共查询到20条相似文献，搜索用时 50 毫秒
1.
拉萨地体南缘汤白地区广泛分布新生代的辉绿岩脉。为探讨该辉绿岩脉形成时代、岩石成因和地质意义,对其开展了详细的岩相学、地球化学、锆石U-Pb年代学及Hf同位素研究。LA-ICP-MS锆石U-Pb定年结果显示辉绿岩脉的结晶年龄为(54±1)Ma,表明其形成于早始新世。微量元素地球化学特征显示富集大离子亲石元素(LILEs:如Rb、Sr和Ba),亏损高场强元素(HFSEs:如Nb、Ta和Ti)。与典型的弧岩浆岩、区域上叶巴组和桑日岩群中的玄武岩相比具有较高的Nb、TiO_2和Zr含量,在微量元素构造环境判别图解中显示出板内玄武岩地球化学属性。微量元素地球化学特征结合锆石Hf同位素表明岩浆源区除被俯冲板片释放的流体交代的岩石圈富集地幔外,还有软流圈亏损地幔物质加入。汤白辉绿岩脉侵入年龄与区域上林子宗群火山活动峰期接近(52 Ma)。同时结合岩石成因及构造背景,作者认为汤白辉绿岩脉是54～52 Ma新特提斯洋壳断离诱发岩浆作用的产物。根据最新大陆碰撞及板片断离的三维数值模型,暗示了印度板块与欧亚大陆碰撞的起始时间为65 Ma或者更早。 相似文献
2.
The Carboniferous–Early Permian rift-related volcanic successions, covering large areas in the Chinese Tianshan and its adjacent areas, make up an important phanerozoic large igneous province in the word, which can be further divided into two sub-provinces: Tianshan and Tarim. The Early Permian volcanic rocks have been considered to be the products of an intraplate volcanism by most researchers. However, there is still strong controversy about the nature and geological setting of the Carboniferous volcanic rocks. The regional angular unconformity of Lower Carboniferous upon basement or pre-Carboniferous rocks, the ages (360–351 Ma) of the youngest ophiolite and the peak of subduction metamorphism of high pressure-low temperature metamorphic belt and the occurrence of Ni-Cu-bearing mafic-ultramafic intrusion with age of ~352 Ma and A-type granite with age of ~358 Ma reveal that the final closure of the Paleo-Asian Ocean might take place in the Early Mississippian. Our studies reveal that although contamination by continental crust or lithosphere can impart subduction-like signature (e.g., low Nb, low Ta and low Ti) and lead to misidentification of contaminated Carboniferous basaltic lavas from the Chinese Tianshan and its neighboring areas as arc related, there are still some essential differences between the Carboniferous basaltic lavas and arc related ones; such as: uncontaminated Carboniferous basaltic lavas have higher Nb concentrations (9–22 ppm), Nb/La > 1, “hump-shaped” OIB-like trace element patterns and moderate positive ɛNd values that distinguish them from the arc related ones; whereas, the contaminated Carboniferous basaltic lavas are characterized by pronounced negative Nb, Ta and Ti anomalies, but, their concentrations of incompatible trace elements are conspicuously higher than those of subduction-zone basalts that also distinguishes them from the arc related ones. Our summation suggests that the Carboniferous volcanic successions did indeed erupt in an intracontinental rift setting and their generation is likely confined to mantle plume. 相似文献
3.
20世纪70～80年代,以Pearce为代表的一批科学家先后提出了玄武岩和花岗岩的构造环境判别图,将构造环境与岩石地球化学特征有机地结合起来,为岩浆岩大地构造环境研究开辟了新途径。但学术界对全球广布的安山岩构造环境及相关地球化学特征问题的讨论则相对不足。本文利用GEOROC 和PetDB 两个数据库对全球新生代安山岩进行数据挖掘,讨论了它们的地球化学特征及形成环境。初步将全球新生代安山岩归属为12个形成构造环境,其中67.71%产出于岛弧、陆缘弧等汇聚板块边缘环境,其余安山岩则形成于大陆板内、大陆溢流、洋岛、大陆裂谷、洋中脊等构造环境。研究表明,常用的玄武岩微量元素判别图以及LILE/HFSE 玄武岩判别图均在一定程度上可用于安山岩成因及环境判别, 暗示安山岩地球化学成分也可用于构造环境的判定。采用大数据思维,探索洋岛安山岩（OIA）和岛弧安山岩（IAA）中地球化学元素的关联关系,从获得的近20 000 个OIA-IAA 判别图中选出lg（Cs/Ta）-lg（Cu/Ta）、lg（CaO/Nb）-lg（Cs/Zr）和lg（Cu/Ta）-lg（Co/Nb）等6个图解,能有效限定它们的构造环境,为安山岩成因及形成环境研究提供了新的思路。这些初步成果说明科学大数据的研究方法可成为岩浆岩构造环境及地球化学研究中的重要有效手段。 相似文献
4.
