Geochemistry of the Cenozoic Potassic Volcanic Rocks in the West Kunlun Mountains and Constraints on Their Sources

The geochemical characteristics of the Cenozoic volcanic rocks from the north Pulu, east Pulu and Dahongliutan regions in the west Kunlun Mountains are somewhat similar as a whole. However, the volcanic rocks from the Dahongliutan region in the south belt are geochemically distinguished from those in the Pulu region (including the north and east Pulu) of the north belt. The volcanic rocks of the Dahongliutan region are characterized by relatively low TiO2 abundance, but more enrichment in alkali, much more enrichment in light rare earth elements and large ion lithosphile elements than those from the Pulu region. Compared with the Pulu region, volcanic rocks from the Dahongliutan region have relatively low 87Sr/86Sr ratios, and high εNd, 207Pb/204Pb and 208Pb/204Pb. Their trace elements and isotopic data suggest that they were derived from lithospheric mantle, consisting of biotite- and hornblende-bearing garnet lherzolite, which had undertaken metasomatism and enrichment. On the primitive mantle-normali     

http://www.sciencedirect.com/science/article/pii/S1674987113001382

The area from the Greater Caucasus to the southeast Turkey is characteri：;.ed and shaped by several major continental blocks. These are Scythian Platform, Pontian-Transcaucasu.,; Continent-Arc System （PTCAS）, the Anatolian-lranian and the Arabian Platforms. The aim of this paper is to define these continental blocks and describe and also compare their boundary relationships along the suture zones. The Scythian Platform displays the evidence of the Hercynian and Alpine orogens. This platform is separated from the PTCAS by the Greater Caucasus Suture Zone. The incipient collision began along this suture zone before middle-late Carboniferous whereas the final collision occurred before Oligocene. The PTCAS can be divided into four structural units： （1） the Georgian Block - northern part of the Pontian-Transcaucasian island-arc, （2） the southern and eastern Black Sea Coast-Adjara-Trialeti Unit, （3） the Artvin-Bolnisi Unit, comprising the northern part of the southern Transcaucasus, and （4） the Imbricated Bayburt-Garabagh Unit. The PTCAS could be separated from the Anatolian Iranian Platform by the North Anatolian-Lesser Caucasus Suture （NALCS） zone. The initial collision was developed in this suture zone during Senonian-early Eocene and final collision before middle Eocene or Oligocene-Miocene. The Anatolian-lranian Platform （AIP） is made up of the Tauride Platform and its metamorphic equivalents together with Iranian Platform. It could be separated from the Arabian Platform by the Southeastern Anatolian Suture （SEAS） zone. The collision ended before late Miocene along this suture zone. The southernmost continental block of the geotraverse is the Arabian Platform, which constitutes the northern part of the Arabian-African Plate. This platform includes a sequence from the Precambrian felsic volcanic and clastic rocks to the Campanian-early Maastrichtian fiyschoidal clastics. All the suture zones include MORB and SSZ-types ophiolites in different ages. However, the ages of the suture     

南海热幔柱构造与油气分布

南海处于欧亚、印度—澳大利亚和太平洋—菲律宾海三大板块的夹持地带,区内以NE向深海区-海盆为中心,周围有众多的含油气盆地。南海区具有"北断(裂)、南褶(皱)、东(俯)冲、西(碰)撞"的构造特征。南海及其周缘新生代玄武岩和花岗岩广为分布,故有潜在的大火成岩省之称。其中,火山岩以碱性玄武岩为主,多为OIB型成因,其成岩年龄自南海中心至外围呈由新逐渐变老的趋势。深部地幔流动呈现出涡旋式上涌的特点,上地幔明显具环带状结构,中心部位为上升流,外围为下降流,表现出热幔柱和冷幔柱活动"双模式"对流。从区域S波速度扰动异常来看,在670km间断面,对热流体上涌确有阻挡作用。通过层析成像研究,证实本区存在巨型复蘑菇云状地幔低速体,演化过程和相邻板块活动构成相辅相成关系。由于地幔热流体上涌,促使地壳-岩石圈上隆、熔融、减薄和断陷,形成南海从边缘向中心(海盆)热流温度逐步升高的轨迹,基本控制油气田"外油内气"环形有序分布的格局。     

