西准噶尔南部晚古生代侵入岩特征和构造背景   总被引：2，自引：0，他引：2  

党飞鹏  王居里  杨猛  宋子升 《地质与资源》2011,20(6):440-451

西准噶尔地区南部达拉布特断裂两侧广泛发育晚古生代花岗岩类,其锆石U-Pb年龄范围为337~276 Ma,属早石炭世-早二叠世.基于前人相关研究资料和成果,总结区内花岗岩类的岩石学、地球化学特征,认为：①岩石类型从早到晚由中性的闪长岩向酸性的花岗岩及碱长花岗岩转变.相应地,成因类型由埃达克岩质花岗岩→岛弧I型花岗岩→A型花岗岩.②岩石系列从早到晚由钙碱性向高钾钙碱性及后期钾玄岩系列转变.相应地,Na₂O/K₂O比值亦由大于1向小于1转变.③从早到晚区内花岗岩类的∑REE、δEu、L/H及Sr、Yb含量均呈规律性变化.并且相对富集LILE,亏损HFSE和不同程度亏损Nb、Ta.④均具有高正εNd（t）、低（⁸⁷Sr/⁸⁶Sr）_i值和Nd模式年龄较小的特征.⑤在构造环境判别图解上,区内花岗岩从早到晚显示出由碰撞挤压向后碰撞伸展体制转换的趋势.上述几点说明区内花岗岩可能主要产出于后碰撞挤压-伸展转换和伸展拉张的构造背景,并且早阶段的岩浆活动可能与俯冲-碰撞背景下的俯冲板片断离密切相关.  相似文献   

内蒙古贺根山蛇纹岩化流体来源的H-O-B同位素地球化学制约   总被引：1，自引：0，他引：1  

龙雄志  郭锋  赵亮  章清文  吴扬名 《大地构造与成矿学》2017,41(3):590-603

对内蒙古贺根山蛇绿岩带内3个采样点的蛇纹岩样品开展了主量、微量元素和H-O-B同位素分析,以揭示其构造属性、蛇纹石化温度和流体来源。贺根山蛇纹岩具有低Al_2O_3含量(0.2%~1.3%)、高Mg~#(89~92)特征,为难熔地幔残余。蛇纹岩的U型稀土元素配分模式、相对富集LILE和亏损HFSE的微量元素地球化学特点,反映其原岩为化学成分高度亏损的俯冲带型(SSZ)超基性岩。样品的dD值相对均一(dD=-120‰~-133‰);理论计算显示,这些蛇纹岩的H同位素组成可能是蛇绿岩剥露地表后与区域大气降水发生再平衡作用的结果。贺根山蛇纹岩的d~(18)O变化在4.3‰~9.8‰之间,反映不同地点蛇纹石化的温度存在差别:其中贺根山东样品具有相对较高的d~(18)O值(d~(18)O=7.7‰~9.8‰),蛇纹石化温度为90~130℃,同时部分样品中出现碳酸盐矿物,表明蛇纹石化作用发生在近海底环境;小坝梁样品具有最低的d~(18)O值(d~(18)O=4.3‰~5.0‰),其蛇纹石化温度在205~235℃之间;贺根山南样品的d~(18)O值变化范围较大(d~(18)O=6.0‰~9.7‰),其蛇纹石化温度在90~170℃之间。3个采样点蛇纹岩的d~(11)B值也显示出一定的变化(d~(11)B=9.1‰~14.7‰),指示蛇纹石化流体来源于脱水的蚀变洋壳和海底沉积物;理论模拟和计算结果显示,这些板片流体的d~(11)B值变化在15‰~25‰之间。  相似文献   

板式基础托换法开发地下空间施工过程的数值分析     

贾强  张鑫 《岩土力学》2010,31(6):1989-1994

板式基础托换法是应用在既有建筑物地下空间开发中的一种方法。它先施工拟建地下室的部分顶板,依靠板下土体支撑既有建筑物的荷载,同时开挖其余部分的土方。土方开挖后,再施工该区域的柱或墙等竖向构件以及底板;然后,依靠这部分底板支撑上部荷载,完成剩余的土方开挖和顶板、底板的施工。利用ANSYS建立三维有限元模型,分5个工况对托换施工过程进行分析,得到各部位柱脚的沉降规律：在土方开挖之前,中间部位柱脚的沉降大于周边部位的柱脚;土方开挖后,由于“卸载”作用中间部位柱脚出现明显的回弹,使得中间部位柱脚的沉降小于周边部位的柱脚。不均匀沉降值的大小和地基土的弹性模量以及上部结构是否加载有关。不均匀沉降产生的上部结构的附加弯矩可以通过建立二维有限元模型求出。  相似文献   