新疆西准噶尔北部地区的早泥盆世马拉苏组出露有少量富钠低钾的拉斑质中基性熔岩,这些分布于谢米斯台断裂北侧的玄武安山岩和玄武岩多呈夹层状断续产出于火山碎屑岩之中。马拉苏中基性熔岩的Mg#与主、微量元素协变关系及Th-Th/Nd图反映了其并非同源岩浆演化的结果。马拉苏火山岩中的玄武安山岩富集LILE、亏损HFSE,具有较高的Th含量及较低的Hf/Th和(Nb/Th)PM比值,显示出弧火山岩的地球化学特征。其中的玄武岩则具有略为平坦的稀土元素分配样式,较低的Th含量及较高的Hf/Th和(Nb/Th)PM比值,此同MORB地球化学特征极为相似;虽然其也显示有轻微的LILE富集、HFSE亏损,但是较高的La/Nb比值则暗示这同地壳或俯冲物质组分的卷入有关,且一系列构造环境判别图解也进一步印证了马拉苏组内的玄武岩应属似MORB基性熔岩。此外,两类岩石的高场强元素比值Zr/Nb、Hf/Ta同全球平均大洋中脊玄武岩的相应比值极为接近,反映了马拉苏组中基性火山岩的物质源区主体均为MORB地幔物质源区。La/Yb-Gd/Yb原始地幔标准化比值的模拟计算进一步显示了马拉苏组玄武安山岩与受改造(俯冲沉积物或地壳物质的混染)的石榴子石或尖晶石-石榴子石地幔橄榄岩物质源区的部分熔融作用有关,而似MORB型玄武岩则源自尖晶石地幔橄榄岩源区的部分熔融。结合区内同期的蛇绿岩、火山岩和碱性花岗岩的地球化学研究,我们可以进一步推断此类兼具有似MORB和弧火山岩地球化学特征的早泥盆世马拉苏火山岩应当是西准噶尔地块北部在早古生代受后期俯冲作用影响下经历弧后扩张形成的火山-岩浆地质记录。 相似文献
5.
Petrographic and geochemical study of basalts in the Kerguelen Plateau basement revealed changes in the composition and character of volcanism during the development of this tectonovolcanic structure. The Kerguelen Plateau is one of the largest intraplate rises in the World Ocean. It started to form about 120 Ma ago. The age of basalts and overlying sediments shows that the plateau formation succeeded in the northwestern direction. Basalts of the Kerguelen Plateau basement are products of tholeiitic melts in terms of geochemistry, but differ from the mid-oceanic ridge basalt (MORB). They are enriched in incompatible trace elements and rare earth elements (REE) relative to MORB, and the degree of enrichment varies in basalts from different segments of the plateau. The composition of basalts does not directly depend on their age. Specific features of the plateau magmatism are commonly explained in terms of a long-living deep magma plume, which variously interacted with a depleted upper mantle source at different stages of the plateau formation. However, taking into account block morphology and deep structure of the plateau, one can suggest that the plateau volcanism was initiated by a large fault. As the volcanism prograded to the northwest, the depth of fault penetration into the mantle changed. The composition of basalts in the plateau basement was also governed by the formation depth of primary melts. 相似文献
6.
全球岛弧玄武岩数据挖掘——在玄武岩判别图上的表现及初步解释 总被引：8，自引：3，他引：5
MORB(洋中脊玄武岩)、OIB(洋岛玄武岩)和IAB(岛弧玄武岩)是学术界最关心的3种玄武岩类型,其中尤以与板块消减作用有关的岛弧岩浆活动备受关注。岛弧可分为洋内岛弧和大陆边缘岛弧(活动陆缘弧)2类。对IAB进行讨论,重点探讨IAB的识别。IAT(岛弧拉斑玄武岩)和IAB是前弧、岛弧和后弧岩浆作用的产物,其中,后弧组分更具多样性,它不同于弧后玄武岩,前者属于弧的范围,而后者形成的动力学过程与俯冲系统有关,但其是独立的构造单元,尽管其岩浆作用可能仍受到俯冲流体的影响。前人对IAB进行了大量研究,提出了多种构造环境判别图解,并得到广泛应用。尝试应用全球玄武岩数据来验证上述判别图的可信度,研究发现,可信度高的判别图不多,且大多与Th、Ta(Nb)和Ti元素有关的,如Hf-Th-Ta(Nb)、TiZr-Sr和Th/Yb-Ta/Yb图,其余判别图的判别效果可信度低且具多解性,建议谨慎使用。IAB与MORB和OIB的区别主要体现在Nb-Ta亏损的特征上,是否受到俯冲流体的影响是区分IAB与MORB和OIB最重要的标志。 相似文献
7.
