Deformation microstructures of olivine and pyroxene in mantle xenoliths in Shanwang,eastern China,near the convergent plate margin,and implications for seismic anisotropy   总被引：1，自引：0，他引：1  

Yong Park 《International Geology Review》2015,57(5-8):629-649

Deformation microstructures, including lattice-preferred orientations (LPOs) of olivine, enstatite, and diopside, in mantle xenoliths at Shanwang, eastern China, were studied to understand the deformation mechanism and seismic anisotropy of the upper mantle. The Shanwang is located across the Tan-Lu fault zone, which was formed due to the collision between the Sino-Korean and South China cratons. All samples are spinel lherzolites and wehrlites, and LPOs of minerals were determined using scanning electron microscope/electron backscattered diffraction. We found two types of olivine LPO: type-B in spinel lherzolites and type-E in wehrlites. Enstatite showed two types of LPO (types BC and AC), and diopside showed four different types of LPO. Observations of strong LPOs and numerous dislocations in olivine suggest that samples showing both type-B and -E LPOs were deformed in dislocation creep. The seismic anisotropy of the P-wave was in the range of 2.2–11.6% for olivine, 1.2–2.3% for enstatite, and 2.1–6.4% for diopside. The maximum seismic anisotropy of the shear wave was in the range 1.93–7.53% for olivine, 1.53–2.46% for enstatite, and 1.81–6.57% for diopside. Furthermore, the thickness of the anisotropic layer was calculated for four geodynamic models to understand the origin of seismic anisotropy under the study area by using delay time from shear wave splitting, and S-wave velocity and anisotropy from mineral LPOs. We suggest that the seismic anisotropy under the study area can be most likely explained by two deformation modes that might have occurred at different times: one of deformed lherzolites with a type-B olivine LPO by lateral shear during/after the period of the Mesozoic continental collision between the Sino-Korean and South China cratons; and the other deformed the wehrlites with a type-E olivine LPO by horizontal extension during the period of change in absolute plate motion in relation to the westward-subducting Pacific plate.  相似文献   

Serpentinized Peridotites at the North Part of the Wadi Allaqi District (Egypt): Implications for the Tectono-Magmatic Evolution of Fore-arc Crust   总被引：2，自引：0，他引：2  

Ahmed E.S. KHALIL  Mohamed A. OBEID  Mokhles K. AZER 《《地质学报》英文版》2014,88(5):1421-1436

The Neoproterozoic Allaqi-Heiani suture （800-700 Ma） in the south Eastern Desert of Egypt is the northernmost linear ophiolitic belt that defines an arc-arc suture in the Arabian- Nubian shield （ANS）. The Neoproterozoic serpentinized peridotites represent a distinct lithology of dismembered ophiolites along the Allaqi-Heiani suture zone. The alteration of peridotites varies, some contain relicts of primary minerals （Cr-spinel and olivine） and others are extremely altered, especially along thrusts and shear zones, with development of talc, talc-carbonate and quartz-carbonate. The fresh cores of the chromian spinels are rimmed by ferritchromite and Cr- magnetite. The fresh chromian spinels have high Cr# （0.62 to 0.79）, while Mg# shows wider variation （0.35-0.59）. High Cr# in the relict chromian spinels and Fo content in the primary olivines indicate that they are residual peridotites after extensive partial melting. The studied ophiolitic upper mantle peridotites are highly depleted and most probably underwent high degrees of partial melting at a supra-subduction zone setting. They can be produced by up to -20%-22% dynamic melting of a primitive mantle source. The mineralogical and geochemical features of the studied rocks reflect that the mantle peridotites of the north part of the Wadi Allaqi district are similar to the fore-arc peridotites of a supra-subduction zone.  相似文献   

东天山圪塔山口铜镍矿区镁铁-超镁铁质岩体橄榄石与尖晶石矿物学特征   总被引：2，自引：0，他引：2  

冯宏业 《地质与勘探》2014,50(2):346-359

新近发现的圪塔山口含铜镍矿化镁铁-超镁铁质岩体位于新疆东天山黄山-镜儿泉铜镍矿带东端,共有4个镁铁-超镁铁质岩体,其中Ⅰ、Ⅱ、Ⅲ号岩体均见铜镍硫化物矿化,研究表明其形成时代(282Ma)及岩浆来源与东天山地区其它铜镍矿化镁铁-超镁铁质岩体一致。本文对主要造岩矿物橄榄石及副矿物尖晶石进行了显微镜下观察及电子探针分析,结果表明橄榄石Fo值介于83.1~86.6之间,平均85.2,为贵橄榄石,其Ni含量变化于1273×10-6~2719×10-6,平均1918×10-6;尖晶石根据铝含量的不同可以分为高铝和低铝两种。圪塔山口岩浆为地幔源区发生15.8%~18.8%的部分熔融,并有过剩橄榄石加入的玄武质岩浆经结晶分异作用形成的派生岩浆。对橄榄石分离结晶和硫化物熔离的计算模拟表明橄榄石结晶前,岩浆已经达到S饱和,结晶过程始终伴随硫化物的熔离作用,虽然早期结晶的橄榄石与硫化物熔体间发生了Fe-Ni交换,但仍有很好的铜镍成矿潜力。  相似文献   

