共查询到20条相似文献，搜索用时 78 毫秒
1.
本文收集了阜平杂岩新太古代早期-古元古代晚期基底岩石的岩石地球化学、锆石U-Pb年代学、同位素地球化学和变质作用资料,以期对阜平杂岩早寒武纪演化历史进行初步总结.阜平新太古代早期~2.7 Ga片麻岩原岩为英云闪长岩,具有TTG质片麻岩的地球化学特征;其锆石εHf（t）具有较高的正值（+5.44~+7.50）,单阶段模式年龄为2 745~2 824 Ma,表明新太古代早期为阜平杂岩强烈的地壳生长时期.新太古代晚期片麻岩的时代集中于2 543~2 484 Ma,主要岩石类型为英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）,同时区域内还存在二长花岗岩.TTG质片麻岩的εNd（t）值为-1.64~+0.96,单阶段模式年龄为2.76~3.04 Ga;锆石εHf（t）值为-1.9~+7.91,单阶段和两阶段模式年龄分别为2 546~2 888 Ma和2 548~3 119 Ma.这些TTG岩石主要为新太古代早期岩石的部分熔融,并有少量中太古代地壳物质参与.近于同期具有岛弧性质的辉长岩和变质作用暗示阜平杂岩新太古代晚期可能经历了俯冲和弧-陆或陆-陆碰撞.古元古代中期（2.1~2.0 Ga）阜平地区花岗质岩浆活动强烈.该阶段花岗岩具有A型花岗岩特征,与同期的火山-沉积岩系形成于华北克拉通古元古代中期伸展的陆内裂谷环境中.阜平杂岩中基性麻粒岩包体记录的变质作用时代为1.89~1.85 Ga,并具有顺时针演化的P-T轨迹,其代表了古元古代晚期裂谷闭合的陆内造山过程,表明华北最终克拉通化. 相似文献
2.
位于华北克拉通中部造山带的阜平杂岩是研究华北克拉通演化历史的理想对象之一。阜平杂岩由一系列高角闪岩相至麻粒岩相变质和多期强烈变形的岩石组成,包括灰色片麻岩、麻粒岩、角闪岩、细粒片麻岩和大理岩,可以分为四个岩性单元:阜平灰色片麻岩、龙泉关眼球状片麻岩、湾子表壳岩和南营花岗片麻。本研究分析了大约200颗来自湾子表壳岩中碎屑锆石的U-Pb年龄和Hf同位素组成。其中锆石变质增生边给出1.82~1.84Ga,对应华北克拉通的最终拼合事件。除了小部分继承锆石具有2.5Ga到2.9Ga的继承年龄外,大部分岩浆锆石给出2.10Ga和2.51Ga两组年龄。这些结果表明湾子表壳岩来源于2.5Ga的阜平TTG片麻岩和2.0~2.1Ga的南营花岗片麻岩,沉积年龄在1.84~2.10Ga之间。所有年龄在2.51Ga的锆石都具有正的εHf初始值( 1.4~ 10.9),指示了一个重要的地壳增生事件发生在2.5Ga,大量的新生岩浆从亏损地幔涌入地壳中。Hf同位素数据还表明年龄在2.8Ga岩石是源区下地壳的重要组成部分,这跟东部陆块的Nd同位素组成相一致。年龄在2.1Ga的岩石εHf初始值为-4.9到 6.1,本文解释为其形成于先成地壳的再... 相似文献
3.
大别造山带新太古代地壳岩石和古元古代混合岩化作用——来自锆石U- Pb年代学和Hf同位素证据 总被引：1，自引：0，他引：1
大别造山带北大别超高压变质带是研究秦岭-大别-苏鲁造山带古老基底演化过程的关键区域,其内广泛发育的混合岩长期被认为主要形成于中生代。本文对北大别团风一带新识别出的一套混合岩开展了锆石U-Pb定年和Hf同位素组成分析,结果显示,混合岩第一类锆石核部具有岩浆锆石特点,组成的不一致线上交点年龄为2850±86 Ma,该年龄代表了混合岩原岩年龄。第二类锆石具有变质深熔锆石特点,其加权平均207Pb/206Pb年龄为2011±12 Ma,代表了混合岩化的时间。岩浆锆石多数具有负的εHf(t)值(-8.1~2.2),对应两阶段Hf同位素模式年龄(TDM2)为3.6~3.0 Ga,表明原岩可能为大别造山带内古太古代地壳物质重熔形成,并可能在形成过程中伴有少量幔源物质加入。与之相比,变质锆石均具有正的εHf(t)值(0.3~8.2),对应TDM2为2.7~2.2 Ga,说明在混合岩化变质深熔过程中锆石Lu-Hf同位素体系完全开放,导致了锆石Hf同位素组成的升高。本文研究表明,大别造山带除了中生代混合岩化作用以外,还存在古元古代与Columbia超大陆聚合过程相关的一期混合岩化作用,为目前已知的大别造山带内最早一期混合岩化作用。此外,该套混合岩原岩为太古宙岩石,且对应模式年龄高达3.6 Ga,这扩展了目前已知的大别造山带最古老岩石信息范围,表明大别造山带内太古宙古老地壳物质可能不仅局限于黄土岭一带,还在北大别更广泛地区出露。 相似文献
4.
