Feng X.-L.,Changan University |
Wang W.-Y.,Changan University |
Liu F.-Q.,Changan University |
Li J.-G.,Shanxi Institute of Geophysical and Geochemical Survey |
Lu B.-L.,Changan University
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2014
The basement relief of rift basin is a non-smooth interface, which cannot be delineated by traditional gravity inversion method. Besides, the gravity observing surface does not coincide with the upper interface of the sedimentary layers in most situations, which should be an up-and-down surface alone. Therefore, the basin model should be a dual interface model composed of an upper interface and its basement. We have developed a 2D gravity inversion method to estimate basement relief of rift basin based on a dual interface model, it can be directly used with gravity data observed on rough terrain. The density contrast between the sediments and the basement is assumed to be decreased monotonically with depth according to the hyperbolic law. The sedimentary layers can be divided into a set of 2D vertical, juxtaposed prisms, whose horizontal sizes are assumed to be known. The top surfaces of prisms coincide with the upper interface of the sedimentary layers. The depths of their bottom surfaces represent the depth of the basement and are the parameters to be calculated from gravity data. We have introduced the total variation (TV) function as constraint to the sedimentary basin model in order to estimate the basement relief caused by faults. The result will be non-smooth, which can well accord with the basement relief of the rift basin. We also use a few known depth points to reduce the multiplicity of the inversion. We build an objective function composed of data misfit function, known depth misfit function and TV function, then we use nonlinear conjugate gradients (NLCG) algorithm to minimize it. Tests conducted with synthetic data show that the inversion method can estimate basement relief of rift basin and also can estimate basement relief of downwarped basin by changing the regularization parameter. We apply the method to process the field data from Huizhou depression in Pearl River Mouth Basin and Yuncheng-linfen Rift Basin, respectively. The results clearly reflect the characteristics of the basement, which can provide important information for researching the structure of sedimentary basin and oil-gas exploration.
Li J.-K.,Chinese Academy of Geological Sciences |
Wang D.-H.,Chinese Academy of Geological Sciences |
Liang T.,Changan University |
Xu Y.-M.,Southern Hunan Institute of Geology and Survey |
And 10 more authors.
Acta Geoscientica Sinica | Year: 2013
In this paper, through a comparative study of the geological and geochemical features of the typical ore concentration areas, the authors summarized the evolution of the crust and regional metallogenic regularities in the western, middle and eastern regions of the Nanling metallogenic belt. In the western region, magmas intruded into the late Paleozoic and early Mesozoic crust in a short time with an explosive type Sn mineralization in late Yanshanian epoch; in the middle region, magmas intruded into the late Paleozoic crust for a long time accompanied by polymetallic and multi-stage mineralization; in the eastern region, magmas intruded into early Paleozoic crust with the W mineralization peak in Yanshanian epoch, indicating that W mineralization might have occurred in the early Paleozoic crust of the western Nanling region. Correspondingly, the concealed granite, the Shizhuyuan-type deposit under Huangshaping type deposit, and the "basement" under the "five-storey" type W deposit should be the deep exploration targets in the western, middle and eastern Nanling regions, respectively. In addition, the deep exploration across the Qitianling intrusion in southern Hunan Province shows the existence of an upwelling pathway for mantle material indicated by artificial earthquake test at the center of the intrusion, where the later fine-grained granite contained more mantle material than the early coarse-grained granite in the light of Os isotope. In addition, the Sn-rich rhyolite subvolcanic rock vein that intruded into the early coarse grained granite in the Bailashui Sn deposit is a indicator of a later magmatism characterized by enrichment of mantle materiald in the depth of Qitianling intrusion. These metallogenic regularities in Nanling have indicating significance for W-Sn exploration in Tibet, i.e., to explore W-Sn mineralization in the depth of epi-mesothermal deposits in low erosion areas, and to explore the meso-hypothermal W-Sn deposits in the high erosion areas.
He H.,Chinese Academy of Geological Sciences |
Wang D.,Chinese Academy of Geological Sciences |
Su X.,China University of Geosciences |
Zhang Y.,Southern Hunan Institute of Geology and Survey |
And 4 more authors.
Geotectonica et Metallogenia | Year: 2014
The Qitianling granites in Chenzhou city, Hunan province, is a Mesozoic batholith. In this study, granitic rock samples across the Qitianling Geological-Geochemical-Geophysical profile were analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to measure the concentrations of rare metal elements, including Li, Rb, Sr, Cs, Nb, Ta, Be, Zr, Hf. The results showed that: (1) samples are significantly enriched in Li, Rb, Cs, Be and Zr, which are higher than the average concentrations of granite in South China, while elements like Sr, Nb and Ta are relatively depleted; (2) the concentrations of elements like Li, Rb, Cs increase gradually from west to east of the batholith, while the concentrations of Sr is gradually decrease. Elements like Nb, Ta and Hf remain stable except occasional "peak value"; (3) compared with the neighborhood Xianghualing pluton that is genetically related to the Xianghualing rare metal deposit, the Qitianling batholith is of the same geological stage, but the rare metal contents in Qitianling are not so high as to be a potential or as a target for exploration. That is to say, it is difficult to find new rare metal deposits as those formed around the Xianghualing pluton, considering the rare metal contents and stronge erosion of the Qitianling batholith. Based on the geophysical and geological characteristics of the rocks, it is considered that the Qitianling batholith was intruded from southeast to northwest, which might be the cause of rare element zonation across the Qitianling batholith.