Petrogenesis of Late Ordovician intrusive rocks in the West Kunlun orogenic belt: Constraints on the subduction process of the Proto-Tethys OceanSCIEI北大核心CSCD     

陶再礼  尹继元  袁超  肖文交  陈文  陈岳龙  王雅美  杨帆 《岩石学报》2022,(11):3321-3340

西昆仑造山带发育有大量的早古生代岩浆岩,它们的形成与原特提斯洋俯冲-碰撞密切相关,然而,对于这些岩浆岩的岩石成因和形成的构造背景仍然存在较大的争议。本文对西昆仑造山带早古生代阿喀孜二长岩和赛图拉石英闪长岩岩体开展了详细的矿物学、锆石U-Pb年代学、全岩地球化学和Sr-Nd-Hf-O同位素研究,以探讨这些侵入岩的岩浆源区与成因,揭示原特提斯洋在这一时期的构造演化过程。这两个岩体的LA-ICP-MS锆石U-Pb年龄分别为456±2Ma和452±2Ma,指示它们形成于晚奥陶世。阿喀孜二长岩具有富碱(K_(2)O+Na_(2)O=10.5%~11.8%)、富钾(K_(2)O/Na_(2)O=1.20~1.44)特征,相对低MgO(0.89%~0.97%)、TiO_(2)(0.42%~0.45%)含量,富集Rb、Th、U等大离子亲石元素,且具有较高的全岩锆饱和温度(T_(Zr)=814~862℃),属于钾质碱性岩石。该岩体具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.72057~0.72186),负的全岩ε_(Nd)(t)值(-5.1~-4.5)和负的锆石ε_(Hf)(t)值(-7.6~-3.4),以及较高的锆石δ^(18) O值(5.39‰~7.94‰),表明其源区可能为伸展环境下古老基性下地壳部分熔融。赛图拉石英闪长岩SiO_(2)含量为56.8%~58.6%,全碱(Na_(2)O+K_(2)O)含量为5.75%~6.39%,具有较低的铝饱和指数(A/CNK=0.85~0.89),相对高的MgO含量(2.93%~3.41%)以及Mg^(#)值(~45),为高钾钙碱性系列岩石。它们富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Nb、Ta、Ti),且具有微弱的Eu异常(δEu=0.72~0.77),类似于俯冲带岩浆岩地球化学特征。这些石英闪长岩具有相对高的(^(87)Sr/^(86)Sr)_(i)比值(0.71317~0.71322),负的全岩ε_(Nd)(t)值(-5.6~-5.1)和负的锆石ε_(Hf)(t)值(-7.8~-2.9),与同时期来源于富集地幔的基性岩同位素特征相似,表明赛图拉石英闪长岩岩浆可能是由俯冲板片流体交代的富集地幔楔部分熔融形成,并在岩浆演化的过程中经历了橄榄石、辉石、角闪石、磷灰石和Fe-Ti氧化物等矿物的分离结晶作用。结合同位素和数字模拟计算(Rhyolite-MELTS)结果表明,赛图拉石英闪长岩可能由塔里木克拉通南缘玄武质岩浆的分离结晶而成。综合前人研究,本文提出晚奥陶世阿喀孜二长岩和赛图拉石英闪长岩形成于原特提斯洋向北俯冲相关的活动大陆边缘环境,该时期原特提斯洋板片回撤,诱发软流圈地幔的上涌,从而产生了大量的弧岩浆岩。  相似文献   

不同变形速率下前陆褶皱冲断带的发育特征——基于砂箱物理模拟实验研究   总被引：1，自引：0，他引：1  

赵高平  刘树根  邓宾  李智武  王兴建  万元博  李金玺 《地质论评》2015,61(4):935-947

构造模拟实验是研究和模拟自然界地质构造现象、变形特征、成因机制和动力学过程的一种物理实验方法。本文基于砂箱构造物理模型高、中、低速7组不同单向挤压速度的构造模拟实验,揭示不同变形速率下砂箱物质变形的几何学、运动学及其演化特征,探讨不同变形速度(尤其是不同量级速度)对前陆褶皱冲断构造变形的重要性。高速单向挤压变形过程中(0.4~0.1mm/s),砂箱模型中石英砂体后缘构造加积强烈,砂体变形主要以楔形体向前扩展变形为主,其构造样式主要表现为前展式叠瓦冲断构造。中速挤压变形过程中(0.05~0.005mm/s),砂体后缘加积相对较弱,构造变形样式主要为砂箱楔形体前缘先形成(前展式为主)逆冲断层,当达到临界楔形体后,反冲断层发育并与前展式逆冲断层构成冲起构造,构造样式上表现为叠瓦构造与冲起构造的无序叠加。低速挤压变形过程中(0.002mm/s),砂箱物质构造样式以典型冲起带为主。由于砂箱模拟过程的时效性,即如何在最有效时间内获得最全面而复杂的演变过程,通过本次系列实验,我们建议将此有效挤压速度设定为0.05~0.005mm/s范围内,可以先后清晰而全面的获得高速和低速挤压下砂体的变形过程和构造样式。  相似文献   

