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1.
碰撞造山带斑岩型矿床的深部约束机制 总被引：19，自引：8，他引：11
在印度-亚洲大陆碰撞过程中,俯冲板片断离触发了幔源岩浆底侵作用、下地壳部分熔融和冈底斯岩基带以及同岩基斑岩的产生.在此过程中,幔源岩浆分离结晶的产物、下地壳岩石部分熔融残余和地壳分异过程中下沉的镁铁质块体,构成了加厚下地壳.随着造山岩石圈的冷却和加厚下地壳重力不稳定性的增加,岩石圈拆沉作用触发了后碰撞斑岩型岩浆活动.与此相应,碰撞造山带斑岩型矿床可以形成于同碰撞和后碰撞两个不同的构造阶段.同碰撞成矿作用发生于岩基带形成时期,成矿物质主要来自于底侵幔源岩浆及更深部的含矿流体,其触发机制是俯冲板片的断离.后碰撞成矿作用发生于加厚下地壳冷却之后,成矿物质主要来自于新生矿源层和更深部的含矿流体,其触发机制为岩石圈拆沉作用.在同碰撞构造阶段,伴随着幔源岩浆的底侵作用,深部流体和幔源岩浆所含的成矿物质被注入到岩基岩浆中,与从岩基岩浆源区萃取的成矿物质汇聚在一起,一部分受岩基热的驱使上升成矿.由于流体中成矿元素的浓度强烈依赖于压力,另一部分成矿元素则滞留在难熔残余中形成新的矿源层.当发生岩石圈拆沉作用时,由此矿源层部分熔融形成的斑岩岩浆将相对富含成矿物质,导致碰撞造山带第二次成矿作用大爆发. 相似文献
2.
西沟钼矿床是东秦岭黄龙铺地区近些年新发现和勘查的碳酸岩脉型钼矿床。钼矿体主要赋存于新太古界太华群变质岩内的石英方解石碳酸岩脉中,呈脉状、似层状或透镜状产出。辉钼矿主要呈浸染状、薄膜状、团块状分布于石英方解石碳酸岩脉中,成矿有关的围岩蚀变有钾长石化、硅化、黄铁矿化、萤石化、硬石膏化等。为查明西沟钼矿床的成矿时代、成矿物质来源、成矿机制、确定矿床类型,文章开展了辉钼矿Re-Os同位素测年,同位素地球化学分析。6件辉钼矿样品Re-Os同位素测年结果,模式年龄为(222.3±3.4)Ma～(226.6±3.7)Ma;加权平均年龄为(225.1±1.4)Ma;等时线年龄为(224.6±9.1)Ma,表明该矿床形成于晚三叠世。硫化物和硫酸盐的S同位素组成、重晶石和方解石Sr-Nd同位素组成及方解石C-O同位素组成均指示:西沟钼矿的成矿物质可能主要来源于地幔。根据其与华北陆块南缘其他碳酸岩型钼矿床地质特征、成矿时代和成矿物质来源等对比,确定西沟钼矿床属碳酸岩型脉状矿床。成矿作用发生于扬子板块与华北板块碰撞造山的后碰撞伸展环境,由于软流圈物质上涌诱发富集岩石圈地幔发生低程度部分熔融,所形成的碳酸质流体携带钼等成矿物质上升,在NW-NWW向深断裂带沉淀富集成矿。 相似文献
3.
对东秦岭-大别山钼成矿带25个钼矿床成矿母岩外接触带的地层及围岩观察统计,可清楚表明,所有钼矿床的赋矿层位均为前寒武纪老地层。成矿母岩侵入寒武系及以后地层中均形不成工业矿床。前寒武系不同的围岩岩性对钼矿床成矿作用的影响也不尽相同。主要反映在:1.地幔分异熔浆上侵时易于捕获前寒武系有用组分钼,而成其主要矿源层;2.成矿母岩的围岩岩性对矿床主要矿种组合有重要制约作用;3.围岩的物理力学性质,尤其是围岩的抗压抗剪强度(即岩石的破裂程度)对钼矿富集起关键作用。围岩容矿裂隙的发育程度决定了矿石的品位,从而控制着矿床的规模。东秦岭-大别山钼成矿带进一步寻找钼矿资源应以前寒武系(尤其是元古代老地层)作为找矿首选区域,特别是元古界岩石组合中的火山岩系列、大理岩及片岩系列构成的成矿有利围岩的地区。 相似文献
4.
