区域岩石圈组成和热状态对岩浆作用和成矿的制约——以秦巴地区为例   总被引：2，自引：1，他引：1       下载免费PDF全文

张本仁 《地球科学》1994,3(3)

遵循区域岩石圈系统的组成和状态制约区域各类地质—地球化学作用过程的性质和特征,以及各类地质—地球化学过程引起的物质分异和循环反映区域岩石圈发展和演化的构想,分析了秦巴地壳的化学和岩石组成特征及岩石圈的高热流状态,并据之阐明秦巴花岗岩类多具有Ⅰ型和Ⅰ—S混合型特征及该区缺乏与花岗岩类有关的典型岩浆期后热液矿床的原因,同时由该区花岗岩类岩石多具有黑云母组合和角闪石组合脱水熔融特征,揭示了多数花岗岩浆形成的较高熔融程度及有大量未经风化沉积旋回的岩浆岩加入了岩浆的源区,从而为秦巴上、下地壳化学成分差异小、物质分异弱找到了较合理的解释。本例表明在区域成岩和成矿研究中,区域岩石圈组成和状态的分析具有重要意义。  相似文献   

Petrogenesis of collision-related plutonics in Central Anatolia, Turkey   总被引：7，自引：0，他引：7  

N. Ilbeyli  J. A. Pearce  M. F. Thirlwall  J. G. Mitchell 《Lithos》2004,72(3-4):163-182

Central Anatolia exhibits good examples of calc-alkaline and alkaline magmatism of similar age in a collision-related tectonic setting (continent–island arc collision). In the Central Anatolia region, late Cretaceous post-collisional plutonic rocks intrude Palaeozoic–Mesozoic metamorphic rocks overthrust by Upper Cretaceous ophiolitic units to make up the Central Anatolian Crystalline Complex.

In the complex, three different intrusive rock types may be recognised based on their geochemical characteristics: (i) calc-alkaline (Behrekdag, Cefalikdag, and Celebi); (ii) subalkaline-transitional (Baranadag); and (ii) alkaline (Hamit). The calc-alkaline and subalkaline plutonic rocks are metaluminous I-type plutons ranging from monzodiorite to granite. The alkaline plutonic rocks are metaluminous to peralkaline plutons, predominantly A-type, ranging from nepheline monzosyenite to quartz syenite.

All intrusive rocks show enrichment in LILE and LREE relative to HFSE, and have high ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd ratios. These characteristics indicate an enriched mantle source region(s) carrying a subduction component inherited from pre-collision subduction events. The tectonic discrimination diagram of Rb vs. (Y+Nb) suggests that the calc-alkaline, subalkaline, and alkaline plutonic rocks have been affected by crustal assimilation combined with fractional crystallisation processes.

The coexistence of calc-alkaline and alkaline magmatism in the Central Anatolian Crystalline Complex may be attributed to mantle source heterogeneity before collision. The former carries a smaller intraplate component and pre-subduction enrichment compared to the latter. Either thermal perturbation of the metasomatised lithosphere by delamination of the thermal boundary layer (TBL), or removal of a subducted plate (slab breakoff) is the likely mechanism for the initiation of the post-collisional magmatism in the Complex.  相似文献   

Temporal, geomagnetic and related attributes of kimberlite magmatism at Ekati, Northwest Territories, Canada     