Clinoform geometry,geomorphology, facies character and stratigraphic architecture of a sand‐rich subaqueous delta: Jurassic Sognefjord Formation,offshore Norway          下载免费PDF全文

Stefano Patruno  Gary J. Hampson  Christopher A.‐L. Jackson  Tom Dreyer 《Sedimentology》2015,62(1):350-388

The integration of core sedimentology, seismic stratigraphy and seismic geomorphology has enabled interpretation of delta‐scale (i.e. tens of metres high) subaqueous clinoforms in the upper Jurassic Sognefjord Formation of the Troll Field. Mud‐prone subaqueous deltas characterized by a compound clinoform morphology and sandy delta‐scale subaqueous clinoforms are common in recent tide‐influenced, wave‐influenced and current‐influenced settings, but ancient examples are virtually unknown. The data presented help to fully comprehend the criteria for the recognition of other ancient delta‐scale subaqueous clinoforms, as well as refining the depositional model of the reservoir in the super‐giant Troll hydrocarbon field. Two 10 to 60 m thick, overall coarsening‐upward packages are distinguished in the lower Sognefjord Formation. Progressively higher energy, wave‐dominated or current‐dominated facies occur from the base to the top of each package. Each package corresponds to a set of seismically resolved, westerly dipping clinoforms, the bounding surfaces of which form the seismic ‘envelope’ of a clinoform set and the major marine flooding surfaces recognized in cores. The packages thicken westwards, until they reach a maximum where the clinoform ‘envelope’ rolls over to define a topset–foreset–toeset geometry. All clinoforms are consistently oriented sub‐parallel to the edge of the Horda Platform (N005–N030). In the eastern half of the field, individual foresets are relatively gently dipping (1° to 6°) and bound thin (10 to 30 m) clinothems. Core data indicate that these proximal clinothems are dominated by fine‐grained, hummocky cross‐stratified sandstones. Towards the west, clinoforms gradually become steeper (5° to 14°) and bound thicker (15 to 60 m) clinothems that comprise medium‐grained, cross‐bedded sandstones. Topsets are consistently well‐developed, except in the westernmost area. No seismic or sedimentological evidence of subaerial exposure is observed. Deposition created fully subaqueous, near‐linear clinoforms that prograded westwards across the Horda Platform. Subaqueous clinoforms were probably fed by a river outlet in the north‐east and sculpted by the action of currents sub‐parallel to the clinoform strike.  相似文献   

THE SAND WEDGE AND MIRABILITE OFTHE LAST ICE AGE AND THEIR PALEOCLIMATICSIGNIFICANCE IN HEXI CORRIDOR     

HU Gang  WANG Nai-ang 《中国地理科学(英文版)》2001,11(1):80-86

Sand wedge is formed under the conditions of coldclimate, and is an important basis for reconstructingpaleoenvironment (LI et al., 1990; WANG, 1991 ). Ithas been reported constantly over the last 20 years inthe Qinghai-Xizang (Tibet) Plateau (GUO, 1979; CUl,1983; XU et al., 1984; LIANG et al.,, 1984; PAN etal., 199 ) and North China (YANG et al., 1983; DONGet al., 1985) and Northeast China (GUO et al.,1981 ). We also found fossil sand wedge groups formedin the end of the Late P…  相似文献   

Are Arc Basalts Dry, Wet, or Both? Evidence from the Sumisu Caldera Volcano, Izu-Bonin Arc, Japan   总被引：2，自引：0，他引：2  

TAMURA  Y.; TANI  K.; ISHIZUKA  O.; CHANG  Q.; SHUKUNO  H.; FISKE  R. S. 《Journal of Petrology》2005,46(9):1769-1803

