闽西南永定大坪辉长岩脉的年代学、地球化学特征及地质意义          下载免费PDF全文

王锦荣  吕新彪  张建平  林晓晖  王继林  林香 《地球科学》2021,46(1):73-86

南岭地区湘南-赣南-粤北-闽西南近东西向的岩浆岩活动带在年龄、成因、动力学背景等方面一直存有争议.以福建西南部永定地区的大坪辉长岩脉为研究对象,在详细的野外工作及镜下岩相学观察的基础上,对其开展了斜锆石U-Pb同位素定年、全岩主微量元素含量以及Sr-Nd同位素比值的测试工作.获得同位素年龄为184.0±6.5 Ma,表明岩浆活动为早侏罗世.其地球化学特征具有高碱高钾的特点,无Nb,Ta的正异常,(87Sr/86Sr)_i初始值变化在0.708 0~0.709 0之间,ε_Nd(t)值在-3.6~-3.0之间,显示辉长岩脉起源于富集岩石圈地幔的部分熔融,未经历过壳源物质的AFC作用.该地区同时发育有双峰式火山岩及A型花岗岩,表明在早侏罗世包括永定在内的该岩浆带处于拉张的动力学背景,软流圈上涌,加热EMII型富集岩石圈地幔,分别形成了藩坑组玄武岩和永定大坪辉长岩脉.   相似文献   

云南永平县水泄辉长岩锆石U- Pb年代学、地球化学及地质意义     

李赛赛  王洋  张洪瑞  刘兴源  王秋宇  杨澍 《地质学报》2023,97(4):1157-1177

滇西地区二叠纪—三叠纪岩浆岩展布还不清楚,导致相关古特提斯构造演化模型还存在争议。本文对兰坪-思茅盆地西缘水泄地区的辉长岩开展了LA-ICP-MS锆石U-Pb定年、锆石Hf同位素、全岩主微量元素及Sr-Nd同位素分析,探讨了岩石成因及地质意义。水泄辉长岩2件样品的锆石U-Pb年龄分别为237.8±3.4 Ma和240.8±3.3 Ma,代表其结晶年龄,属于中三叠世。样品具有较高的Na₂O/K₂O(3.81～49.14),明显富集Ba、Rb、Th、U等大离子亲石元素,相对亏损Nb、Ta等高场强元素,稀土元素弱分馏,轻稀土弱富集,δEu值为0.87～1.07,无明显的Eu异常。锆石ε_Hf(t)值全为正值,主要介于+5.67～+15.75,全岩初始⁸⁷Sr/⁸⁶Sr比值为0.70453～0.70776,ε_Nd(t)值全为正值,介于+4.9～+5.2。地球化学特征显示水泄辉长岩来源于亏损地幔的部分熔融,在岩浆演化过程中发生了镁铁质矿物和铁钛矿物的分离结晶作用。水泄...  相似文献   

Geochemical Characteristics and Geological Significance of Early Permian Baya’ertuhushuo Gabbro in South Great Xing’an Range   总被引：1，自引：0，他引：1  

LIU Jianfeng  CHI Xiaoguo  ZHAO Zhi  ZHANG Xingzhou  MA Zhihong  WANG Tiefu  HU Zhaochu 《《地质学报》英文版》2011,85(1):116-129

Field geological investigation and geochemical analysis are carried out on Baya’ertuhushuo Gabbro in South Great Xing’an Range. Field investigation reveals that the gabbro is a magmatic intrusion rather than a component of an ophiolite suite as previously thought. Zircon laser ablation inductively coupled plasma mass spectroscopy (LA-ICP-MS) U-Pb dating indicates the gabbro was formed in 274–275?Ma, just as the widespread volcanic rocks of Dashizhai Formation (P1d), monzogranites and miarolitic alkali-feldspar granites in the study area. The gabbro has SiO2 content between 47.23 wt% and 50.17 wt%, high MgO and FeOT contents of 6.95–11.29 wt% and 7.32–12.24wt%, respectively, and it belongs to low-K tholeiitic series in the SiO2-K2O diagram. The Chondrite-normalized rare earth element (REE) patterns and primitive mantle-normalized spider diagrams of the gabbro are similar to those of Normal Mid-Ocean Ridge Basalt (N-MORB) except for the enrichment of large ion lithophile elements (LILE), such as Rb, Ba and K. In trace element tectonic discriminative diagrams, the samples are mainly plotted in the N-MORB field, and Zircon in?situ Lu-Hf isotopic analysis also indicates the gabbro originated from depleted mantle. Through synthetic studies of the geochemical characteristics and petrogenesis of Baya’ertuhushuo gabbro, volcanic rocks of Dashizhai Formation and granitoids in the area, it is suggested that the early Permian magmatism in the Xilinhot-Xiwuqi area formed in the tectonic setting of asthenosphere upwelling, which was caused by breaking-off of the subducted Paleo-Asian Ocean slab.  相似文献   

