走滑断裂对超高压变质岩石折返的贡献及青藏高原北部白垩纪隆升之新思考   总被引：5，自引：0，他引：5  

杨经绥  李海兵 《地学前缘》2006,13(4):80-90

青藏高原已识别出柴北缘、南阿尔金和高喜马拉雅三条超高压变质带。这些超高压变质带提供了一个不可多得的研究超高压变质岩石形成和折返的机会。柴北缘超高压变质带位于阿尔金断裂的东边,是柴达木—东昆仑地体与祁连—阿尔金微地体和阿拉善—敦煌地体碰撞的产物,由榴辉岩、石榴石橄榄岩和含柯石英片麻岩组成,榴辉岩形成时代500~440Ma,峰期超高压变质年龄440Ma。南阿尔金超高压变质带位于阿尔金断裂带的西边,以产出榴辉岩和石榴石橄榄岩为特征,榴辉岩形成时代为500Ma。南阿尔金超高压变质带被认为是柴北缘超高压变质带的西延,两者被阿尔金断裂左旋位移约400km。阿尔金断裂是巨大的深度>200km的岩石圈走滑断裂,断裂的活动时代至少早到240~220Ma,认为走滑过程中伴随的隆升作用有可能为柴北缘和南阿尔金超高压变质岩石的折返和出露地表做出了贡献,其中阿尔金断裂起到了类似剪刀型断裂的作用。高喜马拉雅超高压变质带在巴基斯坦和印度被发现,以榴辉岩中含柯石英或金刚石为特征,榴辉岩的超高压变质年龄为46Ma,表明超高压变质岩石发生在雅鲁藏布江缝合线关闭后并快速折返。喀喇昆仑断裂走滑过程中伴随的抬升作用则可能对高喜马拉雅地区超高压变质岩石的折返和出露地表做出贡献。在中国东部出露的大别—苏鲁超高压变质带被巨大郯庐断裂左旋走滑位移约500km,可以看作是走滑作用伴随的抬升运动对超高压变质岩石的最后折返和出露地表做出重要贡献的又一例证。青藏高原的隆升通常被认为是印度板块和欧亚大陆新生代以来的碰撞结果。根据高原北部断裂的时代、火山活动和沉积盆地的形成,我们提出高原的隆升是两次俯冲碰撞的结果。第一次发生在中特提斯班公湖-怒江洋盆在白垩纪时期的关闭,其时由于北部来自塔里木盆地和北中国板块及东部来自太平洋板块俯冲产生的抵柱效应,高原北部开始隆升;第二次发生在印度板块的新生代俯冲碰撞作用,造成高原的整体抬升,由此可以解释高原北部平均海拔(5000m)要高于高原南部(平均海拔4000m)。  相似文献   

中国大陆科学钻探100-2000m超高压变质岩普通Pb同位素地球化学初步研究——俯冲陆壳内脱耦的证据   总被引：1，自引：0，他引：1  

董锋李曙光  李秋立刘贻灿 陈福坤 《岩石学报》2006,22(7):1791-1798

本文首次对中国大陆科学钻探工程100～2000m榴辉岩中的绿辉石和片麻岩中的长石进行了普通Pb同位素研究。钻孔上部岩段（0-800m）样品放射成因Pb同位素含量比较高且变化幅度较小（^206Pb／^204Pb=16．81-17．29，^207Pb／^204Pb=15．37-15．45，^208Pb／^204Pb=37．20-37．66），说明其原岩的U／Pb和Th／Pb或者初始Pb同位素比值比较高。钻孔中部岩段（800-1600m）发育有韧性剪切带，相应的Pb同位素比值开始降低且有起伏（^206Pb／^204Pb=16．26-16．72，^207Pb／^204Pb=15．27～15．38，^208Pb／^204Pb=36．73～37．40）、钻孔下部岩段（800～1600m）样品放射成因Ph同位素含量低但变化幅度较小（^206Pb／^204Pb=16.05～16．46，^207Pb／^204Pb：15．22～15.29，^208Pb／^204Pb=36．68～37．48），说明其原岩的U／Pb和Th／Pb或者初始Ph同位素比值比较低。实测数据同模拟数据对比表明，钻孔上、下两岩段样品普通Ph同位素不同一方面是由于继承了原岩初始Pb同位素不同，另一方面是由它们的μ值不同所致。结合氧同位素研究，本文认为800m以上和1600m以下分属上地壳和中地壳．前者是从俯冲大陆岩石圈解耦的上地壳，在大陆岩石圈俯冲过程中，上部岩片同俯冲的大陆岩石圈发生挤离，率先沿着这一个挤离面逆冲折返至浅部。下岩片是随后从俯冲岩石圈解耦的中地壳岩片，并折返至浅部下伏在先期折返的上部岩片之下。考虑到中部岩段（800～1600m）既发育有韧性剪切带又具有异常低^18O峰值（Xiao et al．，2006），挤离面是在地壳内部晚元古代的断裂带及冷水活动通道基础上发育起来的。  相似文献   