哀牢山构造岩浆带晚二叠世-早三叠世火山岩特征及其构造环境 总被引：15，自引：7，他引：8
本文对中国云南哀牢山构造岩浆带内的雅轩桥、帽盒山、绿春火山岩等开展了相关研究.雅轩桥附近的火山岩为晚二叠世,岩性主要为橄榄粗安岩-玄武岩(少量安山岩),在TAS图上既有碱性又有亚碱性.钾含量较低(＜1.19％),为低钾钙碱-中钾钙碱性,Peacock碱钙指数以钙碱性为主.与MORB相比,其痕量元素蛛网图亏损Nb、Ta,而富集Pb,从Zr-V曲线呈平坦型,并且整体比MORB亏损.稀土元素配分模式与MORB相近,但略显轻稀土元素富集和重稀土元素亏损.在构造环境判别图上均位于火山弧环境.他郎河边(雅轩桥地区)火山岩为英安岩,属亚碱性,中钾钙碱性,Peacock指数为钙性.痕量元素蛛网图、REE模式图以及大地构造环境判别图,均表明其属于弧的构造环境.由上推测雅轩桥火山岩在晚二叠世属于弧火山岩.帽盒山玄武岩的锆石SHRIMP U-Pb测年结果为249±1.6Ma,为早三叠世.岩性为亚碱性钠长玄武岩,低钾钙碱性系列,Peacock碱钙指数以钙性为主.痕量元素蛛网图和REE配分模式图与MORB相比,LREE略微富集.在构造环境判别图中位于从E-MORB向岛弧过渡的构造环境.绿春地区流纹岩的锆石SHRIMP U-Pb年龄为247.3±1.8Ma,为早三叠世,属亚碱性,钾玄岩系列,Peacock碱钙指数为碱钙性.痕量元素蛛网图、REE配分模式图及大地构造环境判别图显示其为成熟岛弧向陆陆碰撞的过渡环境.结合前人研究,推测哀牢山洋在晚泥盆世形成,可能在石炭世-早二叠世(?)处于洋的扩张期.晚二叠世时,在哀牢山洋的西侧出现了雅轩桥的初始孤火山岩,预示着至少在这一时期,哀牢山洋已经开始俯冲.到三叠世早期(249±1.6Ma),在哀牢山洋的东侧出现了具有弧和MORB的双重特性的帽盒山玄武岩,可能指示此时哀牢山洋盆已经变小,或已转化为孤间或弧后盆地,洋的演化进入了晚期阶段,并且在局部地段,如绿春地区,此时(247.3±1.8Ma)已经进入到成熟岛弧向陆陆碰撞的过渡阶段.因此支持哀牢山洋在晚三叠世闭合的结论,亦符合上三叠统一碗水组不整合在哀牢山蛇绿混杂岩之上的事实. 相似文献
8.
蛇绿岩生成构造环境的Ba-Th-Nb-La判别图 总被引：58，自引：24，他引：58
Pearce的Ti-Zr-Y图不能很好区分洋脊和岛弧玄武岩,Ti对岩浆分离结晶作用很敏感,因此用这个图判别蛇绿岩生成构造环境效果不好,本文利用分配系数相近的Ba,Th,Nb,La四个非常不相容元素的(Ba/Nb)-Ba,(Nb/Th)-Nb,(La/Nb)-La和(Ba/Nb)-(Th/Nb)图解很好区分了洋脊、岛弧、洋岛玄武岩。弧后盆玄武岩同时具有洋脊和岛弧玄武岩的特征。这些元素在海水蚀变中较稳定,它们的比值在分离结晶过程中保持不变,因此这些图解有利于判别蛇绿岩(包括熔岩和均质辉长岩)生成的构造环境。 相似文献
9.
弧后盆地玄武岩(BABB)是弧后盆地扩张过程中岩浆作用的主要产物,其地球化学组成是认识弧后盆地演化的关键。现今弧后盆地主要集中在西太平洋地区。本文总结了该地区弧后盆地玄武岩的元素地球化学和同位素组成特征。总体而言,相对于开阔大洋洋中脊玄武岩(MORB),弧后盆地玄武岩的主量元素成分变化范围很大,在Al_2O_3-Mg O、Ti O_2-Mg O相关图上偏离了MORB的演化趋势,在Mg O相同的情况下表现出更高的Al_2O_3含量和更低的Ti O_2含量。弧后盆地玄武岩的微量元素特征一般介于MORB和弧玄武岩之间。一方面,它们与MORB一样在中、重稀土元素之间没有明显分馏;另一方面,与弧玄武岩一样富集大离子亲石元素Rb、Ba、Th、U、K,具有Pb的正异常和Nb、Ta的负异常等。其中,劳海盆、日本海海盆和冲绳海槽有部分样品具有Nb、Ta的正异常,表现出类似于E-MORB的微量元素特征。西太平洋地区弧后盆地玄武岩的Sr-Nd-Pb同位素组成变化范围较大,相对于MORB,其富集组分更常见,总体介于亏损地幔端元(DMM)、1型富集地幔(EM1)和2型富集地幔(EM2)三者之间。不同基底属性(大陆基底和大洋基底)和不同阶段的弧后盆地玄武岩的地球化学组成也有明显区别。弧后盆地玄武岩地球化学成分上的多样性主要受控于源区(地幔楔)的物质组成、熔融程度和岩浆上升过程中的变化等因素。地幔源区的不均一性主要体现在地幔楔自身的化学性质和俯冲板片的物质贡献差异。部分弧后盆地玄武岩具有异常高的地幔潜能温度、高的3He/4He比值以及E-MORB型的微量元素特征,说明其地幔源区还可能受到了地幔柱的影响。地幔潜能温度越高,俯冲流体贡献越多,地幔楔的熔融程度越大。此外,岩浆上升过程中发生的地壳混染、岩石圈中的熔体-岩石反应以及矿物的结晶分离都会改造岩浆的成分。 相似文献
10.