秦岭地区印支期钼矿化特征及找矿前景 总被引：1，自引：0，他引：1
秦岭地区印支期钼矿床包括3种类型:碳酸岩脉型、断控石英脉型及斑岩型.碳酸岩脉型钼矿床与火成碳酸岩密切相关,矿体以含钼碳酸岩脉形式产出,成矿元素出现特殊的Mo+U+REE组合,以黄龙铺和黄水庵钼矿为典型代表.断控石英脉型钼矿受断裂控制明显,矿体以含钼石英脉形式产出,部分蚀变岩亦含矿.该类矿床具有与造山型矿床类似的矿体地质和成矿流体特征,属造山型矿床系列的中高温、中深成端元.典型实例包括外方山石英脉型钼矿田(纸房、前范岭等)、大湖金钼矿床、马家洼金钼矿床等.斑岩型钼矿以温泉钼矿床为代表.该类矿床与印支期中酸性小斑岩体密切相关,矿化呈细脉状、细脉浸染状产出,围岩蚀变包括钾化、绢英岩化、绿泥石化、绿帘石化、碳酸盐化等.综合区域地质情况及已有找矿勘查成果,指出秦岭造山带最北缘的碳酸岩-碱性岩带是寻找碳酸岩脉型钼矿的有利地区;华北克拉通南缘马超营断裂以北、三宝断裂以南有利于断控石英脉型钼矿的产出,其中小秦岭和熊耳山地区可出现石英脉型的Au-Mo矿化;强调应注重对东秦岭地区印支期花岗岩及其钼矿的找矿评价工作. 相似文献
5.
在前人研究成果的基础上,对江西新余良山钼矿床的地质特征进行了详细研究,系统测试了矿床中石英脉型钼矿石样品的氢、氧、硫和铅同位素组成,进而探讨钼矿床的成矿流体性质以及成矿物质来源。良山钼矿床δD值变化范围-61‰~ -57.9‰,平均值-59.1‰;δ18OV-SMOW值变化于7.1‰~10.5‰,平均值9.2‰,流体的δ18OH2O值变化于-3.32‰~-0.52‰,平均值-1.52‰,表明成矿流体具有岩浆水和大气降水混合流体特征。硫化物的δ34SV-CDT值为-1.8‰~2.6‰,极差4.4‰,平均值1.12‰,其中黄铁矿δ34SV-CDT值为-1.8‰~2.6‰,辉钼矿δ34SV-CDT值为0.8‰~2.3‰,硫同位素表现为较小的正值特征,具有典型的岩浆硫组成特点。良山钼矿石中的矿石铅同位素206Pb/204Pb值为17.555~19.474,207Pb/204Pb值15.486~15.768,208Pb/204Pb值37.942~39.943,μ值9.35~9.7,ω值37.06~38.31,Th/U值3.8~3.96,矿石铅为混合铅,表明成矿物质为混合来源。良山钼矿床应为岩浆热液型-石英脉型钼矿床,是中生代华南板块板内构造演化区域金属成矿作用大爆发的产物。 相似文献
6.
为了研究西沟钼矿床的成矿物质来源及矿床成因,对西沟钼矿床进行了地质、地球化学及稳定同位素研究。结果表明,西沟钼矿床的矿体主要以石英-方解石脉、石英脉类分布于太华岩群内,少量长石-石英脉型,辉钼矿、方铅矿、黄铁矿是主要矿石矿物,方解石和石英是主要的脉石矿物;含矿方解石具有较高的Sr、Ba和稀土含量,稀土元素及其特征值具火成碳酸岩组分特征,与黄龙铺矿田碳酸岩脉型钼矿床相似;成矿物质和成矿流体主要来源于深源或上地幔,成矿过程中有少量壳源物质或地下水参与。研究认为西沟矿床为石英-碳酸岩脉型钼铅矿床。 相似文献
7.