为查明全吉地块基底中达肯大坂岩群的最大沉积年龄,用LA-ICP-MS技术测定了钾长石浅粒岩中的锆石U-Pb年龄。CL图像和Th/U比值指示这些锆石均为岩浆成因的锆石。36个测点207Pb/206Pb年龄变化范围为2094～2280Ma,其中年龄谐和度高于90%的30个测点的207Pb/206Pb年龄相对概率密度曲线呈单峰分布特征,峰值年龄为2190Ma左右。结合全吉地块最早一期变质事件的年龄,钾长石浅粒岩原岩碎屑和所在的达肯大坂岩群的沉积年龄范围被约束在1.95～2.19Ga之间。本研究表明,前人在侵入于达肯大坂岩群的伟晶岩脉中获得的约2.42Ga年龄的锆石应捕获于围岩,属于继承性岩浆碎屑成因,该类锆石年龄不能用来约束达肯大坂岩群原岩的最小沉积年龄。 相似文献
5.
锡林浩特杂岩中斜长角闪岩锆石U-Pb年代学及Hf同位素研究 总被引：3，自引：1，他引：2
锡林浩特杂岩是一套经历强变形变质作用的变质岩,主要由黑云斜长片麻岩、角闪斜长片麻岩、斜长角闪片麻岩及变粒岩夹透镜状或脉状斜长角闪岩组成。查明其形成年龄、变质年龄对深入认识中亚造山带的形成演化具有重要意义。本次研究对锡林浩特杂岩中斜长角闪岩进行了SHRIMP锆石U-Pb测年和LA-MC-ICP-MS锆石Hf同位素组成分析,给出了锆石SHRIMP U-Pb的加权平均年龄为(316±4)Ma,该年龄代表斜长角闪岩的原岩形成年龄,表明锡林浩特杂岩不是前寒武纪地质体。通过锆石Hf同位素分析,εHf(t)值主要为正值(+4.1～+17.0),揭示其物源可能来自亏损地幔或壳幔混合。根据亏损地幔和古老地壳的锆石Hf同位素进行两端元的混合计算,得到斜长角闪岩原岩岩浆的源区以幔源增生组分为主体(经过计算壳幔混合比例大约1∶2)。部分锆石的模式年龄在1.8～2.5 Ga之间,表明斜长角闪岩的原岩在形成过程中有古元古代地壳物质的加入,通过兴蒙造山带和锡林浩特杂岩中斜长角闪岩的Hf模式年龄对比可知,物源可能来自兴蒙造山带内部。基于Hf同位素的两端元混合计算表明该区在晚古生代存在地壳增生。根据野外观察和室内岩石特征分析,该套杂岩可能是一套经历强变形与变质作用的晚古生代火山-沉积建造。 相似文献
6.
经过研究 ,将太行山地区原阜平群中一套浅粒岩、斜长角闪岩和钙硅酸盐岩及大理岩构成的稳定组合解体出来 ,建立了湾子群。本文对河北平山板桥沟地区湾子群中的钾长浅粒岩进行了锆石成因和年代学研究。阴极发光 (CL )图像显示浅粒岩中的锆石主要为具有震荡环带的岩浆型碎屑锆石 ,其 Th/ U >0 .38,表明原岩主要为火成岩。SHRIMP分析结果表明碎屑锆石的结晶年龄为 2 5 36 Ma,并且部分颗粒有 2 0 81 Ma深熔作用的增生边。笔者综合各方面研究成果 ,推测湾子群形成于 2 .5～ 2 .1 Ga之间 ,为古元古代的产物。并且在 2 0 81 Ma经历了强烈的深熔作用的影响 ,形成了太行山地区广泛分布的古元古代钾质花岗岩。这一研究结果为探讨太行山地区的地质演化提供了重要的年代学依据。 相似文献
7.
