The Araçuaí-West-Congo Orogen in Brazil: an overview of a confined orogen formed during Gondwanaland assembly

The Neoproterozoic Adamastor-Brazilide Ocean was generated during the breakup of the Rodinia supercontinent, and remnants of its oceanic lithosphere have been found in the Brasiliano-Pan African orogenic system that includes the Araçuaí, West-Congo, Brasília, Ribeira, Kaoko, Dom Feliciano, Damara and Gariep belts. The Araçuaí and the West-Congo belts are counterparts of the same Neoproterozoic orogen. The first belt comprises two thirds of the Araçuaí-West-Congo Orogen. This orogen is rather unique owing to its confined nature within the embayment outlined by the São Francisco and Congo cratons. In spite of this, the presence of ophiolitic remnants, and a calc-alkaline magmatic arc, indicate that the basin/orogen evolution comprise both oceanic spreading and consumption. It is assumed that coeval Paramirim and Sangha aulacogens played a key role by making room for the Araçuaí-West-Congo Basin. Sedimentary successions record all major stages of a basin that evolved from continental rift, when glaciation-related sedimentation was very significant, to passive margin. Rifting started around 1.0–0.9 Ga. The oceanic stage is constrained by an ophiolitic remnant dated at 0.8 Ga. If the cratonic bridge that once linked the São Francisco and Congo palaeocontinental regions did not hinder the opening of an ocean basin, it certainly limited its width. As a consequence, only a narrow oceanic lithosphere was generated, and it was subducted afterwards. This is also suggested by orogenic calc-alkaline granitoids occuping a small area of the orogen. Geochronological data for pre-, syn- and late-collisional granitoids indicate that the orogenic stage lasted from 625 Ma to 570 Ma. A period of magmatic quiescence was followed by intrusion of postcollisional plutons at 535–500 Ma. The features of the Araçuaí-West-Congo Orogen suggest the development of a complete Wilson Cycle in a branch of the Adamastor Ocean, which can be interpreted as a gulf with limited generation of oceanic lithosphere.     

7Be在土壤侵蚀示踪中的应用研究进展

7Be是一种自然产生的放射性核素，由对流层和同温层大气中的氧和氮在宇宙射线作用下分裂生成，其半衰期为53．3天，7Be通过连续的干湿沉降作用到达土表，被土壤颗粒紧密吸附，其土壤环境化学行为与137Cs相似，因此，可以用于示踪某种特定土地利用方式或侵蚀事件下的土壤侵蚀作用的强度，空间分配以及季节性变化，7Be技术可与其它反映中长期土壤侵蚀的放射性核素（137Cs,210Pb)示踪技术相结合，共同表征某个流域的土壤侵蚀状况，对7Be示踪技术现有的土壤侵蚀速率定量估算模型进行了简述，并提出了各自的局限性及今后的研究方向。     

K2B4O7的Pitzer参数的计算

由于硼酸盐在电解质中的特殊性 ,硼酸盐的热力学问题一直被化学家所重视。根据文献数据 ,经多种处理获得K2 B4 O7不同存在形式的硼氧配阴离子的Pitzer纯盐参数、K2 B4 O5(OH) 4电离化学计量平衡常数Km。采用所获得的Pitzer纯盐参数计算K2 B4 O7不同存在形式的硼氧配阴离子的渗透系数 ,并与表观实验值进行比较     

Using cosmogenic beryllium–7 as a tracer in sediment budget investigations

Recent advances in the use of the environmental radionuclides caesium–137 and unsupported lead–210 to quantify medium– and longer–term rates of erosion and sediment accumulation have proved of considerable value in catchment sediment budget investigations. However, there remains a need to explore the potential for using other shorter–lived radionuclides to provide evidence of sediment mobilisation, transport and storage over shorter timescales and particularly for individual events. This contribution reports the results of a study aimed at exploring the potential for using beryllium–7 (⁷Be, t _½= 53.3 days) to meet this requirement. The study investigated the use of ⁷Be as a sediment tracer in three key components of the sediment budget, namely, soil erosion and sediment mobilisation from slopes, the transport, storage and remobilisation of fine sediment in river channels and overbank deposition on river floodplains. The results presented clearly demonstrate the potential for using ⁷Be to obtain information on short–term and event–based sediment redistribution rates for use in catchment sediment budget investigations.     