A Kinematic Thermal Model for Descending Slabs with Velocity Boundary Layers: A Case Study for the Tonga Subducting Slab   总被引：3，自引：0，他引：3  

ZHANG Keliang an  WEI Dongping 《《地质学报》英文版》2011,85(1):211-222

For the purpose of investigating the influence of metastable olivine (MO) phase transformations on both deep seismicity and stagnation of slabs, we constructed a 2-dimensional finite element thermal model for a 120 Ma-old 50o dipping oceanic lithosphere descending at 10 cm/yr with velocity boundary layers, which would mitigate the interference of constant velocity field for the slab. The resulting temperatures show that most of intermediate and deep earthquakes occurring within the Tonga slab are occurring inside the 800oC and 1200oC isotherm, respectively. The elevation of olivine transformation near ~410 km and respective persistence of metastable olivine and spinel within the transition zone and beneath 660 km would thus result in bimodal positive, zonal, negative density anomalies, respectively. These results together with the resulting pressure anomalies may reflect the stress pattern of the Tonga slab: (i) slab pull force exerts above a depth of ~230 km; (ii) MO existence changes the buoyancy force within the transition zone and facilitates slab stagnation at a depth of 660 km; (iii) as the subducting materials accumulated over 660 km, deepest earthquakes occur due to MO transformation; (iv) a flattened ‘slab’ may penetrate into the lower mantle due to the density increment of Sp transformation.  相似文献   

辽宁东部硼矿成矿化学反应特征     

董宽志  王慧雅  武振凯  刘莹莹 《吉林地质》2011,30(1):75-76

辽宁东部早元古宙辽河群变质岩系底部硼矿床,是我国已知的大型热液矿床.通过对矿床地质、矿物岩石特征研究表明,辽东硼镁矿是层控热液交代矿床.其基底混合花岗岩强底劈上涌作用,促使其近接触带的矿物岩石产生热液交代作用,地层中的电气石分解重组,硼酸根交代蛇纹石、镁橄榄石、大理岩,形成硼镁矿,这一成矿化学反应特征的发现,为辽宁东部...  相似文献   

内蒙古北部乌日尼图地区阿仁绍布辉长岩体的形成时代、地球化学特征及成因   总被引：3，自引：0，他引：3       下载免费PDF全文

贺宏云  鞠文信  宝音乌力吉 《沉积与特提斯地质》2011,(4):70-78

本文系统地报道了内蒙古北部乌日尼图地区阿仁绍布辉长岩的主量元素、微量元素和稀土元素特征,重点讨论了阿仁绍布辉长岩体的岩石成因、原始岩浆的源区特征及其地质意义。研究结果表明,阿仁绍布辉长岩体SiO2含量为49.62%,Al2O3为17.34%,CaO为8.94%,TiO2为1.44%,P2O5为0.26%;岩石富集LILE、亏损HFSE。岩体的Mg#值（0.28～0.68,平均为0.52）较高,反映原始岩浆具幔源原生玄武岩浆特征,在上升过程中经历的结晶分异程度较低。U-Pb锆石年龄测定结果为309±2Ma,代表了阿仁绍布辉长岩体的结晶年龄,为晚石炭世。计算出石英结晶温度为928℃,斜长石结晶温度为1206℃;岩浆冷凝矿物共结晶时的深度大于10km,其结晶条件代表岩体侵位时的物理环境,是在较深的岩浆房中结晶的。阿仁绍布辉长岩具有大陆边缘弧的地球化学特征,可能反映在岩浆形成之前,地幔源区发生了俯冲交代富集作用。  相似文献   

地幔橄榄岩中橄榄石的指示意义   总被引：3，自引：0，他引：3  

汤艳杰  张宏福  英基丰  杨蔚  赵新苗  苏本勋  肖燕 《地球科学与环境学报》2011,33(1):24-33

橄榄石是地幔橄榄岩和辉石岩的主要组成矿物,但也经常以斑晶和捕虏晶的形式出现在玄武质岩石中。结合近年来在地幔橄榄岩的主要元素(如Mg和Fe)组成特征以及Li、Mg和Fe稳定同位素地球化学方面的研究成果,重点对橄榄石的地球化学特征与华北克拉通岩石圈地幔演化过程之间的联系进行了讨论,旨在加深对华北克拉通岩石圈地幔演化过程的理解。现有研究表明:地幔橄榄岩中橄榄石的矿物学特征、元素和同位素地球化学组成能够很好地指示岩石圈地幔的特征及其演化过程,因而具有重要的意义。对于克拉通地区的地幔橄榄岩来说,橄榄石的Mg#通常可以指示岩石圈地幔的属性,古老、难熔的地幔橄榄岩中的橄榄石一般具有较高的Mg#(>92),而新生的岩石圈地幔橄榄岩中的橄榄石则具有较低的Mg#(<91)。因此,地幔橄榄岩中橄榄石的Mg#在一定程度上具有年龄意义。橄榄岩中橄榄石的Li、Mg和Fe同位素组成也可以明确指示岩石圈地幔的属性及其所经历的演化过程,正常地幔的δ7Li、δ26Mg和δ57Fe组成相对均一,如果上述同位素组成偏离正常地幔值,则说明岩石圈地幔经历了熔体/流体的交代作用。华北克拉通地区地幔橄榄岩捕虏体中橄榄石的Li、Mg和Fe同位素组成研究表明:该区的岩石圈地幔经历了多个阶段、不同来源的熔体/流体的改造过程。  相似文献   

