共查询到20条相似文献，搜索用时 78 毫秒
1.
扬子地台西南缘古元古代末的裂解事件——来自武定地区辉绿岩锆石U Pb年龄和地球化学证据 总被引：7，自引：0，他引：7
云南省武定地区广泛出露元古宙辉绿岩体,本文报道了武定地区海孜辉绿岩的地球化学特征及锆石的LA-ICP-MS U-Pb年龄,结果为1767±15Ma(MSWD=0.19,n=17),表明本区广泛出露的辉绿岩群侵位时代为古元古代晚期。辉绿岩岩石化学表现为低SiO2、MgO以及高TiO2(3.24%~4.02%)、碱(K2O+Na2O)和P2O5含量(0.32%~0.45%),具有偏碱性的拉斑质玄武岩的岩石化学特征。辉绿岩的大离子半径元素如K、Rb、Ba等富集,高场强元素如Ta、Nb和Zr、Hf没有明显的亏损,其地球化学参数也多与夏威夷碱性洋岛玄武岩相近。辉绿岩的微量、稀土元素的配分模式与典型的OIB和峨眉山高Ti玄武岩具有高度一致性。海孜辉绿岩原始岩浆形成于相对较富集的过渡型地幔的部分熔融,其源区为尖晶石橄榄岩相,演化过程中,有少量下地壳物质的加入。海孜辉绿岩与扬子地台西南缘广泛出露古元古代晚期的岩浆岩一致,形成于全球性Columbia超级大陆裂解的大地构造背景。海孜辉绿岩OIB的地球化学属性,为古元古代晚期全球性Columbia超级大陆裂解的地幔柱活动提供了最重要的地球化学证据。 相似文献
2.
云南省武定县迤纳厂铁铜矿区广泛出露元古宙辉绿岩体。前人对区内基性岩浆岩研究程度较低,缺乏辉绿岩的形成时代资料。本文报道了区内海孜辉绿岩中锆石的LA-ICP-MS U-Pb年龄,为1728±4 Ma。此年龄与古元古代晚期扬子地台西南缘大规模非造山型岩浆活动及全球性Columbia超级大陆裂解时代高度一致,表明其可能为Columbia超级大陆裂解的产物。辉绿岩与区内铁铜矿床成矿时代大致相当,反映了古元古代晚期扬子地台西南缘大规模的岩浆活动也可能是一次重要的成矿事件,可能为铁、铜成矿作用提供主要的成矿物质来源。武定地区被辉绿岩侵入接触的原"美党组"地层的沉积时代应大于辉绿岩的侵位时代,应划入下元古界汤丹群,是昆阳陆内裂谷拉张以前就已存在的基底地层。 相似文献
3.
华北陆块北部燕山地区广泛发育侵位于下马岭组的一套辉绿岩岩床。其岩石地球化学特征表明,燕山地区辉绿岩以高TiO2(1.70%~4.29%),低Al2O3(11.33%~14.98%)和低MgO(4.17%~5.86%),以及Na2OK2O为特征,属大陆拉斑玄武岩系列。稀土元素特征显示,∑REE总量较高,LREE明显富集,轻重稀土分馏不明显;配分曲线右倾,无明显Eu异常。结合Zr-Y、Zr-Nd、Zr/Y-Zr、Ti/100-Zr-Y×3、Ta/Hf-Th/Hf及Nb/Zr-Th/Zr等图解综合分析认为:该辉绿岩岩浆源自过渡性地幔,形成于华北陆块北部中元古代晚期的板内伸展构造背景。 相似文献
4.