江南造山带西段岩浆作用特性 总被引：12，自引：1，他引：11
在湖南浏阳南桥的中元古代冷家溪地层中发现了一种高度亏损、具N—MORB属性的玄武岩一辉绿岩。这种玄武岩的K2O特低,不相容的高场强元素,如Nb,Zr,Hf,Ti等和稀土元素的丰度都低于（少数元素接近）N-MORB的丰度,εNd（1271Ma）为6．86～8、98。在俯冲带附近N—MORB的发现为“九岭古岛弧”的存在提供了新的证据。湘西黔阳、古丈新元古代玄武岩-辉绿岩属碱性玄武岩．其微量元素特征近似于OIB,它的规模值得进一步调查。广西北部丹洲群中基性-超基性岩的TiO2,Ta及Nb的含量低,Hf／Th,Ti／Y和Ti／Zr等的比值也低,La/Ta和Th／Yb等的比值高,具有“弧玄武岩”特性。它们不具有CFB及OIB的地球化学特征,在构造环境判别图解上的标绘点集中在“火山弧玄武岩区”,少数样品位于“弧后盆地玄武岩区”。至今未发现具高温特征的高镁熔岩,也未见大规模放射性岩墙群。这些基性岩的规模极小（约100km^2）,不具有地幔柱来源的镁铁质岩浆的特性。桂北及湘东北的新元古代强过铝（SP）花岗岩体与江西九岭和安敞许村、休宁、歙县等岩体具有相似的特征,它们沿江南造山带呈带状分布,其形成与华夏和扬子板块之间的碰撞事件有关。在全球不同时代的造山带中都有S-型花岗岩出露;地幔柱岩浆作用形成的“镁铁质大火成岩省”中,出现的少量花岗岩是非造山、板内或A-型花岗岩,而不会是S-型花岗岩。不能把S-型花岗岩作为地幔柱岩浆作用的证据。这些都说明“江南造山带”的厘定有充分的岩石学证据。 相似文献
11.
Variable involvements of mantle plumes in the genesis of mid-Neoproterozoic basaltic rocks in South China: A review 总被引：5，自引：0，他引：5
Ca. 825–720 Ma global continental intraplate magmatism is generally linked to mantle plumes or a mantle superplume that caused rifting and fragmentation of the supercontinent Rodinia. Widespread Neoproterozoic igneous rocks in South China are dated at ca. 825–760 Ma. There is a hot debate on their petrogenesis and tectonic affiliations, i.e., mantle plume/rift settings or collision/arc settings. Such competing interpretations have contrasting implications to the position of South China in the supercontinent Rodinia and in Rodinia reconstruction models.Variations in the bulk-rock compositions of primary basaltic melts can provide first order constraints on the mantle thermal–chemical structure, and thus distinguish between the plume/rift and arc/collision models. Whole-rock geochemical data of 14 mid-Neoproterozoic (825–760 Ma) basaltic successions are reviewed here in order to (1) estimate the primary melts compositions; (2) calculate the melting conditions and mantle potential temperature; and (3) identify the contributions of subcontinental lithosphere mantle (SCLM) and asenthospheric mantles to the generation of these basaltic rocks.In order to quantify the mantle potential temperatures and percentages of decompression melting, the primary MgO, FeO, and SiO2 contents of basalts are calculated through carefully selecting less-evolved samples using a melting model based on the partitioning of FeO and MgO in olivine. The mid-Neoproterozoic (825–760 Ma) potential temperatures predicted from the primary melts range from 1390 °C to 1630 °C (mostly > 1480 °C), suggesting that most 825–760 Ma basaltic rocks in South China were generated by melting of anomalously hot mantle sources with potential temperatures 80–200 °C higher than the ambient Middle Ocean Ridge Basalt (MORB)-source mantle.The mantle source regions of these Neoproterozoic basaltic rocks have complex histories and heterogeneous compositions. Enriched mantle sources (e.g., pyroxenite and eclogite) are recognized as an important source for the Bikou and Suxiong basalts, suggesting that their generations may have involved recycled components. Trace elements variations show that interactions between asthenospheric mantle (OIB-type mantle) and SCLM played a very important role in generation of the 825–760 Ma basalts. Our results indicate that the SCLM metasomatized by subduction-induced melts/fluids during the 1.0–0.9 Ga orogenesis as a distinct geochemical reservoir that contributed significantly to the trace-elements and isotope inventory of these basalts.The continental intraplate geochemical signatures (e.g., OIB-type), high mantle potential temperatures and recycled components suggest the presence of a mantle plume beneath the Neoproterozoic South China block. We use the available data to develop an integrated plume-lithosphere interaction model for the ca. 825–760 Ma basalts. The early phases of basaltic rocks (825–810 Ma) were most likely formed by melting within the metasomatized SCLM heated by the rising mantle plume. The subsequent continental rift allowed adiabatic decompression partial melting of an upwelling mantle plumes at relatively shallow depth to form the widespread syn-rifting basaltic rocks at ca. 810–800 Ma and 790–760 Ma. 相似文献
12.