中国大陆科学深钻主孔岩屑中含钠和锌的尖晶石的发现   总被引：1，自引：0，他引：1  

任玉峰  杨经绥Shu Jingfu Mao Hokwang 张仲明 《岩石学报》2006,22(7):1867-1874

一种含钠和锌的尖晶石矿物产于中国大陆科学深钻主孔超镁铁岩中，以出溶的方式存在于钛铁矿和磁铁矿中，长5-60μm，宽2-3μm，化学组成（wB％）为MgO17．143％-22．337％，Al2O3 63．646％～66．492％，FeO9．784％～13．924％，ZnO 1．649％-6．386wt％．Na2O 0．029％～0．219wt％。Na2O与ZnO在尖晶石中的含量呈正相关关系。经同步辐射测得其为尖晶石单晶，空间群为Fm3m，晶胞参数为a=0．83781am。根据尖晶石与钛铁矿、石榴石（pyr=56-58mol％）共生和石榴石退变为顽火辉石和镁绿泥石的特点，表明该尖晶石来自超镁铁岩，它们一起经历了至少为角闪岩相的变质作用。广泛的混溶间断现象及其所造成的出溶结构出现在氧化物中，表现为Mt-Usp、Mt-Spl及Mt-Ilm之间的交生。根据前人有关Mt-Usp和Ilm-Gk-Hem固溶体系的实验。表明主孔岩石的氧逸度相对较低，形成温度应在720℃以上。这些早期在岩浆分离结晶过程中形成的铁钛氧化物出溶体，在后来的超高压变质作用下可能发生再次固溶和因降温减压造成的出溶。  相似文献   

Differential exhumation of tectonic units and ultrahigh-pressure metamorphic rocks in the Dabie Mountains, China   总被引：9，自引：0，他引：9  

Shuwen Dong  Jiangfeng Chen  & Dezhi Huang 《Island Arc》1998,7(1-2):174-183

A model involving buoyancy, wedging and thermal doming is postulated to explain the differential exhumation of ultrahigh-pressure (UHP) metamorphic rocks in the Dabie Mountains, China, with an emphasis on the exhumation of the UHP rocks from the base of the crust to the upper crust by opposite wedging of the North China Block (NCB). The Yangtze Block was subducted northward under the NCB and Northern Dabie microblock, forming UHP metamorphic rocks in the Triassic (240–220 Ma). After delamination of the subduction wedge, the UHP rocks were exhumed rapidly to the base of the crust by buoyancy (220–200 Ma). Subsequently, when the left-lateral Tan–Lu transform fault began to be activated, continuous north–south compression and uplifting of the orogen forced the NCB to be subducted southward under the Dabie Orogen (`opposite subduction'). Opposite subduction and wedging of the North China continental crust is responsible for the rapid exhumation of the UHP and South Dabie Block units during the Early Jurassic, at ca 200–180 Ma at a rate of ∼ 3.0 mm/year. The UHP eclogite suffered retrograde metamorphism to greenschist facies. Rapid exhumation of the North Dabie Block (NDB) occurred during 135–120 Ma because of thermal doming and granitoid formation during extension of continental margin of the Eurasia. Amphibolite facies rocks from NDB suffered retrograde metamorphism to greenschist facies. Different unit(s) and terrane(s) were welded together by granites and the wedging ceased. Since 120–110 Ma, slow uplift of the entire Dabie terrane is caused by gravitational equilibrium.  相似文献   

大别山超高压变质带的大地构造框架   总被引：57，自引：17，他引：40  

王清晨  从柏林 《岩石学报》1998,14(4):481-492

依据岩石学、地球化学、同位素年代学的新资料,对大别山造山带研究中诸如蛇绿混杂岩、碰撞时代、超高压变质岩与围岩的关系、俯冲极性等问题进行了论证,指出大别山超高压变质带是中朝陆块与扬子陆块间碰撞造山的产物。在三叠纪发生的陆－陆碰撞中,扬子陆块向北俯冲至华北陆块之下,但至今尚无发现残存的蛇绿混杂岩,碰撞时缝合带的位置被已经折返出露地表的南大别碰撞杂岩带所取代。  相似文献   

An Archean(?) to Paleozoic Evolution for a Garnet Peridotite Lens with Sub-Baltic Shield Affinity within the Seve Nappe Complex of Jamtland, Sweden, Central Scandinavian Caledonides   总被引：2，自引：0，他引：2  

BRUECKNER  HANNES K.; VAN ROERMUND  HERMAN L. M.; PEARSON  NORMAN J. 《Journal of Petrology》2004,45(2):415-437

