^40Ar／^39Ar Fast Neutron Activation Ages of Quartz from the Jinman Vein Copper Dposit in Western Yunnan and Their Significance

Quartz samples collected from the Jinman vein copper deposit in the Lanping Basin of western Yunnan were determined by⁴⁰Ar/³⁹Ar fast neutron activation techniques, and the spectra are characterized as being saddle-shaped. The samples yielded a plateau age of 58.05 ± 0.54 Ma, a minimum appearance age of 56.76 ±0.81 Ma and an isochron age of 54.30 ± 0.15 Ma, the three ages being close to each other, indicating that the ages of the quartz samples so far determined are true and reliable. The plateau age represents the time of formation of Cu-bearing quartz veins, which is corresponding to Early Himalayan. This age is also consistent with the time at which a tectonically thermal event (60 Ma) took place within the Lanping Basin, Yunnan Province. In consideration of the fact that copper ore and other ore types in the vast area of western Yunnan are concentrated mainly in the Early Himalayan strata, the authors believe that there must have existed some indispensable key factors leading to metallogenesis on a large scale during the Early Himalayan period in western Yunnan and also constraining in union the formation of ore deposits there.     

Continental crust and lithospheric mantle interaction beneath North China: isotopic evidence from granulite xenoliths in Hannuoba, Sino-Korean craton

Mafic granulite and pyroxenite xenoliths from Cenozoic alkaline basalts at Hannuoba, Hebei Province, North China have been selected for a systematic geochemical and Sr–Nd–Pb isotopic study, which provides a unique opportunity to explore nature of the lower crust and the interaction between the continental crust and lithospheric mantle beneath an Archean craton. The major, compatible and incompatible elements and radiogenic isotopes of these xenoliths suggest great chemical heterogeneity of the lower crust beneath the Hannuoba region. Petrological and geochemical evidences indicate a clear cumulate origin, and most likely, they are related to basaltic underplating in different geological episodes. However, the Sr–Nd–Pb isotopic compositions of the xenoliths reveal a profound enriched source signature (EM I) with some influence of EM II, which implies that some portion of pre-existing, old metasomatized subcontinental lithospheric mantle could have played an important role in their genesis. It is suggested that the interaction between continental crust and subcontinental mantle as manifested by basaltic underplating would be closely related to regional tectonic episodes and geodynamic processes in the deep part of subcontinental lithospheric mantle.     

Hydrothermal Redistribution of Rare—Earth Elements in Pingxiang Dacite,Guangxi

Distribution of the rare-earth elements (REE) in dacite has been studied so as to get a better understanding of the migration behavior of REE during alteration. Both unaltered and altered samples were collected in an unpolluted area of Guangxi Zhuang Autonomous Region, southwest China. The REE concentrations were analyzed by ICP-MS. It is concluded that the REE were enriched during dacite alteration in varying degrees. The chondrite-normalized REE patterns of altered samples approximately maintain the characteristics of unaltered samples. However, if we normalize the REE concentrations of altered samples with unaltered dacite, fractionation of REE will appear. The LREE are more enriched than HREE in all altered samples with the LREE possibly precipitated as carbonate minerals. Both positive and negative Eu anomalies exist. Enrichment, immobility and depletion are noticed for the element Lu. Heavy mineral alteration, difference in stability constant between carbonate LREE and HREE complexes, downward migration of weathering fluid and microenvironment change may be responsible for the fractionation of REE in the altered dacite.     

Sm-Nd ISOTOPIC AGE OF LAMPROPHYRES IN THE GEZHEN GOLD-BEARING SHEAR ZONE ON HAINAN ISLAND AND ITS GEOLOGICAL IMPLICATIONS

Sm-Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold-bearing shear zone on western Hainan Island, are measured. The Sm-Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd) 0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole-rock Sm-Nd isochron age (495.98 ± 13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.     

基于GIS的区域地质调查数字制图--以1∶5万<里庄幅>为例

本文以 1∶5万里庄幅为例 ,阐述了运用GIS系统对区调过程中各种资料的处理与编辑方法 ,并介绍了数字制图方法及工艺流程 ,提出了GIS系统在 1∶5万区调工作中的应用前景     

挤扩多支盘桩试桩破坏原因分析

对挤扩多支盘桩这种新桩型在浙江杭州典型软土地质条件下的可应用性进行了试验研究,试验内容包括桩中钢筋应力测试、桩顶及桩端沉降测试等.对试桩破坏的原因作了较全面的分析,得出了一些有益的结论.     

多层复杂结构厂房切割控制爆破技术

武钢三烧I系列烧结主厂房为装配式结构,经改造加固形成框架结构和装配式结构共存的复杂结构.由于生产需要,必须从主厂房爆破切割分离43m高的高架通廊,同时需确保贯穿厂房的地下和地表运料通廊及周边厂房的安全.因此,应先采用切割爆破技术,将需保留的高架通廊分离,并把厂房分割成3个区,然后分别采用定向倒塌和拆叠爆破拆除方法,使爆破达到了预期效果,并可供类似工程参考.     

用现今小震推断洪洞、临汾两次历史大震的震源断层

山西临汾地区是一个历史强震多发区，1303年和1695年发生了洪洞（M＝8）和临汾（M＝73／4）两次特大地震，这两次地震所在区域至今仍在持续不断的小地震活动，具有明显的大震区地震长期活动特征，我们对临汾无线传输地震台网记录的1987－1999年期间发生的1670次中，小地震重新进行了震源定位，根据对这些地震震源位置三维空间分布特征和震源机解制的分析，认为洪洞地震的震源断层应是长80km，埋深5－26km的NNE走向，高倾角的右旋走滑型断层，而临汾地震的震源断层是长70km，埋深5－22km的NWW走向，高倾角的左旋走滑型断层。这与洪洞，临汾两次大震极震区的等震线及该地区应力场的构造环境是吻合的。     

1999年山西大同Ms 5.6地震的震源断层

大同震区先后在 1989、1991和 1999年发生MS >5地震 ,利用大同遥测地震台网的记录资料进行比较精确的地震序列震源定位 ,结合宏观烈度分布和震源机制解资料 ,详细地分析对比了 3次子序列的异同。结果显示 ,1999年MS5 .6地震的震源断层是走向NWW、长 16km、宽12km、埋深 5km以下、倾角近直立的左旋走滑断层。而前 2个子序列是NNE为主的右旋走滑断层活动所致 ,表明地震破裂方向发生了变化。这种 2个以上方向先后出现、并且强弱有别的地震破裂是普遍存在的 ,表明震源环境的复杂程度与地震序列的类型有关。虽然震区存在NE向的大王村断裂和NW向的团堡断裂 ,但目前没有证据说明震源断层和 2条构造断层连通。 3次子序列的震源断层都是走滑断层 ,也和 2条构造正断层有别。 1999年的子序列可能属于新破裂。     

对永胜6级地震的预报及依据

2001年10月27日在云南永胜发生6.0级地震，震前四川省地震局有较准确的中期和短临预报，加强了川滇交界地区的地震监测预报工作，并且向四川省政府作了汇报，取得了明显的社会效益。经验性地震预报重视川滇菱形地块西界断裂带动态活动图像的分析，尤其对历史强震破裂空段附近出现的中小震活动带或新活跃区段的研究；同时，重视4级前震群、川滇交界地区地下水位、水温、形变观测异常的跟踪分析和震情预测。