Fluid flow during exhumation of deeply subducted continental crust: zircon U-Pb age and O-isotope studies of a quartz vein within ultrahigh-pressure eclogite   总被引：15，自引：0，他引：15  

Y.-F. ZHENG  T.-S. GAO  Y.-B. WU  B. GONG  X. M. LIU 《Journal of Metamorphic Geology》2007,25(2):267-283

Quartz veins in high‐pressure to ultrahigh‐pressure metamorphic rocks witness channelized fluid flow that transports both mass and heat during collisional orogenesis. This flow can occur in the direction of changing temperature/pressure during subduction or exhumation. SHRIMP U‐Pb dating of zircon from a kyanite‐quartz vein within ultrahigh‐pressure eclogite in the Dabie continental collision orogen yields two age groups at 212 ± 7 and 181 ± 13 Ma, which are similar to two groups of LA‐ICPMS age at 210 ± 4 and 180 ± 5 Ma for the same sample. These ages are significantly younger than zircon U‐Pb ages of 224 ± 2 Ma from the host eclogite. Thus the two age groups from the vein date two episodes of fluid flow involving zircon growth: the first due to decompression dehydration during exhumation, and the second due to heating dehydration in response to a cryptic thermal event after continental collision. Laser fluorination O‐isotope analyses gave similar δ¹⁸O values for minerals from both vein and eclogite, indicating that the vein‐forming fluid was internally derived. Synchronous cooling between the vein and eclogite is suggested by almost the same quartz–mineral fractionation values, with regularly decreasing temperatures that are in concordance with rates of O diffusion in the minerals. While the quartz veining was caused by decompression dehydration at 700–650 °C in a transition from ultrahigh‐pressure to high‐pressure eclogite‐facies retrogression, the postcollisional fluid flow was retriggered by heating dehydration at ～500 °C without corresponding metamorphism. In either case, the kyanite–quartz vein formed later than the peak ultrahigh‐pressure metamorphic event at the Middle Triassic, pointing to focused fluid flow during exhumation rather than subduction. The growth of metamorphic zircon in the eclogite appears to have depended on fluid availability, so that their occurrence is a type of geohygrometer besides geochronological applicability to dating of metamorphic events in orogenic cycles.  相似文献   

Geodynamic settings and tectonic model of skarn gold deposits in China: An overview   总被引：47，自引：0，他引：47  

Yan-Jing Chen  Hua-Yong Chen  Khin Zaw  Franco Pirajno  Zeng-Jie Zhang 《Ore Geology Reviews》2007,31(1-4):139-169

Seventy skarn-type gold deposits, including 1 super-large, 19 large and 24 medium-sized, are known from different geotectonic units of China. They contain a total resource of approximately 1000 t of gold (625 t in South China), and account for 20% of China's gold reserves. These skarn deposits are sited in collisional orogenic belts, fault-controlled magmatic belts and reactivated cratonic margins. All of the Chinese skarn gold provinces were affected by Phanerozoic collisional orogenesis. The timing of the metallogenic events and the spatial–temporal distribution of the Chinese skarn gold deposits indicates that they were formed during ore-forming processes linked to the transition from shortening to extension in the geodynamic evolution of a collision orogen, and not to subduction systems as is commonly advocated for porphyry copper systems around the Pacific Rim.  相似文献   

渝怀线彭水隧道进口段涌水处理浅析     

张毅 《中国勘察设计》2007,(11):65-67

渝怀线彭水隧道进口段多次发生特大涌水,该段属可溶岩地区,隧道位于岩溶水平循环带及垂直循环的变化带内,岩溶发育,隧道切穿自北向南向乌江侵蚀基准面排泄的岩溶管道发生涌水,涌水受大气降水补给较快,水量大,治理原则以排为主。  相似文献   

巴布亚新几内亚新生代两类埃达克岩的构造环境意义   总被引：3，自引：0，他引：3  

朱章显  杨振强  姚华舟 《华南地质与矿产》2007,(2):1-6,13

本文根据新几内亚安山岩的化学分析数据与典型埃达克岩进行对比,讨论了巴布亚新几内亚埃达克岩的地球化学特征及其大地构造环境意义。对比结果表明:巴布亚新几内亚埃达克岩微量元素特征为高锶(一般>于400×10-6),Sr/Y比值平均>41.7,重稀土元素Y和Yb含量很低(分别为≤20×10-6和1.9×10-6)。在微量元素蛛网图上有Sr,Ba正异常峰和明显的Nb,Th负异常。稀土元素表现为LREE富集模式,(La/Yb)N比值平均为2.19~18.69。巴布亚新几内亚埃达克岩的M g#值>0.45,87Sr/86Sr值一般<0.7045与典型埃达克岩一相致。巴布亚新几内亚埃达克岩分别位于弧-陆碰撞带大地构造环境中的大洋岛弧和大陆边缘造山带中。埃达克岩的分布区域与世界级斑岩铜-金矿和浅成热泉金矿的成矿带的分布相一致。  相似文献   

