辽西100Ma火山事件的动力学过程及其构造背景     

邵济安  路凤香 《岩石学报》2007,23(6):1403-1412

通过辽西及邻区106Ma 来源于软流圈亏损地幔玄武岩的年代学及玄武岩底部不整合面的研究,认识到:(1)这一时期伴随岩石圈地幔物质的更新,存在着"岩浆间隙"和强烈构造运动的现象,从而推断软流圈底辟体上涌、岩石圈减薄、岩浆活动间隙、强烈构造运动这四者之间的因果关系,其中被软流圈熔体带上来的物质和热能是主导因素,岩石圈减薄是关键;(2)106Na 与116Ma、93Ma、80Ma、45Ma 火山岩之间的对比研究,表明106Ma 开始的岩石圈地幔的更新是一个漫长的不可逆转的过程。(3)通过本区火山岩的演变与相邻大洋板块同期热扩张历史的对比研究,推测晚中生代(120～80Ma)大洋与大陆岩石圈板块同步的演化特征可能反映了它们共同受到岩石圈板块之下同一深部热扰动的控制。  相似文献   

Early J_2 basalts in SE China:Incipience of large-scale late Mesozoic magmatism   总被引：9，自引：0，他引：9  

XIE Xin  XU Xisheng  ZOU Haibo  JIANG Shaoyong  ZHANG Ming  QIU Jiansheng 《中国科学D辑(英文版)》2006,49(8)

The voluminous late Mesozoic igneous rocks in SE China were formed by the multi-stage magmatism. Between 204 Ma (the Ar-39Ar age of limburgite sam- 40 pled at Daoxian in Hunan Province[1]) and 180 Ma, magmatism was dormant for a period of about 25 Ma. Then the magmatism started to become active in the study region during 180―170 Ma (early J2), and con-tinued until the end of the Cretaceous[2]. Therefore, the magmatism in 180―170 Ma is the incipience of large-scale late Mesozoic magmat…  相似文献   

Are the crustal and mantle conductive zones isotropic or anisotropic?     

Mark N. Berdichevsky  Pavel Yu. Pushkarev 《Acta Geophysica》2006,54(4):333-342

One of the significant problems of modern deep magnetotellurics is the recognition of anisotropy in the crustal and mantle conductive zones. In the paper we perform numerical experiment comparing several 2D models of crustal and mantle isotropic and anisotropic prismatic conductors. Anisotropy is modeled by alternating horizontal or vertical thin layers of different resistivities (the vertical layers are parallel to the prism strike). Using these models, we examine conditions under which the magnetotelluric and magnetovariational response functions distinguish between isotropy and anisotropy. The resolution of MT and MV studies depends on the sediments conductance, lithosphere resistance and deep conductor width. Calculations show that the most favorable conditions for anisotropy studies are observed in the active regions characterized by small sediments conductance (10–20 S) and moderate lithosphere resistance (10⁸ Ohm·m²). However, in the stable regions, where sediments conductance exceeds 50–100 S and the lithosphere resistance comes up to 10⁹ Ohm·m², the crustal and mantle anisotropic and isotropic conductors manifest themselves in the equivalent magnetotelluric and magnetovariational functions, which cannot distinguish between anisotropy and isotropy and admit both the interpretations.  相似文献   

Intracratonic asthenosphere upwelling and lithosphere rejuvenation beneath the Hoggar swell (Algeria): Evidence from HIMU metasomatised lherzolite mantle xenoliths     

L. Beccaluva  A. Azzouni-Sekkal  A. Benhallou  G. Bianchini  R.M. Ellam  M. Marzola  F. Siena  F.M. Stuart 《Earth and Planetary Science Letters》2007,260(3-4):482-494

