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1.
N. V. Chalapathi Rao 《Journal of Earth System Science》2006,115(1):161-183
Amongst all the perceptible igneous manifestations (volcanic tuffs and agglomerates, minor rhyolitic flows and andesites,
dolerite dykes and sills near the basin margins, etc.) in the Vindhyan basin, the two Mesoproterozoic diamondiferous ultramafic
pipes intruding the Kaimur Group of sediments at Majhgawan and Hinota in the Panna area are not only the most conspicuous
but also well-known and have relatively deeper mantle origin. Hence, these pipes constitute the only yet available ‘direct’
mantle samples from this region and their petrology, geochemistry and isotope systematics are of profound significance in
understanding the nature of the sub-continental lithospheric mantle beneath the Vindhyan basin. Their emplacement age (∼ 1100
Ma) also constitutes the only reliable minimum age constrain on the Lower Vindhyan Group of rocks. The Majhgawan and Hinota
pipes share the petrological, geochemical and isotope characteristics of kimberlite, orangeite (Group II kimberlite) and lamproite
and hence are recognised as belonging to a ‘transitional kimberlite-orangeite-lamproite’ rock type. The namemajhagwanite has been proposed by this author to distinguish them from other primary diamond source rocks. The parent magma of the Majhgawan
and Hinota pipes is envisaged to have been derived by very small (<1%) degrees of partial melting of a phlogopite-garnet lherzolite
source (rich in titanium and barium) that has been previously subjected to an episode of initial depletion (extensive melting
during continent formation) and subsequent metasomatism (enrichment). There is absence of any subduction-related characteristics,
such as large negative anomalies at Ta and Nb, and therefore, the source enrichment (metasomatism) of both these pipes is
attributed to the volatile- and K-rich, extremely low-viscosity melts that leak continuously to semi-continuously from the
asthenosphere and accumulate in the overlying lithosphere. Lithospheric/crustal extension, rather than decompression melting
induced by a mantle plume, is favoured as the cause of melting of the source regions of Majhgawan and Hinota pipes. This paper
is a review of the critical evaluation of the published work on these pipes based on contemporary knowledge derived from similar
occurrences elsewhere. 相似文献
2.
贵州东部石英脉型金矿地质特征和成矿作用 总被引：7，自引：3，他引：7
贵州东部以晚元古代地层为容矿地层的金矿,主要是石英脉型金矿。它们主要分布在从江地区、天柱—锦屏—黎平地区和梵净山地区。前2者处于南华褶皱带西缘,后者处于南华褶皱带与扬子陆块的过渡带。矿体分布在断裂(带)和背斜核部。共伴生矿物为石英、黄铁矿、毒砂、闪锌矿、方铅矿、黝铜矿,黄铜矿,辉锑矿、绿泥石等。矿化蚀变以硅化、黄铁矿化、毒砂化、绿泥石化为主。形成温度主要集中在100℃～350℃,是中低温热液矿床,呈现100～150℃和200～300℃两个区段。金有来源于围岩的、也有来源于深部岩浆的；流体有来源于地层和深部的,也有大气降水的混入。金矿的形成是多时代多阶段形成的：雪峰期提供原始物质；加里东期是一次主要成矿期；燕山时期也是一个重要的金矿形成时期,不但形成新金矿,还改造加里东期形成的金矿 相似文献
3.
马圈一带出露的主要地层为上元古界栾川群和中元古界官道口群 ,是Pb、Zn、Ag的主要含矿地层。燕山期花岗岩在空间上与矿化关系密切。矿体主要受北西向断裂控制 ,常分布在北西、北东向断裂构造交汇部位。根据地球化学特征、矿产分布规律和找矿标志 ,划分出百炉沟西凹—东凹—磨沟、百炉沟—黄花北沟—杨树凹等两个一级和银窝沟—大石渣沟—小石渣沟、板岔沟等两个二级找矿预测区。 相似文献
4.
大别山超高压石榴多硅白云母片岩中钻石U－Pb年龄 总被引：2，自引：0，他引：2
大别山超高压石榴多硅白云母片岩中钻石Ｕ－Ｐｂ年龄刘晓春（中国地质科学院地质力学研究所，北京１０００８１）李惠民，左义成（地质矿产部天津地质矿产研究所，天津３００１７０）关键词石榴多硅白云母片岩，Ｕ－Ｐｈ年龄，早元古代表壳岩，印支期超高压变质，大别山高... 相似文献
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The Proterozoic was the first of severa1 impor-tant transitional periods in the earth's evolutionaryhistory. Linear .rifts over1apped on the b4se ofArchean granite -- greenstone and high -- grade gneissregimes. Along with the formation and evolution ofthe… 相似文献
7.
