基于水准剖面的山西断陷带现今活动性研究

根据跨山西断陷带的水准剖面观测资料,计算其垂直形变量和垂直形变速率,研究其现今垂直活动性。2006年以来的垂直形变揭示,山西断陷带东北段延怀盆地和蔚县盆地呈掀斜上升活动,北段阳原盆地和大同盆地以下降活动为主,晋中盆地为上下波动,临汾盆地呈现上升活动。2013年山西断陷带活动出现转折性变化,蔚县盆地大幅度下降,大同盆地、代县-定襄盆地、晋中盆地和临汾盆地均呈现不同程度的上升。     

西安地区地裂缝带Q3原状黄土流变特性试验研究

汾渭盆地是我国乃至世界上地裂缝最为发育、灾害最为严重的地区。考虑在漫长的地质历史过程中黄土的流变特性对地裂缝破裂扩展模式的影响,采用分级循环加卸载方式,对西安地区长安地裂缝（fc1）带Q3原状黄土进行了不同围压下的固结不排水三轴流变特性试验,得到了地裂缝带Q3原状黄土的蠕变加、卸载曲线和应变速率与时间关系曲线。试验结果表明,不同围压下地裂缝带Q3原状黄土表现为低应力下为减速蠕变,高应力下为减速蠕变和等速蠕变的特征。并基于统一流变力学模型理论,建立了适用于西安地区地裂缝带Q3原状黄土的三维蠕变本构模型,获得了相应的本构模型参数。该成果为研究隐伏地裂缝破裂扩展模式及其力学机制奠定了基础。     

Basin evolution associated to curved thrusts: The Prerif Ridges in the Volubilis area (Rif Cordillera,Morocco)

The Volubilis Basin is located between two structural arcs formed by the Prerif Ridges that developed during and after sedimentation. The arcs correspond with W- to WSW-verging anticline culminations, limited, to the north by a NE-SW strike-slip lateral ramp. Sedimentary infill took place during two stages of ridge formation and propagation. The first stage occurred in the Middle Miocene-early Tortonian and was determined by the deposition of the Nappe Prérifaine in the northern part of the basin, and continental and marine sediments over the Prerif Ridges. The second one, Late Miocene in age (Tortonian–Messinian), corresponds to the sedimentation of calcarenites and bioclastic limestones at the basin edges, with a lateral transition to white and blue marls toward the center of the basin. There is clear evidence of synsedimentary deformation, suggesting the interaction of sedimentation and tectonics. Geophysical data allow us to characterize the stratigraphic architecture of the Volubilis Basin and the geometry of the top of the Paleozoic basement. An approximately N–S Tortonian–Messinian asymmetric depocenter is located close to the front of the eastern arc. This research illustrates the nucleation, progressive thrust bending and segmentation, and the propagation of folds interacting with sedimentation. Thrust nucleation agrees with Paleozoic basement highs under the detachment surface. The progressive development of these tectonic structures conditioned the formation, segmentation and final continentalization of the Volubilis Basin, which can be considered as a piggy-back basin.     

Geodetic and geological evidence of active tectonics in south-western Sicily (Italy)

Integrated geological, geodetic and marine geophysical data provide evidence of active deformation in south-western Sicily, in an area spatially coincident with the macroseismic zone of the destructive 1968 Belice earthquake sequence. Even though the sequence represents the strongest seismic event recorded in Western Sicily in historical times, focal solutions provided by different authors are inconclusive on possible faulting mechanism, which ranges from thrusting to transpression, and the seismogenic source is still undefined. Interferometric (DInSAR) observations reveal a differential ground motion on a SW–NE alignment between Campobello di Mazara and Castelvetrano (CCA), located just west of the maximum macroseismic sector. In addition, new GPS campaign-mode data acquired across the CCA alignment documents NW–SE contractional strain accumulation. Morphostructural analysis allowed to associate the alignment detected through geodetic measurements with a topographic offset of Pleistocene marine sediments. The on-land data were complemented by new high-resolution marine geophysical surveys, which indicate recent contraction on the offshore extension of the CCA alignment. The discovery of archaeological remains displaced by a thrust fault associated with the alignment provided the first likely surface evidence of coseismic and/or aseismic deformation related to a seismogenic source in the area. Results of the integrated study supports the contention that oblique thrusting and folding in response to NW–SE oriented contraction is still active. Although we are not able to associate the CCA alignment to the 1968 seismic sequence or to the historical earthquakes that destroyed the ancient Greek city of Selinunte, located on the nearby coastline, our result must be incorporated in the seismic hazard evaluation of this densely populated area of Sicily.     

