Himalayan magmatism and porphyry copper–molybdenum mineralization in the Yulong ore belt, East Tibet

Summary ?The NW–SE-trending Yulong porphyry Cu–Mo ore belt, situated in the Sanjiang0 area of eastern Tibet, is approximately 400 km long and 35 to 70 km wide. Complex tectonic and magmatic processes during the Himalayan epoch have given rise to favorable conditions for porphyry-type Cu–Mo mineralization. Porphyry masses of the Himalayan epoch in the Yulong ore belt are distributed in groups along regional NW–SE striking tectonic lineaments. They were emplaced mainly into Triassic and Lower Permian sedimentary-volcanic rocks. K–Ar und U–Pb isotopic datings give an intrusion age range of 57–26 Ma. The porphyries are mainly of biotite monzogranitic and biotite syenogranitic compositions. Geological and geochemical data indicate that the various porphyritic intrusions in the belt had a common or similar magma source, are metaluminous to peraluminous, Nb–Y–Ba-depleted, I-type granitoids, and belong to the high-K calc-alkaline series. Within the Yulong subvolcanic belt a number of porphyry stocks bear typical porphyry type Cu–Mo alteration and mineralization. The most prominent porphyry Co–Mo deposits include Yulong, Malasongduo, Duoxiasongduo, Mangzong and Zhanaga, of which Yulong is one of the largest porphyry Cu (Mo) deposits in China with approximately 8 × 10⁶ tons of contained Cu metal. Hydrothermal alteration at Yulong developed around a biotite–monzogranitic porphyry stock that was emplaced within Upper Triassic limestone, siltstone and mudstone. The earliest alteration was due to the effects of contact metamorphism of the country rocks and alkali metasomatism (potassic alteration) within and around the porphyry body. The alteration of this stage was accompanied by a small amount of disseminated and veinlet Cu–Mo sulfide mineralization. Later alteration–mineralization zones form more or less concentric shells around the potassic zone, around which are distributed a phyllic or quartz–sericite–pyrite zone, a silicification and argillic zone, and a propylitic zone. Fluid inclusion data indicate that three types of fluids were involved in the alteration–mineralization processes: (1) early high temperature (660–420 °C) and high salinity (30–51 wt% NaCl equiv) fluids responsible for the potassic alteration and the earliest disseminated and/or veinlet Cu–Mo sulfide mineralization; (2) intermediate unmixed fluids corresponding to phyllic alteration and most Cu–Mo sulfide mineralization, with salinities of 30–50 wt% NaCl equiv and homogenization temperatures of 460–280 °C; and (3) late low to moderate temperature (300–160 °C) and low salinity (6–13 wt% NaCl equiv) fluids responsible for argillic and propylitic alteration. Hydrogen and oxygen isotopic studies show that the early hydrothermal fluids are of magmatic origin and were succeeded by increasing amounts of meteoric-derived convective waters. Sulfur isotopes also indicate a magmatic source for the sulfur in the early sulfide mineralization, with the increasing addition of sedimentary sulfur outward from the porphyry stock. Received August 29, 2001; revised version accepted May 1, 2002 Published online: November 29, 2002     

关于辽宁地区b值方法定量预测的研究

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Delineation of different phytoplankton communities in the East China Sea mackerel and carangoid fishing ground

Delineation of phytoplankton communities in this study was based on: 1) cluster analysis by Preston's Equation (1962) and 2) analysis of the number of individuals. Results obtained by these two methods were very similar to that obtained in a previous study (Fig. 1, Gu and Guo, 1982) based on analysis of the number of planktonic species of different ecological nature. Among these three methods, that based on cluster analysis (by which some subcommunities could be recognized) proved to be the best. Contribution No. 1841 from the Institute of Oceanology, Academia Sinica.     

舟山马岙峡道的水文泥沙特性和峡道效应

根据舟山本岛北部马岙峡道实测水文泥沙资料和沉积物采样分析结果以及对马岙岸段岸滩的现场踏勘结果，分析了马岙峡道的水文泥沙特性及其峡道效应。文章认为，受峡道地形限制，马岙岸段水流呈现显著的往复流特性，潮流流速较强，水体含沙量较低，泥沙淤积较弱，岸滩处于冲淤平衡状态；受峡道内涨落潮流分流和汇流的共同作用，马岙小泥糊礁附近发育水下沙嘴，该沙嘴是以落潮流作用为主形成的浅滩，受涨潮流改造而形成的，并将在涨落潮流作用下逐渐增长，形成连岛沙嘴，使小泥糊礁附近岸线发展成弧形岸线，并达成新的平衡。     

中国大陆1998～1999年地壳运动观测结果

介绍了中国地壳运动观测网络1998～1999年基准站GPS观测概况,简要介绍了用伯尔尼（Bernese）软件对GPS观测数据的处理结果,详细介绍了所获取的1998年９月初～1999年７月初基准网地壳运动,包括各基准站位移与网内各部分的应变．在所述观测期间,我国东部地区较为稳定．相对东部地区,西南部地区以向北运动为主,位移量约17ｍｍ,受北北东向挤压为主;西北部地区以北西向运动为主,位移量约11ｍｍ;而云南地区以向南运动为主,位移量约14ｍｍ．我国中部南北地震带则是一强烈的剪切变形带．网内最大主应变量为2.910-8．观测结果表明,印度板块向北挤压依然是影响我国地壳运动的主要因素．      

立交桥曲线箱梁动力分析模型

提出了1种双脊骨空间有限元模型,用来模拟和分析立交桥曲线箱梁的固有振动特性和动力反应。将曲线箱梁分别看作是由空间梁或壳组成的空间结构,并分别采用分段空间直梁模型、壳元模型和实体元模型进行模拟,分析相同曲线箱梁的振动特性和地震时程反应,通过与双脊骨模型的计算结果的比较验证双脊骨模型的可靠性。初步研究了在相同曲率半径下不同跨度的曲线箱梁的固有振动特性,分析了双脊骨模型的脊骨间距、横向连接间距等参数对模型计算结果的影响。研究结果可为曲线梁桥抗震性能和地震反应分析提供参考。