Melt and fluid inclusion evidence for a genetic relationship between magmatism in the Shuangliao volcanic field and inorganic CO2 gas reservoirs in the southern Songliao Basin,China     

《International Geology Review》2012,54(9):1122-1137

We have studied melt and fluid inclusions in minerals from alkali basalts, mantle xenoliths, and dawsonite-bearing sandstones from the Shuangliao volcanic field in southern Songliao Basin, Northeast China. The inclusions have been investigated using petrographic, geochemical, and laser Raman spectroscopic techniques. Volcanic rocks of the Shuangliao field are predominantly alkali olivine basalts that contain rare mantle xenoliths. Silicate melt and fluid inclusions are common in both olivine phenocrysts and the mantle xenoliths. The fluid inclusions are mainly composed of CO₂ with small amounts of CO, CH₄, N₂, and H₂O, which is consistent with an upper mantle origin. CO₂ gas reservoirs in the southern Songliao Basin are mostly derived from a mantle–magmatic source. Coeval fluid-inclusion homogenization temperatures, coupled with the thermal burial history, show that the CO₂ gas reservoirs in the southern Songliao Basin are Cenozoic (40–63 Ma) and coeval with the magmatism in the Shuangliao volcanic field. Despite the relatively small scale of this volcanic activity, it released large amounts of CO₂. Much of the magma was not erupted, and CO₂- and H₂O-rich magma was probably intruded into the basin along deep faults, acting as a major source of inorganic CO₂ gas in the southern Songliao Basin.  相似文献   

东昆仑希望沟中二叠世辉长岩Sr-Nd-Lu-Hf同位素特征及其地质意义     

张志青  陈静  余福承  李永登  马永成  徐贝贝 《矿物岩石》2019,39(3):26-31

东昆仑东段希望沟-哈陇休玛一带有多处镁铁-超镁铁质岩的出露,针对希望沟地区中二叠世辉长岩3块样品进行的全岩Sr-Nd同位素及锆石Lu-Hf同位素测试,结果表明:希望沟辉长岩87Sr/86Sr为0.707 445~0.707 676,(87Sr/86Sr)i值为0.707 045~0.707 297,高于现代深海拉斑玄武岩(0.702 0~0.703 5),143 Nd/144 Nd的初始计算值为0.512 476~0.512 543,εNd(t)值为-2.65^-1.34,Nd(t)值受蚀变影响较小,基本反映了其源区洋岛玄武岩的同位素特征;176 Lu/177 Hf在0.000 592~0.001 860间,εHf(t)在2.27~5.46间,一阶段Hf模式年龄为691Ma^816Ma,平均为758Ma,表明岩浆源区主要来源于亏损地幔并有少量壳源物质(如洋壳沉积物)的加入。结合区域构造演化特征,认为希望沟辉长岩源区主要为洋岛玄武岩,是东昆仑地区阿尼玛卿古特提斯洋向北俯冲的结果。  相似文献   

东昆仑希望沟橄榄辉石岩LA-ICP-MS锆石U-Pb定年及岩石地球化学特征     

孔会磊  栗亚芝  李金超  贾群子  国显正  张斌 《地质力学学报》2019,25(3):440-452

东昆仑古特提斯域镁铁-超镁铁质岩石的研究极为薄弱,对青海东昆仑东段希望沟镁铁-超镁铁质杂岩体中橄榄辉石岩进行岩相学、地球化学及年代学分析,以期为东昆仑晚古生代-早中生代构造岩浆演化提供新的约束。利用LA-ICP-MS锆石U-Pb定年,获得希望沟橄榄辉石岩加权平均年龄为（262.4±1.6）Ma,表明岩体侵位于中二叠世。岩石地球化学研究显示,希望沟橄榄辉石岩具有较高的Mg#值（85.31~86.27）,m/f比值介于5.50~6.18,属于铁质超基性岩类;具有低TiO₂（0.41%~0.52%）和低Al₂O₃（3.04%~4.57%）,属钙碱性系列。岩石富集大离子亲石元素（Rb、Th、U）和Pb,相对亏损高场强元素（Nb、Ta、P、Ti）,ΣREE为29.79×10-6~38.96×10-6,（La/Yb）_N为1.71~2.51,平均2.15,δEu=0.73~0.86,具有弱的Eu负异常。岩石成因分析表明,岩石源区为被俯冲改造的岩石圈地幔,岩浆在演化过程中遭受了上地壳物质的同化混染作用。结合东昆仑区域构造演化,认为希望沟橄榄辉石岩为阿尼玛卿古特提斯洋俯冲阶段的岩浆记录。   相似文献   

