任楼井田地质构造特征及两期古构造应力场的研究

通过对皖北矿务局任楼矿井宏观地质构造特征及小断裂统计分析,得出该井田含煤田地层沉积后,历经两期或两期以上地质构造运动。两期应力场大角度横跨叠加复合的结果,形成NNW─NE（345°～55°）方位的应力拉伸区,该方位构造形迹一般是压性、压剪性或先引张后压紧等力学性质,是良好的隔水、阻气（瓦斯）构造;而从NNW～SWW（345°－240°）方位为应力压缩区,该方位的中高倾角正断层,一般开启性较好,呈张性、张剪性或先压紧后松张,是良好的储、导水和排气通道。     

An Intelligent Method for Geochemical Discrimination of Tectonic Settings of Basalt Based on Olivine Composition: GWO-SVM Method and its VerificationEI北大核心CSCD

Geochemical discrimination of tectonic settings of basalts has been an important research direction of geochemistry for decades. Olivine is one of the earliest crystallized minerals of basaltic magma, which records a lot of hidden information of the formation and evolution of the magma. Therefore, basic elements in olivine are used to discriminate three tectonic settings, including the mid-ocean ridge basalt (MORB), ocean island basalt (OIB) and island arc basalt (IAB). However, it is still difficult to accurately discriminate the tectonic settings by using these diagrams. The machine learning algorithm is introduced to solve the aforementioned problem. The classification performance of the machine learning discrimination method largely depends on the rationality of parameter determination. To this end, the paper proposes a coupling intelligent method for geochemical discrimination of tectonic settings using olivine composition of the basalts based on the grey wolf optimizer (GWO)-optimized support vector machine (SVM), or GWO-SVM for short. GWO is used to seek the optimal parameter combination of SVM to form the optimal mapping relationship between basic elements in olivine and basalt tectonic settings, so as to realize the accurate discrimination of MORB, OIB and IAB. In addition, according to the published geochemical data of basalt samples, the discrimination performance of GWO-SVM is evaluated by means of the simulation experiment, hold-out validation and k-fold cross-validation. The evaluation results are represented by the confusion matrix and its derived evaluation indicators. The results show that GWO-SVM can discriminate the tectonic settings of the basalts based on olivine compositions with overall classification accuracy of up to 85%. Thus, in comparison with the traditional discrimination diagram method, the machine learning discrimination method based on multi-algorithm fusion can significantly improve the discrimination accuracy of basalt tectonic settings. © 2020, Science Press. All right reserved.     

Reappraisal of the ‘Cullenstown Formation’: Implications for the Lower Palaeozoic tectonic history of SE Ireland

The structurally attenuated greenschist facies metasedimentary succession at Cullenstown Strand in south Co. Wexford comprises three formations which in stratigraphic order are (1) the Quartzite Formation, (2) the Greywacke/Quartzite Formation, and (3) the Greywacke Formation. The entire sequence is inverted and lies within the lower limb of a large scale overturned D1 anticlinal structure that closes towards the southeast. The three formations are lithologically and sedimentologically similar to the Shelmaliere Quartzite, the Cullentra Greywacke, and Newtown Greywacke Formations of the Bray Group in the Forth Mountain - Ferrycarrig area that probably lie on the normal limb of the D1 structure. The Cullenstown strata are therefore considered to be part of the Bray Group in southeast Leinster, and hence Cambrian in age. The rocks were affected by three major phases of deformation. D1 produced an overturned anticline containing an important tectonic slide. The D1 structures are modified by upright D2 and D3 structures, but from regional considerations it is argued that D1 is restricted to strata of Cambrian to Lower Ordovician age in southeast Leinster. A model for the tectonic evolution of the southeastern part of the Leinster Basin during Cambro-Ordovician times is presented and discussed. In this model, the southeast margin of the Leinster Basin was delineated by a mylonite zone along the northwest margin of the Precambrian Rosslare Complex. Bray and Ribband Group sediments close to the margin were deformed during the Llanvirn as a consequence of basin inversion which caused shortening and thrusting of the basin fill across the Rosslare block. The D1 compressional structures were subsequently modified during a period of extension, marked by the resumption of sedimentation and outbreak of voluminous volcanicity near the basin margin during the Llandeilo and Caradoc. The D2 and D3 structures in the Bray and Ribband Groups are an expression of later Caledonian deformation.     

The Pattern and Evolution of the Permian Palaeobiogeography and Tectonic Palaeogeography in Jilin and Heilongjiang Orogenic Belt

The orogenic belt locates between the North China plate and Siberia plate. The Permian palaeobiogeography and tectonic palaeogeography changed quickly and clearly. The line from Changchun to Yanji is an important palaeobiogeographic provincing line, which may be the collission suture belt of the North China plate and north middle massifs. The orogenic belt has been divided into 2 regions: the North middle massif region and the North Margin of North China plate, the pattern and evolution of Permian palaeobiogeography in the present area were discussed and the Permian biota mixture and its significants were analysed. Then, Based on the above, the Permian tectonic palaeogeography of the orogenic belt is reconstructed.     