扬子陆块西缘古元古代基性侵入岩LA-ICP-MS锆石U-Pb年龄和Hf同位素及其地质意义 总被引：7，自引：2，他引：5
扬子陆块西缘康滇南北向构造带内发育大量古元古代基性岩脉(墙),它们对于认识扬子陆块早期的构造演化具有重要意义.对四川会理地区侵入到元古界通安组内的辉长岩进行LA-ICP-MS锆石U-Th-Pb同位素测定,获得的207pb/206Pb加权平均年龄为1694Ma±16Ma(MSWD=0.9),代表了该辉长岩的形成和侵位时代,这一结果指示会理地区通安组应为古元古代地层.辉长岩全岩地球化学具有类似于N-MORB的特征.辉长岩锆石初始(176H f/177Hf)i值为0.281881～0.281982,对应的εHf(t)为6.2～9.8,单阶段亏损地幔Hf模式年龄tDM1为1738～1883Ma,平均值为1803Ma.这些数据表明古元古代辉长岩来源于亏损地幔,指示古元古代晚期扬子西缘之下存在亏损地幔.结合扬子西缘大量古老的碎屑锆石,推测扬子陆块西缘存在太古宙—古元古代的结晶基底.与扬子陆块西缘古元古代晚期基性侵入岩形成有关的幔源岩浆事件明显晚于扬子陆块古元古代碰撞造山及造山后的伸展作用,记录了扬子陆块古元古代晚期一次伸展过程,可能是Columbia超大陆裂解作用在扬子陆块的响应. 相似文献
5.
为了探讨塔里木北缘构造岩浆演化,采用锆石年代学、岩石地球化学方法对柯坪辉绿岩进行研究。LA‐ICP‐MS锆石U‐Pb结果表明其为中‐晚三叠世岩浆活动的产物。辉绿岩SiO2含量为45.68%~46.97%、TiO2为3.98%~4.03%、Al2O3为14.81%~14.90%、K2O/Na2O为0.39~0.42,属于高钾碱性系列。微量元素特征表明,有微弱的Ce负异常(δCe=0.95~0.99),Eu异常不明显(δEu=0.98~1.00),总体富集大离子亲石元素和LREE,高场强元素相对亏损。柯坪辉绿岩、阿图什辉绿岩与柯坪玄武岩、巴楚辉绿岩等具有相似的源区和一致的构造背景,均为拉张背景下形成,但却分属不同的构造事件。研究表明早石炭世南天山洋闭合,晚石炭世—早二叠世柯坪地区为塔里木北缘的具有前陆盆地性质的残留海盆,受地幔柱影响柯坪—巴楚地区出现大规模岩浆活动。二叠纪之后塔里木北缘为后碰撞伸展背景。三叠纪南天山—塔里木北缘为拉伸走滑的构造背景,本文的辉绿岩,正是在这种背景下形成的。 相似文献
6.
新疆东准噶尔卡拉麦里钾质玄武岩的地球化学特征、成因及其构造意义 总被引：2，自引：0，他引：2
卡拉麦里钾质火山岩位于准噶尔盆地的东北缘下石炭统巴塔玛依内山组内。这些火山岩以粗面玄武岩和玄武质粗面安山岩为主,SiO2含量稳定(46.29%～51.56%),具有较高的碱含量(K2O+Na2O=5.39%～6.96%)以及高K2O/Na2O比值(K2O/Na2O=0.5～1.4),TiO2含量相对稳定(0.94%～1.21%),显示钾玄质岩石特征。岩石地球化学表明,钾玄岩强烈富集LILE(如K、Rb和Sr)和LREE((La/Yb)N=4.39～6.25),Eu正异常明显(δEu=1.3～1.7),相对亏损HFSE(如Zr、Hf),Ta、Nb和Ti呈明显的"TNT"负异常,及较高Ba/Nb和Ba/Ta比值(分别为38～93,574～1470),显示典型岛弧岩浆特征,而Nd-Sr同位素显示亏损地幔源区特征。不相容元素(Nb/La)N和Ba/La比值(分别为0.33～0.41,11.07～18.82)以及高Nb含量(4.45×10-6～7.76×10-6),表明这些岩石来自一个交代作用富集的地幔源区。通过钾质火山岩环境的梯次判别图研究,发现巴塔玛依内山组钾玄岩形成于后碰撞环境,显示岛弧的岩石地球化学特征。在后碰撞期,由于陆内调整和均衡作用,东准噶尔东北缘的岩石圈伸展减薄,随着岩石圈地幔的减薄,前期交代富集的下部地幔楔(金云母和/或钾质角闪石-尖晶石相二辉橄榄岩)发生低度部分熔融形成钾玄质母岩浆,诱发了后碰撞型钾玄质岩浆活动(具有弧火山岩岩石地球化学特征),形成了卡拉麦里巴塔玛依内山组钾质玄武岩。 相似文献
7.
