REE concentrations of garnet and omphacite in eclogites from the Dabie Mountain, central China

Distributions of the rare-earth elements (REE) in omphacite and garnet and REE behaviors during metamorphic processes were discussed. The REE concentrations of garnet and omphacite in six eclogite samples from the Dabie Mountain, central China, were measured by inductively coupled plasma-mass spectrometry (ICP-MS). The correlation of δEu ratios between garnet and omphacite indicated that chemical equilibrium of REE distribution between garnet and omphacite could be achieved during ultra-high pressure (UHP) metamorphism. Most of the partition coefficients (Kd=CiOmp/CiGrt) of light rare-earth elements (LREE) are higher than 1. However the partition coefficients of heavy rare-earth elements (HREE) are lower than 1. This indicated that the LREE inclined to occupy site M2 in omphacite, but the HREEs tended to occupy eightfold coordinated site in garnet during the eclogite formation. The REE geochemistry of the eclogites indicated that LREE could be partially lost during the prograde metamorphic process of protolith, but be introduced into the rocks during the symplectite formation. LREE are more active than HREE during the UHP metamorphism. The results are favorable to highlighting the REE behavior and evolution of UHP metamorphic rocks.     

陕西凤县石炭系牙形石组合及其时代

陕西凤县核桃坝剖面含２个牙形石组合，下组合为Ｇｎａｔｈｏｄｕｓｔｙｐｉｃｕｓｓ－Ｓｉｐｈｏｎｏｄｅｌｌａｃｆ．ｉｓｏｓｔｉｃｈａ组合，相当ｔｙｐｉｃｕｓ带和ｉｓｏｓｔｉｃｈａ－上ｃｒｅｎｕｌａｔａ带，属杜内阶；上组合为Ｉｄｉｏｇｎａｔｈｏｄｕｓｄｅｌｉｃａｔｕｓ－Ｎｅｏｇｏｎｄｏｌｅｌｌａｃｌａｒｋｉ组合，其时代为维斯发早期。本文共描述了１５个牙形石种，并讨论了Ｎ．ｃｌａｒｋｉ等３种的个体发育。     

Cooling and exhumation of the oldest Sanqiliu uranium ore system in Motianling district,South China Block

The Sanqiliu uranium deposit belongs to a uranium ore system in Motianling district. It is the oldest uranium deposit in South China. Primary uranium mineralization occurred almost simultaneously with the emplacement of the host granites and subsequent dykes, and it has a relatively high grade of uranium (0.421%). We clarify the age of mineralization and investigate the cooling history through new pitchblende U–Pb and apatite fission‐track thermochronology. The pitchblende U–Pb results indicate that uranium mineralization occurred at ~801–759 Ma. Fractionation of uranium and lead at ~374–295 Ma is interpreted as remobilization and resetting of the original uranium. The Motianling area has apatite fission‐track ages of 57 to 18 Ma. By combining our results with previous work, we conclude that the deposit cooled slowly and was exposed at the surface during the Cenozoic. The timing and depth of exhumation helped to preserve and avoid erosion of the uranium deposit, and highlight the potential for regional uranium exploration.     

碎屑岩成像测井沉积学研究及其在海上油田的应用

基于成像测井技术在我国海域含油气盆地的应用积累,提出了碎屑岩成像测井沉积学的概念。碎屑岩成像测井沉积学的主要研究内容包括地层岩性识别、沉积构造解释、沉积序列与微相分析、砂体物源与古流向分析、砂体分布预测等五个方面。利用南海西部的实际资料,运用成像测井技术,对五方面的应用逐一分析或提出了应用前提、使用步骤、注意要点、已有规律特征以及典型实例。     

河北省石人沟地区麻粒岩-紫苏花岗岩套岩石的矿物学和结晶温压条件

研究区内广泛出露的太古代岩石属于迁西群麻粒岩,包括麻粒岩、紫苏花岗岩、辉石-斜长片麻岩、角闪岩等。对这些岩石中辉石、角闪石、黑云母等矿物的研究结果表明,这些矿物具有明显的麻粒岩相成因特征,角闪石、黑云母同辉石等平衡共存。紫苏花岗岩中矿物除有序度增高外,其他特征与麻粒岩、片麻岩中的矿物相似。 根据矿物对地质温压计计算得到:本区第一期变质作用p-t条件为770-870℃,7.2-8.4k bar第二期为740-760℃,6.6-8.4k bar;矿物氧同位素温度为470-570℃,代表另一次程度较低的变质作用。     

水准测量网监测在德州市地面沉降中的应用

山东地面沉降灾害以鲁北平原最为严重,在德州地区的地面沉降已对当地人民的正常生产和生活构成了威胁,并制约了当地经济的可持续发展。通过建立水准测量网络及监测运行,查明了德州市地面沉降的规模和范围,研究成果表明工作区均存在地面沉降现象,截至2010年,德城区由于地下水开采强度大,地面沉降幅度最大,目前地面累计沉降量为-1186．9～-636．9mm,多年平均沉降速率为59．35mm／a,形成了以市区西北部为中心的地面沉降盆地。超量开采深层地下水是造成大规模地面沉降的重要因素。     