Contemporaneous Convergent Margin and Intraplate Magmatism, North Island, New Zealand 总被引：3，自引：1，他引：2
A convergent margin magma series with characteristic low Nband Ta abundances and enrichments in alkalis and alkaline earthsis intercalated with typical intraplate alkalic basalts in aback-arc setting, 200–250 km above the Wadati-Benioffzone on the North Island, New Zealand. These two contrastingmagma types, together with late-stage K-rich maflc lavas, wereerupted over a short time period (1{dot}60–2{dot}74 Ma)and constitute the Alexandra Volcanics. Field relationshipsindicate that these diverse magma types were contemporaneous,and thus their mantle source regions coexisted, in a singletectonic environment. The convergent margin magma series forms a linear chain of stratovolcanoesaligned at right angles to the present subduction zone. Closed-systempolybaric fractional crystallization models can explain theevolution from ankaramites to transitional olivine basalts toolivine tholeiites to high-Al basalts to medium- and high-Kandesites. The most primitive lavas have geochemical (high LIL/LREEand LIL/HFS element ratios) and Sr, Nd, and Pb isotopic compositionstypical of convergent margin magmas. Calculated source compositionssuggest that three components are involved: a MORB component,a component derived from subducted oceanic crust, and a contributionfrom subducted sediments. The alkalic basalts occur as dispersed monogenetic volcanoesand are intercalated with the larger convergent margin stratovolcanocs.These basalts are enriched in LILE, LREE, Nb, and Ta, and havelow Ba/Nb and Ba/La ratios, all of which are characteristicof ocean island (intraplate) basalts (OIBs). Their relativelyhigh Nd (+5{dot}5 and low 87Sr/86Sr(0{dot}703l–0{dot}7036)are also typical of OIBs. These alkalic magmas were derivedfrom the underlying continental lithospheric mantle that hasbeen enriched by upward-migrating silica-undersaturated melts,probably including volatiles, from the low- velocity zone. Asubducted slab component is not required to account for theirincompatible element enriched character. The K-rich mafic lavas, basanites, and absarokites are volumetricallyminor and cap the largest of the stratovolcanoes, Pirongia.The basanites have geochemical and isotopic compositions whichsuggest they are mixtures of multiple source components, includingthe alkalic and convergent margin region. 相似文献
13.
The subduction system in southern Patagonia provides direct evidence for the variability of the position of an active continental arc with respect to the subducting plate through time, but the consequences on the arc magmatic record are less well studied. Here we present a geochemical and geochronological study on small plutons and dykes from the upper crust of the southern Patagonian Andes at ~?51°S, which formed as a result of the subduction of the Nazca and Antarctic plates beneath the South American continent. In situ U–Pb geochronology on zircons and bulk rock geochemical data of plutonic and dyke rocks are used to constrain the magmatic evolution of the retro-arc over the last 30 Ma. We demonstrate that these combined U–Pb and geochemical data for magmatic rocks track the temporal and spatial migration of the active arc, and associated retro-arc magmatism. Our dataset indicates that the rear-arc area is characterized by small volumes of alkaline basaltic magmas at 29–30 Ma that are characterized by low La/Nb and Th/Nb ratios with negligible arc signatures. Subsequent progressive eastward migration of the active arc culminated with the emplacement of calc-alkaline plutons and dikes?~?17–16 Ma with elevated La/Nb and Th/Nb ratios and typical subduction signatures constraining the easternmost position of the southern Patagonian batholith at that time. Geochemical data on the post-16 Ma igneous rocks including the Torres del Paine laccolith indicate an evolution to transitional K-rich calc-alkaline magmatism at 12.5?±?0.2 Ma. We show that trace element ratios such as Nb/Ta and Dy/Yb systematically decrease with increasing SiO2, for both the 17–16 Ma calc-alkaline and the 12–13 Ma K-rich transitional magmatism. In contrast, Th/Nb and La/Nb monitor the changes in the source composition of these magmas. We suggest that the transition from the common calc-alkaline to K-rich transitional magmatism involves a change in the source component, while the trace element ratios, such as Nb/Ta and Dy/Yb, of derivative higher silica content liquids are controlled by similar fractionating mineral assemblages. Analysis of a global compilation of Nb/Ta ratios of arc magmatic rocks and simple geochemical models indicate that amphibole and variable amounts of biotite exert a major control on the low Dy/Yb and Nb/Ta of derivative granitic liquids. Lastly, we suggest that the low Nb/Ta ratio of silica-rich magmas is a natural consequence of biotite fractionation and that alternative models such as amphibolite melting in subduction zones and diffusive fractionation are not required to explain the Nb/Ta ratio of the upper continental crust. 相似文献
14.