山东胶莱盆地五莲地区早白垩世红层古地磁研究及其构造意义

胶东半岛中生代以来的旋转变形对限定郯庐断裂的剪切走滑活动具有重要意义,然而目前对胶莱盆地中生代旋转变形与否及其幅度仍存在很大争议。本文选择胶莱盆地南部五莲地区早白垩世莱阳群龙旺庄组红层开展系统古地磁学研究,共采集11个采点82个定向古地磁岩芯样品。岩石磁学实验结果表明,样品的载磁矿物主要为赤铁矿,部分样品同时含有少量磁黄铁矿和磁铁矿;系统热退磁实验共分离出8个采点58个样品的稳定特征剩磁方向,并认为其可能代表岩石沉积时期的原生剩磁方向。8个采点的特征剩磁方向平均值为Ds=169. 5°、Is=33.2°、ks=40.9、α95 =8.8。相对于稳定东亚极,五莲地区发生了显著的（22.8°±8.8°）逆时针旋转变形。结合前人在胶莱盆地白垩纪沉积岩中获得的古地磁结果,指示胶莱盆地晚白垩世以来可能经历了整体的逆时针（10°~20°）旋转变形,而沿五莲断裂带向南西方向的逆时针旋转变形幅度增大,表明受郯庐断裂带左行走滑的影响增强。此外,沿郯庐断裂带不同部位在不同时期发生了不同方式和幅度的旋转变形,其不仅受郯庐断裂带左行剪切活动影响,还与断裂带周缘不同地体的性质及其所处的大地构造背景有关。     

An early Paleoproterozoic high-K intrusive complex in southwestern Tarim Block, NW China: Age, geochemistry, and tectonic implications

Systematic geochronologic, geochemical, and Nd isotopic analyses were carried out for an early Paleoproterozoic high-K intrusive complex exposed in southwestern Tarim, NW China. The results provide a better understanding of the Paleoproterozoic tectonic evolution of the Tarim Block. Zircon U–Pb age dating indicates two Paleoproterozoic magmatic episodes occurring at ca. 2.41 Ga and ca. 2.34 Ga respectively, which were followed by a ca. 1.9 Ga metamorphic event. The 2.41 Ga granodiorite–adamellite suite shares characteristics of late to post-orogenic metaluminous A-type granites in its high alkalinity (Na₂O + K₂O = 7.6–9.3%), total REE (410–788 ppm), Zr (370–660 ppm), and Y (21.7–58.4 ppm) contents. εNd(t) values for the suite range from − 3.22 to − 4.71 and accordingly the Nd modal ages (T_2DM) vary between 3.05 Ga and 3.17 Ga. Based on geochemical data, the 2.34 Ga suite can be subdivided into two sub-suites, namely A-type and S-type. However, both types have comparable Nd isotope compositions (εNd(t) ≈ − 0.41 to − 2.08) and similar narrow T_2DM ranges (2.76–2.91 Ga).Geochemical and Nd isotopic data for the high-K intrusive complex, in conjunction with the regional geological setting, suggest that both the 2.41 Ga suite and the 2.34 Ga A-type sub-suite might have been produced by partial melting of the Archean mafic crust in a continental rift environment. The S-type sub-suite is thought to have formed by partial melting of felsic pelites and/or metagreywackes recycled from Archean crust (TTG?). Gabbro enclaves with positive εNd(t) value (2.15) have been found to be intermingling within the 2.34 Ga suite; ca. 2.34–2.36 Ga gabbroic dykes and adamellites have previously been documented in eastern Tarim. These observations indicate that the high-K intrusions may reflect the emergence of depleted mantle upwelling beneath the Tarim Block at that time. We suggest a three-stages model for the Precambrian crustal evolution in the Tarim Block: (1) the formation of proto-crust (TTG) by ca. 2.5 Ga, (2) episodes of felsic magmatism possibly occurring in continental rift environments at ca. 2.41 Ga and ca. 2.34–2.36 Ga, and (3) ca. 1.9 Ga metamorphism that may represent the solidification of the Precambrian basement of the Tarim Block.     

Fluids migration and dynamics of a blocks-and-faults system

We explore the impact of fluids migrating through a fault network on the dynamics of lithosphere, both on slow movements and seismicity. For that purpose fluids in the fault zones are incorporated into modelling of blocks-and-faults systems, which takes into account driving forces and the system's geometry. Simulations have been performed for two-dimensional models: an idealised “brick wall” structure, and a coarse image of Sinai Subplate. Migrating fluids originating in different locations are considered, as well as fluids trapped in closed pockets. Basic features of the modelled and observed seismicity are in good accord, as shown by comparison with the earthquake catalog compiled by Geophysical Institute of Israel.