东坪金矿床上水泉花岗岩单颗粒锆石U—Pb年龄及其地质意义   总被引：1，自引：1，他引：0  

莫测辉  王秀璋  梁华英  程景平 《矿物学报》1998,18(3):298-302

本文对与东坪金矿有密切空间关系的上水泉花岗岩进行了单颗粒锆石U－Pb同位素定年,结果为135．5±0．4Ma,与东坪金矿的成矿年龄有几千万年的时差,表明该岩体与东坪金矿无成因联系,两者分别是不同地质作用的产物。研究结果对目前流行的把金矿与花岗岩密切的空间关系等同于成因联系的传统认识提出异议。  相似文献   

地幔柱构造与地幔动力学--兼论其在中国大陆地质历史中的表现   总被引：5，自引：0，他引：5  

肖龙 《矿物岩石地球化学通报》2004,23(3):239-245

地幔柱构造是基于全地慢对流模式、主要依据热点火山活动提出的新的全球构造理论。它的主要表现形式和产物是地幔柱头上部地壳抬升、岩浆活动形成大火成岩省、大型放射状岩墙群，并导致大陆裂解、板块运动和大规模成矿，是生物灭绝、磁极倒转的诱因。中国大陆的地质演化历史中保存了多期地幔柱活动印记，它们主要是华南新元古代Rodinia地幔柱、古生代古特提斯和峨眉山地幔柱和中一新生代中国东部地慢柱构造事件。上述地幔柱活动产生了地壳抬升、强烈岩浆活动、大陆伸展与裂解、岩石圈剧烈减薄和大规模成矿等重要地质事件。  相似文献   

On the Origin of Crystal-poor Rhyolites: Extracted from Batholithic Crystal Mushes   总被引：22，自引：3，他引：22  

BACHMANN  OLIVIER; BERGANTZ  GEORGE W. 《Journal of Petrology》2004,45(8):1565-1582

The largest accumulations of rhyolitic melt in the upper crustoccur in voluminous silicic crystal mushes, which sometimeserupt as unzoned, crystal-rich ignimbrites, but are most frequentlypreserved as granodioritic batholiths. After approximately 40–50%crystallization, magmas of intermediate composition (andesite–dacite)typically contain high-SiO₂ interstitial melt, similar to crystal-poorrhyolites commonly erupted in mature arc and continental settings.This paper analyzes the feasibility of system-wide extractionof this melt from the mush, a mechanism that can rationalizea number of observations in both the plutonic and volcanic record,such as: (1) abrupt compositional gaps in ignimbrites; (2) thepresence of chemically highly evolved bodies at the roof ofsubvolcanic batholiths; (3) the observed range of ages (up to200–300 ka) recorded by zircons in silicic magmas; (4)extensive zones of low P-wave velocity in the shallow crustunder active silicic calderas. We argue that crystal–meltsegregation occurs by a combination of several processes (hinderedsettling, micro-settling, compaction) once convection is hamperedas the rheological locking point of the crystal–melt mixture(  相似文献   

埃达克岩的特征、成因及构造意义   总被引：26，自引：1，他引：26  

罗照华柯珊  谌宏伟 《地质通报》2002,21(7):436-440

与多数弧岩浆岩具有玄武岩、安山岩、英安岩和流纹岩的岩石组合不同,有一种弧岩浆岩以英安岩及与其成分相当的深成岩为主,由于其独特的地球化学特征被定义为埃达克岩。埃达克岩的显著特征是高Al2O3、Sr、Sr/Y、La/Yb、Zr/Sm而低Y、Yb、Sc。根据熔浆-矿物平衡热力学,岩浆被认为起源于榴辉岩相条件下俯冲板片的部分熔融。这样的熔融条件一般认为要求年轻(<25Ma)而热(≈10℃/km)的水化玄武质洋壳岩石发生俯冲作用,并在大约75～90km深处发生脱水部分熔融形成埃达克岩岩浆。在岩浆弧岩石成因体系中,这样的熔融条件最可能出现在板块俯冲的初始阶段。因此,埃达克岩概念的提出与研究可能具有重要的构造意义。  相似文献   

