鄂尔多斯地块深部岩石圈电性结构研究

近年来新的研究成果反应出鄂尔多斯地块岩石圈并不是一个具有深根的完整的刚性块体,尤其在鄂尔多斯北部以及河套地堑发现有大范围的下地壳-上地幔低速低阻物质,如果这一情况属实,那么人们对鄂尔多斯地块的认识将发生大的变化.为此,我们在华北克拉通西部布设了一条穿过鄂尔多斯地块、河套地堑和阴山造山带的南北向大地电磁剖面,试图通过深部电性结构的探测提供更多信息.该剖面全长约850 km,共布设54个宽频测点和17个长周期测点.二维和三维反演结果均表明:鄂尔多斯地块内部以38°N为界,南部和北部电性结构存在明显差异.鄂尔多斯地块南部地壳至上地幔150 km深度范围内整体表现为高阻,具有刚性克拉通的特征;鄂尔多斯地块北部到河套地堑之间下地壳出现低阻层,特别是鄂尔多斯北端与河套地堑接壤地段,深部存在一个规模较大的下地壳-上地幔低阻异常体,该异常体从河套地堑开始,横向上向南延伸到鄂尔多斯地块内部约200 km,纵向上从下地壳向下延伸到上地幔(约100 km深度).根据该异常体的空间特征,参考该区地震波低速异常体的分布,我们认为鄂尔多斯北部及河套地堑中下地壳到上地幔存在热物质,其原因与深部的构造活动有关(软流圈热物质上涌、侧向流动等),这一情况可能反映出鄂尔多斯地块北部岩石圈深部正处于被改造(或者破坏)阶段,这对进一步认识青藏高原东北缘与华北克拉通之间的深部关系具有一定的启示作用.     

鄂尔多斯地块北部至阴山造山带深部电性结构特征研究

在SinoProbe-01项目的资助下,完成了一条跨越鄂尔多斯地块北部、河套断陷盆地和阴山造山带的大地电磁剖面,剖面长约440 km,共包括24个宽频测点和4个宽频一长周期联合测点.采用NLCG算法对TE和TM模式数据进行了二维反演,获得了该剖面的二维电性结构模型.结果表明:鄂尔多斯地块北部由浅至深电性结构比较简单,成层性较好,大体可分为低阻沉积盖层-高阻上地壳-低阻下地壳和上地幔顶部三层;河套断陷盆地和阴山造山带电性结构相对复杂,电阻率高低相间.鄂尔多斯地块北缘、河套断陷盆地以及阴山造山带区域的壳幔高导体可能与硫化物和部分熔融作用有关,而鄂尔多斯地块内部大规模的壳幔高导层可能是由高导矿物引起的.河套断陷盆地的沉降、阴山造山带的地势抬升和鄂尔多斯地块北缘东胜一杭锦旗一带的的隆起之间有着紧密的关系,它们的形成可能与区域伸展构造环境条件下的软流圈物质上涌有关.     

江西银山铜多金属矿床矿石特征研究及成因意义

江西银山矿床是一个大型的铜多金属矿床。通过对野外地质调查及结合室内显微镜鉴定,利用扫描电镜和X射线能谱分析技术对矿石矿物组分及赋存状态进行了深入研究。在银山矿床新发现铋铬合金、锌铜(镍)合金、自然镍3种罕见矿物。能谱分析显示铋铬合金中铬质量百分含量普遍在8%~10%之间。锌铜(镍)合金中Cu质量分数53.93%~65.85%,Zn质量分数30.67%~41.03%,部分合金含镍。自然镍中Ni质量分数高达96.19%。此外,在银山矿床中发现了与次火山热液有关的碲银矿矿物和地下水热液有关的银金矿,能谱分析显示碲银矿中Ag质量分数约36%~42%,银金矿中Au质量分数约为67.96%~81.45%,银金矿主要以裂隙充填式赋存于碲银矿裂隙内。结合本次在银山矿床矿石样品中新发现了黄铁矿的显微霉群构造,认为银山矿床成矿后期可能有地下水热液的参与。综上,根据银山矿床中矿石矿物共生组合特征,划分出该矿床成矿过程经历了3个成矿期和3个成矿阶段,重新厘定银山矿床可能经历了岩浆期成矿作用。岩浆热液期中的中低温热液阶段是期主要成矿期,矿床成因类型为次火山热液矿床。     

Ore Zoning and Dynamics of Ore—Forming Processes of Yinshan Polymetallic Deposit in Dexing,Jiangxi

The Yinshan deposit,one of the large-scale Cu-Pb-Zn-Au-Ag polymetallic deposits,may be named a middle-low temperature subvolcanic hydrothermal deposit and referred to as the “transitional deposit“linking mineralization of the epithermal and porphyry coppertypes.In this paper,the characteristics and structures of ore zoning are briefly described.On the basis of the dynamics of ore-forming processes and applying computer numerical simulation technique,the mechanism of ore zoning is discussed and a concealed igneous body controlling ore deposition at depth of the Yinshan mine is predicted.     