在鄂尔多斯地块西南缘的六盘山断裂带内出露铁马河辉绿岩。铁马河辉绿岩相对贫CaO、MgO和K_2O;富集FeOT、TiO_2和Na_2O。轻稀土相对富集,重稀土平坦,不显示Eu异常,稀土配分曲线显示右倾型;高场强元素无异常,大离子亲石元素K、Rb、Ba相对富集,显示富集地幔源的地球化学特征。对辉绿岩样品进行LA-ICP-MS锆石U-Pb测年,获得上交点年龄2018±16Ma,说明岩体形成于古元古代。样品具有低的(~(87)Sr/~(86)Sr)i值(07003～07064)和正的εNd(t)值(+514～+433),Nd同位素一阶段模式年龄(约20Ga)与LA-ICP-MS锆石U-Pb年龄基本一致,暗示其来源于软流圈地幔的部分熔融。结合区域地质资料的研究表明,华北克拉通西部地块(鄂尔多斯地块)在20Ga期间的伸展背景与东部陆块一致,暗示整个华北克拉通在20Ga左右存在广泛的裂解事件。 相似文献
8.
北山磁海辉绿岩型铁矿区基性杂岩锆石U-Pb年代学及岩石成因 总被引：1，自引：0，他引：1
磁海辉绿岩型铁矿位于塔里木北缘北山裂谷带,主要岩石类型为辉绿岩,岩石具有较高的Mg#(55.7～70.1)、中铝Al2O3(13.75～14.65)特征,Na2O/K2O(1.79～14.04)变化较大,整体属于钙碱性系列(K2O/Na2O=0.07～0.56,FeO/MgO=0.77～1.46)。稀土元素方面,磁海辉绿岩具有较高的稀土元素质量分数和δEu异常特征[w(∑REE)=88.01×10-6～213.07×10-6,δEu=0.63～1.44],球粒陨石标准化稀土元素配分模式为缓右倾型[(La/Yb)N=1.32～3.87,(La/Sm)N=1.05～2.17,(Gd/Yb)N=1.12～1.58],微量元素上选择性富集大离子亲石元素(Rb、K),亏损高场强元素(Nb、Ta)。岩浆演化过程中斜长石和单斜辉石的分离结晶作用是岩浆演化的主要机制,同时伴有较为明显的地壳混染作用。LA-ICP-MS锆石U-Pb年代学指示该辉绿岩形成于约291.9Ma,构造环境分析表明磁海辉绿岩为板内拉张环境的产物。 相似文献
9.
油洞断裂带中辉绿岩脉的全岩Ar-Ar年龄为110.6 ± 2.0Ma,属于燕山晚期岩浆活动产物。辉绿岩具有较高的SiO2（平均为50.65%）、Al2O3（平均为15.10%）、CaO（平均为10.48%）、MgO（平均为7.80%）含量和较低的TiO2（平均为1.13%）、FeOt（平均为9.90%）、Na2O（平均为2.28%）、K2O （平均为0.90%）、P2O5（平均为0.11%）含量。在微量元素方面,大离子元素Rb、Th、Ba、K的富集明显,而Nb、Ta、Zr 、Hf、P、Ti显示亏损。稀土元素总量低,轻稀土相对富集,分布模式略呈右倾型,Eu亏损弱（δEu平均为0.92）。辉绿岩的上述元素地球化学特征非常相似于活动大陆边缘钙碱性玄武岩,反映原始岩浆来源于受太平洋板块俯冲产生的流体对上覆地幔楔交代改造形成的富集地幔源区。 相似文献
10.
扬子陆块古-中元古代地质演化与Columbia超大陆重建 总被引：3，自引：0，他引：3
扬子陆块在古-中元古代时期经历了较为强烈的岩浆-变质-沉积-成矿等地质事件,这些事件是理解该陆块陆壳演化和成矿效应内在联系及动力学的关键,也是探讨该陆块在Columbia超大陆中古地理重建的前提。本文以古-中元古代地质单元出露较为完整的扬子西南缘为重点研究对象,在总结已有资料的基础上,对扬子陆块古-中元古代时期地质事件进行剖析和讨论,明确了扬子陆块西南缘在古-中元古代时期经历了由Columbia超大陆初始裂解引起的陆内裂谷相关的沉积作用,岩浆侵位及矿产富集等地质过程。通过与全球陆块进行对比,发现相似的裂谷的相关沉积-岩浆-成矿事件在劳伦大陆西北部、澳大利亚北部及Siberian克拉通都有体现。本文认为扬子陆块在2. 4～2. 3 Ga通过增生拼贴到劳伦大陆Rae克拉通。在共同经历过Columbia超大陆聚合的峰期变质作用(2. 03～1. 81 Ga)之后,超大陆开始逐步裂解并形成大陆内部裂谷,最终在古元古代后期(～1. 66～1. 60 Ga)扬子陆块和Columbia超大陆主体分离。 相似文献
11.
