Journal of China University of Geosciences最新文献

By a detailed investigation of geometry and kinematics of the Shangma fault in Dabieshan, three different crust levels of extension movement have been recognized in sequence from the deep to the shallow:

In this study, Raman scattering measurements were obtained for momo corals covering their typical range of colors. Three different excitation wavelengths (785, 633, 514 nm) are used for the same samples at the same points. All the samples show the two major Raman features of polyenic compounds assigned to double carbon-carbon (C=C) stretching vibration at approximately 1 500 cm⁻¹ and single carbon-carbon (C—C) stretching vibration at approximately 1 130 cm⁻¹ bond stretching mode. These peaks are not detected in the corresponding white parts of momo corals. However, some changes in intensities, shape, and position of C=C stretching vibrations of the same point are observed by using different excitation wavelengths. The exact position of C—C stretching vibration of polyenic molecules depends strongly on the number of double bonds contained in their polyenic chain. In addition, the number of double bonds contained in the polyenic chains shows that different colors of the red momo coral are caused by different mixtures of polyenic compounds.

Zircon U-Pb age, trace elements, and Hf isotopes were determined for granulite and gneiss at Huangtuling, which is hosted by ultrahigh-pressure metamorphic rocks in the Dabie orogen, east-central China. Cathodoluminescence (CL) images reveal core-rim structure for most zircons in the granulite. The cores show oscillatory zoning, relatively high Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, and high rare earth element (HREE)-enriched pattern, consistent with magmatic origin. They gave a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of (2 766 ± 9) Ma, dating magma emplacement of protolith. The rims are characterized by sector or planar zoning, low Th/U and ¹⁷⁶Lu/¹⁷⁷Hf ratios, negative Eu anomalies and flat HREE patterns, consistent with their formation under granulite-facies metamorphic conditions. Zircon U-Pb dating yields an age of (2 029 ± 13) Ma, which is interpreted as a record of metamorphic event during the assembly of the supercontinent Columbia. The gneiss has a protolith age of (1 982 ± 14) Ma, which is similar to the zircon U-Pb age for the granulite-facies metamorphism, suggesting complementary processes to granulite-facies metamorphism and partial melting. A few inherited cores with igneous characteristics have ²⁰⁷Pb/²⁰⁶Pb ages of approximately 3.53, 3.24, and 2.90 Ga, respectively, suggesting the presence of Mesoarchean to Paleoarchean crustal remnants. A few Triassic and Cretaceous metamorphic ages were obtained, suggesting the influences by the Triassic continental collision and postcollisional collapse in response to the Cretaceous extension. Comparing with abundant occurrence of Triassic metamorphic zircons in ultrahigh-pressure eclogite and granitc gneiss from the Dabie-Sulu orogenic belt, however, very limited availability of aqueous fluid or hydrous melt is evident for zircon growth in the Huangtuling granulite and gneiss during the continental collision. The magmatic protolith zircons from the granulite show a large variation in ¹⁷⁶Hf/¹⁷⁷Hf ratios from 0.280 809 to 0.281 289, corresponding to ɛ_Hf(t) values of -7.3 to 6.3 and Hf model ages of 2.74 to 3.34 Ga. The 2.90 Ga inherited zircons show the similar Hf isotope features. These indicate that both growth of juvenile crust and reworking of ancient crust took place at the time of zircon formation. It is inferred that the Archean basement of the Yangtze block occurs in the north as the Dabie orogen, with ca. 2.90–2.95 Ga and 2.75–2.80 Ga as two major episodes of crustal formation.

To look for gas hydrate, 22 multi-channel and 3 single-channel seismic lines on the East China Sea (ECS) shelf slope and at the bottom of the Okinawa Trough were examined. It was found that there was indeed bottom simulating reflector (BSR) occurrence, but it is very rare. Besides several BSRs, a gas seepage was also found. As shown by the data, both the BSR and gas seepage are all related with local geological structures, such as mud diapir, anticline, and fault-controlled graben-like structure. However, similar structural “anomalies” are quite common in the tectonically very active Okinawa Trough region, but very few of them have developed BSR or gas seepage. The article points out that the main reason is probably the low concentration of organic carbon of the sediment in this area. It was speculated that the rare occurrence of gas hydrates in this region is governed by structure-controlled fluid flow. Numerous faults and fractures form a network of high-permeability channels in the sediment and highly fractured igneous basement to allow fluid circulation and ventilation. Fluid flow in this tectonic environment is driven primarily by thermal buoyancy and takes place on a wide range of spatial scales. The fluid flow may play two roles to facilitate hydrate formation: to help gather enough methane into a small area and to modulate the thermal regime.

The appearance of 3D laser scanning technology is one of the most important technology revolutions in surveying and mapping field. It can be widely used in many interrelated fields, such as engineering constructions and 3D measurements, owing to its prominent characteristics of the high efficiency and high precision. At present its application is still in the initial state, and it is quite rarely used in China, especially in geotechnical engineering and geological engineering fields. Starting with a general introduction of 3D laser scanning technology, this article studies how to apply the technology to high rock slope investigations. By way of a case study, principles and methods of quick slope documentation and occurrence measurement of discontinuities are discussed and analyzed. Analysis results show that the application of 3D laser scanning technology to geotechnical and geological engineering has a great prospect and value.