中国东南部晚中生代-新生代玄武岩与壳幔作用

中国东南部的火山活动在早中生代时期仅有很小规模,晚中生代最早的、较大规模的岩浆活动始于中侏罗世早期,至早白垩世是火山岩浆活动的鼎盛期,在近100个Ma的时间内形成了大面积分布的晚中生代火山-侵入岩,而在新生代则以面积较小的玄武岩浆喷出活动为主,局限分布于沿海一带。以晚中生代湘南、赣南和闽西南的近EW向火山岩带和浙、闽沿海地区的近NNE向火山岩带,以及新生代近NNE向火山岩带为研究对象,对这些火山岩的地球化学特征对比研究,结合时空分布,讨论了它们的起源及其与壳幔相互作用的关系,以及它们形成的构造环境,其结果显示,EW向晚中生代火山岩带（180～170Ma）的西段玄武岩独立产出,且明显属碱性系列;而中段和东段玄武岩和流纹岩伴生,其中的玄武岩均为亚碱性系列的拉斑玄武岩。它们形成于板内拉张构造环境,是中国东南部特提斯构造域向太平洋构造域转换、晚中生代大规模岩浆作用的序幕。研究表明,该火山岩带自西向东表现出不同程度的壳幔相互作用,玄武岩在成岩过程中有少量陆壳组分加入。NNE向晚中生代火山岩带（130～90Ma）主要为流纹质岩石,安山岩和玄武岩很少。即使是双峰式火山岩也以酸性岩为主,玄武岩仅占全部火山岩体积的30％以下。其中的玄武岩主要属钙碱性系列,少数属拉斑系列。它们形成于火山弧构造环境,是中国东南部受太平洋构造域影响发生大规模火山岩浆作用的主旋律。其中玄武岩岩浆成分受到了较高程度的陆壳物质混染,同时代的中性火山岩是由底侵的玄武岩岩浆和陆壳物质来源的酸性岩浆发生岩浆混合作用而形成的,反映了强烈的壳幔相互作用。NNE向新生代火山岩带,分布在浙闽沿海,以碱性系列玄武岩为主,均含幔源包体,并受NNE向大陆边缘断裂构造的控制。它们形成于板内裂谷环境,是中国东南沿海由晚中生代火山弧构造环境转换为新生代板内裂谷环境的标志,起源于软流圈地幔,并有EMII岩石圈地幔的混合组分,但基本没有受到陆壳物质的混染。     

Discussion on the dextral movement and its effect in continental China and adjacent areas since Cenozoic

Continental China has moved dextral Eastward since Cenozoic time, driven by the collision of the Indian with the Eurasian plate. Evidence for this comes from landscape evolution, the distribution of earthquake epicenters, Cenozoic sedimentary and volcanic rocks, and the measurement of GPS velocity vectors, the distribution of crustal stress, paleomagnetic data, and deep mantle structure, among others. This movement commenced around 40 Ma, coupled with thickened lithosphere and widespread stress release along strike-slip faults that bound the continental Chinese block. Because of continued Northward subduction of the Indian plate, manifestation of the dextral movement has intensified since 25 Ma. Far-reaching effects include extensive strike-slip movement on the Tan-Lu fault in Eastern China, formation of the Dabie ultrahigh pressure metamorphic terrane, extensive thrust faults in East China, delamination and thickening of the lithosphere of South China, a possible tectonic doubling of the Middle-Lower Yangtze Valley metallogenic belt, and the formation of the Japan, Huanghai (East China), and South China Sea.     

Formation of the Late Cenozoic volcanic complexes of the Lesser Caucasus

The paper considers the role of the lithospheric mantle and asthenosphere during the Late Cenozoic collision volcanism of the Lesser Caucasus. The results of petrogeochemical studies show that the products of volcanism of the West Volcanic Zone of Armenia and the calc-alkaline andesite–dacite–rhyodacite complex of the Neogene Kelbadzhar and Karabakh plateaus were formed from an enriched source in a suprasubduction setting. Late Pliocene–Quaternary moderately alkaline and alkaline volcanic rocks of the Lesser Caucasus differ in petrogeochemistry from suprasubduction volcanic rocks. In trace element contents and patterns, they are similar to rocks formed from an enriched mantle source. Comparative analysis of the geological and geophysical data suggests the model of lithospheric slab break-off of the thickened lithosphere as the triggering mechanism for Late Cenozoic magmatism of the Lesser Caucasus.     