12.
Over the past decade researchers working on the rocks of the Beaufort Group in the main Karoo Basin of South Africa have vastly increased our understanding of this important Permo-Triassic sequence. Many new fossil forms have been discovered, allowing for breakthroughs into the biodiversity, biogeography and biostratigraphy of the group. Taxonomic and phylogenetic advances are many and varied, and cover most of the vertebrate taxa, but with emphasis placed on the temnospondyl amphibians, archosauriforms and non-mammalian synapsids, in particular the anomodontia. Biostratigraphic breakthroughs have centered on the Middle Permian Eodicynodon and Tapinocephalus assemblage zones, the Late Permian Dicynodon Assemblage Zone, and the Triassic Lystrosaurus and Cynognathus assemblage zones. Correlation of these biozones with better dated sequences in Europe, Russia and China has allowed for many chronostratigraphic refinements, which are in turn vital for sequence stratigraphical analysis of the basin fill. Based on fossil data, both the lower (Ecca–Beaufort) and upper (Beaufort–Molteno) contacts of the group have been proved to be highly diachronous. The refined chronostratigraphic framework has also allowed for a better analysis of the basin evolution through time, particularly in terms of the correlation of external stimuli that affect basin sedimentation patterns. 相似文献
13.
藏北羌塘丁固—加措地区康托组的时代 总被引：2，自引：0，他引：2
自西藏区域地质调查大队创建康托组以来,康托组岩石地层单位广泛应用于羌塘地区,普遍认为其时代为新近纪.笔者于丁固-加措地区的康托组地层中采获古近纪轮藻化石Obtusocharat sp.,O.lanpingenis,Gyrogona qinajiangica和部分孢粉化石,并在康托组底部安山岩中获K-Ar年龄65.1～66.5Ma.上述轮藻组合与同位素年龄指示的地层时代为古新世-始新世,据此将测区康托组的时代确定为古近纪.由于测区康托组之上被唢纳湖组或鱼鳞山组角度不整合覆盖,因此康托组时代的确定不仅进一步完善了测区新生代地层系统,还指示测区在康托组与唢纳湖组或鱼鳞山组之间发生了一次强烈的构造运动. 相似文献
14.
新疆维吾尔自治区阿图什市木吉地区邻近帕米尔,是印度板块与欧亚板块碰撞挤压应力最集中的地区,地层变质和变形强烈,研究基础薄弱。木吉群由变质砂岩、板岩、千枚岩、石英岩、钙质石英岩、变粒岩、二云石英片岩、大理岩等组成,一直未发现任何化石。最近,笔者在木吉乡的喀拉足克沟和阿拉木陶沟的粉砂岩、钙质粉砂岩中发现了一些植物管胞片和孢粉化石:Gran-ulatisporites sp.,Cycloranisporites sp.,Verrucosisporites sp.,Pityosporites sp.,Punetatosporites sp.,Leiotriletes sp.,Apicu-latisporites sp.,Platysaccus sp.,Cycodopites sp.等。从地层接触关系和孢粉化石的整体面貌看,木吉地区含上述孢粉化石的木吉群的时代可能为泥盆纪—石炭纪。 相似文献
15.
西藏阿里札达盆地上新统中犀类化石的发现及意义 总被引：9，自引：10，他引：9
首次在西藏阿里札达盆地上新世河湖相沉积地层中发现了犀类化石，对其基本特征进行了描述，初步鉴定为犀类额鼻角犀亚科第三庶骨化石，在同一层位中还采集了大量孢粉、微体古生物和植物化石。结合区域地质特征和产出犀类化石地层的沉积学特征等的分析，认为札达盆地上新世时代表着温暖湿润向寒冷潮湿-温和干旱的气候变化过程。这一发现有助于进一步认识青藏高原新近纪上新世的生物演化、气候变化和构造活动，为研究青藏高原新近纪以来的生物进化、湖泊与河流演化、气候变化．古地理与古环境变迁，以及新生代地层的划分对比等提供了新资料。 相似文献
16.