北祁连山构造－火山岩浆演化动力学   总被引：44，自引：0，他引：44  

夏林圻  夏祖春  徐学义 《西北地质科学》1995,(1)

笔者以区域构造－火山岩浆演化动力学为主线，从研究区域火山岩岩石学的角度探索北祁连山古板块构造体制与火山岩浆作用的关系，主要强调区域上不同特点火山岩的成因，其形成应直接与构造环境有关。作者的研究查明，从元古代末至泥盆纪，北祁连山经历了一个由大陆裂开→大洋化→洋盆扩张并俯冲消减→沟、弧、盆体系形成和完善→洋盆收缩闭合→碰撞造山的全过程，每一阶段均发育有相应岩石地球化学特征的海相火山活动。经确定有如下５种特定的火山岩浆产生环境：（１）元古代末－寒武纪大陆裂谷型火山作用，（２）寒武纪末－早奥陶世洋脊－洋岛型火山作用，（３）奥陶纪岛弧火山作用，（４）中－晚奥陶世弧后盆地火山作用，（５）晚奥陶世－志留纪海盆闭合期火山作用。作者的研究揭示，海底块状硫化物矿床的形成与拉张环境下火山岩浆的产生密切相关。因为海底循环的热卤水在此类矿床的形成中起着决定作用，而这种循环作用受与拉张环境相伴的局部高热流和海底火山活动所驱动。  相似文献   

造山带火山岩浆作用   总被引：9，自引：2，他引：9  

夏林圻 《西北地质》2001,34(3):18-28

造山带火山岩石学研究的主要目的在于重溯造山带的构造－岩浆演化历史。纵观我国到至全球的大陆造山带形成－演化历史，一个造山带往往经历了古大陆裂解，洋陆转换，陆块拼合，碰撞，陆内伸展－盆山耦合和新构造隆升（陆内造山）等众多不同的构造演化阶段，这些不同的构造演化阶段和不同的构造环境均有特定火山岩浆民之相伴。因此，我们可以根据造山带形成－演化不同阶段火山岩浆作用的特点来重溯造山带的的构造－岩浆演化历史，并进而从更大尺度上加以对比，探索全球动力学乃至比较行星学等重大学问题。本文对造山带火山岩石学研究中的一些重要问题进行了讨论和评述，这些问题包括有：板块内部火册浆活动，离散板块边界上的火山岩浆活动，会聚板块边缘的火山岩浆活动。  相似文献   

Petrology, geochemistry and uranium mineralisation of post-collisional magmatism around Goanikontes, southern Central Zone, Damaran Orogen, Namibia     

Paul A.M Nex  Judith A Kinnaird  Grahame J.H Oliver 《Journal of African Earth Sciences》2001,33(3-4)

The Goanikontes area lies within the southern Central Zone of the northeast trending branch of the Damara Orogen. The cover succession around Goanikontes, which comprises Etusis to Chuos Formation metasediments, is in tectonic contact with older pre-Damaran basement rocks. The area can be divided into three structural domains with basement in the east, a northeast-plunging anticline of Damaran metasediments to the west and a high strain zone up to 1 km wide that separates them and truncates the anticline. The high strain zone has provided an important focus for the emplacement of sheeted granites adjacent to the basement-cover contact. Goanikontes is also one of several significant uranium anomalies within the Damaran Orogen, and the excellent 3D exposure of the Swakop river has provided evidence for an interpretation of the tectono-metamorphic setting of magmatism and mineralisation. The granitoids have been divided into equigranular granites and sheeted leucogranites. The sequence of emplacement of the equigranular granites is from red syenogranite (534±7 Ma) to later grey monzogranite (517±7 Ma) with foliated basement-hosted granite of probable time equivalence to the syenogranites. Each type can be distinguished on major- and trace-element geochemistry. The later sheeted leucogranites, which are volumetrically the most important, intrude both basement and cover rocks. These have been divided into six distinct types based on field characteristics and structural setting backed by geochemical data and fluid extraction analyses. The earliest type A are irregular in form, boudinaged and folded by D₃, and geochemically distinct with notably low HFSE; type B's are white, weakly foliated, folded by D₃, garnetiferous and highly peraluminous; type C are tourmaline-bearing, occasionally boudinaged and exhibit the typical sheet-form within the cover rocks. Of the post-D₃ sheets, type D, which is restricted to the high strain zone is characterised by smoky quartz, high radioactivity and often by visible betafite or beta-uranophane; type E, the dominant type within the high strain zone contains prominent oxidation haloes and type F is red in colour, coarsely pegmatitic and has the highest concentration of alkalis. The uranium-mineralised type D sheets have consistently higher fluid and CO₂ content than other sheeted leucogranites. The close correlation between sheet type and uranium abundance, supported by linear trends on LIL plots suggests that the distribution of radiogenic elements is primarily magmatic with more recent meteoric re-distribution, rather than due to substantial hydrothermal modification  相似文献   