Grant Lockhart  Herman Grütter  Jon Carlson 《Lithos》2004,77(1-4):665-682

This paper outlines the development of a multi-disciplinary strategy to focus exploration for economic kimberlites on the Ekati property. High-resolution aeromagnetic data provide an over-arching spatial and magnetostratigraphic framework for exploration and kimberlite discovery at Ekati, and hence also for this investigation. The temporal, geomagnetic, spatial and related attributes of kimberlites with variable diamond content have been constrained by judiciously augmenting the information gathered during routine exploration with detailed, laboratory-based or field-based investigations. The natural remanent magnetisation of 36 Ekati kimberlites has been correlated with their age as determined by isotopic dating techniques, and placed in the context of a well-constrained geomagnetic polarity timescale. Kimberlite magmatism occurred over the period 75 to 45 Ma, in at least five temporally discrete intrusive episodes. Based on current evidence, the older kimberlites (75 to 59 Ma) have low diamond contents and are distributed throughout the property. Younger kimberlites (56 to 45 Ma) have moderate to high diamond contents and occur in three distinct intrusive corridors with NNE to NE orientations. Economic kimberlite pipes erupted at 55.4±0.4 Ma along the A154-Lynx intrusive corridor, which is 7 km wide and oriented at 015°, and at 53.2±0.3 Ma along the Panda intrusive corridor, which is 1 km wide and oriented at 038°. The intrusion ages straddle a paleopole reversal at Chron C24n, consistent with the observation that the older economic kimberlites present as aeromagnetic “low” anomalies while the younger economic pipes are characterised as aeromagnetic “highs”. The aeromagnetic responses for these kimberlites are generally muted because they contain volcaniclastic rock types with low magnetic susceptibility. Kimberlites throughout the Ekati property carry a primary natural magnetic remanence (NRM) vector in Ti-bearing groundmass magnetite, and it dominates over vectors related to induced magnetisation. Magnetostratigraphic correlation of Ekati kimberlites may therefore present a powerful adjunct to existing exploration techniques, mainly because the diamond content of Ekati kimberlites apparently is related more to the age of eruption than to any other parameter investigated in this work.  相似文献   

Nature of the Source Regions for Post-collisional, Potassic Magmatism in Southern and Northern Tibet from Geochemical Variations and Inverse Trace Element Modelling   总被引：20，自引：0，他引：20  

WILLIAMS  H. M.; TURNER  S. P.; PEARCE  J. A.; KELLEY  S. P.; HARRIS  N. B. W. 《Journal of Petrology》2004,45(3):555-607

Neogene potassic lavas in northern and southern Tibet have differentisotopic (  相似文献   

Small-scale convection under the back-arc occurring in the low viscosity wedge     

Satoru Honda  Mitsunobu Saito 《Earth and Planetary Science Letters》2003,216(4):703-715

Water released from subducting slabs through a dehydration reaction may lower the viscosity of the mantle significantly. Thus, we may expect a low viscosity wedge (LVW) above the subducting slabs. The LVW coupled with a large-scale flow induced by the subducting slabs may allow the existence of roll-like small-scale convection whose axis is normal to the strike of the plate boundary. Such a roll structure may explain the origin of along-arc variations of mantle temperature proposed recently in northeast Japan. We study this possibility using both 2D and 3D models with/without pressure- and temperature-dependent viscosity. 2D models without pressure and temperature dependence of viscosity show that, with a reasonable geometry of the LVW and subduction speed, small-scale convection is likely to occur when the viscosity of the LVW is less than 10¹⁹ Pa s. Corresponding 3D model studies reveal that the wavelength of rolls depends on the depth of the LVW. The inclusion of temperature-dependent viscosity requires the existence of further low viscosity in the LVW, since temperature dependence suppresses the instability of the cold thermal boundary layer. Pressure (i.e. depth) dependence coupled with temperature dependence of the viscosity promotes short wavelength instabilities. The model, which shows a relatively moderate viscosity decrease in the LVW (most of the LVW viscosity is 10¹⁸∼10¹⁹ Pa s) and a wavelength of roll ∼80 km, has a rather small activation energy and volume (∼130 kJ/mol and ∼4 cm³/mol) of the viscosity. This small activation energy and volume may be possible, if we regard them as an effective viscosity of non-linear rheology.  相似文献   