青藏高原新生代三阶段造山隆升模式:火成岩岩石学约束

从岩石从地构造学的角度,分析讨论了青藏高原新生代岩浆作用的特点、差异、成对性及其对高魇隆升深部动力学过程的岩石约束,在此基础上是提出青藏高原是以冈底斯－羌塘造山带为核心,通过三次造山幕事件而形成的高原隆升新模式。     

Complex geometry of the Cenozoic magma plumbing system in the central Sahara,NW Africa

Topographic uplifts in the central Sahara occur in the Hoggar-Aïr and Tibesti-Gharyan swells that consist of Precambrian rocks overlain by Cenozoic volcanic rocks. The swells and associated Cenozoic volcanism have been related either to mantle plumes or to asthenospheric upwelling and to partial melting due to rift-related delamination along pre-existing Pan-African mega-shears during the collision between Africa and Europe. The Cenozoic volcanic rocks in the Hoggar generally range from Oligocene tholeiitic/transitional plateau basalts, which occur in the centre of the dome, to Neogene alkali basalts characterized by a decrease in their degree of silica undersaturation and an increase in their La/Yb ratios. The alkali basaltic rocks occur mainly along the margins of the dome and typically have less radiogenic Nd and Sr isotopic ratios than the tholeiitic/transitional basalts. The geochemistry of the most primitive basaltic rocks resembles oceanic island basalt (OIB) tholeiitic – in particular high-U/Pb mantle (HIMU)-type – and is also similar to those of the Circum-Mediterranean Anorogenic Cenozoic Igneous (CiMACI) province. These characteristics are consistent with, but do not require, a mantle plume origin. Geophysical data suggest a combination of the two mechanisms resulting in a complex plumbing system consisting of (a) at depths of 250–200 km, an upper mantle plume (presently under the Aïr massif); (b) between 200 and 150 km, approximately 700 km northeastward deflection of plume-derived magma by drag at the base of the African Plate and by mantle convection; (c) at approximately 150 km, the magma continues upwards to the surface in the Tibesti swell; (d) at approximately 100 km depth, part of the magma is diverted into a low S-wave velocity corridor under the Sahara Basin; and (e) at approximately 80 km depth, the corridor is tapped by Cenozoic volcanism in the Hoggar and Aïr massifs that flowed southwards along reactivated Precambrian faults.     

Geochemical and geochronological study of the Sanshui basin bimodal volcanic rock suite,China: Implications for basin dynamics in southeastern China

Sanshui basin is one of the typical Mesozoic–Cenozoic intra-continental rift basins with voluminous Cenozoic volcanic rocks in southeastern China. Thirteen cycles of volcanic eruptions and two dominant types of volcanic rocks, basalt and trachyte–rhyolite, have been identified within the basin. Both basalt and trachyte–rhyolite members of this bimodal suit have high values of εNd (+2.3 to +6.2) and different Sr isotopic compositions (initial ⁸⁷Sr/⁸⁶Sr ratios are 0.70461–0.70625 and 0.70688–0.71266 for basalts and trachyte–rhyolite, respectively), reflecting distinct magma evolution processes or different magma sources. The results presented in this study indicate that both of the trachyte–rhyolite and basaltic magmas were derived from similar independent primitive mantle, but experienced different evolution processes. The trachyte-rhyolitic magma experienced significant clinopyroxene and plagioclase fractionational crystallization from deeper magma chamber with significant crustal contamination, while the basaltic magmas experienced significant olivine and clinopyroxene fractionational crystallization in shallower magma chamber with minor crustal contamination. New zircon U–Pb dating confirms an initial volcanic eruption at 60 Ma and the last activity at 43 Ma. Geologic, geochemical, and geochronological data suggest that the inception of the Sanshui basin was resulted from upwelling of a mantle plume. The Sanshui basin widened due to subsequent east–west extension and the subsequent volcanism constantly occurred in the center of the basin. Evidence also supports a temporal and spatial association with other rift basins in southeastern China. The upwelling mantle plume became more active during late Cenozoic time and most likely triggered opening of other basins, including the young South China Sea basin.     

