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1.
Kirsten L. Rasmussen David R. Lentz Hendrik Falck David. R.M. Pattison 《Ore Geology Reviews》2011,41(1):75-111
A field and petro-chemical classification of felsic magmatic phases (FMPs) at the world-class Cantung W skarn deposit was undertaken to document the evolution of magmatism and the relationships between different FMPs, metasomatism, and mineralization. Early FMPs include moderately differentiated (Zr/Hf = 18–26, Ti/Zr = 14–15) biotite monzogranitic plutons and early biotite-rich granitic dykes, and compositionally similar quartz–feldspar porphyry dykes. Late, highly fractionated (Zr/Hf = 8–17, Ti/Zr = 3–13) FMPs sourced from a deeper monzogranitic intrusion include: (1) leucocratic biotite- or tourmaline-bearing dykes derived from localized entrapments of residual magma; and, (2) sub-vertical NE-trending aplitic dykes derived from a larger segregation of residual fluid- and incompatible element-enriched magma. The aplitic dykes have textures, morphologies, spatial associations, and a pervasive calcic metasomatic mineral assemblage (Ca-plagioclase + quartz or clinozoisite) indicative of syn-mineralization emplacement. Very late-stage overpressuring and initiation of sub-vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aCa2+ in the fluid and the concurrent precipitation of W skarn. Residual magma also ascended with, and quenched in equilibrium with the magmatic fluid to from the aplitic dykes, then was metasomatized by the fluid as it interacted with calcareous country rocks. Overall, highly fractionated and moderately to very highly undercooled FMPs at Cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid- and incompatible element-enriched residual magma until the latest stages of crystallization. The detailed study of FMPs associated with magmatic-hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion-related mineralization. 相似文献
2.
T. Radhakrishna 《Journal of the Geological Society of India》2009,73(1):131-142
South Indian granulite terrain had witnessed significant part of Precambrian mafic igneous activity in the form of episodic
mafic dyke intrusions of the Palaeoproterozoic period. Strike trends of these dykes are not uniform over the region and the
dykes are generally fresh, massive, black dolerites except in the Bhavani shear zone bordering the southern fringes of Nilgiri
massif. In Agali-Coimbatore area of our study in the western Bhavani shear zone, the dykes appear to be penecontemporaneous
with shearing. Isotopic data place age of Agali-Coimbatore dyke intrusions at about 2.1 Ga. The age of these dykes is significant
to constrain an early Palaeoproterozoic age for major shearing event in the Bhavani shear zone. Other dyke emplacement ages
are placed at about 1.8 Ga and 1.65 Ga based on the Ar/Ar and K-Ar isotopic results of dykes in Dharmapuri and Tiruvannamalai
areas. Older ages comparable to those of the Dharwar craton are not known and in this respect future isotopic dating is vital.
Geochemically, these dykes are quartz/hypersthene normative subalkalic tholeiites. An attempt is made here to provide insights
into the general petrogenetic history of the Precambrian dykes. Compositional trends are explained by the fractional crystallization
of ferromagnesian phases and plagioclase control is conspicuous at the advanced stages of fractionation. Geochemical characteristics
suggest that the dykes have tapped Fe-rich non-pyrolite mantle sources with LIL and LREE enrichment as in many continental
basalts. The data suggest that role of crustal contamination is limited in petrogenesis; crustal signatures are noticed in
the more mafic end members formed in early stage of evolution suggesting that contamination was temperature controlled with
most primitive high temperature magmas being most vulnerable to the process. Nd-Sr isotopic data, at present restricted to
Agali-Coimbatore dykes, suggest that Palaeoproterozoic magmas tapped subcontinental lithosphere that may have stabilized in
the Archaean times at about 3 Ga during the major crustal building activity in the shield region. Further work coupled with
isotopic and mineral chemistry will improve our knowledge on the petrological evolution of the dyke magmas and mafic magmatism
in general. 相似文献
3.
We approach the reconstruction of the recent structural evolution of Stromboli volcano (Italy) and the analysis of the interplay between tectonics, gravity and volcanic deformation. By tying together structural, lithostratigraphic and rock mechanics data, we establish that since 100 ka BP, the edifice has faulted and jointed mainly along NE-striking planes. Faults mostly dip to the NW with normal displacement. Taking also into account the presence of a NW-trending regional least principal stress and of tectonic earthquake hypocenters inside the cone, we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone. Dyking concentrated along a main NE-trending weakness zone (NEZ) across the volcano summit, resembling a volcanic rift, whose geometry is governed by the tectonic field. In the past 13 ka, Stromboli experienced a reorganisation of the strain field, which was linked with the development of four sector collapses affecting the NW flank, alternating with growth phases. The tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders. We propose that tectonics control the geometry of dykes inside the cone and that these, in turn, contribute to destabilise the cone flanks. 相似文献
4.