内蒙古北山额济纳旗小红山钒钛磁铁矿床SHRIMP锆石U-Pb定年及其意义   总被引：1，自引：0，他引：1  

杨建国  王磊  王小红  谢燮  姜安定 《地质通报》2015,34(9):1699-1705

小红山钒钛磁铁矿床是近年内蒙古北山地区新发现的一个中型钒钛磁铁矿床,含矿辉长岩体侵位于蓟县系平头山组,岩体具全岩矿化,工业矿体主要赋存于中粗粒辉长岩中。采用SHRIMP锆石U-Pb定年方法对小红山中粗粒辉长岩体进行了年代学研究,获得该岩体的锆石微区原位SHRIMP U-Pb年龄为424±6Ma,表明小红山钒钛磁铁矿成岩成矿事件发生于中志留世。该时期钒钛磁铁矿床的发现,揭示了北山地区早古生代处于陆缘裂谷环境,这对研究和认识北山地区地质构造演化及开展岩浆矿床找矿具有重要意义。  相似文献   

The effect of a hydrous phase on P‐wave velocity anisotropy within a detachment shear zone in the slow‐spreading oceanic crust: A case study from the Godzilla Megamullion,Philippine Sea          下载免费PDF全文

Katsuyoshi Michibayashi  Tohru Watanabe  Yumiko Harigane  Yasuhiko Ohara 《Island Arc》2016,25(3):209-219

We studied the contributions of plagioclase, clinopyroxene, and amphibole to the P‐wave velocity properties of gabbroic mylonites of the Godzilla Megamullion (site KH07‐02‐D18) in the Parece Vela Rift of the central Parece Vela Basin, Philippine Sea, based on their crystal‐preferred orientations (CPOs), mineral modes, and elastic constants and densities of single crystals. The gabbroic mylonites have been classified into three types based on their microstructures and temperature conditions: HT1, HT2 and medium‐temperature (MT) mylonites. The P‐wave velocity properties of the HT1 mylonite are dominantly influenced by plagioclase CPOs. Secondary amphibole occurred after deformation in the HT1 mylonite, so that its effect on P‐wave velocity anisotropy is minimal due to weak CPOs. Although the HT2 mylonite developed deformation microstructures in the three minerals, the P‐wave velocity properties of the HT2 mylonite are essentially isotropic, resulting from the destructive interference of different P‐wave velocity anisotropy patterns produced by the distinct CPOs of the three constituent minerals (i.e., plagioclase, clinopyroxene, and amphibole). The P‐wave velocity properties of the MT mylonite are influenced mainly by amphibole CPOs, whereas the effect of plagioclase CPOs on P‐wave velocity anisotropy becomes very small with a decrease in the intensity of plagioclase CPOs. As a result, the gabbroic mylonites tend to have weak P‐wave velocity anisotropy in seismic velocity, although their constituent minerals show distinct CPOs. Such weakness in the whole‐rock P‐wave velocity anisotropy could result from the destructive contributions of the different mineral CPOs with respect to the structural framework (foliation and lineation). These results show that amphibole has a high potential for P‐wave velocity anisotropy by aligning both crystallographically and dimensionally during deformation in the hydrous oceanic crust. The results also suggest that the effect of a hydrous phase on P‐wave velocity anisotropy within the detachment shear zone in a slow‐spreading oceanic crust varies depending on the degree of deformation and on the timing of hydrothermal activity.  相似文献   

大麻坪橄榄石冲击波实验研究与高压态物态方程参数的确定          下载免费PDF全文

陈祖安  袁贤昊  黄晓葛  刘福生  地力夏提  白武明 《地球物理学报》2016,59(1):152-156

利用冲击波进行的动高压实验对研究超高压下的物质性质也是十分有效的.本文报告了对大麻坪采集的橄榄石进行压力在10~45GPa范围的冲击波动高压实验结果.结合前人等温冷压实验结果,确定了实验过程的温度,对于冲击波实验压力从10GPa变化到30GPa时,温度在摄氏几十度到摄氏800多度之间.测量了岩石超高压下密度变化,在3.627~4.009g·cm~(-3)之间.通过回收实验和确定的温度,表明小于30GPa压力实验条件下,没有发生相变过程.同时也确定了状态方程的参数.最后,指出了实验结果在上地幔地球内部物质运动过程的含义,即冷板块中的亚临界橄榄岩可以存在地幔转换带中.  相似文献