东秦岭钼矿带是我国最重要的钼多金属成矿带,近年来在东秦岭板厂地区取得了新的找矿突破。本文利用区域成矿动力学、硫化物的硫、铅同位素组成研究,结合成矿地质特征,对板厂铜钼多金属矿床成矿物质来源进行示踪,并以板厂矿床为基点总结东秦岭钼矿带的稳定同位素时空分布特征。板厂矿床12件硫化物样品δ(34S)范围为1.2×10-3~5.7×10-3,平均值0.6×10-3,与地幔(0±3×10-3)硫同位素值相近;东秦岭钼矿床δ(34S)位素值有随成矿时代渐新而逐渐升高的趋势,印支期钼矿床(221~226Ma)δ(34S)同位素值偏负,燕山期第一阶段钼矿床(138~151Ma)δ(34S)值由"0"值向正值变化,燕山期第二阶段钼矿床(113~131 Ma)δ(34S)值较高(平均4.93‰)。板厂矿床深部硫化物206Pb/204Pb值为17.121~17.798,207Pb/204Pb值为15.369~15.433,208Pb/204Pb值为36.867~37.485,具有明显的低放射性成因铅特征,其铅同位素组成与华北克拉通南缘的类熊耳群和太华群相似,幔源特征明显;浅部硫化物铅同位素值相对较高,206Pb/204Pb值为18.266~18.392,207Pb/204Pb值为15.560~15.622,208Pb/204Pb值为37.611~38.438,反映了造山带混合铅特征。板厂矿床形成于中国东部构造体制转折阶段,深部构造体制重新调整导致地幔物质上侵以及壳幔混合物的重新熔融,岩浆沿着深大断裂上涌,并将一定规模的含矿流体运移至浅部,由于物理化学条件的变化以及浅部流体的混合,成矿流体在最终构造薄弱带沉淀Cu、Mo等金属,形成板厂铜钼多金属矿床。综上,在晚侏罗世-早白垩世,东秦岭地区地幔熔体活动强烈,板厂铜钼多金属矿床成矿物质来源以幔源为主,有少量壳源物质混入。 相似文献
8.
东秦岭南泥湖钼（钨）矿床和秋树湾铜（钼）矿床成岩成矿特征对比研究 总被引：1，自引：0，他引：1
东秦岭钼矿带内的南泥湖钼（钨）矿床和秋树湾铜（钼）矿床同为斑岩型矿床,地理位置相近,却在成矿类型和规模上差异显著。通过对两个矿床的矿床地质特征、成矿斑岩体的地球化学特征、成矿时代及其成矿物质来源（S同位素、流体包裹体和Re含量）进行对比分析,确定南泥湖钼（钨）矿床和秋树湾铜（钼）矿床类型均为壳幔混源型,后者成岩成矿过程有更多的幔源物质参与,并且两个矿床同时形成于秦岭造山带中生代燕山期伸展减薄的机制下,但所处构造单元（华北陆块南缘和北秦岭）不同,以上这些都导致了成矿的差异性,并为日后在东秦岭钼矿带中钼铜两类矿床的找矿工作提供参考。 相似文献
9.
在近年来中亚造山带东段多金属矿床研究取得新进展的基础上,选择铀、钼两类矿床,结合铀、钼元素的地球化学行为探讨成矿物质来源的多样性和成矿的多阶段演化。此外,从构造研究角度,结合中亚造山带东段中大量中间地块存在的构造现象,讨论中间地块与成矿作用的关系:中间地块经历了从大陆边缘的裂解、漂移和板块碰撞造山作用,在漫长而复杂的地质过程中遭受的多次改造,有利成矿物质的反复被萃取和聚集。最后提出印支期华北克拉通北缘和北部造山带的成矿作用与底侵背景下的伸展作用密切相关。 相似文献
10.
东秦岭钼矿床及其深部构造制约 总被引：1，自引：0，他引：1
在东秦岭地区分布14个大型、中、小型的钼矿床,构成了长200 km、宽20 km的巨量钼矿化集中区.根据对钼矿床特征分析,矿床形成在燕山期活动的中酸性小岩体内部、接触带和外围,岩石类型主要有花岗斑岩和石英二长岩,它们具有较高的酸、碱和钾含量特征.主要的矿床类型有:①斑岩型钼矿;②斑岩-夕卡岩型钼矿;③夕卡岩型钼矿;④爆破角砾岩型钼矿;⑤热液脉型钼矿.尽管这些矿床类型不同,但是他们都与花岗斑岩的活动有关,深部格子状构造控制了一系列中酸性花岗岩浆的侵位和构造-岩浆-流体成矿作用. 相似文献
11.