Ken Thomson 《Bulletin of Volcanology》2007,70(2):183-201
Three-dimensional seismic data from the Faeroe-Shetland Basin provides detailed information on the relationships between sills,
dykes, laccoliths and contemporaneous volcanic activity. The data shows that sills are predominantly concave upwards, being
complete or partial versions of radially or bilaterally symmetrical forms that possess flat inner saucers connected to a flat
outer rim by a steeply inclined sheet. Such morphologies are only partially modified by pre-existing faults. Sills can be
sourced from dykes or the steep climbing portions of deeper sills. Both sills and dykes can provide magma to overlying volcanic
fissures and sills can be shown to feed shallow laccoliths. Magma flow patterns, as revealed by opacity rendering, suggest
that sills propagate upwards and outwards away from the magma feeder. As an individual sill can consist of several leaves
emplaced at different stratigraphic levels, and as a sill or dyke can provide magma to volcanic fissures, other sills and
laccoliths, the data suggests that neutral buoyancy concepts may not provide a complete explanation for the mechanism and
level of sill emplacement. Instead, the data suggests that the presence of lithological contrasts, particularly ductile horizons
such as overpressured shales may permit sill formation at any level below the neutrally buoyant level.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Ken Thomson–deceased, April 2007 相似文献
5.
R. K. Chadha 《Pure and Applied Geophysics》1995,144(1):155-165
The geological and hydrological conditions near the reservoir site play an important role in the generation or absence of seismic activity. Near Bhatsa reservoir, along the west coast of India intense seismic activity occurred during August–September 1983, after a lag of six years of initial impounding. From July 1983 to September 1990, 15,388 earthquakes (mostlyM
1<3.0) were recorded, the largest being of magnitude 4.9. The spatial distribution of well located 172 earthquakes suggest a strong correlation between the epicenters and the disposition of dykes and faults around the Bhatsa region. It is inferred that these dykes have acted as barriers for the diffusion of water from the reservoir, thereby becoming zones of instability due to increased pore pressure not only along them but also over the volume they bound. 相似文献
6.
新疆西准噶尔红山岩体及其中闪长质岩墙的时代——来自锆石LA-ICP-MS定年的证据 总被引：4，自引：2，他引：2
作为一种特殊产状的岩浆岩,岩墙保存有岩浆活动和地球动力学背景等方面的重要信息。为了研究和探讨西准噶尔乃至中亚地区古生代晚期的地球动力学环境,我们对西准噶尔地区侵入花岗岩的暗色岩墙开展了卫星遥感影像解译、地表地质调查和相关室内研究工作。研究发现,新疆西准噶尔红山花岗岩体中发育大量环状和非环状闪长岩岩墙。环状岩墙从中心到外围,岩墙宽度逐渐变窄,矿物粒度也逐渐变细;非环状岩墙切割环状岩墙,宽度和矿物粒度都没有明显变化。为了确定这些岩墙的形成时代,对3个环状岩墙样品、2个非环状岩墙和1个花岗岩样品进行了锆石LA-ICP-MSU-Pb定年,得到环状岩墙的年龄为:304±1Ma、302±1Ma、303±1Ma;非环状岩墙的年龄为:302±1Ma、302±1Ma;花岗岩的年龄为304±1Ma。结合不同类型岩墙及其与岩体的穿切关系,确定红山岩体的形成时代为304Ma左右,环状岩墙的形成时代为303Ma左右,非环状岩墙的形成时代为302Ma左右。这一年代学研究成果揭示出西准噶尔地区在石炭纪末期发育不同类型的岩浆活动,闪长质岩墙所占据的裂隙是在石炭纪末期形成的;为从岩浆活动和由这些岩墙所占据的裂隙研究,探讨该区古生代晚期的地球动力学环境,提供了有力的时间约束。 相似文献
7.
西藏林周盆地中酸性脉岩的年代学、地球化学和岩石成因 总被引：5，自引：2，他引：3
林子宗火山岩(也称林子宗群)出露在青藏高原拉萨地块南部,被认为是印度与欧亚大陆发生碰撞的岩浆作用响应。发育在拉萨东北林周盆地的林子宗火山岩剖面完整,是最初的命名地,在过去的20年来已经完成了较好的研究工作。本文对林周盆地林子宗火山岩地层中产出的中性(闪长玢岩)和酸性(花岗斑岩)脉岩开展了研究,新获得了5个样品的锆石UPb定年和Hf同位素数据和11套主量和微量元素地球化学数据。这些脉岩侵入到林子宗群的典中组和年波组地层中。所有样品均为亚碱性岩石,在钾质特征上属于钙碱性到高钾钙碱性系列岩石。样品均为过铝质(除了一个样品为铝质岩石,A/CNK=0.86)。一个闪长玢岩样品的年龄为62.4Ma,具有正的εHf(t)值(+5.1~+7.6),显示了与典中组安山岩相似的地球化学成分。其余的花岗斑岩侵入时代为55.1~61.1Ma,εHf(t)范围为-1.1~+10.4(仅有一个负值,其余全部为正值),它们与近于同时代的年波组流纹质火山岩具有相似的地球化学特征。林周盆地脉岩的主要特征可以归纳为:(1)岩石具有类似地幔的Hf同位素特征,总计86个Hf同位素中仅有一个负值,所有样品平均的εHf(t)为5.9;(2)每个样品具有变化范围很宽的εHf(t)值,4个花岗斑岩样品每个样品内部的εHf(t)值变化达到3.5~8.8个ε单位,显示了不均一的源区组成;(3)从主量元素的成分变化趋势(FeO T-MgO关系图)指示了岩浆混合作用的成分趋势。这些特征表明在冈底斯带南缘发生的古新世-始新世大规模幔源岩浆底侵作用和岩浆混合作用,也可以用来解释林周盆地脉岩的形成过程。这些脉岩作为浅成的侵入体,与其同时代的林子宗火山岩(典中组和年波组)一样,都是伴随着冈底斯带南缘从特提斯洋俯冲削减过渡到印度与欧亚大陆碰撞的构造转化过程中形成的。 相似文献
8.