吐哈盆地早二叠世玄武岩原始岩浆性质:来自熔融包裹体成分的制约 总被引：3，自引：3，他引：0
东天山地区的二叠纪玄武岩沿着区域的北东东向断裂呈脉状分布,吐哈盆地玄武岩的40Ar-39Ar坪年龄为298.2±3.8Ma,为早二叠世,与前人的玄武岩年龄结果在误差范围内一致。可能与东天山地区二叠纪岩浆铜镍矿床镁铁-超镁铁岩有密切的成因联系。吐哈玄武岩的主微量成分显示其为岛弧拉斑、大陆弧玄武岩,轻稀土富集和Nb、Ta负异常,指示源区可能经历过俯冲作用的改造。吐哈盆地二叠纪玄武岩含有新鲜的橄榄石和长石斑晶,橄榄石斑晶中熔融包裹体较发育。熔融包裹体为玻璃质、气相和玻璃质、气相、固相两种类型。包裹体中不透明矿物主要为磁铁矿,说明捕获包裹体时岩浆的氧逸度和Fe含量较高。熔融包裹体分为高MgO和低MgO含量两种。高MgO含量的包体同时具有低SiO_2、低微量和稀土元素含量的特征,可能为地幔高部分熔融的产物,且经历过深部演化程度较弱。该高MgO熔体的微量元素显示Nb、Ta亏损的特征,具有N-MORB特征的微量和稀土元素分配模式,预示该熔体为受到俯冲交代的地幔熔融形成。熔融包裹体相对玄武岩具有低的Th和Ta含量、相对弱的Nb和Ta的负异常的特征,指示熔融包裹体的成分经受改造程度低于玄武岩,暗示可能为经历过较少后期作用改造的相对原始的熔体。熔体中Cu含量(12.4×10~(-6)~299×10~(-6))在正常玄武质岩浆含量范围内,而Ni含量(236×10~(-6)~697×10~(-6))高于高镁溢流科马提岩和洋中脊玄武岩。该Cu、Ni含量略显解耦的熔体可能代表了经历过深部少量的硫化物熔离,带走小部分Cu和Ni等成矿元素之后所捕获的岩浆。如果将该熔体视为东天山地区二叠纪岩浆铜镍硫化物矿床的母岩浆,该母岩浆中Ni含量相对较高可能是岩浆铜镍硫化物矿床中矿石的Ni/Cu比值大多大于1.0的主要因素。 相似文献
15.
S. Sheppard I. M. Tyler T. J. Griffin W. R. Taylor 《Australian Journal of Earth Sciences》2013,60(5):679-690
Palaeoproterozoic basaltic rocks in the Halls Creek Orogen form part of two stratigraphic sequences on either side of a major structure, the Angelo‐Halls Creek‐Osmond Fault System. The two sequences have contrasting geological histories and probably formed in different tectonostratigraphic terranes. To the east, basalts of the Biscay Formation, which are part of the Halls Creek Group, were erupted at ca 1880 Ma and deformed and metamorphosed first at low grade between ca 1845 and ca 1820 Ma. To the west, basalts of the Tickalara Metamorphics were deposited after 1865 Ma, and were metamorphosed at medium to high grade and intruded by tonalite and leucogranite sheets at 1850 to 1845 Ma. Two groups of metabasalts are identified in the Biscay Formation. Group 1 samples have compositions similar to enriched (E‐)MORB. Group 2 samples have lower TiO2, P2O5, Cr, Y, Nb and Zr contents, and trace‐element ratios (e.g. Ti/V and Zr/Nb), similar to low‐TiO2 continental flood basalts. Metabasalts from the Tickalara Metamorphics consist of depleted and enriched types. The depleted samples have high field strength element (HFSE) and rare‐earth element (REE) abundances similar to oceanic island arc/backarc basin tholeiites. The enriched samples have compositions similar to E‐MORB, and are similarto group 1 samples from the Biscay Formation. Basalts of the Biscay Formation were erupted on a passive continental margin, whereas those of the Tickalara Metamorphics formed in an oceanic island arc/backarc basin or ensialic marginal basin, the two terranes being brought together by ca 1820 Ma. This is consistent with the evolution of the Halls Creek Orogen during the Palaeoproterozoic by plate‐tectonic processes similar to those operating in the Phanerozoic. 相似文献
16.
滇西至滇中一带新元古代镁铁质岩类、花岗岩类等岩浆岩有广泛分布，前人利用不同岩石组合指示这些岩浆岩形成于不同的地质构造背景.通过对祥云一带调查研究，新确定了南华纪花岗岩体，花岗岩体中含有大量的超镁铁质岩（橄榄辉长岩）、闪长岩类包体，包体与花岗岩不规则边界呈成分渐变，混合形成为花岗闪长岩、石英闪长岩、英云闪长岩类岩石.对花岗岩和铁镁质包体进行锆石U-Pb LA-ICP-MS同位素测年，获得了相近的206Pb/238U平均年龄:761.9±4.1 Ma、761.7±4.2 Ma、761.3±3.7 Ma和757.5±5.9 Ma.花岗岩主量元素显示具有高碱（alk）、中等Mg#（38~57，平均值为50）、低TiO2、P和亏损Ta、Nb、Sr特点，展现了富集轻稀土元素（LREEs）、亏损重稀土元素（HREEs）和选择性富集大离子亲石元素（LILEs）等特点，并且其εNd（t）为负值（-2.73~-4.90），表明花岗岩浆的物质应为早期古老地壳部分熔融的产物；橄榄辉长岩包体地球化学特征为:低K2O，低稀土总量，LREEs和LILEs略富集或不富集，具明显P负异常，Nb-Ta和Zr-Hf无亏损，具有非常高的Mg#（71~83）等特点，这些特征都指示这些橄榄辉长岩来源于幔源，应为地幔边缘岩浆熔融的产物.花岗闪长岩、闪长岩具有略富集LREE和LILE、亏损HREE，其Mg#（45~71）较高，P亏损、负εNd（t）值等特征，Ta、Nb、Ti、Sr、P略亏损或不亏损，组分介于花岗岩和橄榄辉长岩之间，显示了幔源和古老地壳部分熔融混合特点.这些岩石都展示陆源弧岩浆岩的构造背景，大洋板块向扬子板块俯冲导致幔源物质重熔的结果. 相似文献
17.
