computed the residual gravity anomaly caused by the 3-D residual density structure.The 3-D density structure shows that the Pleistocene to pre-Miocene sedimentary strata are broadly divided into four density layers at 0 to 6 km depths,i.e.the 2.0-2.30 g/cm~3,2.30-2.45 g/cm~3,2.45-2.60 g/cm~3 and 2.60-2.70 g/cm~3 layers.There is a relatively large sedimentary depression at 2-4 m km depths in the middle and lower parts of the continental margins of the Taichung basin.The density there is 0.05-0.10 g/cm~3 lower than that in the surroundings.The gravity calculation indicates that the residual gravity anomaly produced in the sedimentary strata in the area ranges from (-20) to (+15) mGal,and that the deep depression corresponds with a trap with a low negative anomaly,whose shape and value are consistent with those and the measured gravity anomaly.
Abstract Late Cretaceous (ca. 100–80 Ma) magmatism in southern Lhasa subterrane records critical geological events, which can provide important insights into the regional tectonic evolution and geodynamic process of South Tibet. This study presents new zircon U-Pb ages, whole-rock geochemistry and Sr-Nd-Fe and zircon U-Pb-O isotopic data for two dioritic plutons in the southern Lhasa subterrane. Secondary ion mass spectrometry U-Pb dating on magmatic zircons from these rocks yielded a consistent age at ca. 90 Ma. The rocks exhibit variable SiO2 contents (52–59 wt%), high Fe2O3T contents (7.1–10.0 wt%), and low K2O/Na2O ratios (0.18–0.48). Most samples have high Al2O3 (17.0–19.5 wt%) and Sr (493–678 ppm), but low Yb (0.9–2.4 ppm) and Y (9–25.2 ppm) concentrations, and thus high Sr/Y (23–74) ratios, typical of adakite-like geochemical features. The adakitic rocks have relatively uniform initial 87Sr/86Sr isotopic ratios (0.7043–0.7046) and εNd(t) values (+3.67 to +4.16), indicating derivation from similar parental magmas. The δ56Fe values of whole-rock samples vary from 0.011 to 0.091‰ with an average of 0.045 ± 0.046‰ (two standard deviations), reflecting a homogeneous Fe isotopic composition, which is associated with melt-mantle interaction. In addition, the rocks are characterized by relatively high zircon δ18O values of 5.72–7.19‰, indicating the involvement of an 18O-enriched component during magma formation. The calculation of Al-in-hornblende barometer indicates that the adakitic rocks were emplaced at pressures of 6.4–9.8 kbar. Therefore, it is proposed that the adakitic rocks were most likely generated by partial melting of mantle wedge that had been previously modified by slab-melts at a relatively shallow depth, followed by minor fractional crystallization of hornblende. Taking into account previously published data in the southern Lhasa subterrane, we suggest that the ca. 90 Ma magmatism could be related to a period of Neo-Tethyan oceanic slab roll-back, which can provide new insights into the revolution process of the Neo-Tethyan ocean realm and the accretion of the Himalaya-Tibetan Plateau.
Abstract To improve the accuracy of quantitative precipitation estimation (QPE) in complex terrain, a new rainfall rate estimation algorithm has been developed and applied on two C-band dual-polarization radars in Taiwan. In this algorithm, the specific attenuation A is utilized in the rainfall rate R estimation, and the parameters used in the R(A) method were estimated using the local drop size distribution (DSD) and drop shape relation (DSR) observations. In areas of complex terrain where the lowest antenna tilt is completely blocked, observations from higher tilts are used in radar QPE. Correction of the vertical profile of rain rate estimated by the R(A) algorithm (VPRA) is applied to account for the vertical variability of rain. It has been found that the VPRA correction improved the accuracy of estimated rainfall in severely blocked areas. The R(A)–VPRA scheme was tested for different precipitation cases including typhoon, stratiform, and convective rain. Compared to existing rainfall estimation algorithms such as rainfall–reflectivity (R–Z) and rainfall–specific differential phase (R–KDP), the new method is able to provide accurate and robust rainfall estimates when the radar reflectivity is miscalibrated or significantly biased by attenuation or when the lower tilt of the radar beam is significantly blocked.
The input files necessary for the numerical subduction models contained within Dong et al.(submitted to GRL). The version of ASPECT and plugin refer to Holt and Condit ,2021, G-cubed. （https://doi.org/10.5281/zenodo.4543413）
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