The cordierite‐bearing anatectic rocks of the higher Himalayan crystallines (eastern Nepal): low‐pressure anatexis,melt productivity,melt loss and the preservation of cordierite

Cordierite‐bearing anatectic rocks inform our understanding of low‐pressure anatectic processes in the continental crust. This article focuses on cordierite‐bearing lithologies occurring at the upper structural levels of the Higher Himalayan Crystallines (eastern Nepal Himalaya). Three cordierite‐bearing gneisses from different geological transects (from Mt Everest to Kangchenjunga) have been studied, in which cordierite is spectacularly well preserved. The three samples differ in terms of bulk composition likely reflecting different sedimentary protoliths, although they all consist of quartz, alkali feldspar, plagioclase, biotite, cordierite and sillimanite in different modal percentages. Analysis of the microstructures related to melt production and/or melt consumption allows the distinction to be made between peritectic and cotectic cordierite. The melt productivity of different prograde assemblages (from two‐mica metapelite/metagreywacke to biotite‐metapelite) has been investigated at low‐pressure conditions, evaluating the effects of muscovite v. biotite dehydration melting on both mineral assemblages and microstructures. The results of the thermodynamic modelling suggest that the mode and type of the micaceous minerals in the prograde assemblage is a very important parameter controlling the melt productivity at low‐pressure conditions, the two‐mica protoliths being significantly more fertile at any given temperature than biotite gneisses over the same temperature interval. Furthermore, the cordierite preservation is promoted by melt crystallization at a dry solidus and by exhumation along P‐T paths with a peculiar dP/dT slope of about 15–18 bar °C^?1. Overall, our results provide a key for the interpretation of cordierite petrogenesis in migmatites from any low‐P regional anatectic terrane. The cordierite‐bearing migmatites may well represent the source rocks for the Miocene andalusite‐bearing leucogranites occurring at the upper structural levels of the Himalayan belt, and low‐P isobaric heating rather than decompression melting may be the triggering process of this peculiar peraluminous magmatism.     

大别山北麓佛子岭群的特征及其形成的大地构造环境

佛子岭群主要由一套绿片岩相的变质岩组成,分布在安徽境内的大别山北麓。其上部为一套变质的复理石建造,下部为变质的火山-沉积岩建造。佛子岭群的变质火山岩的岩石化学特征及佛子岭群的岩石组合特征表明,佛子岭群是发育在一断陷盆地中,该断陷盆地可能在晚元古代早期开始拉张,在晚元古代末期闭合。在此期间,郯-庐断裂带在华北断块和大别山古老断块之间的拉张与闭合过程中可能起着类似于转换断层的作用。     

华南变质基底的组成、边界与构造演化（研究综述）

本文据作者调查并综合有关资料，就华南变质基底的组成结构、边界性质、构造型式及演化过程作了较全面阐述；就板溪群是否为构造混杂岩，及其所代表的地质体性质作了深入分析和讨论，作者认为：华南可能存在晚太古－早元古统一变质基底，中元古末至印支期为板块活动期，印支期后，由于受太平洋板块作用影响而进入新的构造活动期。     

试论中国南北大陆的碰撞造山带

中国北方的中朝克拉通与南方的扬子克拉通无论在基底年代及盖层发育程度、沉积环境及古生物群上都有差异。它们是两个构造发育史不同的大陆。这两个古大陆之间的大洋究竟有多宽？是何时关闭的？合并时的构造运动强烈程度？在挽近地质历史时期有无相类似的情况？这些问题一直是中外地质学家所关注，并在不同程度上讨论过的问题。近年来的地质工作，提供了一些可据以回答上述问题的成果，但全面可靠地回答上述全部问题还有待今后的努力。笔者在过去的文章（1-3）曾讨论一些有关问题。本文，拟就近期国内外的研究成果，发表一些评论，并提出作者的看法     

红水河中游地区地质构造稳定性的遥感图像分析

红水河中游地区是以北西向和北东向断裂相交叉为基本构造格局。在新构造运动时期,这两组老构造分段复活,将该区分割成一个相对独立的活动块体。 遥感信息与岩相古地理及汞矿化带相结合的分析结果表明:发震的垭都—紫云深大断裂,在新构造运动时期并未进入断块。遥感信息与历史震中的时空分布和断块结合分析表明:中强震震中绝大多数分布在断块以外,并以右江断裂带以南的频率为最大,由于这里已远在百公里之外,今后若再发生中强震,经过长途衰减,波及坝址的影响有限。 断块内距坝址15—20公里的巴鱼地区,近期发生过4.6级地震。这是一个处在乐业环状构造长轴转折端前沿,也是逻西活动断裂等多组断裂交叉处,小型环状构造也很发育,构造应力容易在此集中,历史震中与小型环状构造同断裂的交叉点关系密切。影像显示该区是相对孤立的局部地段,小震频繁,应力分阶段释放,不具备孕育强震的条件。 龙滩和岩滩电站坝址周围8公里内无大型或活动断裂通过,亦无两组以上断裂交叉点出现,构造稳定性良好,但应注意水库诱发地震的研究。     

新疆古地磁研究及几个地质构造问题探讨

通过对塔里木、准噶尔、伊犁、昆仑山等地区古地磁研究获得了大量数据,结合磁性地层、古生物、沉积相等综合分析,对塔里木地块构造演化、新疆晚古生代构造分区划分、伊犁地块、天山板块等几个地质构造问题进行了探讨.     

Generation of Muscovite/ Two-Mica Granil and Intracontinental Subduction

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