青海可可西里地区新生代火山岩的岩石特征与时代

可可西里地区的新生代火山岩属于藏北火山岩带的东段。火山岩主要以熔岩台地、桌状山的形式产出，熔岩厚约４０—１００ｍ。除少量的高钾流纹岩、粗面岩和粗面英安岩外，在数量和分布上以普遍含二辉石斑晶的安粗岩占优势。岩石以富碱（尤其富钾）和富ＬＲＥＥ为特征。火山活动发生在中新世，根据Ｋ／Ａｒ定年结果划分为早、中、晚三期。本区火山岩的特征与西藏境内的同时代岩石完全可以对比。火山活动与高原新生代以来的岩石圈演化有密切的关系     

地壳深俯冲与富钾火山岩成因

富钾火山岩是一类兼具壳幔双重地球化学特征的特殊岩石组合 ,它们不可能由亏损或原始地幔所派生 ,成岩过程中必须有地壳物质的参与 ,将地壳物质引入富钾火山岩成岩过程的主要动力机制即是深俯冲作用。洋壳和陆壳均可以通过俯冲进入地幔 ,俯冲地壳物质析出流体对地幔岩石的交代作用是导致富钾火山岩具特殊地球化学特征的主要原因。根据对大别—苏鲁造山带南北两侧晚中生代富钾火山岩的实例研究 ,表明该区火山岩的形成均受到了俯冲洋壳析出流体的交代作用 ,但造山带北侧富钾火山岩的形成还叠加了俯冲的扬子陆壳析出流体的交代作用 ,是多次富集事件综合作用的结果。文中还对富钾火山岩成因研究中值得进一步深入探索的问题进行了讨论。     

中国北方大陆下的地幔热柱与岩石圈运动

本文首次提出中国北方大陆下存在一个地幔热柱的论证,并提出亚热柱(sub—plume)的新概念。热柱的中心与边缘部分的隙间熔浆分别为苦橄质玄武岩与碱性玄武岩。在渐新世到中新世约18.4 Ma内,北方大陆以3.26cm/a的速率向东南飘移了约600km,使日本海、渤海—华北平原等脱离热柱。导致晚第三纪日本海扩张的停止,渤海—华北平原等早第三纪火山喷发的突然中止。火山喷发期间,在热柱头部若干个亚热柱的形成,好似若干个“铆钉”穿入岩石圈,有效地阻止了岩石圈的飘移(这时的飘移速率只有0.05cm/a),我们把火山喷发称为固定岩石圈的“铆钉效应”。     

http://www.sciencedirect.com/science/article/pii/S1674987111001125

<正>Greenstone belts of the eastern Dharwar Craton,India are reinterpreted as composite tectonostratigraphic terranes of accreted plume-derived and convergent margin-derived magmatic sequences based on new high-precision elemental data.The former are dominated by a komatiile plus Mg-tholeiitic basalt volcanic association,with deep water siliciclastic and banded iron formation(BIF) sedimentary rocks.Plumes melted at90 km under thin rifted continental lithosphere to preserve inlraoceanic and continental margin aspects.Associated alkaline basalts record subduction-recycling of Mesoarchean oceanic crust,incubated in the asthenosphere.and erupted coevally with Mg basalts from a heterogeneous mantle plume.Together.komaliites-Mg basalts-alkaline basalts plot along the Phanerozoic mantle array in Th/Yb versus Nb/Yb coordinate space,representing zoned plumes,establishing that these reservoirs were present in the Neoarchean mantle. Convergent margin magmatic associations are dominated by tholeiitic to calc-alkaline basalts eompositionally similar to recent intraoceanic arcs.As well,boninitic flows sourced in extremely depleted mantle are present,and the association of arc basalts with Mg-andesites-Nb enriched basalts-adakites documented from Cenozoic arcs characterized by subduction of young(20 Ma),hot,oceanic lithosphere. Consequently.Cenozoic style "hot" subduction was operating in the Neoarchean.These diverse volcanic associations were assembled to give composite terranes in a subduction-accretion orogen at～2.1 Ga,coevally with a global accretionary orogen at ~2.7 Ga,and associated orogenic gold mineralization. Archean lithospheric mantle,distinctive in being thick,refractory,and buoyant,formed complementary to the accreted plume and convergent margin terranes.as migrating arcs captured thick plumeplateaus. and the refractory,low density.residue of plume melting coupled with accreted imbricated plume-arc crust.     