岩浆长期分离结晶对岩石锶同位素初始比值的影响   总被引：6，自引：0，他引：6  

刘昌实  杨心宜 《大地构造与成矿学》1991,15(2):152-159

讨论了在岩浆长期分离结晶作用的模式,由于晚期残留熔体相对于早期结晶相其Rb/Sr比增高,当有一定滞留时间条件下,将导致晚期结晶相~(87)Sr/~(86)Sr初始比增高,因而在一个复式岩基内会形成具有不同锶同位素初始比的多个岩石单元。文中以安徽地洼阶段的黄山一狮子岭岩体为例,通过模拟计算,得到其初始岩浆(?)=0.7122,(Rb/Sr)0=3,该岩浆的80％分离结晶形成黄山岩体,其(?)=0.7143(t=130Ma),其余20％的残余熔体结晶后形成狮子岭岩体,其(?)=0.7180(t=123.1Ma)。  相似文献   

Oblique subduction, collision of microcontinents and subduction of oceanic ridge: Their implications on the Cretaceous tectonics of Japan   总被引：2，自引：1，他引：2  

Kenshiro  Otsuki 《Island Arc》1992,1(1):51-63

Abstract The Izanagi plate subducted rapidly and obliquely under the accretionary terrane of Japan in the Cretaceous before 85 Ma. A chain of microcontinents collided with it at about 140 Ma. In southwest Japan the major part of it subducted thereafter, but in northeast Japan it accreted and the trench jumped oceanward, resulting in a curved volcanic front. The oblique subduction and the underplated microcon-tinent caused uplifting of high-pressure (high-P) metamorphic rocks and large scale crustal shortening in southwest Japan. The oblique subduction caused left-lateral faulting and ductile shearing in northeast Japan. The arc sliver crossed over the high-temperature (high-T) zone of arc magmatism, resulting in a wide high-T metamorphosed belt. At about 85 Ma, the subduction mode changed from oblique to normal and the tectonic mode changed drastically. Just after this the Kula/Pacific ridge subducted and the subduction rate of the Pacific plate decreased gradually, causing the intrusion of huge amounts of granite magma and the eruption of acidic volcanics from large cauldrons. The oblique subduction of the Pacific plate resumed at 53 Ma and the left-lateral faults were reactivated.  相似文献   

Sulfur isotopic characteristics of late Cenozoic ore deposits at the arc junction of Hokkaido, Japan     

Shunso  Ishihara Akira  Sasaki 《Island Arc》1994,3(2):122-130

Abstract Sulfide minerals of late Cenozoic vein-type deposits of southwest Hokkaido and Kuril Islands yielded δ³⁴_CDT S values of 2 to 8 permil, which are typical green-tuff values of magnetite-series igneous terrane. Sulfides of the Kitami district of northeast Hokkaido, on the other hand, are characterized by negative δ³⁴S_CDT values, ranging from 0 to - 7 permil. This unique value among ore deposits in the late Cenozoic back-arc terranes in the Japanese Islands is considered to have resulted from extraction of ³²S enriched sulfur from the basement rocks, because of well-developed N-S fracturing in the basement, which is characteristic of the axial belt and Kitami district of Hokkaido.  相似文献