Study of the cross-stratification and other sedimentary structures in the Lower Greensand of the Weald, England, and Bas-Boulonnais, France, indicates that the sediments were deposited by the lateral migration of sand waves in a neritic sea. Comparison of the Lower Greensand sea with the modern North Sea was attempted. If those sediments were deposited as a result of tidal current similar to the present-day North Sea then the Lower Greensand shoreline could be deduced as running northwest-southeast, indication that the western part of the London Platform was submerged. 相似文献
17.
A. A. Ariskin Yu. A. Kostitsyn E. G. Konnikov L. V. Danyushevsky S. Meffre G. S. Nikolaev A. McNeill E. V. Kislov D. A. Orsoev 《Geochemistry International》2013,51(11):859-875
The paper reports newly obtained data on the geochronology of the Dovyren intrusive complex and associated metarhyolites of the Inyaptuk Formation in the Synnyr Range. The data were obtained by local LA-ICPMS analysis of zircons in samples. The U-Pb age of olivine-free gabbronorite from near the roof of the Yoko-Dovyren Massif is 730 ± 6 Ma (MSWD = 1.7, n = 33, three samples) is close to the estimated age of 731 ± 4 Ma (MSWD = 1.3, n = 56, five samples) of a 200-m-thick sill beneath the pluton. These data overlap the age of recrystallized hornfels found within the massif (“charnockitoid”, 723 ± 7 Ma, MSWD = 0.12, n = 10) and a dike of sulfidated gabbronorite below the bottom of the massif (725 ± 8 Ma, MSWD = 2.0, n = 15). The estimates are also consistent with the age of albite hornfels (721 ± 6 Ma, MSWD = 0.78, n = 12), which was produced in a low-temperature contact metamorphic facies of the host rocks. The average age of the Dovyren Complex is 728.4 ± 3.4 Ma (MSWD = 1.8, n = 99) based on data on the sill, near-roof gabbronorite, and “charnockitoid”) and is roughly 55 Ma older than the estimate of 673 ± 22 Ma (Sm-Nd; [13]). The U-Pb system of zircon in two quartz metaporphyre samples from the bottom portion of the Inyaptuk volcanic formation in the northeastern part of the Yoko-Dovyren Massif turns out to be disturbed. The scatter of the data points can be explained by the effect of two discrete events. The age of the first zircon population is then 729 ± 14 Ma (MSWD = 0.74, n = 8), and that of the second population is 667 ± 14 Ma (MSWD = 1.9, n = 13). The older value pertains to intrusive rocks of Dovyren, and the age of the “rejuvenated” zircon grains corresponds to the hydrothermal-metasomatic processes, which affected the whole volcano-plutonic sequence and involved the serpentinization of the hyperbasites. This is validated by the results of Rb-Sr isotopic studies with the partial acid leaching of two serpentinized peridotite samples from the Verblyud Sill. These studies date the overprinted processes at 659 ± 5 Ma (MSWD = 1.3, n = 3). 相似文献
18.
Pressure Increases, the Formation of Chromite Seams, and the Development of the Ultramafic Series in the Stillwater Complex, Montana 总被引：1，自引：1，他引：0
This paper explores the hypothesis that chromite seams in theStillwater Complex formed in response to periodic increasesin total pressure in the chamber. Total pressure increased becauseof the positive V of nucleation of CO2 bubbles in the melt andtheir subsequent rise through the magma chamber, during whichthe bubbles increased in volume by a factor of 4–6. Byanalogy with the pressure changes in the summit chambers ofKilauea and Krafla volcanoes, the maximum variation was 0•2–0•25kbar, or 5–10% of the total pressure in the Stillwaterchamber. An evaluation of the likelihood of fountaining andmixing of a new, primitive liquid that entered the chamber withthe somewhat more evolved liquid already in the chamber is basedupon calculations using observed and inferred velocities andflow rates of basaltic magmas moving through volcanic fissures.The calculations indicate that hot, dense magma would have oozed,rather than fountained into the chamber, and early mixing ofthe new and residual magmas that could have resulted in chromitecrystallizing alone did not take place. Mixing was an important process in the Stillwater magma chamber,however. After the new magma in the chamber underwent {smalltilde}5% fractional crystallization, its composition, temperature,and density approached those of the overlying liquid in thechamber and the liquids then mixed. If this process occurredmany times over the course of the development of the Ultramaficseries, a thick column of magma with orthopyroxene on its liquiduswould have been the result. Thus, the sequence of multiple injections,fractionation, and mixing with previously fractionated magmacould have been the mechanism that produced the thick bronzitecumulate layer (the Bronzitite zone) above the cyclic units. 相似文献
19.