Preference ratios for mercury and other chemical elements in the Madeira River, Brazil

Samples of water, suspended solids, and bottom sediments from the Madeira River, Rondônia state, Brazil, were physically and chemically analyzed to investigate the actual Hg mobilization in the aquatic environment and compare it with that of other heavy metals and elements in the area. Two dimensionless Hg preference ratios were defined, expressing (1) the ratio of Hg and other elements in the liquid phase divided by the ratio of Hg and other elements in bottom sediments (P_l.phase) and (2) the ratio of Hg and other elements in the particulate matter divided by the ratio of Hg and other elements in bottom sediments (P_s.solids). These preference ratios are useful for comparing Hg transport in three different phases (liquid, particulate matter, and bottom sediments). They also were applicable to any analyzed element in the area studied, because they generated an almost constant value when the maximum calculated was divided by the minimum (P_l.phase=2931; P_s.solids=84) and because of their sensitivity to the dominance of sorption processes by Fe oxides and hydroxides. Mercury could be transported preferentially to other analyzed elements in the particulate phase only if its concentration reached values at least 10⁴-fold higher than those expected or quantified in the area.     

粒度统计分析方法在青藏高原隆升研究中的运用及效果--以昌马洪积扇为例

通过运用粒度统计方法对昌马洪积扇沉积物进行研究，结果显现自早更新世晚期以来存在7次沉积物粒度变粗事件，说明青藏高原东北缘自早更新世晚期以来发生了7次隆升，其间为稳定期.该结论与通过青藏高原东北缘盆地沉积分析、活动断裂及河流阶地活动时代对比而厘定的青藏高原东北缘构造活动时段基本一致，同时与整个青藏高原自早更新世晚期以来的隆升具有很好的耦合.由此为山前洪积扇研究提供了新的方法和线索。     

丽江7.0级地震地表破裂与形变特征

丽江７．０级地震序列发生在该地区属次级构造的断裂上，而且这次地震的烈度分布，地表破坏分布和强余震分布都表现了异常不均匀性。根据大震震害损失评估调查和大震现场地面破坏调查取得的资料，对上述异常现象的原因进行了初步分析，认为主震发震构造为玉龙山山前近南北向断裂，但其破裂过程可能存在“跳跃”和偏转。     

丽江7.0级地震前后滇西实验场的重力异常变化特征

１９９６年２月３日，在云南省西北部的丽江县境内发生了一次Ｍｓ７．０级强烈地震。此次地震前后滇西实验场重力网共进行２７期流动重力观测，其重力变化的总体特征为：１．震中附近地区的丽江－剑川－洱源－带震前为下降变化，下降变化的幅值平均约３０×１０＾－８ｍｓ＾－２左右，震后重力变化继续下降；２．距震中稍远一点的渡口附近地区震前为持续上升变大，累计上升变化的最大幅值达１２３×＾－８ｍｓ＾－２，震后重力变化下     

丽江7.0级地震土木结构房屋破坏比和损失比

本根据丽江地震区１１３个自然村震害调查资料，对不同烈度区土木房屋不同破坏等级破坏比的分布特点进行了初步研究，对破坏比与烈度的关系进行了统计分析，并给出了相应的统计关系，另外，通过实地调查，给出了本次地震土木结构房屋不同破坏等级的损失比。     

山东角07井注(漏)水诱发地震——震源参数与地震序列特征

本文利用山东地震台网仪器记录资料,研究了1985年12月28日山东胜利油田角07井因漏水而诱发的震群活动。认为震群的发生可能与水的非均匀渗透有关,是在特定的地质条件与低初始应力条件下发生的一次深井漏水诱发地震事件。