官都岩群是华北克拉通中部造山带赞皇杂岩中重要的变质火山-沉积岩系,经历了高绿片岩相-高角闪岩相变质,准确限定其沉积时代与物质来源对探究中部造山带新太古代-古元古代构造演化过程具有重要意义。利用LA-MC-ICP-MS(多接收激光剥蚀电感耦合等离子质谱仪)与TIMA(矿物自动分析系统)对官都岩群中黑云变粒岩与石英岩进行了锆石矿物包体、U-Pb-Hf同位素与稀土元素原位分析。根据碎屑锆石内部矿物包体组成、阴极发光图像特征与U-Pb年龄结果,认为黑云变粒岩与石英岩中碎屑锆石中最年轻一组的207Pb/206Pb谐和年龄分别为2 544 Ma或2 536 Ma,大致限定了其原岩的最老沉积时代,结合区内黄岔花岗岩岩体侵入官都岩群的野外地质关系,推测官都岩群沉积时代为新太古代末期,并非古元古代。官都岩群黑云变粒岩与石英岩碎屑锆石年龄图谱十分相似,最主要的峰值年龄为2 512 Ma,结合碎屑锆石内部矿物包体与结构特征,认为官都岩群主要物源为新太古代晚期中酸性岩浆岩。两阶段锆石Hf模式年龄揭示2 850～2 700 Ma为赞皇杂岩最强烈的地壳生长阶段。综合本文... 相似文献
8.
扬子陆核的生长和再造：锆石U-Pb年龄和Hf同位素研究 总被引：5，自引：2，他引：5
对宜昌三峡附近崆岭杂岩中混合岩、片麻岩和变沉积岩以及莲沱砂岩进行了锆石U-Pb和Hf-O同位素研究,研究结果深化了我们对扬子陆核生长和再造的认识。在莲沱砂岩中发现了老达3.8Ga的碎屑锆石,说明扬子陆块可能存在这个年龄的地壳物质;其Hf同位素组成指示初生地壳生长出现在4.0Ga。崆岭杂岩中混合岩和片麻岩的U-Pb年龄表明,在3.2～3.3Ga和2.9～3.0Ga有两期重要的岩浆活动,指示扬子陆核可能于中太古代就开始形成。锆石Hf同位素研究则指示,其原岩至少从3.5Ga就开始从亏损地幔分异出来。混合岩和变沉积岩中所记录的1.9～2.0Ga变质事件,是扬子陆核再造并发生克拉通化的主要时期。而广泛分布于扬子陆块周边的新元古代岩浆活动不仅导致了许多太古宙和古元古宙地壳重熔,而且引起了初生地壳的快速再造。 相似文献
9.
《吉林大学学报(地球科学版)》2015,(Z1)
出露于豫西地区的陡岭杂岩传统上被认为是南秦岭地体最古老的地质单元,并且南秦岭地体与毗邻的扬子板块在前寒武纪有密切联系。然而,陡岭杂岩形成时代以及与扬子地体的地质-构造关系一直以来缺乏共识。本文对陡岭杂岩中主要的岩石类型——正片麻岩和副片麻岩进行了岩石学、锆石U-Pb年代学和地球化学分析,对深入认识南秦岭地体乃至扬子地体前寒武纪演化历史具有重要的意义。地球化学组成表明,陡岭杂岩正片麻岩主要由TTG系列、富K花岗岩组成,原岩时代侵位集中在~2.5 Ga。3个正片麻岩样品的锆石谐和U-Pb年龄为2 446、2 447和2 478 Ma,原岩形成年龄接近,表明应该为同一构造旋回作用的岩浆产物。一些颗粒也记录了~3.0 Ga继承锆石年龄信息,~2.0 Ga变质热事件信息。副片麻岩的碎屑锆石U-Pb年龄峰值主要集中在2.5和2.0 Ga两个峰值,与正片麻岩形成时代和记录的变质热事件记录一致,可能表明正片麻岩是主要的沉积物源构成。少量碎屑锆石颗粒具有新元古代年龄值,最年轻的谐和年龄限制了副片麻岩原岩最大沉积时代为~900 Ma。碎屑锆石边部记录了~800 Ma变质生长作用,锆石内部结构(CL图像)和REE含量特征可能表明其形成于角闪岩相变质条件。正片麻岩全岩初始εNd值为1.8~7.0,锆石初始εHf值为-5.0~0.0。Nd-Hf同位素组成特征表明,其源岩来自于新生地壳和部分古老的地壳再造。陡岭杂岩记录的太古宙岩浆活动和地壳生长历史与扬子地体存在差异,但都记录了~2.0 Ga变质事件。而~800 Ma角闪岩相变质事件可能代表扬子地体与华夏地体拼合作用的年龄记录。 相似文献
10.
