Petrology and PGE Abundances of High‐Cr and High‐Al Podiform Chromitites and Peridotites from the Bulqiza Ultramafic Massif,Eastern Mirdita Ophiolite,Albania

The Bulqiza ultramafic massif, which is part of the eastern Mirdita ophiolite of northern Albania, is world renowned for its high-Cr chromitite deposits. High-Cr chromitites hosted in the mantle section are the crystallized products of boninitic melts in a supra-subduction zone (SSZ). However, economically important high-Al chromitites are also present in massive dunite of the mantle-crust transition zone (MTZ). Chromian-spinel in the high-Al chromitites and dunites of the MTZ have much lower Cr# values (100Cr/(Cr+Al)) (47.7–55.1 and 46.5–51.7, respectively) than those in the high-Cr chromitites (78.2–80.4), harzburgites (72.6–77.9) and mantle dunites (79.4–84.3). The chemical differences in these two types of chromitites are reflected in the behaviors of their platinum-group elements (PGE). The high-Cr chromitites are rich in IPGE relative to PPGE with 0.10–0.45 PPGE/IPGE ratios, whereas the high-Al chromitites have relatively higher PPGE/IPGE ratios between 1.20 and 7.80. The calculated melts in equilibrium with the high-Cr chromitites are boninitic-like, and those associated with the high-Al chromitites are MORB-like but with hydrous, oxidized and TiO2-poor features. We propose that the coexistence of both types of chromitites in the Bulqiza ultramafic massif may indicates a change in magma composition from MORB-like to boninitic-like in a proto-forearc setting during subduction initiation.     

The Fragmentation in a Protoplanetary Disk and the Properties of the Resultant Self-Gravitating Clumps

We study the fragmentation properties in the protoplanetary disk and properties of the resultant self-gravitating clumps using our newly constructed disk model. Our disk model includes the mass inflall term from a molecular cloud core and the photoevaporation winds effect. We adopt the conventional fragmentation criterion to judge whether a protoplanetary disk can fragment. In this work, we follow our previous work to investigate the properties of the resultant self-gravitating clumps. In our calculation, the initial masses of the resultant self-gravitating clumps lie in the range of tens of M_J to more than one hundred of M_J, where M_J is the Jupiter mass. These initial masses can seemingly account for the masses of extrasolar planets in magnitude. We also calculate the subsequent gas accretion of clumps in 1.27 × 10⁴ yr after the formation of self-gravitating clumps. We find that the subsequent gas accretion of self-gravitating clumps is very efficient, and the clump masses grow to hundreds of M_J and the physical radii R_c of clumps increase to about 10 AU. Additionally, we also calculate the orbital migration of clumps. We find that most clumps have short migration timescale to be accreted onto the protostar, and only a small fraction of clumps have long migration timescale (>10⁶ yr) to successfully become gas giant planets. These results are consistent with previous studies.     

A nonlinear multiparameter prestack seismic inversion method based on hybrid optimization approach

Multiparameter prestack seismic inversion is one of the most powerful techniques in quantitatively estimating subsurface petrophysical properties. However, it remains a challenging problem due to the nonlinearity and ill-posedness of the inversion process. Traditional regularization approach can stabilize the solution but at the cost of smoothing valuable geological boundaries. In addition, compared with linearized optimization methods, global optimization techniques can obtain better results regardless of initial models, especially for multiparameter prestack inversion. However, when solving multiparameter prestack inversion problems, the application of standard global optimization algorithms maybe limited due to the issue of high computational cost (e.g., simulating annealing) or premature convergence (e.g., particle swarm optimization). In this paper, we propose a hybrid optimization-based multiparameter prestack inversion method. In this method, we introduce a prior constraint term featured by multiple regularization functions, intended to preserve layered boundaries of geological formations; in particular, to address the problem of premature convergence existing in standard particle swarm optimization algorithm, we propose a hybrid optimization strategy by hybridizing particle swarm optimization and very fast simulating annealing to solve the nonlinear optimization problem. We demonstrate the effectiveness of the proposed inversion method by conducting synthetic test and field data application, both of which show encouraging results.     

Synthesis and characterisation of a multifunctional oil-based drilling fluid additive

An oil-based drilling fluid additive H-DEA (or humic acid-cocamide diethanolamine) was synthesised using humic acid and cocamide diethanolamine as raw materials. The rheological behaviors of H-DEA showed that the synthesised product has the good properties in both decreasing the filtrate loss and improving rheology property of oil-based drilling fluids compared with other commercially available additives. Under the optimal additive amount of 3%, both API filtrate loss and yield point changed remarkably from 5.40 to 0.41 mL and 9.0 to 25.6 Pa, respectively. Furthermore, differential scanning calorimetry (DSC) showed that H-DEA has good thermal stability in a wide temperature range up to 170 °C. Infrared spectroscopy (IR) and rheological analysis revealed that the possible mechanism of the multifunctional effects may be attributed to the existing of high density of strong polar groups, hydrogen bonds, electrostatic forces, and intermolecular association on H-DEA molecular structure. The results of the study showed that the synthesised H-DEA can be potentially used as a multifunctional oil-based drilling fluid additive in oil-drilling excavation.     