Basalt–basaltic andesite (<55 wt % SiO₂) and dacite–rhyolite(66–74 wt % SiO₂) are the predominant eruptive productsin the Sumisu caldera volcano, Izu–Bonin arc, Japan. Themost magnesian basalt (8·5% MgO), as well as some ofthe other basalts, has a low Zr content (20–25 ppm), andcannot yield basalts with higher Zr contents (29–40 ppm)through fractionation and/or assimilation. The high- and low-Zrbasalts have different phenocryst assemblages, olivine, plagioclaseand pyroxene phenocryst chemistries, REE (rare earth element)patterns, and fluid-mobile element/immobile element ratios.Estimated primary olivine compositions are more magnesian (>Fo₉₁)in the low-Zr basalts compared with those in high-Zr basalts(<Fo₈₉). The low-Zr basalts contain up to 11 vol. % augite,but many high-Zr basalts are free of augite, which appears onlyin their more differentiated products. The low-Zr basalts areconsidered to be hydrous magmas in which olivine crystallizesfirst followed by augite and plagioclase, whereas the high-Zrbasalts are dry. The low-Zr basalts have higher U/Th ratiosthan the high-Zr basalts. We suggest that both dry and wet primarybasalts existed in the Sumisu magmatic system, each having differenttrace element concentrations, mineral assemblages and mineralchemistry. The lower contents of Zr and light REE and magnesianprimary olivines in the wet basalts could have resulted froma higher degree of partial melting (20%) of a hydrous sourcemantle compared with 10% melting of a dry source mantle. TheSr, Nd and Pb isotope compositions of the wet and dry basaltsare similar and are limited in range. These lines of evidenceindicate that a mantle diapir model might be applicable to satisfythe configuration of such a mantle source region beneath a singlevolcanic system such as Sumisu. KEY WORDS: degree of melting; hot fingers; isotopes; mantle diapir; mantle wedge  相似文献   

Slab-fluid metasomatism in the Early Paleozoic forearc mantle deduced from the Motai serpentinites,South Kitakami Belt,northeast Japan     

Ayaka Okamoto  Yuji Ichiyama  Akihiro Tamura  Tomoaki Morishita 《Island Arc》2021,30(1):e12387

The present study examines the petrology and geochemistry of the Early Paleozoic Motai serpentinites, the South Kitakami Belt, northeast Japan, to reveal the subduction processes and tectonics in the convergent margin of the Early Paleozoic proto-East Asian continent. Protoliths of the serpentinites are estimated to be harzburgite to dunite based on the observed amounts of bastite (orthopyroxene pseudomorph). Relic chromian spinel Cr# [=Cr/(Cr + Al)] increases with decreasing amount of bastite. The compositional range of chromian spinel is similar to that found in the Mariana forearc serpentinites. This fact suggests that the protoliths of the serpentinites are depleted mantle peridotites developed beneath the forearc regions of a subduction zone. The Motai serpentinites are divided into two types, namely, Types 1 and 2 serpentinites; the former are characterized by fine-grained antigorite and lack of olivine, and the latter have coarse-grained antigorite and inclusion-rich olivine. Ca-amphibole occurs as isolated crystals or vein-like aggregates in the Type 1 serpentinites and as needle-shaped minerals in the Type 2 serpentinites. Ca-amphibole of the Type 1 serpentinites is more enriched in LILEs and LREEs, suggesting the influence of hydrous fluids derived from slabs. By contrast, the mineral assemblage, mineral chemistry, and field distribution of the Type 2 serpentinites reflect the thermal effect of contact metamorphism by Cretaceous granite. The Ca-amphibole of the Type 1 serpentinites is different from that of the Hayachine–Miyamori Ophiolite in terms of origin; the latter was formed by the infiltration of melts produced in an Early Paleozoic arc–backarc system. Chemical characteristics of the Ca-amphibole in the ultramafic rocks in the South Kitakami Belt reflect the tectonics of an Early Paleozoic mantle wedge, and the formation of the Motai metamorphic rocks in the forearc region of the Hayachine–Miyamori subduction zone system, which occurred at the Early Paleozoic proto-East Asian continental margin.  相似文献   

It starts at home? Climate policies targeting household consumption and behavioral decisions are key to low-carbon futures     

《Chemie der Erde / Geochemistry》2003

Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy.  相似文献   

It starts at home? Climate policies targeting household consumption and behavioral decisions are key to low-carbon futures     