Dmitry P. Gladkochub Sergei A. Pisarevsky Tatiana V. Donskaya Richard E. Ernst Michael T.D. Wingate Ulf Söderlund Anatoliy M. Mazukabzov Eugene V. Sklyarov Michael A. Hamilton John A. Hanes 《Precambrian Research》2010
We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton, including recently published U–Pb and 40Ar–39Ar dates. These new precise ages suggest that at least some of the previously published K–Ar ages of Siberian mafic bodies should be ignored. The time–space geochronological chart, or the ‘barcode’ of mafic magmatic events shows significant differences between northern and southern Siberia. Both are characterized by ∼1900–1700 Ma magmatic events, but then there was an almost 1 Ga mafic magmatic ‘pause’ in south Siberia until ∼800 Ma. Meanwhile there are indications of multiple mafic magmatic events in North Siberia (Anabar shield and Olenek uplift) between ∼1600 and 1000 Ma. A series of magmatic events probably related to the breakup of Rodinia occurred in southern Siberia after ∼800 Ma. So far, there are no indications of late Neoproterozoic mafic magmatism in North Siberia. Ca. 1000–950 Ma mafic sills were reported from Meso- to Neo-Proterozoic sedimentary successions in the Sette-Daban area on the east side of the Siberian craton, but their tectonic setting is debated. Recent Ar–Ar dates of ∼1750 Ma for NW-trending dykes in the Aldan and Anabar shields, together with similar-age NNE-trending Baikal uplift dykes in south-eastern Siberia suggest the existence of a giant radial dyke swarm possibly related to a mantle plume centred in the Vilyui River area. 相似文献
9.
新疆西准噶尔克拉玛依岩体中暗色岩墙的形成时代及地质意义 ——来自锆石LA-ICP-MS和角闪石Ar-Ar定年的证据 总被引：3，自引：2，他引：1
新疆西准噶尔克拉玛依岩体以及周围地层中存在着大量暗色闪长玢岩岩墙,是岩浆物质贯入3组走向不同的裂隙形成的。对其中一个闪长玢岩岩墙样品进行锆石LA-ICP-MS年代学测试,得到303.1±1.2Ma的锆石206Pb/238U加权平均年龄,对从该闪长玢岩中分离出的角闪石进行Ar-Ar年代学测试,得到312.1±2.8Ma的坪年龄(1120～1400℃)和313.6±6.9Ma的反等时线年龄。对该闪长玢岩岩墙附近的含角闪石黑云母二长花岗岩进行的锆石LA-ICP-MS年代学测试,获得其206Pb/238U加权平均年龄为319.0±1.0Ma。对侵入石炭纪地层的一个花岗斑岩岩脉样品进行锆石LA-ICP-MS年代学测试,得到了315.3±1.0Ma的206Pb/238U加权平均年龄。上述年代学测试结果表明克拉玛依市以西地区的暗色岩墙形成时代是石炭纪末期,不是前人所说的二叠纪。在这些岩墙形成之前,该区在石炭纪晚期还发育以克拉玛依岩体及附近酸性岩脉为代表的花岗质岩浆活动。上述围岩和岩墙的年代学资料揭示出该区闪长玢岩岩墙所占据的裂隙形成时代在315～303Ma之间,为新疆西准噶尔地区晚古生代地球动力学背景及岩浆活动的深入研究,提供了时间方面的约束。 相似文献
10.
New radiometric dating of the dykes from the Hurd Peninsula, Livingston Island, South Shetland Islands 总被引：1，自引：0，他引：1
Fifteen new K–Ar ages in the range of 79–31 Ma are partially confirmed by three 40Ar/39Ar plateaus and isochron data of 64.9±0.4, 55.5±0.1 and 52.8±0.6 Ma. The new geochronological data reveal a much more detailed picture of the subduction imprint in the Hurd Peninsula. Using cutting relationships, the dyke emplacement history is divided into four episodes. The Late Cretaceous–Paleocene dykes in the range of 80–60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of subduction of the proto-Pacific oceanic crust. The Early Eocene dykes (56–52 Ma) fill the gap in volcanic activity 70–50 Ma ago. They are the only magmatic event manifested at this time in the region. The 45–42 Ma dykes may be related to the intrusion of the Barnard Point tonalite. Three samples of Oligocene age appear to represent the last igneous activities on the Hurd Peninsula prior to the opening of the Bransfield Strait. 相似文献