浙闽沿海晚中生代伸展构造的岩石学标志:东极岛镁铁质岩墙群   总被引：5，自引：4，他引：1  

董传万  闫强  张登荣  杜振永  竺国强 《岩石学报》2010,26(4):1195-1203

在浙江舟山群岛之东极岛上,出露大规模的镁铁质岩墙群,它们沿晚中生代花岗岩和火山碎屑岩的节理侵位,产状近于直立且与围岩截然接触,指示岩墙岩浆以主动方式沿构造裂隙侵入。东极岛镁铁质岩墙群的岩性主要是角闪辉绿岩,全岩Ar-Ar年龄为93.4Ma。在地球化学上,它们属弱碱性系列,SiO_2含量为46.88%～52.55%,CaO 5.40%～7.82%,Al_2O_316.30%～17.31%,TiO_2 1.53%～1.18%,(Na_2O+K_2O)4.62%～6.88%,Mg~#=34～42;具有轻稀土元素和大离子亲石元素(LILE,如Sr、K、Rb、Ba等)富集、高场强元素(HFSE,如Nb、Ta等)亏损等特点,它们的I_(Sr)为0.7084～0.7098,ε_(Nd)(t)为-3.21～-8.11,与福建沿海的镁铁质岩墙群及浙闽沿海晚中生代基性岩浆岩(辉长岩/辉绿岩和玄武岩)相似。它们由起源于受消减作用影响的岩石圈地幔部分熔融而产生并受地壳混染的玄武岩浆,在伸展构造环境中形成,是浙闽沿海晚中生代伸展构造的重要岩石学标志。  相似文献   

Isotope geochemistry of the mafic dikes from the Vazante nonsulfide zinc deposit, Brazil   总被引：2，自引：0，他引：2  

M. Babinski  L.V.S. Monteiro  A.H. Fetter  J.S. Bettencourt  T.F. Oliveira   《Journal of South American Earth Sciences》2005,18(3-4):293-304

The Vazante Group, located in the northwestern part of Minas Gerais, hosts the most important zinc mine in Brazil, the Vazante Mine, which represents a major known example of a hypogene nonsulfide zinc deposit. The main zinc ore is represented by willemite and differs substantially from other deposits of the Vazante-Paracatu region, which are sulfide-dominated zinc-lead ore. The age of the Vazante Group and the hosted mineralization is disputable. Metamorphosed mafic dikes (metabasites) that cut the metasedimentary sequence and are affected by hydrothermal processes recently were found and may shed light on the geochronology of this important geological unit. Zircon crystals recovered from the metabasites are xenocrystic grains that yield U–Pb conventional ages ranging from 2.1 to 2.4 Ga, so the basement of the Vazante Group is Paleoproterozoic or has metasedimentary rocks whose source area was Paleoproterozoic. Pb isotopes determined for titanite separated from the metabasites have common, nonradiogenic Pb compositions, which prevents determination of their crystallization age. However, the Pb signatures observed for the titanite crystals are in agreement with those determined for galena from the carbonate-hosted Zn–Pb deposits hosted by the Vazante Group, including galena from minor sulfide ore bodies of the Vazante deposit. These similarities suggest that the metalliferous fluids that affected the metabasites may have been those responsible for galena formation, which could imply a similar lead source for both nonsulfide and sulfide zinc deposits in the Vazante–Paracatu district. This common source could be related to deep-seated, basin-derived, metalliferous fluids associated with a long-lived hydrothermal system related to diagenesis and deformation of the Vazante Group during the Neoproterozoic.  相似文献   

塔里木盆地志留系震积岩特征及其意义   总被引：11，自引：3，他引：11       下载免费PDF全文

魏垂高张世奇  姜在兴朱井泉 《地质学报》2007,81(6):827-833866

在区域构造背景研究和岩心观察的基础上,在塔里木盆地志留纪地层中识别出震积岩。震积岩的主要标志是发育各种类型的软沉积变形构造,包括微阶梯状正断层、层内小褶皱、扭曲变形、振动液化砂岩脉、震塌岩等。通过对中1井、顺1井、沙98井等岩心的系统观察,发现由于地震强度的不同,震积岩的垂向序列有所不同,地震越强烈,其震积岩序列的完整性越好,确定出震积岩的两种垂向序列。由于不同的震积岩构造特征对应不同的地震强度,因此进一步研究了各种震积岩构造与地震强度的关系。这些研究为塔里木盆地构造演化研究及震积岩的识别和描述提供了重要的地质理论依据,并可为研究该区古地震提供依据。  相似文献   

变形岩石的体积变化及研究意义     

王涛  王晓霞 《地球科学与环境学报》1994,(3)

变形岩石中普遍存在有不同程度的体积损耗。本文介绍了这方面的研究历史、现状及新进展，总结了三类体积损耗的估算方法．第一类方法是直接对比未变形的和已变形的标志体的体积；第二类方法是基于有限应变类型变化的分析对比；第三类方法是依据变形前后物质成分的变化。  相似文献   