http://dx.doi.org/10.1016/j.gsf.2015.11.004

The alkali-basalt and basaltic trachy-andesites volcanic rocks of south Marzanabad were erupted during Cretaceous in central Alborz, which is regarded as the northern part of the Alpine-Himalayan orogenic belt. Based on petrography and geochemistry, en route fractional crystallization of ascending magma was an important process in the evolution of the volcanic rocks. Geochemical characteristics imply that the south Marzanabad alkaline basaltic magma was originated from the asthenospheric mantle source,whereas the high ratios of(La/Yb)Nand(Dy/Yb)Nare related to the low degree of partial melting from the garnet bearing mantle source. Enrichment pattern of Nb and depletion of Rb, K and Y, are similar to the OIB pattern and intraplate alkaline magmatic rocks. The K/Nb and Zr/Nb ratios of volcanic rocks range from 62 to 588 and from 4.27 to 9 respectively, that are some higher in more evolved samples which may reflect minor crustal contamination. The isotopic ratios of Sr and Nd respectively vary from 0.70370 to0.704387 and from 0.51266 to 0.51281 that suggest the depleted mantle as a magma source. The development of south Marzanabad volcanic rocks could be related to the presence of extensional phase,upwelling and decompressional melting of asthenospheric mantle in the rift basin which made the alkaline magmatism in Cretaceous, in northern central Alborz of Iran.     

西秦岭中—晚三叠世板块碰撞事件的记录:来自合作地区火山岩的锆石U-Pb年龄和地球化学证据

西秦岭造山带发育了大量印支期钙碱性花岗岩,其中在甘肃合作地区以早印支期形成的为主,并伴有少量中酸性火山岩浆活动。合作地区火山岩主要分布在德乌鲁、扎油沟口一带,整体以安山质晶屑熔岩、安山质熔岩为主,并含英安斑岩、英安岩、火山角砾岩、晶屑岩屑凝灰岩、杏仁状安山岩的中酸性火山岩组合。德乌鲁安山质晶屑熔岩锆石U-Pb测年结果为(237.7±1.9) Ma,扎油沟口安山质熔岩锆石U-Pb测年结果为(234.8±2.1) Ma,限定了其喷发时代为晚三叠世早期。岩石地球化学分析结果显示该区火山岩属于富钾、高铝、高镁钙碱性系列;Rb、Ba、Th、U、La、Ce、Sr元素强烈富集,Ti、Y、Yb等元素略显富集;稀土总量偏低,LREE/HREE值为6.79~17.15;δEu为0.76~0.86,略显负铕异常。以上结果指示火山岩物质源于富集地幔,成岩过程或成岩后有壳源物质的强烈混染。扬子板块与华北板块汇聚时期,其间小洋盆与微板块发生强烈的挤压、俯冲,在后碰撞松弛阶段,出现了强烈的壳幔物质交换和岩浆上升的现象。多次的碰撞挤压-后碰撞松弛运动,在研究区域形成了一系列晚三叠世不同时间段的火山岩。     

东北亚中生代火山岩研究若干问题的思考

东北亚中生代火山岩包括大陆边缘北北东向线型火山岩带,以及大陆内部俄罗斯西伯利亚、蒙古、中国大兴安岭等面型火山岩带。它们是东北亚古亚洲洋构造域向太平洋构造域转换时期深部地幔地球化学过程以及东亚大陆与古太平洋板块相互作用的产物。对它们的研究涉及古生代古亚洲构造域闭合过程的深部地幔的动力学和地球化学演化历史,以及东亚大陆边缘由被动边缘向活动大陆边缘转换历史。古亚洲域大洋岩石圈向地幔深部潜入而引发的热地幔     

华北板块北缘中元古代造山带的确立及其构造演化

华北板块北缘发育一条中元古代晚期大陆边缘碰撞造山带 ,它由内蒙西部狼山起向东延伸到辽西和吉林东部一带 ,全长 2 0 0 0余km。造山带内部发育了不同类型变质的沉积岩、火山沉积岩 ,以及各种类型深成侵入岩。在 1.0Ga左右 ,由西伯利亚板块和华北板块对接碰撞 ,形成了巨大陆缘碰撞造山带。这次构造事件是Rodinia超大陆拼合事件的一部分 ,表明了在Rodinia超大陆时期华北板块和西伯利亚板块是连在一起的。     