新疆阿尔金山喀腊大湾地区玄武岩的地球化学特征及地质意义 总被引：3，自引：0，他引：3
对新疆阿尔金山东段喀腊大湾地区玄武岩进行了系统的岩石地球化学分析, 结果表明, 喀腊大湾地区的玄武岩具有低的Mg#值(Mg#=Mg/(Mg+Fe)×100)。稀土元素的含量变化范围较大, 轻重稀土分异不明显, 具有轻微的轻稀土富集, 弱的Eu负异常。微量元素Ni、Co、Cr与MgO呈正相关, 微量元素多元素标准化图解中, 普遍具有Nb、Ta的负异常, 部分样品具有Ti的负异常。在Th/Yb-Ta/Yb和Th/Hf-Ta/Hf构造环境判别图解中, 分别落入活动大陆边缘环境和大陆拉张(或初始裂谷)环境, 结合本区双峰式火山岩中玄武岩的地球化学特征, 以及与北阿尔金蛇绿混杂岩带其它地区玄武岩的对比, 认为喀腊大湾地区的玄武岩可能形成于紧邻北阿尔金地区古洋盆的活动大陆边缘环境。 相似文献
18.
Temporal evolution of the kerguelen plume: Geochemical evidence from 38 to 82 ma lavas forming the Ninetyeast ridge 总被引：1，自引：0，他引：1
Abstract Basaltic basement has been recovered by deep-sea drilling at seven sites on the linear Ninetyeast Ridge in the eastern Indian Ocean. Studies of the recovered lavas show that this ridge formed from ~ 82 to 38 Ma as a series of subaerial volcanoes that were created by the northward migration of the Indian Plate over a fixed magma source in the mantle. The Sr, Nd and Pb isotopic ratios of lavas from the Ninetyeast Ridge range widely, but they largely overlap with those of lavas from the Kerguelen Archipelago, thereby confirming previous inferences that the Kerguelen plume was an important magma source for the Ninetyeast Ridge. Particularly important are the ~ 81 Ma Ninetyeast Ridge lavas from DSDP Site 216 which has an anomalous subsidence history (Coffin 1992). These lavas are FeTi-rich tholeiitic basalts with isotopic ratios that overlap with those of highly alkalic, Upper Miocene lavas in the Kerguelen Archipelago. The isotopic characteristics of the latter which erupted in an intraplate setting have been proposed to be the purest expression of the Kerguelen plume (Weis et al. 1993a,b). Despite the overlap in isotopic ratios, there are important compositional differences between lavas erupted on the Ninetyeast Ridge and in the Kerguelen Archipelago. The Ninetyeast Ridge lavas are dominantly tholeiitic basalts with incompatible element abundance ratios, such as La/Yb and Zr/Nb, which are intermediate between those of Indian Ocean MORB (mid-ocean ridge basalt) and the transitional to alkalic basalts erupted in the Kerguelen Archipelago. These compositional differences reflect a much larger extent of melting for the Ninetyeast Ridge lavas, and the proximity of the plume to a spreading ridge axis. This tectonic setting contrasts with that of the recent alkalic lavas in the Kerguelen Archipelago which formed beneath the thick lithosphere of the Kerguelen Plateau. From ~ 82 to 38 Ma there was no simple, systematic temporal variation of Sr, Nd and Pb isotopic ratios in Ninetyeast Ridge lavas. Therefore all of the isotopic variability cannot be explained by aging of a compositionally uniform plume. Although Class et al. (1993) propose that some of the isotopic variations reflect such aging, we infer that most of the isotopic heterogeneity in lavas from the Ninetyeast Ridge and Kerguelen Archipelago can be explained by mixing of the Kerguelen plume with a depleted MORB-like mantle component. However, with this interpretation some of the youngest, 42–44 Ma, lavas from the southern Ninetyeast Ridge which have206pb/204Pb ratios exceeding those in Indian Ocean MORB and Kerguelen Archipelago lavas require a component with higher206Pb/204Pb, such as that expressed in lavas from St. Paul Island. 相似文献
19.