欧亚地震带地震活动增强与中国大陆地区7级以上地震发生的关系分析

根据欧亚地震带7级以上地震释放能量与全球7级以上地震释放总能量之比,利用χ²检验方法对欧亚地震带地震活动增强与中国大陆地区7级以上地震发生的关系进行了统计检验。结果表明,当出现欧亚带年地震释放能量比高于50%且有8级以上地震发生时,其后3年内中国大陆地区将有发生多次7级以上地震或8级地震的可能性,这个关系在10%的显著水平下通过显著性检验。     

Chronology and petrogenesis of the Hejiazhuang granitoid pluton and its constraints on the Early Triassic tectonic evolution of the South Qinling Belt

The Hejiazhuang pluton is located in the South Qinling Tectonic Belt(SQTB)in the north side of the Mianxian-Lueyang Suture Zone,and consists dominantly of granodiorites.LA-ICP-MS zircon U-Pb dating and Lu-Hf isotopic analyses reveal that these granodiorites of the Hejiazhaung pluton emplaced at~248 Ma,and show a large variation in zirconεHf(t)values from4.8 to 8.8.These granodiorite samples are attributed to high-K to mid-K calc-alkaline series,and characterized by high SiO2(66.6%–70.0%),Al2O3(15.04%–16.10%)and Na2O(3.74%–4.33%)concentrations,with high Mg#(54.2–61.7).All samples have high Sr(627–751 ppm),Cr(55–373 ppm)and Ni(17.2–182 ppm),but low Y(5.42–8.41 ppm)and Yb(0.59–0.74 ppm)concentrations with high Sr/Y ratios(84.90–120.66).They also display highly fractionated REE patterns with(La/Yb)N ratios of 18.9–34.0 and positive Eu anomalies(δEu=1.10–2.22)in the chondrite-normalized REE patterns.In the primitive mantle normalized spidergrams,these samples exhibit enrichment in LILEs but depletion in Nb,Ta,P and Ti.These geochemical features indicate that the granodioritic magma of the Hejiazhuang pluton was derived from the partial melting of hybrid sources comprising the subducted oceanic slab and sediments,and the melts were polluted by the mantle wedge materials during their ascent.The emplacement ages and petrogenesis of the Hejiazhuang pluton prove that the initial subduction of the Mianlue oceanic crust occurred at~248 Ma ago,and the SQTB was still under subduction tectonic setting in the Early Triassic.     

Diagenetic fluid evolution and water-rock interaction model of carbonate cements in sandstone: An example from the reservoir sandstone of the Fourth Member of the Xujiahe Formation of the Xiaoquan-Fenggu area,Sichuan Province,China

Carbonate cement is the most abundant cement type in the Fourth Member of the Xujiahe Formation in the Xiaoquan-Fenggu area of the West Sichuan Depression. Here we use a systematic analysis of carbonate cement petrology, mineralogy, carbon and oxygen isotope ratios and enclosure homogenization temperatures to study the precipitation mechanism, pore fluid evolution, and distribution of different types of carbonate cement in reservoir sand in the study area. Crystalline calcite has relatively heavy carbon and oxygen isotope ratios(δ13C = 2.14‰, δ18O = -5.77‰), and was precipitated early. It was precipitated directly from supersaturated alkaline fluid under normal temperature and pressure conditions. At the time of precipitation, the fluid oxygen isotope ratio was very light, mainly showing the characteristics of a mixed meteoric water-seawater fluid(δ18O = -3‰), which shows that the fluid during precipitation was influenced by both meteoric water and seawater. The calcite cement that fills in the secondary pores has relatively lighter carbon and oxygen isotope ratios(δ13C = -2.36‰, δ18O = -15.68‰). This cement was precipitated late, mainly during the Middle and Late Jurassic. An important material source for this carbonate cement was the feldspar corrosion process that involved organic matter. The Ca2+, Fe3+ and Mg2+ ions released by the clay mineral transformation process were also important source materials. Because of water-rock interactions during the burial process, the oxygen isotope ratio of the fluid significantly increased during precipitation, by about 3‰. The dolomite cements in calcarenaceous sandstone that was precipitated during the Middle Jurassic have heavier carbon and oxygen isotope ratios, which are similar to those of carbonate debris in the sandstone(δ13C = 1.93‰, δ18O = -6.11‰), demonstrating that the two are from the same source that had a heavier oxygen isotope ratio(δ18O of about 2.2‰). The differences in fluid oxygen isotope ratios during cement precipitation reflect the influences of different water-rock interaction systems or different water-rock interaction strengths. This is the main reason why the sandstone containing many rigid particles(lithic quartz sandstone) has a relatively negative carbon isotope ratio and why the precipitation fluid in calcarenaceous sandstone has a relatively heavier oxygen isotope ratio.     