江苏徐州塔山橄榄玄武玢岩地球化学特征及其与金刚石成因关系     

黄友波  周琦忠  张琪  冯学知  王国强  张凤鸣  蔡逸涛 《地质通报》2019,38(1):132-142

通过研究徐州塔山地区橄榄玄武玢岩的地球化学特征,对其岩石成因及构造环境进行判别,并进一步对其金刚石成矿前景进行探讨。结果表明,橄榄玄武玢岩属于大陆板内玄武岩,总体上略富集轻稀土元素,是在板内拉张构造背景下由石榴子石相的富集地幔经不同程度部分熔融形成的,且在岩浆结晶过程中存在一定程度的斜长石堆晶作用。其所含微粒金刚石与安徽栏杆金刚石相似,显示出金刚石生长初期的特点,应为幔源捕获成因。与金伯利岩相比,橄榄玄武玢岩在地球化学特征方面存在明显差异,整体表现为古近纪伸展期玄武岩浆的特征,不具备携带大量深源包体的条件,难以形成原生金刚石矿床。  相似文献   

浅谈吉林敦化意气松南山橄榄石宝石矿矿床地质特征及宝石级橄榄石品级划分方法     

徐光龙  周朋富 《吉林地质》2019,38(2):64-67,94

本文在野外地质勘查及系统分析前人工作、资料的基础上,对吉林敦化意气松南山橄榄石宝石矿成矿地质背景、控矿因素等进行了归纳总结。对宝石级橄榄石品级的划分方法进行了探讨。  相似文献   

鲁西地区新生代周村玄武岩的成因研究     

张银慧  任钟元  洪路兵  张乐  钱生平  吴亚东  丁相礼  徐义刚  陈林丽 《大地构造与成矿学》2017,41(1)

山东地区新生代玄武岩主要分布在郯庐断裂带及其以东地区,在鲁西地区分布较少。本文报道了鲁西地区周村玄武岩的全岩主、微量元素组成、橄榄石斑晶及其熔体包裹体Pb同位素组成。结果表明,周村玄武岩为弱碱性玄武岩,其主量元素具有较高SiO_2和Al_2O_3,较低碱(Na_2O+K_2O)、CaO/Al_2O_3、Fe_2O_3~T(Fe_2O_3~T=Fe O/0.8998+Fe_2O_3)的特征;微量元素在原始地幔标准化蛛网图上与EMI洋岛玄武岩(OIB)相似,表现为明显的Ba、K和Sr正异常,Th和Pb负异常,无Nb、Ta和Ti异常;熔体包裹体~(207)Pb/~(206)Pb和~(208)Pb/~(206)Pb分别为0.894~0.921和2.166~2.213,略高于EMI-OIB。这些特征和鲁西地区无棣大山玄武岩有明显区别,但与山东其它地区的弱碱性-拉斑玄武岩相似。周村玄武岩的橄榄石斑晶Ni、Fe/Mn和Ca分别为1403~2611μg/g,70~93和824~2003μg/g。与橄榄岩熔体结晶的橄榄石成分相比,给定橄榄石Fo值,周村玄武岩橄榄石斑晶具有高Ni和Fe/Mn比值,低Ca的特征。结合全岩低CaO和高FeO/MnO比值,橄榄石成分指示周村玄武岩的源区岩性为辉石岩,其形成需要高比例的来自再循环地壳的英安质熔体交代地幔橄榄岩。高比例的英安质熔体和周村玄武岩的微量元素特征,进一步说明该再循环地壳为含辉长岩洋壳。本文的研究结果暗示山东地区弱碱性-拉斑玄武岩的源区辉石岩,主要与再循环洋壳有关。  相似文献   

Rare Earth Element Determination in Olivine by Laser Ablation‐Quadrupole‐ICP‐MS: An Analytical Strategy and Applications          下载免费PDF全文

Clare V. Stead  Emma L. Tomlinson  Balz S. Kamber  Michael G. Babechuk  Cora A. McKenna 《Geostandards and Geoanalytical Research》2017,41(2):197-212

Olivine offers huge, largely untapped, potential for improving our understanding of magmatic and metasomatic processes. In particular, a wealth of information is contained in rare earth element (REE) mass fractions, which are well studied in other minerals. However, REE data for olivine are scarce, reflecting the difficulty associated with determining mass fractions in the low ng g^?1 range and with controlling the effects of LREE contamination. We report an analytical procedure for measuring REEs in olivine using laser ablation quadrupole‐ICP‐MS that achieved limits of determination (LOD) at sub‐ng g^?1 levels and biases of ~ 5–10%. Empirical partition coefficients (D values) calculated using the new olivine compositions agree with experimental values, indicating that the measured REEs are structurally bound in the olivine crystal lattice, rather than residing in micro‐inclusions. We conducted an initial survey of REE contents of olivine from mantle, metamorphic, magmatic and meteorite samples. REE mass fractions vary from 0.1 to double‐digit ng g^?1 levels. Heavy REEs vary from low mass fractions in meteoritic samples, through variably enriched peridotitic olivine to high mass fractions in magmatic olivines, with fayalitic olivines showing the highest levels. The variable enrichment in HREEs demonstrates that olivine REE patterns have petrological utility.  相似文献