Geology of the Yap Trench: new observations from a transect near 10°N from manned submersible Jiaolong

This paper describes the petrology and geochemistry of rocks from the Yap Trench acquired by three dives of the Jiaolong research submarine. Combining the geophysical data and submersible observations, this paper describes the geomorphology, shallow structures, and sedimentology of the Yap Trench and further discusses the tectonics and activities of this region. Two obvious slope breaks are found on the landward slope, and horsts and grabens with small fault offsets are observed in the ocean-ward slope of the trench. Peridotites sampled from the Yap Trench inner wall are highly depleted subduction-related mantle residues. Volcanic rocks in the northern segment of the trench have subduction-related characteristics that Yap fore-arc rocks underwent metasomatism during Cenozoic subduction. The rocks with remarkable lithologic difference from lithospheric mantle and upper crust sampled in the break slopes suggest that the slope break area may represent a lithologic boundary or transition zone. The landward slope of the Yap Trench was removed by subduction erosion as a result of collision with the Caroline Ridge. The bending of the down-going plate caused normal faults, horsts, and grabens with little or no sediments indicating that the Caroline Ridge is subducting beneath the Yap arc along the trench even though the convergence rate is very slow.     

渝东北城口地区Y1井页岩有机地球化学特征及勘探前景

基于钻井资料,以总有机碳(TOC)、干酪根显微组分、等效镜质体反射率(Ro)及碳同位素等测试数据系统分析了渝东北城口地区Y1井五峰组—龙马溪组页岩的有机地球化学特征,利用页岩流体包裹体的显微特征、均一温度及激光拉曼数据深入分析了Y1井页岩气成藏特征。结果表明:Y1井上奥陶统五峰组—下志留统龙马溪组炭质页岩发育,TOC含量2%的富含有机质页岩厚度达83 m,干酪根类型以Ⅰ型干酪根为主,处于湿气生烃阶段。页岩裂缝脉体中大量烃包裹体和富含甲烷气体的含烃盐水包裹体证实城口地区五峰组—龙马溪组页岩发生了充足页岩气供给,具有高均一温度、高盐度的伴生盐水包裹体表明城口地区页岩气成藏时期的保存条件良好。这些Y1井页岩有机地球化学特征研究成果揭示了城口地区下古生界具备良好的页岩气勘探前景。     

川北地区寒武系筇竹寺组钙质结核裂缝充填物特征及指示意义

川北地区寒武系筇竹寺组钙质结核泥页岩中早成岩期钙质结核较发育,结核裂缝中见多期次矿物充填。为揭示钙质结核裂缝形成机理,本次结合岩石学特征及地球化学特征等开展系统研究。川北筇竹寺组钙质结核裂缝中见三~四期矿物充填。第一期微晶方解石表面较脏,阴极发光暗淡,δ13C_(PDB)、δ18O_(PDB)平均值分别为-4.26‰及-7.69‰;第二期为细—中晶粒状方解石充填,阴极发光为橘黄色,流体包裹体均一温度为平均值为86.4℃,δ13C_(PDB)、δ18O_(PDB)平均值分别为-3.15‰及-7.41‰;第三期为粗晶方解石充填阴极发光暗淡,流体包裹体均一温度平均值为96.6℃,δ~(13)C_(_(PDB))、δ~(18)O_(_(PDB))平均值分别为-1.73‰及-10.28‰;第四期为重晶石充填。结合区域构造史—热演化史分析表明,钙质结核裂缝中四期充填物分别指示早期脱水、烃源岩早成熟期生烃、加里东构造运动抬升释压及深埋藏期硫酸盐热还原作用事件。     

黑龙江铁力鹿鸣斑岩型钼矿床埃达克岩的发现及其地质意义

鹿鸣钼矿是伊春-延寿成矿带内近年发现的大型斑岩钼矿,矿区主要出露含矿的二长花岗岩、花岗斑岩,不含矿的花岗闪长岩及似斑状花岗闪长岩四种岩性。二长花岗岩与花岗斑岩具有相似的低Sr高Y等地球化学特征,形成于194.8±0.7Ma~184Ma前后的早侏罗世,是斑岩型矿床的赋矿围岩。花岗闪长岩及似斑状花岗闪长岩含有暗色岩包体,主要为高钾钙碱性系列岩石,但以高Sr、低Y及富Na为特征,部分地球化学指标与中国东部埃达克岩极为相似,形成于176.2±2.1Ma并与辉钼矿Re-Os法获得的成矿年龄一致,被认定为斑岩型矿床的成矿母岩。高Sr和低Sr两类花岗岩形成于不同的构造背景,与中生代时期中国东部及其邻区几次重大地质事件密切相关。鹿鸣斑岩型钼矿床与中侏罗世太平洋板块俯冲在高氧逸度条件下熔融形成的埃达克质岩浆高侵位有关。鹿鸣矿区埃达克岩的发现表明中侏罗世太平洋板块已经发生了萎缩与消减,与之相关的岩浆作用及成矿应该具有广泛的区域性,扎实的岩石学工作可为区域更多斑岩型矿床的发现提供线索。