东昆仑东段巴隆花岗质片麻岩年代学、地球化学特征及地质意义 总被引：9，自引：5，他引：4
东昆仑东段巴隆南侧古元古界白沙河岩组中可识别出一套花岗质片麻岩。采用LA-MC-ICP-MS方法进行锆石UPb年代学分析,获得加权平均年龄为870.6±7.7Ma(MSWD=2.6)和875.3±6.3Ma(MSWD=0.92),显示该岩体形成于新元古代早期,并经历了早古生代变质作用。地球化学特征显示,岩石具有高Si O2、Al2O3、K2O,低Ti O2、Na2O的特征,A/CNK平均为1.14,A/NK平均为1.47,矿物组合中出现石榴子石和白云母等富铝矿物,显示S型过铝质花岗岩特征;球粒陨石标准化配分曲线显示轻稀土元素富集((La/Yb)N=6.22~25.37),有明显的铕负异常(δEu=0.16~0.44)。原始地幔标准化蛛网图显示,岩石富集Rb、Th,明显亏损Ba、Ta、Nb、Sr、P和Ti元素。综合分析,岩浆来源于陆壳部分熔融,可能为古元古界白沙河岩组长英质岩石发生脱水熔融的产物,形成于同碰撞环境,是东昆仑地区响应Rodinia超大陆汇聚事件的物质记录。 相似文献
12.
Petrology, geochemistry and paleogeographic reconstruction of the East Sulawesi Ophiolite, Indonesia
Ade Kadarusman Sumio Miyashita Shigenori Maruyama Christopher D. Parkinson Akira Ishikawa 《Tectonophysics》2004,392(1-4):55
The East Sulawesi Ophiolite (ESO) is tectonically dismembered and widely distributed in Central and East Sulawesi. It comprises, from base to top, residual mantle peridotite and mafic–ultramafic cumulate through layered to isotropic gabbro, to sheeted dolerites and basaltic volcanic rocks. Residual peridotite is dominantly spinel lherzolite intercalated with harzburgite and dunite. Ultramafic rocks from different locations display significant differences in rock composition and mineral. However, the clinopyroxene of peridotite displays REE pattern similarities with those of mid-ocean ridge (MOR) origin, rather than those of suprasubduction zone (SSZ) origin. The gabbroic unit consists of massive gabbro, layered gabbro, mafic and ultramafic cumulate and anorthosite. The observed crystallization sequence of gabbroic unit, which is olivine→(spinel)→plagioclase→clinopyroxene→(orthopyroxene)→(hornblende), and the mineral chemistry data indicate that the ESO gabbro has similarities with MOR setting.Major and trace element geochemistry of basalt and dolerite suggests MOR, oceanic plateau and minor SSZ origins. A possible oceanic plateau origin is supported by the following: (i) the 15-km thickness is comparable with the thickness of oceanic plateau rather than normal oceanic lithosphere; (ii) there are no or only minor olivine phenocrysts in the basalt; and (iii) predominance of aphyric texture in the basalts. The REE pattern of ESO basalt exhibits N-MORB-like signatures. However, a negative Nb anomaly in the trace element spider diagram may be attributed to mantle heterogeneity of an OPB source.The geochemical variations and disparities for both peridotite and basalt and the noncogenetic relationship between crust and mantle sections in several locations suggest that the ESO may have been formed at one tectonic setting and was later overprinted by magmatism in different environments through its birth to emplacement. A possible Cretaceous origin of an oceanic plateau component of the ESO is indicated on the basis of calculated paleopositions using plate trajectory analyses together with previously published paleolatitude data. The ESO can be traced back to the proximity of the presently active region of the SW Pacific Superplume. 相似文献
13.