滇西澜沧岩群钠长浅粒岩锆石U- Pb测年、Hf同位素组成及构造意义 总被引：1，自引：0，他引：1
澜沧岩群位于滇西“三江”地区的昌宁—孟连结合带,是研究特提斯造山带重要组成部分。本文对双江地区出露的钠长浅粒岩进行锆石U- Pb定年、Hf同位素及岩石地球化学分析,讨论了岩石的成因和形成时代,以及大地构造演化。利用LA- ICP- MS对钠长浅粒〖JP2〗岩中具有典型岩浆震荡环带的锆石U- Pb定年,获得了206Pb/238U加权平均年龄为476. 5±1. 6Ma,形成时代为早奥陶世(O1)。Hf同位素原位分析获得锆石εHf(t)值为-5. 6～-2. 2,TDMc年龄为1591～1802Ma,表面源区物质形成于早元古代晚期—中元古早期古老地壳物质的部分熔融。岩石地球化学分析,钠长浅粒岩的原岩为花岗闪长岩,具有高硅SiO2=67. 89%～68. 91%、富铝Al2O3=14. 48%～15. 14%、高钾钙碱性过铝质S型花岗岩特征;轻稀土富集,整体呈“右”倾型;δEu值介于0. 60～0. 64之间,呈现强Eu负异常,表明斜长石从岩浆中结晶分离。分析认为,钠长浅粒岩的原岩应特为昌宁—孟连特提斯洋在弧—陆碰撞阶段形成的岛弧花岗岩,与奥陶纪惠民岩组火山岩具有相同的大地构造背景;随着特提斯洋俯冲消减进入陆内挤压阶段,岛弧花岗岩呈俯冲增生杂岩拼贴到昌宁—孟连结合带与临沧花岗岩带之间,组成了澜沧岩群构造岩片。 相似文献
11.
S. Viswanathan K. Surya Prakash Rao B. Mahabaleswar 《Journal of the Geological Society of India》2013,82(6):621-627
Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours. 相似文献
12.
13.
奥地利安东帕有限公司 《岩矿测试》2009,28(3):306-306
最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提 相似文献
14.
E. M. Prasolov S. A. Sergeev B. V. Belyatsky E. S. Bogomolov K. A. Gruzdov I. N. Kapitonov R. Sh. Krymsky V. O. Khalenev 《Geochemistry International》2018,56(1):46-64
This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others. 相似文献
15.
Mining induced subsidence can significantly affect mining costs where major surface facilities and natural environment need to be protected. Overburden grout injection is a technology used to control coal mine subsidence by injecting the mine waste material extracted from the coal back into the inter-burden rock during longwall mining. The flowing slurry is here categorised as a nonlinear viscous cohesive (Bingham plastic) fluid. During longwall mining the grout slurry is pumped into the separated beds of the rock mass through a central vertical borehole, which is drilled deep into the inter-burden rock strata above the coal seam. However, a blockage can occur in the injection system when the slurry velocity falls below a certain critical threshold velocity, indicating a material phase change from cohesive-viscous to cohesive-frictional. In situ field injection tests through boreholes have been simulated at a smaller scale at the CSIRO laboratory in Brisbane by pumping the slurry through a radial disk (gap = 4 mm) from its centre. Laboratory experiments indicate a general, nonlinear, cohesive, viscous, frictional model for shear behaviour of the slurry, in which the material shear parameters are functions of the disk radial distance. Complete dimensional and dimensionless analytical solutions have been developed based on an approach related to Bingham–Herschel–Bulkley fluid mechanics. The derived formulae include relations for minimum pump pressure, local pressure and pressure gradient, wall shear stress, volume rate, velocity and velocity gradient. The theoretical results match the experimental measurements. The experiments covered slurries with maximum particle sizes of 0.5 to 2 mm with about 50% being larger than 100 µm. The viscosities at the various solids concentrations were measured with a standard torsion viscometer. This study differs from the previous research in several distinct aspects, namely, consideration of the variable shear parameters rather than fixed values, inclusion of total nonlinear behaviour, and implementation of a friction function to mimic behaviour of the deposited and consolidating stiff slurry, which can cause a significant pressure rise as a result of the increased shear resistance. 相似文献
16.
17.