防水措施对堤坝地震液化影响的数值分析     

夏志凡  叶冠林  王建华  叶斌  张锋 《岩土力学》2010,31(8):2682-2688

通过基于有效应力的完全耦合动力分析方法,研究了混凝土面板坝在地震作用下的动力响应,详细地讨论了堤坝迎水面斜坡上铺设的防水毯对堤坝地震液化的影响。计算中土体采用Cyclic mobility本构模型,该模型通过在修正剑桥模型上增加应力诱导各向异性、超固结和结构性的概念及其相关发展准则,可以很好地描述可液化土体的动力特性。计算结果表明防水毯的存在可以有效降低坝体的地下水位浸润线,增加坝基的初始有效应力,从而降低坝基地震液化发生的可能性,同时坝体的变形明显减小。  相似文献   

Ridge subduction and porphyry copper-gold mineralization:An overview   总被引：35，自引：0，他引：35  

SUN WeiDong    LING MingXing    YANG XiaoYong  FAN WeiMing  DING Xing & LIANG HuaYing CAS Key Laboratory of Isotope Geochronology  Geochemistry  Guangzhou Institute of Geochemistry  Chinese Academy of Sciences  Guangzhou  China  Research Center for Mineral Resources  School of Earth  Space Sciences  University of Science  Technology of China  Hefei  Graduate University of Chinese Academy of Sciences  Beijing  Key Laboratory for Metallogenic Dynamics  ... 《中国科学:地球科学(英文版)》2010,(4)

Many large porphyry Cu-Au deposits are connected to adakitic rocks known to be closely associated with ridge subduction. For example, there are several subducting ridges along the east Pacific margin, e.g., in Chile, Peru, and South America, most of which are associated with large porphyry Cu-Au deposits. In contrast, there are much fewer ridge subductions on the west Pacific margin and porphyry Cu-Au deposits are much less there, both in terms of tonnage and the number of deposits. Given that Cu and Au are...  相似文献   

Dissecting large earthquakes in Japan: Role of arc magma and fluids     

Dapeng  Zhao  M. Santosh    Akira  Yamada 《Island Arc》2010,19(1):4-16

We synthesized information from recent high-resolution tomographic studies of large crustal earthquakes which occurred in the Japanese Islands during 1995–2008. Prominent anomalies of low-velocity and high Poisson's ratio are revealed in the crust and uppermost mantle beneath the mainshock hypocenters, which may reflect arc magma and fluids that are produced by a combination of subducting slab dehydration and corner flow in the mantle wedge. Distribution of 164 crustal earthquakes ( M 5.7–8.0) that occurred in Japan during 1885–2008 also shows a correlation with the distribution of low-velocity zones in the crust and uppermost mantle. A qualitative model is proposed to explain the geophysical observations recorded so far in Japan. We consider that the nucleation of a large earthquake is not entirely a mechanical process, but is closely related to the subduction dynamics and physical and chemical properties of materials in the crust and upper mantle; in particular, the arc magma and fluids.  相似文献   

藏北双湖山字形山玄武岩锆石U-Pb年龄、地球化学特征及其地质意义     

马龙  李忠雄  李勇  刘函  吴成书  卫红伟  邓奇 《现代地质》2016,30(4):748-759

次对藏北双湖山字形山玄武岩进行了同位素年代学和岩石地球化学研究。锆石LA ICP MS U Pb测年结果表明,玄武岩形成时代为中三叠世Ladinian期((2358±27) Ma)。主量元素SiO2质量分数为4284%~5222%,TiO2为161%~269%,FeOT/MgO为152~194,属亚碱性系列拉斑玄武岩。稀土元素∑REE含量为11409×10-6~20847×10-6,(La/Yb)N为490~650,相对富集LREE。微量元素配分模式曲线与OIB型玄武岩相似。岩石成因研究表明岩浆在演化过程中主要受分离结晶作用控制,La/Nb、La/Ta、Zr/Ba等不相容元素比值与Ti含量表明,山字形山玄武岩可能是软流圈地幔与岩石圈地幔相互作用的产物。玄武岩较高的Zr含量与Zr/Y比值显示其处于板内伸展构造背景。结合区域地质资料推测,中三叠世玄武质岩浆是南、北羌塘地块碰撞造山过程中板片断离、软流圈物质上涌熔融的产物,而晚三叠世偏铝质-过铝质岩浆岩及高压变质岩折返剥露为造山带垮塌引起的伸展作用的结果。  相似文献   