华北燕山带:构造、埃达克质岩浆活动与地壳演化(英文)   总被引：19，自引：6，他引：19  

GregoryA．DAVIS 《地学前缘》2003,10(4):373-384

埃达克质火成岩在中国东部,包括燕山带是很常见的,一般认为它们是下地壳不均匀的镁铁质岩石及/或富集的上地幔岩石在高压(≥1.5 GPa)下部分熔融的结果。在燕山带内埃达克岩浆的形成有一个很长的时间(约190～80 Ma),然而岩浆活动的峰期却与约170～130 Ma间有基底岩石卷入的陆壳收缩期相一致。尽管埃达克质岩浆活动的历史很长,但那种把岩浆活动与岩石圈的拆沉效应相联系的模式似乎是不适当的。在该带内,埃达克质与非埃达克质岩浆活动有一部分是同时的,而且在地理分布上也是相间的,这说明了在下地壳和上地幔岩石的部分熔融中成分是相当不均匀的。侏罗纪及白垩纪熔融作用的热源应当是与古太平洋板块俯冲相关的中生代板底垫托的玄武岩浆。除了局部例外,在燕山带,埃达克质岩浆活动的终结和碱性岩浆活动的开始约在130～120 Ma,在此时期收缩作用使东亚大达200万km~2以上的地区发生了NW—SE向的区域性伸展作用。强烈的地壳伸展仅局限于华北克拉通北缘分布的少数几个变质核杂岩中。陆壳的伸展减薄合理地解释了130～120 Ma间发生高压埃达克质熔融条件的终结,尽管还有局部年轻的埃达克火山活动(约120～80Ma)可以在伸展规模有限而厚的地壳依然存在的地区继续出现。燕山区早白垩世的碱性侵入体中的锆石不存在前寒武纪?  相似文献   

Isotopic evidence for the magmatic and tectonic histories of the Carolina terrane: implications for stratigraphy and terrane affiliation     

Stephanie Ingle  Paul A. Mueller  Ann L. Heatherington  Marianne Kozuch 《Tectonophysics》2003,371(1-4):187-211

Establishing the age and crustal nature of exotic terranes and their underlying basements helps to determine their paleogeographic origin and tectonic histories. We present U–Pb ages of zircons and Sm–Nd whole rock isotopic data for volcanic and plutonic rocks of the Carolina terrane, one of several peri-Gondwanan terranes that were accreted to the margins of the circum-Atlantic continents during the Paleozoic. Volcanism in this subduction-related arc culminated in the eruption of the Morrow Mountain rhyolite, at ca. 540 Ma; thus, magmatism in the Carolina terrane ceased at the beginning of the Cambrian. The presence of inherited zircons and non-juvenile depleted mantle model ages of Carolina slate belt rocks favor a basement that is, at least in part, composed of evolved continental crust. Ages of inherited xenocrystic zircons cluster at ca. 1000, 2100 and 2500 Ma. These ages, in addition to volcanism at ca. 618–540 Ma, correlate best with well-known tectonic events in present-day northern South America. Specifically, the Orinoquian-Sunsas, the Trans-Amazonian and the Central Amazonian orogenic zones are likely candidates for potential basement correlatives to the Carolina terrane. Sm–Nd isotopic signatures vary significantly, but permit assimilation of Orinoquian age (1000 Ma) crust by magmas derived from the depleted mantle in a subduction (arc-related) setting. Our findings are also consistent with proposed correlations between the Carolina terrane and Avalonia which is likewise believed to have formed along the northern margin of present-day South America.  相似文献   

Paleomagnetism of Middle Proterozoic mafic intrusions and Upper Proterozoic (Nankoweap) red beds from the Lower Grand Canyon Supergroup, Arizona     

Arlo B. Weil  John W. Geissman  Matt Heizler  Rob Van der Voo 《Tectonophysics》2003,375(1-4):199