多地震活动性参数在断裂带现今活动习性与地震危险性评价中的应用与问题   总被引：12，自引：0，他引：12  

易桂喜  闻学泽 《地震地质》2007,29(2):254-271

为了分析将地震活动性参数用于判定断裂带现今活动习性、进而评估长期地震危险性的可行性,文中介绍了沿断裂带进行b值扫描与填图的方法,以及进行断裂带分段的多参数值(—b、E、n和—a/—b)组合分析的资料处理、计算及分析步骤;提出了为进行多参数计算的、断裂带分段的参考判据,进而概括了根据计算的参数值、结合强震历史背景、现今地震分布综合分析断裂带现今活动习性空间差异的方法与思路。以5条地震活动水平和监测能力各异的断裂带为试验对象,基于归纳的方法综合分析了各断裂带现今活动习性的空间差异及潜在的地震危险段。文中还就断裂的震后调整运动与低b值的关系以及精定位的地震资料在参数计算中的合理使用等问题进行了讨论。主要认识为:以b值为主的若干地震活动性参数的空间分布可有效地用于断裂带现今活动习性及潜在强震危险段落的判定。沿断裂带b值扫描与填图以及断裂带分段多参数值组合分析两种方法,可分别应用于地震监测能力强和一般的地区;若在监测能力强的地区将两种方法结合起来使用,可获得更可靠的结果。晚期余震活跃或者大震后调整运动的断裂段也可表现出较低b或—b值的特点  相似文献   

India-Eurasian collision vs. ocean-continent collision＊     

曾融生吴庆举  丁志峰朱露培 《地震学报(英文版)》2007,20(1):1-10

Introduction Major tectonic activities occur in collisions zones between plates or intra-plate continental blocks. Therefore, it is significant to investigate collision processes. We know that orogenic and seismic belts in plate margins are closely relate…  相似文献   

新疆3次6级强震前的短期前兆异常     

龙海英  聂晓红  孙甲宁  杨晓芳 《内陆地震》2007,21(4):304-310

分析了新疆3次6级强震前的短期前兆异常动态演化图像特征。这3次地震前兆异常的共性是地震前半年都出现了不同程度的短期前兆异常变化,且在震前2个月,短期异常均超过8项。但是3次6级强震发生前前半年的短期前兆异常变化不一致,有向震中迁移的,有包围震中的,还有前兆异常逐渐减少的。这些前兆异常现象同通常认为的越临近地震前兆异常数目越多是不一致的。  相似文献   

Time Series Analysis on the Ratio for Pixels with Abnormal Brightness Temperature Increase and Its Variation Before Some Earthquakes with Ms ≥ 5.0 in the Taiwan Area     

Liu Fang 《中国地震研究》2007,21(4):437-444

In the study of the application of MODIS satellite remote sensing data to earthquake prediction, the paper puts forward for the first time a quantitative method to estimate the ratio for the pixels with abnormal brightness temperature (BT) increase and a preliminary scheme for cloud removal. The principle is that, firstly, the cloudless data observed by the same satellite at the same period of time but in different days (usually 1 day to 3 days) are mosaiced to get high ratio of clear sky, and then the BT variation curve and mean square difference (MSD) of each pixel are calculated with the data from the covered area to determine daily whether the BT data of the day is normal or not at a certain pixel by using double the MSD as the criterion. The ratio for the pixels with abnormal BT increase can be calculated by dividing the total number of abnormal pixels with the total pixels of the whole area. Analysis on a series of recent earthquakes in the Taiwan area shows that the ratio for pixels with abnormal BT increase, which normally undulates around zero, has a sudden enhancement 1 day to 20 days before medium-strong earthquakes. It is expected that a new method for identifying earthquake auspice could be found through special studies in regions with frequent seismic activity by analyzing the change of the ratio for the pixels with abnormal BT increase from MODIS satellite remote sensing infrared (IR) information from which the effect of clouds has been removed to a certain extent.  相似文献   

一种新的气候分型区划方法   总被引：16，自引：1，他引：16       下载免费PDF全文

丁裕国  张耀存  刘吉峰 《大气科学》2007,31(1):129-136

从理论上证明统计聚类检验(CAST)与旋转经验正交函数或旋转主分量分析(REOF/RPCA)用于气候聚类分型区划的关联性。研究表明，CAST在一定的意义上可认为是REOF/RPCA用于气象要素场(气候)分型区划的理论基础。由此，作者提出CAST与REOF/RPCA相结合的一种新的分型区划方法，并用仿真随机模拟资料和实例计算验证了理论与实际结果的一致性，从而证实了这种分型区划方法的有效性及其优点。  相似文献   

断面测量内外业一体化和程序开发     

詹美斌 《四川测绘》2007,30(1):34-36,40

本文系统地介绍了拓普康(Topcon)210/220/310系列及600系列带有内存的全站仪在断面测量中进行自动数据采集过程以及数据传输及处理程序的开发应用。  相似文献