阿尔金山米兰红柳沟的席状岩墙群：海底扩张的重要证据   总被引：21，自引：7，他引：21  

杨经绥  吴才来等 《地质通报》2002,21(2):69-74

米兰红柳沟一带的蛇绿岩位于青藏高原的北部边缘,属于北阿尔金蛇绿岩带的西段,由变质橄榄岩、辉长岩、辉绿岩和基性熔岩组成。野外调查发现约50m厚的均由岩墙组成的岩墙群,其产状近直立,单个岩墙厚约30～40cm。岩墙和与其相伴的熔岩成分相同,属拉斑玄武岩系列,可与典型的洋底玄武岩对比。成分特点:SiO2含量为45wt%～49wt%,TiO2为～1wt%,K2O小于0.3wt%,P2O5为0.1wt%);LREE轻微富集到平坦型,(La/Sm)N0.86～1.74;Cr、Ni、Co和V等过渡金属元素含量高。岩墙群的发现为古海底扩张形成洋壳提供了关键性证据,并可进一步研究洋壳的形成过程和构造背景。  相似文献   

滑坡破坏时间预报新理论探讨   总被引：5，自引：0，他引：5  

廖小平 《地质灾害与环境保护》1994,5(3):25-29

本文概述了当前滑坡破坏时间预报的研究水平和现状。为了完善滑坡预报方法和提高滑坡预报水平,作者从滑坡破坏的基本概念入手,提出了一种滑坡破坏时间预报的新理论,推导和确定了预报标准,比较科学地建立了预报参数,并具体地探讨了各阶段预报的预报策略及其分析处理方法。同时,还展望了滑坡动力反应及其应用研究的广阔前景。  相似文献   

Zircon U-Pb age,geochemical, and Sr-Nd-O isotopic constraints on the origin of the youngest Mesozoic adakitic dikes in Jiaodong peninsula,North China Craton: implications for Early Cretaceous crustal evolution     

Dongsheng Ding  Enpu Gong  Xinfu Zhao 《International Geology Review》2020,62(4):446-464

ABSTRACT

The adakitic dikes with zircon ages of ~120–118 Ma are identified in the Xiejiagou gold deposit, Jiaobei terrain. The Early Cretaceous intermediate-acidic dikes include monzonite, quartz monzonite, and monzogranite, which have SiO₂, Al₂O₃, K₂O, Na₂O contents ranging from 61.01 to 74.72 wt. %, 14.42 to 17.28 wt.%, 2.55 to 4.45 wt.%, and 3.09 to 4.64 wt.%, respectively. The dikes are enriched in large ion lithophile elements (LILEs) (e.g., Rb, Sr, and Ba) and light rare earth elements (LREEs), but are depleted in high field strength elements (HFSEs) (e.g., Nb, Ta) and heavy rare earth elements (HREEs). They are also characterized by continental crust-like isotopic compositions: whole-rock δ¹⁸O = 7.6–9.9‰, (⁸⁷Sr/⁸⁶Sr)_i = 0.70893–0.71036, and ε_Nd(t) = ?13.16 to ?17.06. Assimilation and fractional crystallization are limited, and partial melting of source rock is the main mechanism in controlling the compositional variation. The high Sr/Y (41.51–93.25) and (La/Yb)_N (22.9–44.7) ratios imply that the dikes have affinities similar to adakitic rocks. The regional geological setting, coupled with the geochemical and isotopic data, indicate that the adakitic dikes were unlikely produced by partial melting of a subducted oceanic slab or a thickened/delaminated lower crust, or AFC processes of mantle-derived magmas. We conclude that the adakitic dikes are generated by partial melting of lower crust which was triggered and modified by underplating of the lithospheric mantle. We also propose that the eastern part of the North China Craton experienced severe thinning in the Early Cretaceous (~135–120 Ma), and the lithospheric thinning is related to delamination of the lower crust.  相似文献   

Structural geology of the Mesozoic Miers Bluff Formation and crosscutting Paleogene dikes (Livingston Island, South Shetland Islands, Antarctica) – Insights into the geodynamic history of the northern Antarctic Peninsula     

S. Kraus  H. Miller  D. Dimov  E. Hegner  M. McWilliams  Z. Pecskay 《Journal of South American Earth Sciences》2008,26(4):498-512