Mineralogical, isotopic, geochemical and geochronological evidencedemonstrates that the Friningen body, a garnet peridotite bodycontaining garnet pyroxenite layers in the Seve Nappe Complex(SNC) of Northern Jämtland, Sweden, represents old, certainlyProterozoic and possibly Archean, lithosphere that became incorporatedinto the Caledonian tectonic edifice during crustal subductioninto the mantle at c. 450 Ma. Both garnet peridotite and pyroxenitecontain two (M₁ and M₂) generations of garnet-bearing assemblagesseparated by the formation of two-pyroxene, spinel symplectitearound the M₁ garnet and the crystallization of low-Cr spinel_1Cin the matrix. These textures suggest initial high-pressure(HP) crystallization of garnet peridotite and pyroxenite succeededby decompression into the spinel stability field, followed byrecompression into the garnet peridotite facies. Some pyroxenitelayers appear to be characterized solely by M₂ assemblages withstretched garnet as large as several centimeters. Laser ablationmicroprobe–inductively coupled plasma mass spectrometryRe–Os analyses of single sulfide grains generally definemeaningless model ages suggesting more than one episode of Reand/or Os addition and/or loss to the body. Pentlandite grainsfrom a single polished slab of one garnet peridotite, however,define a linear array on an Re–Os isochron diagram that,if interpreted as an errorchron, suggests an Archean melt extractionevent that left behind the depleted dunite and harzburgite bodiesthat characterize the SNC. Refertilization of this mantle bymelts associated with the development of the pyroxenite layersis indicated by enriched clinopyroxene Sr–Nd isotope ratios,and by parallel large ion lithophile-enriched trace elementpatterns in clinopyroxene from pyroxenite and the immediatelyadjacent peridotite. Clinopyroxene and whole-rock model Sm–Ndages (T_DM = 1·1–2·2 Ga) indicate that fertilizationtook place in Proterozoic times. Sm–Nd garnet₂–clinopyroxene₂–wholerock ± orthopyroxene₂ mineral isochrons from three pyroxenitelayers define overlapping ages of 452·1 ± 7·5and 448 ± 13 Ma and 451 ± 43 Ma (2  相似文献   

苏鲁地体超高压和退变质时代的厘定:来自片麻岩锆石微区SHRIMP U-Pb定年的证据   总被引：31，自引：16，他引：31       下载免费PDF全文

刘福来  许志琴  宋彪 《地质学报》2003,77(2):229-237

锆石微区矿物包体的激光拉曼和阴极发光测试以及相应的SHRIMP U-Pb定年结果表明,苏鲁地体片麻岩锆石微区记录了十分复杂的年代学信息。其中副片麻岩锆石核部记录了345～743 Ma的继承性锆石年龄,标志着原岩碎屑锆石来源的复杂性;含柯石英的锆石微区记录了220～234 Ma的超高压变质年龄;而含石英包体的边部则记录了202～219 Ma的退变质年龄。正片麻岩继承性锆石核部所记录的年龄为574～680 Ma,表明原岩锆石曾经历了部分Pb丢失,原岩的形成年龄应大于680 Ma;含柯石英锆石微区所记录的超高压变质年龄为224～242 Ma;而锆石边部所记录的退变质年龄为209～219 Ma。两类片麻岩锆石微区所隐藏的超高压变质和退变质年龄信息十分相近,平均值分别为229±4Ma和211±4Ma,标志着苏鲁地体超高压变质时代应为印支期,相应的构造抬升速率约5.6 km/Ma。该项成果不仅确定了苏鲁地体超高压变质和退变质时代,而且对于深入探讨苏鲁地体快速折返过程中的动力学机制有着重要的科学意义。  相似文献   

Petrogenesis of the Maowu pyroxenite–eclogite body from the UHP metamorphic terrane of Dabieshan: chemical and isotopic constraints     