Geochemistry of meta-volcanic rocks from the Longbohe Cu deposit, Yunnan Province, China： Implications for the genesis and tectonic setting

The Longbohe Cu deposit, which is located in the southern part of the Honghe ore-forming zone, Yunnan Province, China, belongs to a typical ore field where volcanic rocks are of wide distribution and are associated with Cu mineralization in time and space. The volcanic rocks in the ore field, which have experienced varying degree of alteration or regional metamorphism, can be divided into three types, i.e., meta-andesite, meta-subvolcanic rock and meta-basic volcanic rock in accordance with their mineral assemblages. These three types of volcanic rocks in the ore field are relatively rich in Na and the main samples plot in the area of alkali basalts in the geochemical classification diagram. With the exception of very few elements, these three types of volcanic rocks are similar in the content of trace elements. In comparison to the basalts of different tectonic settings, the meta-volcanic rocks in the ore field are rich in high field strength elements (HFSE) such as Th, Nb, etc. and depleted in large ion lithophile elements (LILE) such as Sr, Ba, etc. and their primary mantle-normalized trace element patterns show remarkable negative Th and Nb anomalies and negative Sr and Ba anomalies. These three types of volcanic rocks are similar in REE content range and chondrite-normalized REE patterns with the exception of Eu anomaly. Various lines of evidence show that these three types of volcanic rocks in the ore field have the same source but are the products of different stages of magmatic evolution, their original magma is a product of partial melting of the metasomatically enriched mantle in the tensional tectonic setting within the continent plate, and the crystallization differentiation plays an important role in the process of magmatic evolution.     

Catastrophic debris flows triggered by a 14 August 2010 rainfall at the epicenter of the Wenchuan earthquake

The Wenchuan earthquake of May 12, 2008 produced large amounts of loose material (landslide debris) that are still present on the steep slopes and in the gullies. This loose material creates an important hazard as strong rainfall can cause the development of devastating debris flows that will endanger the resettled population and destroy the result of reconstruction efforts. On 14 August 2010, a total of 21 debris flows were triggered by heavy rainfall around the town of Yingxue, located near the epicenter of the Wenchuan earthquake. One of these debris flows produced a debris dam, which then changed the course of the river and resulted in the flooding of the newly reconstructed Yinxue town. Prior to this catastrophic event, debris flow hazard had been recognized in the region, but its potential for such widespread and devastating impacts was not fully appreciated. Our primary objective for this study was to analyze the characteristics of the triggering rainfall and the sediment supply conditions leading to this event. Our field observations show that even small debris flow catchment areas have caused widespread sediment deposition on the existing fans. It is concluded that the whole of the area shaken by the Wenchuan earthquake is more susceptible to debris flows, initiated by localized heavy rainfall, than had been assumed earlier. The results of this study contribute to a better understanding of the conditions leading to catastrophic debris flow events in the earthquake-hit area. This is essential for the implementation of proper early warning, prevention, and mitigation measures as well as a better land use planning in this area.     

康西瓦南岔路口地区早石炭世地层化石的发现

本次区调在1:25万岔路口幅向阳峰一带地质填图和实测地层剖面中,在原划中泥盆统落石沟组中采到了大量腕足、珊瑚类化石,经鉴定其形成时代为早石炭世中期.该套地层与西邻<神仙湾>幅区域地层对比,厘定为早石炭世帕斯群.该生物化石的取得,为该套地层时代划分提供了依据,填补了岔路口地区缺失早石炭世地层的空白,为进一步详细研究甜水海微陆块地层层序格架及地层演化,提供了新的基础资料.     

东天山觉罗塔格带黄山地区角闪辉长岩岩体的年代学、地球化学特征及岩石成因

为了确定东天山觉罗塔格带黄山地区单一的角闪辉长岩岩体的形成时代、源区性质及其构造属性,本文对东天山觉罗塔格带黄山地区早二叠世角闪辉长岩岩体进行了系统的LA-ICP-MS锆石U-Pb定年与地球化学分析。结果表明：2个岩体中的锆石在CL图像上主要呈条痕状吸收,Th/U值较高（0.23~0.58）,指示其岩浆成因,成岩年龄为早二叠世（281.1~282.3 Ma）。这些岩体均由单一的角闪辉长岩构成,w（SiO₂）为46.45%~52.76%,w（MgO）为5.15%~8.42%,w（Al₂O₃）为14.52%~16.84%,Mg^#主要为0.55~0.63;稀土元素配分模式呈右倾型,LREE/HREE=3.36~5.11,（La/Yb）_N=2.64~4.41,δEu值多为1.06~1.98;在微量元素蛛网图上,Rb、Ba、K、Sr等大离子亲石元素相对富集,高场强元素Nb、Ta及Zr、P、Hf相对亏损;ε_Nd（t）=10.66~12.54（t=282 Ma）,平均为11.60。综上所述,东天山觉罗塔格带黄山地区早二叠世角闪辉长岩的岩浆源区主要为受俯冲流体交代的亏损地幔楔。结合同时代火成岩的组合特征、沉积作用以及区域构造演化历史,认为东天山觉罗塔格带黄山地区早二叠世角闪辉长岩体形成于吐哈地块与中天山地块碰撞后的伸展背景。