银山矿床成矿作用微量元素地球化学研究

对银山矿床中矿石，岩体和矿体的蚀变围岩及其原岩的稀土及微量元素特征研究表明，热液蚀变作用导致蚀变岩的∑REE普遍升高，而近岩体∑REE则稍低于原岩，蚀变围岩出现Eu亏损，ω（LREE）／ω（HREE）值亦较原岩低，定量计算表明，∑ω（REE）总升幅中有31％下是由围岩质量迁移引起的表观浓缩现象，而另外的69％以上的效应则因流体带入了REE所致，热液具有ω（LREE）／ω（HREE）值低，强Eu正异常的特征，热液的还原性质促使Eu^3 还原为Eu^2 而被活化迁出，导致围岩的Eu负异常扩大；Sr普遍地比原岩降低，Ba普遍显著地升高，而Rb则相对稳定，:Hf,Rh,U,V,Cr,Co,Mo,Ra,Zr表现为不活动或弱活动性，成矿元素Cu,Pb,Zn,Ag Sn等被大量带入，Y，Sc被活化迁出。     

一种特殊的矿化分带──银山Cu－Au多金属矿床多级多中心矿化分带模式

根据银山Ｃｕ－Ａｕ多金属矿床是由构造动力热液和火山－岩浆热液双重耦合成矿作用而形成的新认识，建立了银山矿床新的矿化分带体系──二级多中心矿化分带模式，并探讨了其形成机制及找矿意义。     

Hydrogen and Oxygen Isotope Study on the Water-Rock Interaction of the Yinshan (Cu-) Pb-Zn-Ag Ore Deposit, Jiangxi Province

The δ18O values of vein quartz of different stages from the Yinshan ore deposit are constant around 16‰ and the calculated δ18OH2O values attain 8‰± ; the δDH2O values of fluid inclu-sions in vein quartz are constant at about-60‰. From the surface down to 1200 m below the δ18O values of altered rocks gradually decrease from 15‰± to 11‰± . Various water-rock inversion calculations indicate that the ore fluids were formed by the interaction between meteoric water and phyllite at 350℃ and the effective W/ R value of around 0.1. When the water-rock exchange in the upper mineralization system took place, the effective W / R value increased to 5.0 or more. As a result, an evolution and mineralization model of a buffered open system with two-stage water-rock interactions is proposed in this study.     

江西银山矿床矿物共生组合的重新厘定及其成因意义

江西银山多金属矿床发育南北不对称的矿化与蚀变分带，并以矿区南部的分带性较完整。研究表明，其矿区南部矿化分带的形成，是在成矿热液的缓慢演化过程中各种成矿元素依次沉淀的结果，其中石英或菱铁矿的梳状构造发育，线型蚀变较强，所形成的矿物自形程度高，杂质组分含量低；矿区北部九区含铜Ｚｎ－Ｐｂ矿化带有矿体系中有大量蒸汽加热酸性地下水的混入，这种酸性地下热水在矿床上部产生了大量高岭石化和重晶石化等酸性蚀变，并且     

内蒙古阴山北部四子王旗土壤风蚀量的测试分析

内蒙古阴山北部地区风蚀沙化十分严重,而风蚀量是判断土壤流失和荒漠化的重要指标。以阴山北部乌兰察布市四子王旗典型农牧交错带的耕地为试验地点,根据表层土壤多年的粒径变化,利用粒径对比法,对土壤风蚀量进行估算;并利用插钎法对一次强沙尘暴进行野外实测,推求土壤风蚀量;两种方法互相验证,近而对内蒙古阴山北部乌兰察布市的四子王旗土壤风蚀量进行较为准确测算。同时根据裸露耕地与未耕地(草地)的粒径对比分析,初步了解了该地区的由于传统耕作导致的土壤风蚀的程度,得出了耕地土壤风蚀的主要损失粒径为<0.05 mm的悬移质粉尘颗粒,该区域每年的平均风蚀模数达6 214.7 t/km2a,为干旱区耕地保护性耕作的研究提供基础理论依据。     

What drove late Mesozoic extension of the northern China–Mongolia tract?

The northern China–Mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late Mesozoic time. Late Middle to early Late Jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated North China–Mongolia block and the Siberian plate, but widespread late Late Jurassic–Early Cretaceous extension has not been satisfactorily explained by existing models. Some prominent features of the extensional tectonics of the northern China–Mongolia tract are: (1) Late Jurassic voluminous volcanism prior to Early Cretaceous large-magnitude rapid extension; (2) overlapping in time of contractional deformation in the Yinshan–Yanshan belt with development of extension-related basins in the interior of the northern China–Mongolia tract; and (3) widespread occurrence of alkali granitic plutonism, extensional basins and metamorphic core complexes in the Early Cretaceous. A new explanation is advanced in this study for this sequence of events. The collision of amalgamated North China–Mongolia with Siberia led to crustal overthickening of the northern China–Mongolia tract and formation of a high-standing plateau. Subsequent breakoff at depth of the north-dipping Mongol–Okhotsk oceanic slab is suggested as the main trigger for late Mesozoic lithospheric extension of that tract. Slab breakoff resulted in mantle lithospheric stretching of the adjacent northern China–Mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust. Collectively, these phenomena triggered gravitational collapse of the previously thickened crust, leading to late Late Jurassic–Early Cretaceous crustal extension, and importantly, coeval contraction along the southern margin of the plateau in the Yinshan–Yanshan belt. The proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena, such as the synchronous extension of northerly terranes during major contraction in the neighboring Yanshan–Yinshan belt.