水淹坝岩溶内涝是安顺市西秀区发育最大范围的岩溶内涝,严重制约了当地经济发展。本文以岩溶地下水系统为单元,通过开展1:10000水文地质调查、地球物理勘探、水文地质钻探等手段,查明内涝所在区的岩溶发育特征、水文地质条件。在此基础上分析得出,水力坡度小、岩层倾角缓造成地下河管道淤塞;人类工程活动使有水落水洞口堵塞,加之广阔的集雨面积和连续的强降雨是造成水淹坝岩溶内涝的主要原因。通过对水淹坝内涝成因分析,为岩溶内涝灾害综合整治提供参考依据。 相似文献
20.
The Qinghai–Tibet plateau is a composite continental fragment formed by collision of multiple terranes and island arcs.The Lhasa terrane,which is located in the central part of the plateau,is bounded by the Yarlung–Zangbo suture to the south and Bangong-Nujiang suture to the north.An E–W–trending belt of(ultra)-high pressure eclogite was discovered in the Sumdo region of the Lhasa terrane.Careful field studies combined with petrological,geochemical and isotopic analyses show that the Sumdo eclogites mark a Carboniferous–Permian suture zone,at least 100 km long,containing ophiolite fragments,eclogites and Indosinian post–orogenic granitoids.This suture divides the Lhasa block into a northern and southern segment.Sumdo eclogite occurs about 200 km east of Lhasa city,and extends over 100km in an E–W direction.Sumdo eclogites were accompanied by garnet amphibolite and plagioclaseamphiboliteformedbyretrograde metamorphism of the eclogites.The eclogites were derived from oceanic basalts.LA–ICPMS U–Pb dating of zircon from the Sumdo eclogites indicates a Permian metamorphic age(260–270 Ma)and a Carboniferous protolith age of 303±4.8 MaThe ophiolite fragments in the Sumdo suture zone are composed of the ultramafic rocks,MORB–type basalt,OIB–type basalt and island arc basaltic andesite,some of which are intruded by post-collisional granites.The ultramafic body,a typical tectonic block in the suture zone,is completely serpentinized.Its geochemical features suggest that it is composed of harzburgite,typical of depleted mantle peridotite.The MORB and OIB–type basalts crop out in the Chasagang Formation,and the basaltic andesite crops out in the Leilongku Formation,both of which make up the Sumdo Group.Zircons from the OIB–type basalt with typical magmatic characteristics yield an average U–Pb age of306(95%)Ma,suggesting formation in a Paleo–Tethyan basin in the Carboniferous.U–Pb dating of zircon from the basaltic andesites yielded a concordant age of 265±3.1Ma,similar to the metamorphic age(266–270 Ma)of the eclogites,suggesting formation during subduction of the oceanic crust.Indosinian granodiorite with an age of194±4.3 Ma crops out north of the Sumdo suture.These granodiorites are similar to the late Indochina granites in the Lhasa block,and most likely formed during continent-arc collision or during closure of the Paleo-Tethyan Ocean.A four–stage model for the evolution of the Sumdo Paleo–Tethyan suture is proposed:1)From the Ordovician to the Devonian Gondwanaland was part of an epicontinental sea;2)In the Carboniferous,continental rifting produced a local basin,which then evolved into a Paleo-Tethyan ocean basin,dividing the Lhasa block into two segments;3)From the Permian to the early Triassic,Paleo-Tethyan oceanic crust was subducted northward and;4)In the middle Triassic and early Jurassic,the two fragments collided to form the modern Lhasa block. 相似文献