日本俯冲带地震发生过程的数值模拟研究   总被引：1，自引：1，他引：0       下载免费PDF全文

姜辉  邓志辉  高祥林  陈梅花  杨竹转 《地球物理学报》2013,56(7):2303-2312

了解地震发生的动力学机制是研究地震发震原因的关键,而数值模拟的方法是高速、有效的手段.2011年3月11日日本东北部宫城县发生9.0级大地震,文中以该次大地震所在的日本俯冲带为研究对象,通过使用黏弹性有限元数值模拟,并引用接触对,建立了研究区二维数值模型,模拟俯冲带与上覆板片之间的滑动、黏滞到再滑动的过程,亦即断层失稳发生地震的过程.模拟结果显示,随着太平洋板块不断俯冲,在俯冲带上自发出现了断层闭锁、解锁到再闭锁的黏滑过程,且这种过程呈现一定的准周期性,大事件主要集中分布在20~30 km的深度范围内.根据俯冲带可能在俯冲过程中角度的变化,建立了不同的模型,进行模拟对比研究,结果表明,俯冲带的几何形态,以及俯冲角度变化所在的不同深度,对模拟的结果有不同的影响.  相似文献   

Slab break-off model for the Triassic syn-collisional granites in the Qinling orogenic belt,Central China: Zircon U-Pb age and Hf isotope constraints     

《International Geology Review》2012,54(4):492-507

Numerous Triassic granitoids in the Qinling orogenic belt related to the Late Triassic collision between the North China Craton (NCC) and the Yangtze Block (YB) are important for determining the crustal composition at depth and the geodynamic processes by which the orogen formed. Most of the Triassic plutons in the Qinling orogen were emplaced between 205 and 225 Ma. The granitoid rocks from the southern margin of the NCC, North Qinling, South Qinling, and the northern margin of the YB that were emplaced during this interval have two-stage Hf model ages of 0.60–2.52 Ga (average 2.19 Ga), 0.90–2.66 Ga (average 1.29 Ga), 0.41–3.04 Ga (average 1.48 Ga), and 1.00–1.84 Ga (average 1.34 Ga), respectively, and mean ε_Hf(t) values of ?14.5, ?0.32, ?1.36, and ?3.98, respectively. The Hf isotope compositions of the granitoids in different tectonic units differ significantly, mirroring the diverse history of crustal growth of the four units.

The temporal and spatial distribution and Hf isotope compositions of the granitoids suggest that there was a unified geodynamic process that triggered the magmatism. Formation of the Triassic granitoid plutons at 225–205 Ma was a consequence of slab break-off or E–W-striking slab tearing, related to slab rollback in the west part of the Qinling orogen and oblique continental collision in the east. Upwelling of the asthenospheric mantle led to partial melting of the subcontinental lithospheric mantle and the lower crust, and mixing and/or mingling of the resulting magmas resulted in the formation of granitoids with diverse geological and geochemical characteristics.  相似文献   

Mg-Sr isotopes of low-δ26Mg basalts tracing recycled carbonate species: Implication for the initial melting depth of the carbonated mantle in Eastern China     

《International Geology Review》2012,54(11):1350-1362

ABSTRACT

Recent studies show that crustal carbonates recycled into the mantle can be traced using Mg isotopes of basalts. However, the species of recycled carbonates are poorly constrained. Carbonates have lower δ²⁶Mg values and higher ⁸⁷Sr/⁸⁶Sr ratios relative to the mantle, but different carbonate species display different mixing curves with the mantle in the Mg-Sr isotopic diagram because of differences in their Sr and Mg contents. Thus a combined study of Mg-Sr isotopes can constrain the species of deeply recycled carbonates. Here, we present newly determined ⁸⁷Sr/⁸⁶Sr ratios of the <110 Ma basalts from Eastern China, and together with published Mg isotopic data we evaluate the species of recycled carbonates in the mantle and discuss their implication. The <110 Ma basalts display low δ²⁶Mg values of ?0.60 to ?0.30‰ and relatively low initial ⁸⁷Sr/⁸⁶Sr ratios of 0.70328 to 0.70537, suggesting that their mantle source was hybridized by recycled carbonates with a light Mg isotopic composition which had more significant effects on Mg than Sr isotope ratios. Mg-Sr isotopic data indicate that the recycled carbonates consist of magnesite and aragonite, but the possibility of calcite and dolomite cannot be eliminated. Based on the carbonated peridotite solidus, the equilibrium line between dolomite and magnesite + aragonite, as well as the mantle adiabat, the initial melting depth of the carbonated mantle, the source region of the studied basalts, was constrained at ~300–360 km. Thus, the subducted depth of the west Pacific slab underlying the carbonated mantle and supplying recycled carbonates should be greater than ~300–360 km, consistent with the seismic tomography result that the west Pacific slab now stagnates in the mantle transition zone.  相似文献