Bor-ming Jahn  Qicheng Fan  Jian-Jun Yang  O Henin 《Lithos》2003,70(3-4):243-267

The Maowu eclogite–pyroxenite body is a small (250×50 m) layered intrusion that occurs in the ultra-high-pressure (UHP) metamorphic terrane of Dabieshan, China. Like the adjacent Bixiling complex, the Maowu intrusion was initially emplaced at a crustal level, then subducted along with the country gneisses to mantle depths and underwent UHP metamorphism during the collision of the North and South China Blocks in the Triassic. This paper presents the results of a geochemical and isotopic investigation on the metamorphosed Maowu body. The Maowu intrusion has undergone open system chemical and isotopic behavior three times. Early crustal contamination during magmatic differentiation is manifested by high initial ⁸⁷Sr/⁸⁶Sr ratios (0.707–0.708) and inhomogeneous negative _Nd(T) values of −3 to −10 at 500 Ma (probable protolith age). Post-magmatic and pre-UHP metamorphic metasomatism is indicated by sinusoidal REE patterns of garnet orthopyroxenites, lack of whole-rock (WR) Sm–Nd isochronal relationship, low δ¹⁸O values and an extreme enrichment of Th and REE in a clinopyroxenite. Finally, K and Rb depletion during UHP metamorphism is deduced from the high initial ⁸⁷Sr/⁸⁶Sr ratios unsupported by in situ Rb/Sr ratios. Laser ICP-MS spot analyses on mineral grains show that (1) Grt and Cpx attained chemical equilibrium during UHP metamorphism, (2) Cpx/Grt partition coefficients for REE correlate with Ca, and (3) LREE abundances in whole rocks are not balanced by that of the principal phases (Grt and Cpx), implying that the presence of LREE-rich accessory phases, such as monazite and apatite, is required to account for the REE budget.

Sm–Nd isotope analyses of minerals yielded three internal isochrons with ages of 221±5 Ma and (T)=−5.4 for an eclogite, 231±16 Ma and (T)=−6.2 for a garnet websterite, and 236±19 Ma and (T)=−6.9 for a garnet clinopyroxenite. The Cpx/Grt chemical equilibrium and the consistent mineral isochron ages indicate that the metasomatic processes mentioned above must have occurred prior to the UHP metamorphism. These Sm–Nd ages agree with published zircon and monazite U–Pb ages and constrain the time of UHP metamorphism to 220–236 Ma. The Maowu and Bixiling layered intrusions are similar in their in situ tectonic relationship with their country gneisses, but the two bodies are distinguished by their magma-chamber processes. The Bixiling magmas were contaminated by the lower crust, whereas the Maowu magmas were contaminated by the upper crustal rocks during their emplacement and differentiation. The two complexes represent two distinct suites of magmatic rocks, which have resided in the continental crust for about 300–400 Ma before their ultimate subduction to mantle depths, UHP metamorphism and return to the crustal level.  相似文献   

微观结构超压机制与超高压矿物的形成   总被引：3，自引：0，他引：3  

武红岭  池顺良 《岩石学报》2003,19(4):739-744

提出了由岩石及矿物的结构形态、岩石力学性质不同引起的微结构超压机制。对影响结构超压的诸因素(弹性参数、热物理性质)进行了数值模拟实验和定量分析。研究结果表明，结构压力对超高压岩石、矿物的形成具有重要的意义。结构压力随弹性模量差异、围限压力、温度改变量及热膨胀系数差异的增加而增大。在岩石、矿物的弹性模量相差5倍的条件下，结构附加压力可达到静岩压力的45％左右。如果再考虑热膨胀系数不同及降温引起的附加压力，在较一般的情况下，60公里左右深处就有可能具备柯石英等超高压矿物形成的下限压力条件。  相似文献   

大陆板块俯冲和折返的同位素地球动力学   总被引：5，自引：1，他引：5  

郑永飞  傅斌  龚冰 《高校地质学报》2002,8(4):365-379

大别 -苏鲁造山带是扬子大陆板块与华北大陆板块之间在三叠纪时期俯冲 -碰撞所形成的超高压变质带。对该带超高压变质岩的稳定同位素研究发现 ,不仅含柯石英榴辉岩出现局部氧同位素负异常 (δ18O =- 10‰ ) ,而且区域上存在氧同位素分布的不均一性 (δ18O =- 10‰～+10‰ )。前者要求榴辉岩原岩在变质前经历过大气降水热液蚀变 ,说明俯冲板块具有大陆地壳特点 ;后者反映扬子板块具有快速俯冲变质的特征 ,否则将达到同位素均一化。榴辉岩氧同位素负异常的保存显示 ,这些超高压变质岩与地幔之间没有发生显著的化学相互作用。因此 ,载有榴辉岩原岩的板块俯冲到 2 0 0多公里深的地幔内部时 ,超高压岩石形成后在地幔中的滞留时间很短(<10Ma) ,致使它们与地幔之间的氧同位素交换没有达到再平衡。榴辉岩中不同矿物对氧同位素测温不仅给出了相互一致的结果 (6 5 0～ 75 0℃ ) ,而且这些温度与阳离子交换温度计的结果 (6 0 0～80 0℃ )相一致。因此 ,在榴辉岩相变质温度下共生矿物之间的氧同位素平衡已被“冻结” ,岩石冷却过程中的氧同位素交换再平衡没有发生 ,从而证明超高压榴辉岩在变质作用后经历了快速降压/冷却过程 ,对应于板块的快速抬升。这些结果首次从地球化学角度证明了大陆板块俯冲—超高压变质—折  相似文献