Characteristics and accumulation mechanisms of the Dongfang 13-1 high temperature and overpressured gas field in the Yinggehai Basin,the South China Sea

The Dongfang 13-1 is located in the diapiric structure belt of the Yinggehai Basin. The formation pressure of its main gas reservoir in the Miocene Huangliu Formation is up to 54.6 MPa(pressure coefficient=1.91) and the temperature is as high as 143°C(geothermal gradient 4.36°C/100 m), indicating that it is a typical high-temperature and overpressured gas reservoir. The natural gas is interpreted to be coal-type gas derived from the Miocene mature source rocks containing type II2-III kerogens as evidenced by high dryness index of up to 0.98 and heavy carbon isotopes, i.e., the δ13C1 ranging from -30.76‰ to -37.52‰ and δ13C2 ranging from -25.02‰ to -25.62‰. The high temperature and overpressured Miocene petroleum system is related mainly to diapir in the Yinggehai Basin and contains more pore water in the overpressured reservoirs due to undercompaction process. The experimental and calculated results show that the solubility of natural gas in formation water is as high as 10.5 m3/m3 under the temperature and pressure conditions of the Sanya Formation, indicating that at least part of the gas may migrate in the form of water-soluble phase. Meanwhile, the abundant gas source in the Basin makes it possible for the rapid saturation of natural gas in formation water and exsolution of soluble gas. Therefore, the main elements controlling formation of the Dongfang 13-1 gas pool include that(1) the diapir activities and accompanying changes in temperature and pressure accelerate the water-soluble gas exsolution and release a lot of free gas;(2) submarine fan fine sandstone in the Huangliu Formation provides good gas-water segregation and accumulation space; and(3) the overlying overpressured mud rocks act as effective caps. The accumulation mechanism reveals that the high temperatural and high pressure structure belt near the diapir structures has a good potential for large and medium-sized gas field exploration.     

Formation mechanism of in-situ volcanic reservoirs in eastern China:A case study from Xushen gasfield in Songliao Basin

A large number of in-situ volcanic reservoirs have been discovered from the Meso-Cenozoic rift basin group in eastern China.Based on drilling results in combination with geological and geophysical analysis,a case study from the Early Cretaceous Xujiaweizi fault-depression shows that the formation mechanism of in-situ volcanic reservoirs is characterized by"fault-controlled body,body-controlled facies,facies-controlled reservoir,and reservoir-controlled accumulation".In other words,deep faults control the volcanic eruption type,volcanic body,and gas reservoir distribution;the volcanic body determines the spatial distribution of volcanic facies and volcanic gas reservoir size;the volcanic facies control reservoir physical properties and effective thickness of gas formation;the volcanic reservoir properties control gas reservoir type and gas productivity.The result is useful to guiding the discovery of in-situ volcanic gas reservoirs in faulted basins in both theory and practice.     

安徽巢湖地区中二叠统栖霞组灰岩中燧石成因

安徽省巢湖地区中二叠统栖霞组以发育一套滨海沼泽－浅海碳酸盐台地环境为主的细碎屑岩至碳酸盐岩沉积建造为特征,灰岩中常见结核状及条带状燧石。燧石多为椭球状和串珠状,部分燧石与灰岩间发育宽约0.5 cm的过渡带。镜下观察灰岩为微晶生物碎屑灰岩;过渡带也多由微晶方解石组成,多数钙质生物壳体被石英充填或半充填,扫描电镜下可见方解石微溶、石英充填溶孔的现象;燧石主要为隐晶及微晶石英,生物碎屑类型与灰岩中基本一致,且多被石英交代。岩石学特征表明死亡的生物在腐烂降解过程中形成的有机酸抑制了碳酸钙的沉淀,并使部分生物碎屑及灰泥发生溶蚀,胶质二氧化硅沉淀,形成燧石结核。燧石中w(Al)/w(Al+Fe+Mn)平均值为0.63,远大于热水沉积硅质岩的最大值0.35;Fe/Ti平均值为9.5,小于热水成因的最小值20;Al-Fe-Mn三角图投点位于非热液成因区域;燧石中Al₂O₃含量平均值为0.20%,远高于MgO、Na₂O、K₂O的含量。分析认为,该区燧石结核的二氧化硅可能来源于陆源物质。