The Cretaceous crustal shortening and thickening of the South Qiangtang Terrane and implications for proto-Tibetan Plateau formation

The timing and magnitude of deformation across the central Tibetan Plateau, including the South Qiangtang Terrane (SQT), are poorly constrained but feature prominently in geodynamic models of the Tibetan Plateau formation. The Ejiu fold and thrust belt (EFTB), which is located in the SQT, provides valuable records of the Mesozoic-Cenozoic deformation history of the central Tibetan Plateau. Here we integrate geochronology of volcanic rocks, low-temperature thermochronology, geologic mapping and a balanced cross section to resolve the deformation history of the SQT. Geochronologic data suggest that major deformation that initiated in the early Cretaceous continued until at least 80 Ma and ceased by ∼40 Ma. The balanced cross section resolves ∼66 km upper crustal shortening (34%) mainly during the Cretaceous Qiangtang-Lhasa collision. However, the Cenozoic crustal shortening is not well constrained because of a lack of successive Cenozoic strata. We also discussed whether the observed crustal shortening can account for the modern crustal thickness and elevation in the SQT. Our observations indicate that crustal shortening and thickening within the central Tibetan Plateau was mostly accomplished during the Cretaceous Lhasa-Qiangtang collision. A thick crust could be maintained since the Cretaceous due to slow erosion rates since ∼40 Ma. Minor Late Cenozoic shortening also contributed to a small amount of crustal thickening in the central Tibetan Plateau. However, close to modern >4700 m elevation was finally attained by lithospheric mantle foundering in the Qiangtang Terrane at ∼25 Ma.     

欧洲大高加索厄尔布鲁斯山的形成与演化①

厄尔布鲁斯山位于土耳其板块俯冲至西徐亚板块之下而形成 的大高加索弧形构造带的弧顶部位,本身为晚更新世和全新世两个火山口组成的复式火山锥 。厄尔布鲁斯山隆升过程和机制可划分为4个阶段中生代板块俯冲形成大高加索相对隆起 区;新生代早期板块碰撞使大高加索成为强烈隆起区;新生代晚期发育了厄尔布鲁斯复式火 山锥,并使之成为欧洲最高峰;许多迹象表明,厄尔布鲁斯火山现代并未熄灭,厄尔布鲁斯 山以10 mm/a的速度继续隆升。     

大南海地区新生代板块构造活动

在新生代澳大利亚板块和欧亚板块之间的大洋中，存在一些地块(微板块)；同时，澳大利亚板块北部边缘的一些地块先后和澳大利亚板块分离，向北运动，与一些和欧亚板块分离出来的地块先后发生碰撞缝合。在此期间，由于地块分离而发生海底扩张，产生许多小洋盆，如南海、苏录海、苏拉威西海、安达曼海等，最后形成了东南亚地区今日的构造景观。笔者从大南海地区新生代的构造演化史之框架来研究南海地区新生代的构造演化历史，认为南海地区新生代的构造活动既与印度板块和欧亚板块的碰撞有关，也与太平洋板块向欧亚板块的俯冲活动有联系；同时，还受到澳大利亚板块向北运动之影响。南海地区在新生代发生过两次海底扩张，第一次海底扩张发生在42～35Ma前．是受印度板块和欧亚板块碰撞而引起欧亚大陆之下向东南方向之地幔流的影响而发生的，其海底扩张方向为NWSE，产生了南海西南海盆；第二次海底扩张发生于32～17Ma前。由于太平洋板块向欧亚板块俯冲，俯冲的大洋岩石圈已达700km深处，阻挡了欧亚大陆的上地幔向东南方向之流动，从而转向南流动。引起南海地区南北向海底扩张，即新生代第二次海底扩张，产生了南海中央海盆。南海新生代洋盆诞生之后，由于大南海地区继续有地块碰撞和边缘海海底扩张，对南海南部地区产生挤压，从而使这里的沉积发生变形，这就引起万安运动(南海南部)。