Mercury,arsenic, antimony,and selenium contents of sediment from the Kuskokwim River,Bethel, Alaska,USA 总被引：1，自引：0，他引：1
The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources. 相似文献
18.
滇东南锡、银、铅、锌多金属矿床主要分布在个旧、白牛厂、都龙3个矿区,而滇东南较大的3个花岗岩体又分别出露在3个矿区或附近.花岗岩体均形成于燕山晚期,岩石化学、矿物成分相似,富含锡、银、铅、锌、钨、铜等成矿元素.矿床主金属元素组合与岩体之间的距离由远而近出现由锡、钨、(铍、铌、钽)→锡、钨、(铁)、铜、铟→锡、铅、锌、银、铟、(锑)有规律的变化.花岗岩浆是成矿物质来源和成矿热源.岩浆侵入初期使上覆地层隆起产生背斜(凹陷部位成向斜);同时使地层产生一系列裂隙、压性断层或层间断裂;岩浆侵入晚期,这些断层再次活动,表现为张性,岩浆产生的含矿热液沿由其活动所造成的断裂迁移、充填、交代、沉淀而形成矿床. 相似文献
19.
Alexander E. C. Broberg J. S. Kehren A. R. Graziani M. M. Turri W. L. 《Environmental Geology》1993,22(4):353-361
Bellechester, Minnesota, is a small community of approximately 155 residents located on the county line between Goodhue and Wabasha counties in southeast Minnesota's karst region. Bellechester is served by a 21-year-old wastewater treatment facility (WWTF) consisting of three waste-stabilization ponds. On 28 April 1992 six sinkholes were discovered to have drained cell 2 of the WWTF resulting in the loss of approximately 8.7×106 1 of partially treated effluent and about 600 m3 of soil into previously undetected subsurface voids of unknown dimensions. In the week following the collapse, approximately 200 water wells located within a 5-km radius of the WWTF were sampled in an after-the-fact, emergency sampling program. Twelve samples with elevated fecal coliform levels, 18 samples with nitrate-nitrogen greater than the 10 mg/1 standard, and no samples with elevated chlorides were found. However, the elevated levels could not be unambiguously attributed to the WWTF collapse. This is the third WWTF to fail by sinkhole collapse in southeast Minnesota since 1974. All three collapsed lagoons have been located in similar geomorphic and stratigraphic settings. However, at least two lagoons have collapsed in the adjacent area in northeast Iowa, and these lagoons are located at different stratigraphic positions. Twenty-two WWTFs constructed in southeast Minnesota's karst region in the last 25 years have been identified as subject to potential sinkhole collapse. An unknown but significant number of manure storage lagoons, flood control structures, etc., have also been constructed in the karst region and are at risk. Public agencies are beginning to develop plans to deal with the risk associated with existing and future waste lagoons in this environment. The critical hydrogeologic parameters that can be used to prioritize the risk of collapse at existing facilities include: (1) the lithology of the first bedrock beneath each lagoon, (2) the thickness of surficial materials between the lagoon and the bedrock surface, (3) the presence and construction of liners (seepage rate), and (4) the proximity to existing sinkholes. 相似文献
20.
岩石密度和超高压岩石折返速率 总被引：1，自引：3，他引：1
在常温常压条件下对中国大陆科学钻CCSD主孔100-3000米岩心样品进行了密度测量,建立了密度连续剖面,并界定了不同超高压岩石的密度值。通过对比高温高压物性实验资料,岩石密度随着退变程度增强而降低,榴辉岩密度变化序列为3.52g/cm3→3.49g/cm3→3.07g/cm3→2.93g/cm3。超高压长英质岩石密度变化序列为3.00g/cm→2.80g/cm3→2.65g/cm3。上述实验资料是讨论不同折返阶段岩石所受浮力的基础,为研究折返速率大小提供了基本参数。本文通过折返板块运动平衡时,上浮力与粘滞力平衡这一关系式,定量研究了大陆俯冲板块的折返速率,认为密度差产生上浮力从而引起折返,温度对板块折返速率的影响最为显著;密度差大小、折返角度、折返板块大小对折返速率也有直接的影响。定量模拟分析表明,在温度高于850℃时,板块的折返速率可以超过100mm/a;当温度降至700℃时,折返速率则低于1.5mm/a。作者认为在折返早期,温度较高,板块快速折返至60-70km榴辉岩相深度;随着传导散热,温度降低,板块以较慢的速率折返至中下地壳。折返速率的估算表明,浮力是板块折返第一阶段(从>100km深部折返至<40km的中下地壳)的主要驱动力。 相似文献