五台山地区分布着复杂的变质杂岩。过去人们把这些变质岩作为地层分成群组段。龙泉关剪切构造岩的发现突破了这种传统观念。野外工作中发现所谓五台群主要包含了三个蛇绿混杂带;阜平群和恒山群的主要成分是灰片麻岩,它们构成两个太古代陆块的基底。五台地区的花岗岩类由代表弧环境的双花岗岩带的I型和S型花岗岩组成,它们与变质的钙碱性火山岩代表了古代的岩浆弧。滹沱群的豆村和东冶亚群以及过去划入阜平群和五台群的某些变沉积岩是阜平陆块被动大陆边缘的沉积。滹沱群的郭家寨亚群则是前陆盆地的磨拉石沉积。因此可以认为,这是一个由恒山仰冲陆块、北台-车厂弧和阜平俯冲陆块构成的碰撞造山带,碰撞时间大致是距今2050Ma。闭合的弧前大洋和弧后盆地形成了三条蛇绿混杂带。 相似文献
8.
A reappraisal of polymetamorphism in the Eastern Ghats belt — A view from north of the Godavari rift
Evidence collated from different parts of the Eastern Ghats belt north of the Godavari rift (barring the “Western Charnockite
Zone” ) indicates that this sector evolved through a series of compressive structures (F1 to F3), with prolific migmatization in quartzofeldspathic and metapelitic gneisses synchronous with F1 shortening, as was the syn-F1 emplacement of profuse megacrystic K-feldspar-bearing granitoid bodies. Thereafter, melt productivity of the rocks (synchronous
withF
2– F3 folding) sharply decreased. Mineral parageneses stable in the S1, S2 and S3 fabrics indicate persistence of granulite facies conditions. P-T estimates on orthopyroxene + garnet + plagioclase + quartz
assemblages anchored to recrystallized mosaic that overgrow all penetrative fabric elements in mafic granulites, granitoids
and quartzofeldspathic gneisses are in the range of 900‡-950‡C and P≅ 8–9 kbar. This estimate is comparable to those retrieved
from sapphirine-bearing paragenesis in Mg-Al metapelites that appear to be diachronous in relation to the fabric elements,
and arguably disrupt the granoblastic mosaic. These facets in the northern sector of the orogenic belt are compatible with
either a single cycle of tectonic events (i.e., F1, F2 and F3 in continuum), or temporally-separate thermo-tectonic events, with the peak of earlier metamorphism (pre- to syn-F1) at lower temperature (in the granulite facies) in comparison to the record of high post-F3-Tmax values.
It is suggested on the basis of the above evidence that the late Proterozoic/Pan-African granulites in the Eastern Ghats belt
north of the Godavari rift, are unlikely to be reworked equivalents of any older granulitic crust, such as the ∼1.6 Ga granulites
south of the rift. Instead, the temporally disparate sectors may represent different crustal segments with unconnected pre-amalgamation
tectonic history. However, if the ∼ 1.6 Ga granulites of the Western Charnockite Zone continue northwards across the rift,
as suggested by recent isotope data, there are serious doubts as to the validity of a north-south division within the Eastern
Ghats belt. 相似文献
9.
库车坳陷东部侵入于元古宇基底变质岩中的黑云母二长花岗岩属于高钾钙碱性岩系,岩石具有富硅(SiO2=75.77%～77.79%)、高碱(Na2O+K2O=6.90%～7.95%)、富钾(K2O/Na2O=1.21～1.98)、低TiO2(0.06%～0.13%,平均0.08%)和准铝质(铝饱和指数A/CNK=0.92～1... 相似文献
10.
辽东古元古代侵入岩广泛分布于太子河凹陷以南的营口、宽甸、丹东、桓仁等地。本文概述了侵入岩地质、岩石、岩石化学及地球化学等特征 ,探讨了其源区有幔源型、壳幔混源型、壳源型的属性。岩浆演化规律为：造山前富 Mg质玄武岩、拉斑玄武岩系列与钙碱系列双向演化；造山期由中酸性→酸性，由钠质→钾质；造山后崩塌期由基性→中性→酸性，由拉斑玄武岩系列→钙碱系列，由钠质→钾质。构造岩浆大陆动力学演化过程和模式为造山前毗芦寺超基性－基性杂岩侵喷就位，造山早期条痕状花岗岩同构造底劈侵位，造山主期片麻状黑云－二云母二长花岗岩同构造中高位侵入，造山晚期块状花岗闪长岩－二长花岗岩组合高位侵入，造山期后构造崩塌期辉长－辉绿岩组合、闪长岩－斜长花岗岩－钾长花岗岩组合伸展就位。 相似文献