Paleomagnetic data from lavas and dikes of the Unkar igneous suite (16 sites) and sedimentary rocks of the Nankoweap Formation (7 sites), Grand Canyon Supergroup (GCSG), Arizona, provide two primary paleomagnetic poles for Laurentia for the latest Middle Proterozoic (ca. 1090 Ma) at 32°N, 185°E (dp=6.8°, DM=9.3°) and early Late Proterozoic (ca. 850–900 Ma) at 10°S, 163°E (dp=3.5°, DM=7.0°). A new ⁴⁰Ar/³⁹Ar age determination from an Unkar dike gives an interpreted intrusion age of about 1090 Ma, similar to previously reported geochronologic data for the Cardenas Basalts and associated intrusions. The paleomagnetic data show no evidence of any younger, middle Late Proterozoic tectonothermal event such as has been revealed in previous geochronologic studies of the Unkar igneous suite. The pole position for the Unkar Group Cardenas Basalts and related intrusions is in good agreement with other ca. 1100 Ma paleomagnetic poles from the Keweenawan midcontinent rift deposits and other SW Laurentia diabase intrusions. The close agreement in age and position of the Unkar intrusion (UI) pole with poles derived from rift related rocks from elsewhere in Laurentia indicates that mafic magmatism was essentially synchronous and widespread throughout Laurentia at ca. 1100 Ma, suggesting a large-scale continental magmatic event. The pole position for the Nankoweap Formation, which plots south of the Unkar mafic rocks, is consistent with a younger age of deposition, at about 900 to 850 Ma, than had previously been proposed. Consequently, the inferred 200 Ma difference in age between the Cardenas Basalts and overlying Nankoweap Formation provides evidence for a third major unconformity within the Grand Canyon sequence.  相似文献   

Mineralization Controls in Island Arc Settings: Insights from Philippine Metallic Deposits   总被引：1，自引：0，他引：1  

G.P. Yumul  Jr.  C.B. Dimalanta  V.B. Maglambayan  R.A. Tamayo  Jr. 《Gondwana Research》2003,6(4):767-776

A review of the gold-copper, volcanogenic massive sulfide and ultramafic-hosted (i.e., chromitite, nickel sulfide, platinum-group minerals) deposits in the Philippines is presented. It is critical that a thorough understanding of the spatial and temporal relationship among magmatism, structures and mineralization must be gained if the correct evaluation of the economic potential of a particular deposit is to be done. Structural features conducive to precious and base metal mineralizations are associated with shear zones, extensional jogs and collision zones. In Northern Luzon, alkali and adakitic magmatism are considered good markers for gold-copper mineralization. Volcanogenic massive sulfide deposits are hosted by either ophiolites of marginal basin origin or metamorphic terranes. Exploration works on these deposits have been geared in determining the gold content of the massive sulfides. Chromitite deposits are related with ultramafic rock-hosted deposits. Their occurrence is attributed to crystallization, magma mixing and mantle-melt interaction processes in subduction-related settings. The multiple stages of partial melting responsible for the formation of supra-subduction zone ophiolites result in the generation of second to third stage melts that are enriched in nickel sulfides and platinum group minerals. On the basis of structural, geochemical and tectonic controls, Panay, Mindoro and Central Mindanao and the Sierra Madre, Leyte, and Samar are good exploration targets for precious and base metal deposition in the western and eastern sides of the Philippines, respectively.  相似文献   

滇西大理—剑川地区钾玄质岩浆作用：后碰撞走滑拉伸环境岛弧型岩浆作用的地球化学研究   总被引：13，自引：8，他引：13  

王建  李建平等 《岩石学报》2003,19(1):61-70

岩石学、元素地球化学研究表明，在滇西大理－剑川地区分布的富碱斑岩群属钾玄质系列岩石，具有产出于与红河－哀牢山走滑剪切带伴生的早第三纪拉张盆地中，这套钾玄质系列岩石富集大离子亲石元素LILE（Rb,Ba,K,Sr），轻稀土元素（LREE）和一组相容元素（Cr,Ni,V,Sc），具有明显的Nb,Ta,Ti,P负异常，反映了后碰撞岛弧型钾玄岩系特征。钾玄质母岩浆主要源于含金云母的尖晶石相地幔橄榄岩低度部分熔融，并在演化过程中经历了充分的分离结晶作用。  相似文献