Eine Tonmineralfolge vom Beckenrand zum Beekeninneren im Buntsandstein Nordost-Bayerns

Analysis of samples taken from combined profiles of the ?Buntsandstein” (Lower Triassic in Germanic facies) has furnished proof of a regional change in clay mineral composition from its depositional margin to the centre of the sedimentary basin. this alteration occuring both vertically and horizontally, and hence in geologically comparable strata. Altogether five different characteristic mineral associations were found. arranged in a “sequence” and save two explicable in terms of environmental conditions. The horizontal and vertical range of these distinctive, characteristic slay mineral associations has been alloted to provinces. Factors alien to those arising from these provincial environments like influences of distributive areas. of climate and diagenesis, have but subordinate significance or none at all. Moreover, a comparison with the work ofSchnitzer (1957) has shown that the distribution of heavy minerals and that of clay mineral assemblages are independent of each other; the latter being indicative of differences in environmental conditions. whereas study of heavy mineral suites makes possible the reconstruction of source areas.     

Early Permian plutons from the northern North China Block: constraints on continental arc evolution and convergent margin magmatism related to the Central Asian Orogenic Belt

Recent zircon dating identified several late Carboniferous to early Permian hornblende gabbro–diorite–quartz diorite–granodiorite–tonalite–granite plutons in lithological assemblages at the northern margin of the North China Block (NCB) that were previously regarded as Archaean to Palaeoproterozoic. Our geochronological results indicate that emplacement of these plutons was a continuous process during the late Carboniferous to early Permian, from 324 ± 6 to 274 ± 6 Ma, and lasted for at least 50 Ma. In this paper, the early Permian components with compositions from gabbro to granite within the intrusive complex were studied. The early Permian plutons exhibit calc-alkaline or high-K calc-alkaline, metaluminous geochemical features and highly variable SiO₂ contents. They have no significant Eu anomaly in their REE patterns, and in primitive-mantle-normalized spidergrams they display depletion in Th, U, Nb, Ta, P and Ti, and enrichment in Ba, K, Pb and Sr. The granitoid bodies within these plutons display I-type and adakitic geochemical signatures. The early Permian rocks exhibit low whole-rock initial ⁸⁷Sr/⁸⁶Sr ratios from 0.70520 to 0.70615 and have negative whole-rock ε _Nd(t) values ranging from −17.4 to −9.3 and zircon ε _Hf(t) values of −23.2 to −10.5. The gabbros exhibit higher ε _Nd(t) values from −11.1 to −9.3 and ε _Hf(t) values from −16.5 to −10.5, and one granodiorite exhibits an even lower ε _Nd(t) value of −17.4 and zircon ε _Hf(t) values of −23.2 to −15.1. Geochemical, Sr–Nd and in situ zircon Hf isotopic compositions suggest that the hornblende gabbros were derived from a metasomatized lithospheric mantle, and the diorite and quartz diorite were generated from a gabbroic magma by fractional crystallization, coupled with differential assimilation of ancient lower crustal material. The granodiorite was likely derived from partial melting of ancient lower crust with involvement of some mantle components. Involvement of both lithospheric mantle and ancient lower crust in the generation of the early Permian plutons indicates strong crust–mantle interaction in the northern NCB. Petrological associations as well as geochemical and Sr–Nd–Hf isotopic results show that the early Permian plutons were emplaced along an Andean-type active continental margin during southward subduction of the Palaeo-Asian oceanic plate beneath the NCB. Integration of our results with previously published data for late Carboniferous and late Permian to middle Triassic intrusions suggests that the continental arc on the northern margin of the NCB existed for at least 50 Ma during the late Palaeozoic, and final amalgamation of the Mongolian arc terranes with the northern NCB likely occurred during a period from ~270 to ~250 Ma, i.e, in the late Permian to earliest Triassic.     

2018年9月4日伽师5.5级地震序列震源机制解及震源处应力场特征

本文采用新疆测震台网数字波形记录，利用CAP和P、S波初动和振幅比方法计算2018年9月4日伽师5.5级地震序列中M_S≥2.5地震的震源机制解，结合地震烈度等震线和双差重定位后的地震序列空间展布等特征分析了此次地震的发震构造，反演了震源处应力场。结果表明，伽师5.5级地震呈NE向的节面I为发震断层面，属于左旋走滑断层，震源深度为9km，发震构造可能为浅部超基底断裂；地震序列中有21次为走滑型，4次为正断型，说明绝大多数序列的破裂方式与主震相近，表明余震应力场主要受主震震源应力场控制；P轴方位在NNE向有明显的优势分布且倾伏角较小，T轴方位在NWW向有明显的优势分布且倾伏角较小，说明震源处主要以NNE向水平挤压和NWW向水平拉张作用为主；此次伽师5.5级地震序列表现的浅部应力场与已有研究得出的震源区深部应力场基本一致，应力形因子R的最优解为0.17，说明震源处近NE向中间主应力σ₂有一定挤压成分。     

西昆仑东段震源机制和构造应力场特征

本文利用新疆测震台网记录的宽频带波形数据，采用CAP方法反演西昆仑东段2010年1月—2018年12月M_S≥3.0地震震源机制，并结合研究区早期的震源机制数据分区反演构造应力场。结果表明:研究区地震破裂类型以逆断型和走滑型为主，其次为正断型，过渡型最少；震源机制节面在NWW向存在明显优势分布且倾角较陡，压应力P轴在NNE向有优势分布且倾角较小，张应力T轴在NW-SE向有优势分布且倾角较小，说明研究区总体上主要以NNE向的水平挤压和NW-SE向水平拉张作用为主；西南区域应力结构为走滑型，东北区域应力结构为逆断型，最大主应力轴σ₁方位的最优解都呈NNE向，但西南区域更偏东，东北区域水平作用更明显。东北区域的应力形因子R值较小，体现该区域的物质隆升相对于西南区域物质隆升分量大。     

Textures in Partially Solidified Crystalline Nodules: a Window into the Pore Structure of Slowly Cooled Mafic Intrusions

Abundant glass is present along grain boundaries in coarse-grained,glass-bearing, crystalline gabbroic and peridotitic nodulesentrained and erupted in lavas from Iceland, Santorini and MaunaLoa (Hawaii), even when the total porosity is less than a fewvolume per cent. The glass films vary from a few microns toa few tens of microns thick, and are associated with stringsof small lensoid grain boundary pockets formed by impingementduring crystal growth. Additional porosity occurs as extensiveliquid-filled pockets adjacent to included grains within oikocrystsand as large triangular pockets formed by impingement of planar-sidedgrains. Interstitial material within glass films, and the irregularityof film thickness along a single grain boundary, suggest thatthe present pore structure is representative of the pore structurebefore entrainment and eruption. Pore geometry is consistentwith a dominant control by crystal growth during solidification,with little or no evidence for control by minimization of internalenergies driven by textural equilibration. Similarities betweenliquid distribution in the crystalline nodules and that of late-stage,interstitial phases in fully solidified mafic cumulates fromthe Rum and Skaergaard intrusions demonstrate that the crystallinenodules provide information about the latest stages of solidificationin slowly cooled mafic plutons. The highly permeable networkof intersecting liquid films, lenses and pockets may promotein situ crystallization in the solidifying mush, explainingthe common presence of adcumulates in such intrusions. KEY WORDS: textures; liquid distribution; mafic cumulates; crystalline nodules