The Antarctic Peninsula has been part of a magmatic arc since at least Jurassic times. The South Shetland Islands archipelago forms part of this arc, but it was separated from the Peninsula following the Pliocene opening of the Bransfield Strait. Dikes are widespread throughout the archipelago and are particularly accessible on the Hurd Peninsula of Livingston Island. The host rocks for the dikes are represented by the Miers Bluff Formation, which forms the overturned limb of a large-scale fold oriented 63/23 NW. The orientation of minor structures indicates a fold axis oriented NNE–SSW (24/0). Structural analysis of the dikes and their host rocks shows that the tectonic regime was similar to other parts of the archipelago and that only minor changes of the stress field occurred during dike emplacement.Based on crosscutting field relationships and geochemical data, six early Paleocene to late Eocene intrusive events can be distinguished on Hurd Peninsula. In contrast to calc-alkaline dikes from other parts of the South Shetland Islands, the majority of the Hurd Peninsula dikes are of tholeiitic affinity. Nd and Pb isotope data indicate a significant crustal component, particularly during initial magmatic activity.Plagioclase ⁴⁰Ar/³⁹Ar and whole rock K–Ar ages show that dike emplacement peaked during the Lutetian (48.3 ± 1.5, 47.4 ± 2.1, 44.5 ± 1.8 and 43.3 ± 1.7 Ma) on Hurd Peninsula and also further northeast on King George Island. Dike intrusion continued on Livingston Island at least until the Priabonian (37.2 ± 0.9 Ma). The type of magma sources (mantle, slab, crust and sediment) did not change, though their relative magmatic contributions varied with time.During Cretaceous and Early Paleogene times, the Antarctic Peninsula including the South Shetland Islands was situated southwest of Patagonia; final separation from South America occurred not before the Eocene. Thus, the geological evolution of Livingston Island is related as much to the development of Patagonia as of Antarctica, and needs to be considered within the history of southernmost South America.  相似文献   

Liquefaction evidence for strong earthquakes of Holocene and latest Pleistocene ages in the states of Indiana and Illinois, USA   总被引：5，自引：0，他引：5  

S. F. Obermeier 《Engineering Geology》1998,50(3-4):227-254

Sand- and gravel-filled clastic dikes of seismic liquefaction origin occur throughout much of southern Indiana and Illinois. Nearly all of these dikes originated from prehistoric earthquakes centered in the study area. In this area at least seven and probably eight strong prehistoric earthquakes have been documented as occurring during the Holocene, and at least one during the latest Pleistocene. The recognition of different earthquakes has been based mainly on timing of liquefaction in combination with the regional pattern of liquefaction effects, but some have been recognized only by geotechnical testing at sites of liquefaction.

Most paleo-earthquakes presently recognized lie in Indiana, but equally as many may have occurred in Illinois. Studies in Illinois have not yet narrowly bracketed the age of clastic dikes at many sites, which sometimes causes uncertainty in defining the causative earthquake, but even in Illinois the largest paleo-earthquakes probably have been identified.

Prehistoric magnitudes were probably as high as about moment magnitude M 7.5. This greatly exceeds the largest historic earthquake of M 5.5 centered in Indiana or Illinois. The strongest paleo-earthquakes struck in the vicinity of the concentration of strongest historic seismicity. Elsewhere, paleo-earthquakes on the order of M 6–7 have occurred even where there has been little or no historic seismicity.

Both geologic and geotechnical methods of analysis have been essential for verification of seismic origin for the dikes and for back-calculating prehistoric magnitudes. Methods developed largely as part of this study should be of great value in unraveling the paleoseismic record elsewhere.  相似文献   

Geochemical Characteristics,Petrogenesis of the Sanukitic Dikes in the Miaoergou Area of West Junggar,Xinjiang, NW China and Their Geological SignificanceEI北大核心CSCD     

Duan F.  Li Y.  Zhi Q.  Wan Y.  Ren Y. 《大地构造与成矿学》2018,(4):759-776

NS-trending dikes which contain dioritic enclaves widely occur in the Miaoergou pluton, West Junggar, Xinjiang. The dikes are composed of quartz diorite and quartz diorite porphyrite. LA-ICP-MS zircon U-Pb ages of the quartz diorite and diorite are 298.0±3.7 Ma and 299.4±2.5 Ma, respectively, corresponding to the end of the Late Carboniferous to beginning of the Early Permian. The dikes and enclaves have similar geochemical properties with island arc features. They are calc-alkaline, with moderate SiO2 (53.58% to 57.89%), high MgO (3.09% to 4.83%, Mg# values ranging from 44.69 to 54.12), TiO2 (1.17% to 1.66%), Cr (51.24×10-6 to 126.1×10-6), Ni (35.91×10-6 to 57.55×10-6) contents and K/Na ratios (0.35 to 0.70). Moreover, all samples are enriched in large-ion lithophile elements (LILEs: e.g. K, Rb, Ba and U) and light rare earth elements, but strongly depleted in high field strength elements (HFSEs: e.g. Nb, Ta and Ti), with insignificant Eu anomalies (δEu=0.67 to 1.08). In contrast, the dikes and enclaves in the Miaoergou pluton show geochemical signatures similar to those of the Cenozoic sanukitoids in Setouchi volcanic belt of SW Japan and the sanukitoids in the Hatu area, West Junggar. The source of the dikes might be the depleted mantle previously metasomatized by fluids released from subduction slabs. These sanukitic dikes may be generated by interaction of the mantle wedge with fluids derived from dehydration of the subducting oceanic slab, resulting in 2% to 5% partial melting of amphibole-spine peridotite. The identification of the sanukitic dikes in the Miaoergou pluton, together with previous studies, suggest that the southern West Junggar region was still dominated by subduction-related island arc setting at the beginning of the Early Permian, and multi-stage subduction-accretionary orogeny may account for the difference of subduction duration between the north and the south of West Junggar. © 2018, Science Press. All right reserved.  相似文献