藏北羌塘丁固—加措地区康托组的时代

自西藏区域地质调查大队创建康托组以来,康托组岩石地层单位广泛应用于羌塘地区,普遍认为其时代为新近纪.笔者于丁固-加措地区的康托组地层中采获古近纪轮藻化石Obtusocharat sp.,O.lanpingenis,Gyrogona qinajiangica和部分孢粉化石,并在康托组底部安山岩中获K-Ar年龄65.1～66.5Ma.上述轮藻组合与同位素年龄指示的地层时代为古新世-始新世,据此将测区康托组的时代确定为古近纪.由于测区康托组之上被唢纳湖组或鱼鳞山组角度不整合覆盖,因此康托组时代的确定不仅进一步完善了测区新生代地层系统,还指示测区在康托组与唢纳湖组或鱼鳞山组之间发生了一次强烈的构造运动.     

东天山哈密地区赤湖钼铜矿区斜长花岗斑岩锆石SHRIMP U-Pb年龄

东天山赤湖斑岩钼铜矿床的形成时代和成矿地质背景至今尚存在争议,前人根据同一成矿带中土屋-延东斑岩铜矿的同位素地质年龄信息,认为赤湖钼矿的形成时代为中-晚泥盆世,系塔里木板块北部活动陆缘泥盆纪岛弧火山-深成作用的产物;近期一些研究者根据赤湖斑岩钼铜矿区斜长花岗斑岩锆石U-Pb和谐曲线年龄,认为矿化斜长花岗斑岩的侵位时代为晚石炭世,成矿作用与哈萨克斯坦-准噶尔板块南部活动陆缘晚石炭世汇聚阶段钙碱性岩浆侵入作用有关.在前人研究基础上,笔者对赤湖斑岩钼铜矿区矿化斜长花岗斑岩体进行了锆石SHRIMP U-Pb定年研究,获得322Ma±10Ma(95%可信度)的年龄值,表明赤湖斑岩铜矿床的形成时代为晚石炭世,成矿作用与晚石炭世钙碱性岩浆浅成侵位有关.     

桂东南云开地区变质杂岩锆石SHRIMP U-Pb年代学

对位于华夏古陆东南部的广西云开地区大面积出露的晚前寒武纪变质杂岩中的主体花岗质片麻岩、中深变质的天堂山岩群石榴辉石岩和中浅变质的云开岩群洋中脊型变质基性火山岩(斜长角闪岩)进行了高精度锆石SHRIMP U-Pb定年.获得天堂山岩群石榴辉石岩的形成年龄为1894Ma±17Ma和1847Ma±59Ma,表明其时代为古元古代;云开岩群洋中脊型变质基性火山岩(斜长角闪岩)的喷发年龄为1462Ma±28Ma,证明该地区存在中(-新)元古代的古洋壳残片;获得花岗质片麻岩的侵入年龄为906Ma±24Ma,应为1000Ma前后发生的全球性Grenville期(四堡期)造山作用的产物,并获得2702Ma±13Ma的继承碎屑锆石年龄,这是云开地区乃至华夏古陆目前获得的最古老年龄,证明华夏古陆曾存在新太古代陆壳物质.     

哈尔里克山早古生代岩浆弧的初步确定——来自塔水河一带花岗质岩体锆石SHRIMP U-Pb测年的证据

哈尔里克山南坡塔水河一带花岗质岩体的锆石SHRIMPU-Pb定年结果显示:钾长花岗岩中的锆石8个测点的206Pb/238U加权平均年龄为(462±9)Ma;花岗闪长岩中的锆石8个测点的206Pb/238U加权平均年龄为(447±11)Ma;石英闪长岩中的锆石8个测点的206Pb/238U加权平均年龄为(448±7)Ma。这些年龄值是在哈尔里克古生代复合岛弧带首次获得的中—晚奥陶世中酸性侵入岩的时代,为探讨该古生代复合岛弧带的构造发展历史提供了新的资料。     

东天山库姆塔格沙垄东二长花岗岩锆石SHRIMP U-Pb测年

库姆塔格沙垄东二长花岗岩体由于缺乏同位素年龄依据,其时代厘定一直存在疑问.1∶5万区域地质矿产调查时,对该岩体进行了锆石SHRIMP U-Pb年龄测定,获得了293Ma±6Ma年龄值,表明该岩体形成于晚石炭世.     

东天山大盐池西闪长岩锆石SHRIMP U-Pb测年——对伴生超基性岩时代下限的制约

大盐池西超基性岩一直缺乏可靠的年龄资料,因此时代厘定一直存在疑问.该超基性岩侵入于一个闪长岩体中,1∶5万区域地质矿产调查获得该闪长岩的年龄为303Ma±15Ma.这表明该超基性岩形成于晚石炭世以后.     

红粘土地区水泥土强度的试验研究

红粘土是亚热带气候条件下形成的一种特殊土质。含有红粘土的地基多具有上硬下软的特点,下部红粘土为天然地基软弱下卧层。采用深层搅拌法处理,可充分发挥上部硬塑红粘土的作用,形成复合地基。通过试验得到了水泥红粘土的基本力学参数。在对试验结果进行回归分析后,给出了水泥土强度的影响因素及其与强度的关系,以及不同水泥掺量、龄期水泥土之间的强度推算公式。     

LA-ICPMS U-Pb Ages of Zircon from Metaleucosomes, Olongbuluke Microcontinent, North Qaidam, and Implications on the Response to the Global Rodinia Supercontinent Assembly Event in NW China

INTRODUCTION The Olongbuluke microcontinent , which wasdisintegratedfromthe northern margin of the Qaidamblock (Lu,2002) ,is composed of a two-fold base-ment with cover strata . The lower basement is themedium- to high-grade Delingha complex and theDakendaban Group, and the upper is the low-gradeWandonggou Group. The Wandonggou Group of theupper basement experienced a Late Mesoproterozoicmetamorphic event (see Yu et al .,1994) ,consistentwith the early isotopic geochronological respo…     

胶东西北部玲珑、郭家岭超单元花岗岩成因探讨

玲珑、郭家岭超单元花岗岩的源岩均为胶东岩群变质岩;玲珑超单元花岗岩表现出岩石的不均匀性,其成因为原地、半原地交代-重熔型花岗岩;郭家岭超单元花岗岩则属于有幔源物质参入的同熔型花岗岩.两个花岗岩均经历了多期构造-岩浆作用,最终形成于燕山期;郭家岭超单元最终形成晚于玲珑超单元花岗岩.     

Zircon LA-ICP-MS U-Pb dating and Sr-Nd isotope study of the Guposhan granite complex, Guangxi, China

Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)i value of 0.7064 with an average of εNd(t)=-3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)i value of 0.7173 but a lower εNd(t) value of -5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a 206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.