Dr. Wolf Stefan Vogler Prof. Dr. Gerhard Voll 《International Journal of Earth Sciences》1981,70(3):1232-1262
Deformation and metamorphism of rock series at the South-margin of the Alps, E of Bellinzona, are studied. Magmatic relics and metamorphic Minerals and rock types of the Tonalite and of the Augengneiss of Melirolo are examined. These bodies are regarded as of magmatic origin. Zoning of plagioclase is ascribed to rise of melts and cooling under loss of volatiles. Subvolcanic dykes branch off the Augengneiss into the Tonale Series. The magmatics are late-alpine and intruded into the Southerly cover plate on top of the subduction zone. The cover plate was still cold and unaffected by alpine deformation during this intrusion. Later deformation and heating of cover plate and magmatics is late-alpine. The Tonalite-deformation was quantified by a study of xenolith-deformation. The Tonalite was flattened to 1/20 of its original width. We extrapolate this flattening to the Southerly steep zone, now 5 km broad. We conclude that this zone was 100 km wide befor late-alpine flattening. This deformation occurred during the higher T part of lepontine heat-rise. A maximum T of ca 580 C and pH20 5–6 kbar is reached after the main deformation. Considerable stretching upward buried the niveau of intrusion, formerly shallow, under 15–20 km of rocks. The Tonale Series suffered 3-fold rotational refolding under subsiding T after the main deformation. An early-alpine subduction eclogite was found imbricated into the Tonale Series. It still contains parts of the subduction paragenesis preserved or pseudomorphosed and relics of subduction preferred orientation. Under late-alpine deformation it is changed into amphibolite. This proves continuation of subduction from Val Sesia to our area and further E. The magmatics are interpreted as subduction-magmatites. They cannot be derived as partial melts from the subducted slice which underlies the Tonale Series, from which the eclogite was imbricated into the Tonale Series during late-alpine movements.Voll has found a more Northerly subduction zone (Adula Nappe, Misox Zone). This may have reached our area in sufficient depth to produce partial melts before late-alpine flattening of the marginal zone. Last movements at the Insubric Line formed blastomylonites at 300 C indicating vertical movements. In our area lepontine garnet-staurolite-kyanite-schists abut directly against the Insubric line and the Seealpen. Lower T areas towards the S are cut off by the Insubric Line.
List of symbols D Diameter of a sphere of equal volume to the strain ellipsoid - 1,2,3 Natural Strain - s Strain-Magnitude - v Strain-Symmetry - r Radius - s1, str1 First cleavage and first stretching lineation of late-alpine age - B1 Axis of folds round str1, folding s1 - s2–4, b2–4 Cleavage planes and axes of 2nd-4th folds - T Temperature (C) - X, Y, Z Principal axes of the Strain Ellipsoid 相似文献
Zusammenfassung Die Arbeit studiert und korreliert Deformation und Metamorphose der Gesteinsserien am Alpen-S-Rand E von Bellinzona. Magmatische und metamorphe Minerale von Tonalit und Augengneis von Melirolo werden erfa\t, ferner Gesteinstypen ausgegliedert. Beide Körper werden als magmatisch angesehen. Zonierung im Plagioldas wird Aufstieg von Schmelzen und Abkühlung unter Entgasung zugeschrieben. Vom Augengneis nach S abzweigende Subvulkanit-GÄnge wurden gefunden. Die Magmatite sind jungalpin in den alpin noch nicht deformierten, kalten Teil der südlichen Deckelplatte über der Subduktionszone eingedrungen. Ebenfalls noch jungalpin werden dann Magmatite und Deckelplatte deformiert und geheizt. Quantifizierung der Tonalit-Deformation mittels Schollen ergibt PlÄttung auf im Mittel 1/20 der Ausgangsbreite. Diese PlÄttung wird auf den heute 5 km breiten, steilen Alpen-S-Rand extrapoliert, damit für diesen eine Breite von 100 km vor der jungen Einengung ermittelt. Die Deformation fÄllt in den Hoch-T-Teil des aufsteigenden Metamorphose-Astes der Lepontin-Heizung. Das T-Maximum bei ca. 580 C, 5–6 kbar, überlebt die Deformation. Hochdehnung hat das erst seichte Inlrusionsniveau betrÄchtlich belastet. 3fache Wiederfaltung in der Tonale-Serie erfolgt rotational, meist S-vergent, bei fallender T. In der Tonale-Serie wurde ein eoalpiner Subduktions-Eklogit gefunden, der eoalpine Paragenesen und Regelung erhalten hat, jungalpin deformiert und in Amphibolit umgewandelt wurde. Er beweist: Subduktion hÄlt vom Val Sesia über unser Gebiet nach E an. Wir fassen die Magmatite als Subduktions-Magmatite auf. Sie können nicht der schon obduziert seicht unter der Tonale-Serie liegenden Subduktions-Serie entstammen, aus der der Eklogit jungalpin in die Tonale-Serie eingeschuppt ist. Im N fandVoll eine zweite, subduzierte Serie: Aduladecke + Misoxer Zone. Es scheint möglich, da\ diese vor der jungen Einengung des S-Randes unter unserem Gebiet die nötige Tiefe für Teilschmelzbildung erreichten. Letzte Bewegungen direkt an der Insubrischen Linie erzeugen bei ca. 300 C Blastomylonite, deuten auf Vertikalbewegung. Das Areal der Lepontin-Metamorphose grenzt mit Granat-Staurolith-Disthen-Glimmerschiefern direkt an Insubrische Linie und Seealpen. Einst nach S zu OberflÄchen-T vermittelnde Teile sind durch die Insubrische Linie weggeschnitten.