《Chemie der Erde / Geochemistry》2002

Through their consumption behavior, households are responsible for 72% of global greenhouse gas emissions. Thus, they are key actors in reaching the 1.5 °C goal under the Paris Agreement. However, the possible contribution and position of households in climate policies is neither well understood, nor do households receive sufficiently high priority in current climate policy strategies. This paper investigates how behavioral change can achieve a substantial reduction in greenhouse gas emissions in European high-income countries. It uses theoretical thinking and some core results from the HOPE research project, which investigated household preferences for reducing emissions in four European cities in France, Germany, Norway and Sweden. The paper makes five major points: First, car and plane mobility, meat and dairy consumption, as well as heating are the most dominant components of household footprints. Second, household living situations (demographics, size of home) greatly influence the household potential to reduce their footprint, even more than country or city location. Third, household decisions can be sequential and temporally dynamic, shifting through different phases such as childhood, adulthood, and illness. Fourth, short term voluntary efforts will not be sufficient by themselves to reach the drastic reductions needed to achieve the 1.5 °C goal; instead, households need a regulatory framework supporting their behavioral changes. Fifth, there is a mismatch between the roles and responsibilities conveyed by current climate policies and household perceptions of responsibility. We then conclude with further recommendations for research and policy.  相似文献   

冷泉系统甲烷气体渗漏的声学特征及潜在环境效应     

尉建功  吴婷婷  邓希光  于宗泽  王力峰 《海洋学报(英文版)》2020,42(5):133-144

The amount of methane leaked from deep sea cold seeps is enormous and potentially affects the global warming,ocean acidification and global carbon cycle. It is of great significance to study the methane bubble movement and dissolution process in the water column and its output to the atmosphere. Methane bubbles produce strong acoustic impedance in water bodies, and bubble strings released from deep sea cold seeps are called "gas flares"which expressed as flame-like strong backscatter in the water column. We characterized the morphology and movement of methane bubbles released into the water using multibeam water column data at two cold seeps. The result shows that methane at site I reached 920 m water depth without passing through the top of the gas hydrate stability zone(GHSZ, 850 m), while methane bubbles at site II passed through the top of the GHSZ(597 m) and entered the non-GHSZ(above 550 m). By applying two methods on the multibeam data, the bubble rising velocity in the water column at sites I and II were estimated to be 9.6 cm/s and 24 cm/s, respectively. Bubble velocity is positively associated with water depth which is inferred to be resulted from decrease of bubble size during methane ascending in the water. Combined with numerical simulation, we concluded that formation of gas hydrate shells plays an important role in helping methane bubbles entering the upper water bodies, while other factors, including water depth, bubble velocity, initial kinetic energy and bubble size, also influence the bubble residence time in the water and the possibility of methane entering the atmosphere. We estimate that methane gas flux at these two sites is 0.4×10~6–87.6×10~6 mol/a which is extremely small compared to the total amount of methane in the ocean body, however, methane leakage might exert significant impact on the ocean acidification considering the widespread distributed cold seeps. In addition, although methane entering the atmosphere is not observed, further research is still needed to understand its potential impact on increasing methane concentration in the surface seawater and gas-water interface methane exchange rate, which consequently increase the greenhouse effect.  相似文献   

硼的地球化学性质及其在俯冲带的循环与成矿初探   总被引：2，自引：1，他引：1  

林秋婷  陈晨  刘海洋 《岩石学报》2020,36(1):5-12

硼是广泛应用于化工、农业、材料科学及核工业领域的重要元素。硼与氢的核聚变反应是未来具备运用潜力的清洁能源。硼作为典型的亲石元素,是高度不相容元素。硼元素容易富集于蚀变洋壳及蛇纹石化地幔橄榄岩中。而在板块俯冲过程中,由于硼具有强的流体活动性,会优先赋存于流体中。因此,当蛇纹石化的大洋岩石圈及覆于其上的沉积物在俯冲过程中发生脱水,这使得弧前地幔楔发生大规模的蛇纹石化。此时大量硼元素很可能随俯冲流体释放并封存于弧前地幔楔中。目前已发现的超大型硼矿床主要位于聚合型板块边缘,尤其土耳其拥有世界上最大的硼酸盐储量。我们推测这些矿床的形成基础条件之一可能与弧前高度蛇纹石化的地幔楔有关。尤其是在洋 陆俯冲环境,弧前蛇纹岩或蛇绿混杂岩首先通过俯冲侵蚀再循环到火山弧岩浆中,使得岩浆更富集硼。随后弧火山喷发大量富硼的火山岩、岩浆热液及水气。在岩浆冷却过程中,硼元素析出、沉淀于火山表面,并伴随风化、侵蚀过程汇聚至碰撞造山带的封闭湖盆之中。此外,干冷的气候条件下也进一步促进了硼的成矿。我国具有形成大型、超大型硼矿的地质条件,应加大研究及探勘力度,并适当购买硼作为战略储备。  相似文献