辽宁岫岩地区岫玉成矿规律探讨

岫岩是我国主要蛇纹石玉产地,辽河群大石桥组大理岩层是岫岩玉石矿最重要的蕴矿层位,矿体严格受地层中韧性变形变质构造带和元古宙花岗岩的控制。在岫岩不仅产有蛇纹石岫玉,还产出透闪石岫玉。矿体形态呈不规则脉状及透镜状产出。岫岩地区的岫玉矿床成因应属于热液交代蚀变矿床类型。     

祁漫塔格地区十字沟蛇绿岩地质特征

十字沟蛇绿岩产出于东昆仑西段祁漫塔格结合带东部,主要由蛇纹岩、辉长岩、辉绿岩、基性火山岩及硅质岩等组成。其中,从超基性岩—基性岩—基性火山岩,具稀土总量逐渐增加,轻稀土弱亏损型特征,基性火山岩为洋脊玄武岩,总体岩石化学成分与大洋中脊低钾拉斑玄武岩相当,三者的配分型式基本一致,说明其继承了源区地幔的特征,微量元素显示基性火山岩具弧后盆地玄武岩特点。Nεd(t)比值表明玄武岩来自亏损地幔源区,总体地球化学特征显示以N-M ORB型为主,兼具有E-M ORB型的特征,形成于与俯冲作用有关的弧后盆地环境,形成时代为晚奥陶世。后期至少经历了3期以上构造变形变质作用的叠加改造,于早志留世运移至地表。     

中国东部郯庐断裂南延新解

本文依据构造、地球化学、地球物理资料的综合分析,特别是对含地幔岩包体的基性岩带的研究,提出了郯庐断裂南延带是呈两个主干夹一断裂束的形式,从湖北广济,经江西修水,湖南连云山、衡阳、江永,直抵广西大容山—六万大山(广济—六万大山断裂),南延带已趋近郯庐断裂尾端。以广泛的韧性变形变质代替了中带的破裂大平移。它是华南的一条重要动-热-地球化学分界带。     

Stepping stones and pitfalls in the determination of an anticlockwise P-T-t-deformation path: the low-P, high-T Cooma Complex, Australia

Abstract Low-pressure/high-temperature (low-P/high-T) metamorphic rocks of the Cooma Complex, southeastern Australia, show evidence of an anticlockwise pressure-temperature-time-deformation (P-T-t-D) path, similar to those of some other low-P/high-T metamorphic areas of Australia. Prograde paths are reasonably well constrained in cordierite-andalusite schists, cordierite-K-feldspar gneisses and andalusite-K-feldspar gneisses. These paths are inferred to be convex to the temperature axis, involving increase in pressure with increase in temperature. Evidence of the retrograde path is inconclusive, but is consistent with approximately isobaric cooling, as are available isotopic data on the Cooma Granodiorite, which indicate initially rapid cooling following attainment of peak temperatures. The retrograde path is inconsistent with either a clockwise P-T-t-D path involving rapid or even moderate decompression immediately post-dating the peak of metamorphism, or a path in which the retrograde component simply reverses the prograde component, because both these paths should cross reactions forming cordierite from aluminosilicate, for which no evidence has been observed. Determination of the deformational-metamorphic history of the complex is not straightfoward and depends on careful examination of critical samples. Evidence necessary for successful elucidation of the prograde, and part of the retrograde, deformational-metamorphic history in the Cooma Complex includes: (1) sequentially grown porphyroblasts that can be timed relative to surrounding foliations; (2) partial replacement microstructures providing relative timing of metamorphic reactions that cannot be timed relative to foliation development; (3) a tectonic marker foliation (S4 at Cooma) that allows correlation of foliations from one location to another; and (4) single samples containing all of the foliations and all generations of porphyroblast growth within a single metamorphic zone. The latest two or three foliations involve low strain accumulation, allowing relative timing relationships between foliations and porphyroblasts to be more clearly determined. Sequential porphyroblast growth and foliation development in the cordierite-andalusite schists is examined for situations involving rotation and non-rotation of porphyroblasts relative to geographically fixed coordinates. Although the number of foliations developed varies in the rotational situation, depending on the deformation history proposed, the sequential order of porphyroblast growths does not differ from the non-rotational situation. Thus, whether or not porphyroblasts rotated in the Cooma rocks, the sequence of reactions, and therefore P-T-t paths inferred from the relative timing of porphyroblast growths, remain the same, for the deformational histories evaluated.