Résumé Les auteurs étudient et mettent en corrélation la déformation et le métamorphisme des séries de roches au bord sud des Alpes, à l'E. de Bellinzona. Les minéraux magmatiques et métamorphiques de la tonalité et du gneiss oeillé de Melirolo sont examinés, ainsi que les types de roche. Les deux massifs sont considérés comme magmatiques. La zonation du plagioclase est attribuée à la montée du magma et à son refoidissement avec dégazéification. On a trouvé des filons de roche subvolcanique émanant du gneiss oeillé. Les magmatites, d'âge alpin tardif, ont été mises en place dans une partie froide, encore exempté de toute déformation alpine, de la fraction méridionale de la plaque de couverture au-dessus de la zone de subduction. La magmatites et la plaque de couverture ont été ensuite déformées par le mouvement alpin tardif et soumises à un échauffement. Le degré de déformation de la tonalité, évalué à partir des enclaves, donne un applatissement de l'ordre de 1/20 de l'épaisseur originelle. Cet applatissement est extrapolé à la bordure méridionale des Alpes, aujourd'hui redressée et large de 5 km., ce qui conduit pour cette dernière à une largeur de 100 km. avant son amincissement récent. La déformation s'est produite lors de la phase à haute température de la phase ascendante du métamorphisme de réchauffement lépontien. La température maximum d'environ 580 C, sous 5 à 6 kbar, s'est prolongée après la déformation. Une forte extension a considérablement affecté ce niveau d'intrusion, alors à faible profondeur. Il s'en est suivi, dans la série du Tonale, une plissement 3 fois répété, rotationel, le plus souvent déversé vers le sud, par température descendante. Dans la série de Tonale, fut découverte une eclogite de subduction éoalpine, qui est marquée par une paragenèse et un réglage éoalpins, et qui déformée par les mouvements alpins récents, a été transformée en amphibolite. Ceci montre que la subduction s'étend du Val Sesia vers l'E. par delà notre région. Nous considérons les magmatites comme étant de subduction. Elles ne peuvent pas dériver de la série en subduction se trouvant à faible profondeur sous la série du Tonale, déjà soumise à une obduction, et qui a incorporé l'éclogite dans la série du Tonale lors des mouvements alpins récents. Au nord,Voll a trouvé une deuxième série marquée par la subduction: la nappe de l'Adula + la zone de Misox. Il semble possible que celles-ci aient atteint, sous notre région, les températures nécessaires à une fusion partielle, et ce, avant l'amincissement récent de la bordure méridionale. Les derniers mouvements survenus directement le long de la ligne insubrique ont produit des blastomylonites à une température de quelque 300 C, en impliquant des mouvements verticaux. L'aire du métamorphisme lépontien, à schistes à grenat, staurotide et disthène, touche directement la ligne insubrique et les Seealpes. Les parties formant la transition aux températures de surface ont été supprimées par le jeu de la ligne insubrique.
. . , . . , . , . - . , 1/20 . , 5 , 100 . - . 580 C 5–6 . - . . , , . . . , - . , . , , . : . , , . 300 C , . - - . , , .
List of symbols D Diameter of a sphere of equal volume to the strain ellipsoid - 1,2,3 Natural Strain - s Strain-Magnitude - v Strain-Symmetry - r Radius - s1, str1 First cleavage and first stretching lineation of late-alpine age - B1 Axis of folds round str1, folding s1 - s2–4, b2–4 Cleavage planes and axes of 2nd-4th folds - T Temperature (C) - X, Y, Z Principal axes of the Strain Ellipsoid 相似文献
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《中国地球化学学报》2006,25(B08):157-158
17.
P. E. Brown R. D. Brown A. D. Chambers N. J. Soper 《Contributions to Mineralogy and Petrology》1978,67(1):25-34
The Borgtinderne nepheline-sodalite syenite is one of the major intrusions in the Tertiary igneous province of East Greenland. The syenite magma, which was evolving towards an undersaturated peralkaline residuum, underwent extensive modification by incorporation of country rock basalt, resulting in the production of a variety of hybrid syenites. Major element variation in the hybrids is essentially linear. Break-up and mechanical incorporation of the basic material was aided by amphibolitisation and metasomatism of the basalt xenoliths. 相似文献
18.