The mantle xenoliths included in Quaternary alkaline volcanics from the Manzaz-district (Central Hoggar) are proto-granular, anhydrous spinel lherzolites. Major and trace element analyses on bulk rocks and constituent mineral phases show that the primary compositions are widely overprinted by metasomatic processes. Trace element modelling of the metasomatised clinopyroxenes allows the inference that the metasomatic agents that enriched the lithospheric mantle were highly alkaline carbonate-rich melts such as nephelinites/melilitites (or as extreme silico-carbonatites). These metasomatic agents were characterized by a clear HIMU Sr–Nd–Pb isotopic signature, whereas there is no evidence of EM1 components recorded by the Hoggar Oligocene tholeiitic basalts. This can be interpreted as being due to replacement of the older cratonic lithospheric mantle, from which tholeiites generated, by asthenospheric upwelling dominated by the presence of an HIMU signature. Accordingly, this rejuvenated lithosphere (accreted asthenosphere without any EM influence), may represent an appropriate mantle section from which deep alkaline basic melts could have been generated and shallower mantle xenoliths sampled, respectively. The available data on lherzolite xenoliths and alkaline lavas (including He isotopes, Ra < 9) indicate that there is no requirement for a deep plume anchored in the lower mantle, and that sources in the upper mantle may satisfactorily account for all the geochemical/petrological/geophysical evidence that characterizes the Hoggar swell. Therefore the Hoggar volcanism, as well as other volcanic occurrences in the Saharan belt, are likely to be related to passive asthenospheric mantle uprising and decompression melting linked to tensional stresses in the lithosphere during Cenozoic reactivation and rifting of the Pan–African basement. This can be considered a far-field foreland reaction of the Africa–Europe collisional system since the Eocene.  相似文献   

江南造山带西段桂北龙胜地区金车辉长岩矿物化学研究及其地质意义          下载免费PDF全文

寇彩化  刘燕学  李廷栋  丁孝忠  张恒 《岩石矿物学杂志》2017,36(1):20-35

桂北龙胜地区位于江南造山带西段,本文利用电子探针对桂北龙胜地区金车辉长岩单斜辉石和斜长石进行了详细的矿物学和矿物化学研究,研究表明单斜辉石的成分为Wo27~28En47~57Fs15~22,属于普通辉石,斜长石的成分为An1.35~9.05Ab90.34~97.45Or0.36~1.05,为钠长石。单斜辉石温压估算结果显示,其形成温度为1 250~1 350℃,该温度基本与软流圈地幔温度(1 280~1 350℃)相当,其形成压力为1.31~2.25 GPa,对应深度为43.2~74.3 km。单斜辉石成分特征指示金车辉长岩为板内拉斑玄武岩,结合区域地质特征,推测金车辉长岩是裂谷构造背景下软流圈地幔物质上涌并发生减压熔融的产物。  相似文献   

大别造山带天柱山中酸性岩起源及地质意义     

刘磊  徐夕生 《高校地质学报》2011,17(1):136-150

天柱山岩体是大别造山带具代表性的中生代中酸性岩体,为两阶段岩浆侵入形成。早阶段角闪石英二长岩具有较大 的SiO2含量变化范围（59.83%~70.12%）,全碱含量为7.02%~9.56%,晚阶段黑云母二长花岗岩SiO2含量为72.46%~78.65%, 具较高的全碱含量（8.05%~10.22%）,两者可归为钙碱性-碱钙性花岗岩类;它们明显富集Rb,Th,K等大离子亲石元素 和Pb,U元素,显著亏损Nb,Ta,Ti等高场强元素;与早阶段相比,晚阶段具显著的Eu负异常,表明其经历了斜长石的分 离结晶过程。Sr,Nd同位素特征显示,天柱山中酸性岩可能来源于化学组成与北大别变质杂岩类似的古老的下地壳物质。 LA-ICP-MS定年结果显示天柱山岩体的侵位年龄为（127±1）Ma~（131±1）Ma,与大别山大规模分布的中酸性岩及基性- 超基性岩的侵位年龄（120~135 Ma）一致。天柱山花岗岩是在陆内伸展的构造环境中形成的,早白垩世大别造山带大规模 岩浆热事件的产生与岩石圈拆沉和软流圈上涌有关,古太平洋板块俯冲远程效应加剧了大别造山带在早白垩世的拉伸,从 而导致岩石圈拆沉。  相似文献   

多玛-德庆-达孜断面壳幔密度结构特征   总被引：1，自引：0，他引：1  

郑洪伟  贺日政 《吉林大学学报(地球科学版)》2006,36(1):113-116,122

利用人机交互重震联合反演的方法研究了多玛-德庆-达孜断面的二维壳幔横向密度结构特征。模拟结果显示,剖面下的地壳内部大部分存在低速层,念青唐古拉山两侧的德庆、羊八井附近存在两条深大正断层,切割并抬升了其下的中地壳低密度层,低密度层整体被向上抬升5～10 km,使得念青唐古拉山深部表现为一个地垒构造。念青唐古拉山位于莫霍面由浅变深的缓坡上,向东逐渐变深。软流圈在念青唐古拉山下形状发生变化,表现为“上凸”特征。  相似文献