XU Xueyi CHEN Junlu LI Xiangmin MA Zhongping WANG Hongliang LI Ping LI Ting 《《地质学报》英文版》2011,85(6):1336-1350
On the basis of petrogeochemical data, the volcanic lavas of the Baimianxia Formation can be classified into two units: high TiO2 and low TiO2. The TiO2 concentration of the former is generally higher than 1%, which occurs in the lower part with high-grade metamorphism, but the latter is less than 1% and crops out in the upper part with low-grade metamorphism. The high-TiO2 unit is dominated by tholeiitic lavas showing high rare earth element (REE) contents (ΣREE?=?83.4–180.8?μg/g), high light/heavy REE (LREE/HREE) ratios (LREE/HREE=2.17–5.85) and weak negative Eu anomaly (Eu=0.79–1.01). Its trace element patterns display weak Nb-Ta anomalies with respect to Th, K, La, Ce, showing within-plate basalt affinities. In contrast, the low-TiO2 unit is characterized by low REE contents, low LREE/HREE ratios, and pronounced Nb-Ta anomalies, indicating typical arc or continental arc signature. Chondrite-normalized REE patterns of basalts and andesites from the Sanwan Formation are flat or LREE depletion, which is very similar to normal mid-oceanic basalt. Therefore, we suggest that these lavas should be formed in a back-arc basin setting. Sr-Nd isotopic data of the basalt in the lower part suggest that the rocks would have been formed in ~1144?Ma. Based on the geochemical and isotopic features of the basalts, we suggest that these rocks in the low part of the Baimianxia Formation should originate from an asthenospheric oceanic-island basalt-like mantle source, which may be produced by partial melting of garnet lherzolite, and significantly underwent fractional crystallization and crustal or lithospheric mantle contamination en route to the surface. However, laser ablation inductively coupled plasma mass spectrometry zircon U-Pb dating of the basalt sample from the upper part of the Baimianxia Formation gives a 437 Ma, indicating a Early Paleozoic age. The geochemical analysis in this paper suggests that they may originate from an arc or continental arc in response to aqueous fluids or melt expelled from a subducting slab, and the partial melting occurred in the garnet stability field. The samples of basalts and andesites in the Sanwan Formation show they are derived from depleted mantle source similar to normal mid-oceanic basalt. Finally, we can conclude that the lavas in the lower part of the Baimianxia Formation represent the geological records of rift-related volcanism in the middle Proterozoic, which is commonly considered to be the precursor of continental breakup and followed by oceanic basin forming from Neoproterozoic to early Paleozoic. Whereas, the lavas in upper part of the Baimianxia Formation and Sanwan Formations may have been generated by the oceanic and continental conversion that occurred in the early Paleozoic. 相似文献
20.
Recycled crust controls contrasting source compositions of Mesozoic and Cenozoic basalts in the North China Craton 总被引：7，自引：0，他引：7
We explore Fe/Mn and Nb/Ta ratios of basalts as potential tracers for differentiating melts of recycled mafic crustal lithologies from peridotitic melts. Trace elements and Fe/Mn ratios of the Mesozoic and Cenozoic basalts from East China were analyzed by ICP-MS. Low Nb/Ta ratios (15.4 ± 0.3 (2σ, n = 45)), high Nb and Ta contents (60.1 and 4.01 ppm) and high Fe/Mn ratios (64.7 ± 1.5 (2σ, n = 45)) characterize the <110 Ma basalts. Mesozoic basalts with ages >110 Ma are characterized by superchondritic Nb/Ta ratios (20.1 ± 0.3 (2σ, n = 25)), low Nb and Ta contents (10.8 and 0.54 ppm) and slightly lower Fe/Mn ratios (60.0 ± 1.1 (2σ, n = 25)). Both the Mesozoic and Cenozoic basalts have Fe/Mn ratios higher than basaltic melt formed by partial melting of peridotite at the same MgO and CaO levels. Although both the Mesozoic and Cenozoic basalts are characterized by highly fractionated REE patterns, the >110 Ma basalts have island arc-type trace element patterns (i.e., depletion in Nb and Ta), whereas OIB-type trace element patterns (e.g., no depletion in Nb and Ta) are characteristic of the <110 Ma basalts. Based on DFe/Mn values for olivine, clinopyroxene, orthopyroxene and garnet, high Fe/Mn ratios and negative correlations of Fe/Mn with Yb (Y) of the <110 Ma basalts suggest clinopyroxene/garnet-rich mantle sources. The lower Fe/Mn ratios and positive correlations of Fe/Mn with Y and Yb in the >110 Ma basalts suggest orthopyroxene/garnet-rich mantle sources. Combining these data with Sr-Nd isotopes, we present a conceptual model to explain the Nb/Ta ratios and PM-normalized trace element patterns of the >110 and <110 Ma basalts. Preferential melting of recycled ancient lower continental crust during Mesozoic lithospheric thinning resulted in (1) peridotite-melt/fluid reaction that formed the orthopyroxene/garnet-rich mantle sources for the >110 Ma basalts, and (2) peridotite + rutile-bearing eclogite mixing that formed the clinopyroxene/garnet-rich mantle sources for the <110 Ma basalts. The choice of models may indeed be arbitrary and non-unique, but the goal is to seek relatively simple forward models that explain the characteristics of the lavas, and the differences between the >110 and <110 Ma basalts, in a relatively consistent geodynamic framework. 相似文献