Joep E.A. Storms Robert M. Hoogendoorn Rien A.C. Dam A.J.F. Hoitink S.B. Kroonenberg 《Sedimentary Geology》2005,180(3-4):149-166
The late-Holocene Mahakam delta, located along the tropical eastern shore of Kalimantan, Indonesia, is considered to be a textbook example of a mixed tide–fluvial dominated delta system. The delta prograded about 60 km during the past 5000 years, which led to the development of a distinct network of distributary and tidal channels. Wave action is low due the limited fetch in the narrow strait of Makassar. Mahakam River discharge is about a quarter of the Mississippi River discharge and is characterized by absence of flood surges. Therefore, natural levees, crevasse splays and avulsions are absent in the delta plain. For the past four decennia, both modern and ancient Mahakam delta deposits have been studied in detail in order to better understand subsurface Miocene and Tertiary Mahakam deposits, which host large volumes of hydrocarbons.
This study focuses on the dynamics and stratal patterns of delta plain, delta-front platform deposits and suspended sediments. Due to the predominance of semi-diurnal tides and the associated flow reversals, depositional patterns are highly variable which has resulted in the formation of characteristic sand–mud couplets. The distribution of the sand–mud couplets found in this study differs from previously proposed conceptual models. They are limited to the fluvial domain and form in the distributary channels (lateral channel bar) or at the fluvial dominated delta-front platform, which flanks the mouth bar deposits in offshore direction. The sand–mud couplets which formed as delta-front platform and lateral channel bar deposits are similar and can only be identified based on their 14C age. The sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity. Turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments.
Some 22 new AMS 14C dates show that late Holocene sea level history resembles the eustatic sea level curve giving a first approximation of the Late Holocene sea level history for East Kalimantan. The dates suggest that the progradational delta system evolved under conditions of slowly rising sea level, which compares well to the eustatic sea level curve. In addition, calculated averaged deposition rates of the sand–mud couplets indicate that deposition is driven by the spring–neap tide cycles instead of the daily tidal cycle. 相似文献
19.
WHITE CRAIG M.; GEIST DENNIS J.; FROST CAROL D.; VERWOERD WILHELM J. 《Journal of Petrology》1989,30(2):271-298
The Vandfaldsdalen macrodike is a layered and differentiatedgabbroic dike approximately 3?5 km long and from 200 to 500m wide. It appears to cut the eastern margin of the Skaergaardintrusion and may have served as a feeder for the Basistoppensill. The macrodike can be divided into three series of rocks:a marginal series of differentiated gabbros adjacent to thewalls of the dike; a central series of differentiated and subhorizontallylayered gabbros and ferrodiorites in the interior of the dike;and an upper felsic series of granophyric rocks with abundantquartzo-feldspathic xenoliths. The mineral and bulk-rock compositionsthrough both the marginal series and central series show progressiveiron enrichment. The most Ca-rich plagioclase (An69) and mostmagnesian pyroxene (Wo42 En46 Fs12) occur in olivine-bearingrocks of the marginal series about 5 m from the contact withwall rocks. The most Na-rich plagioclase (An39) and Fe-richpyroxene (Wo38 En24 Fs38) are in olivine-free ferrodiorite ofthe central series, about 20 m below the contact with the felsicseries. Evidence from field observations, bulk-rock chemical compositions,and Sr and Nd isotopic data indicate the felsic series formedas a mixture of the initial macrodike magma and granitic countryrock. 87Sr/86Sr ratios of specimens from the felsic series rangebetween 0?7129 and 0?7294. 143Nd/144Nd ratios vary between 0?51208and 0?51118. Both ratios vary serially with the SiO2 contentsof the specimens. We suggest that the felsic series evolvedas a separate body of low density liquid which floated on thedenser gabbroic magma of the central series. Heat from crystallizationof the gabbroic magma must have diffused into the felsic layer,enabling extensive assimilation of the granitic xenoliths, butour data indicate there was very little exchange of chemicalcomponents between the two liquids. 相似文献
20.
N. I. Filatova 《Doklady Earth Sciences》2007,413(2):362-366