Helium and Argon Isotopic Composition of Cenozoic Alkali Basalts and Mantle-Derived Xenoliths from Kuandian, Liaoning Province, China     

吴茂炳  王先彬  叶先仁  刘春燕 《中国地球化学学报》2004,23(2):141-147

The noble gas isotopic composition and content data of 2 alkali basalts, 3 Iherzolite xenoliths and one clinopyroxene megacryst from the Kuandian region have confirmed the occurrence of a fractionation of noble gases during magmatism. Light noble gases such as He and Ne are high in mobility and appear to be incompatible as compared with heavy ones ( such as Kr and Xe). Therefore, light noble gases are abundant in volcanics, especially in the volcanics with bubbles; lherzolite xenoliths have relatively high heavy noble gases. The clinopyroxene megacryst has the lowest abundance of noble gases, probably due to its high P-T origin. Noble gas isotopic composition of the clinopyroxene megacryst reveals that the mantle source beneath the Kuandian area has an MORB-like reservoir with^3 He/^4He ratio of—10 Ra(Ra: atmospheric^3 He/^4He ratio) and^40 Ar/^36 Ar ratio of 345.6. The Iherzolite xenoliths possess moderate^3 He/^4He ratios of 2.59 -4.53 Ra, reflecting the loss of primary helium during rock deformation or metasomatism caused by enriched mantle fluids during the up-lifting. The alkali volcanics have very low^3 He/^4 He ratios(0.47—0.61 Ra),indicating a contribution of radiogenic^4 He, probably having resulted from crust contamination. Most of the samples have excess^21 Ne and^22 Ne as compared with atmospheric neon, but Kr and Xe isotopic compositions are indistinguishable from atmospheric values within uncertainties with only individual samples having excess^129Xe,^134Xeand^136 Xe.  相似文献   

Mineralogy, Textures and P-T Relationships of a Suite of Xenoliths from the Monaro Volcanic Province, New South Wales, Australia     

ROACH  IAN C. 《Journal of Petrology》2004,45(4):739-758

Intraplate basalts of the Eocene–Oligocene Monaro VolcanicProvince (MVP), in southeastern New South Wales, include lower-crustaland refractory to weakly metasomatized upper-mantle xenoliths.Lower-crustal-derived xenoliths appear to be all two-pyroxeneplagioclase granulites (Cpx_{Fe:Mg:Ca 0·17–0·56:0·63–0·77:0·28–0·89}Opx_{Fe:Mg:Ca 0·39–0·52:1·37–1·47:0·02}An_72–86 and An_48–50) but may also include garnetpyroxenites at depth. Mantle-derived xenoliths are principallyspinel-bearing lherzolites (Fo_{89·8–90·6}Cpx_{Fe:Mg:Ca 0·07–0·45:0·70–1·70:0·01–0·94}Opx_{Fe:Mg:Ca 0·16–0·19:1·62–1·75:0·01–0·10})but also include amphibole ± spinel-bearing lherzolite(Fo_{88·7–89·1} Cpx_{Fe:Mg:Ca 0·09–0·21:0·61–0·91:0·73–0·93}Opx_{Fe:Mg:Ca 0·09–0·31:0·70–1·54:0·03–0·91}),spinel-bearing harzburgite (Fo_{90·5–90·7}Cpx_{Fe:Mg:Ca 0·08:0·91–0·93:0·74–0·84}Opx_{Fe:Mg:Ca 0·16–0·18:1·73–1·79:0·00–0·02}),wehrlite, pyroxenite (Cpx_{Fe:Mg:Ca 0·08–0·10:0·84–0·90:0·80–0·85}Opx_{Fe:Mg:Ca 0·16–0·33:1·51–1·73:0·02–0·03})and rare garnet pyroxenite (Gt_{Fe:Mg:Ca 0·83–0·95:1·60–1·70:0·45–0·48}Cpx_{Fe:Mg:Ca 0·14–0·21:0·69–0·77:0·78–0·86}Opx _{Fe:Mg:Ca 0·31–0·42:1·43–1·56:0·02–0·03})and amphibole–apatite composites. Xenolith textures aregenerally weakly to moderately foliated, a few are mosaic-porphyroblasticand rare samples are veined or highly strained. MVP xenolithsappear to have equilibrated under similar pressure–temperature(P–T) conditions to other southeastern Australian xenolithsequivalent to the South Eastern Australia (SEA) palaeogeotherm.P–T estimates for the MVP suite of xenoliths reveal aheterogeneous lower crust and upper mantle that is thickly underplatedto c. 1·8 GPa or c. 50 km depth. MVP xenolith P–Tdata are compared with those used to derive the SEA palaeogeotherm,which is shown to be in need of revision using more modern geothermometersand geobarometers and new xenolith coexisting mineral data. KEY WORDS: xenolith; petrography; texture; geotherm; Monaro; eastern Australia  相似文献   

信阳基性麻粒捕虏体及其华北南缘早中生代下地壳性质   总被引：1，自引：1，他引：1  

郑建平　孙敏路凤香  余淳梅王方正 《岩石学报》2005,21(1):91-98

报道了信阳早中生代火山角砾岩中高压基性麻粒岩捕虏体的岩相学、矿物化学、和岩石主元素、微量元素、Nd同位素组成及计算的温压条件和岩石物性结果。这些基性麻粒岩主体为具细粒变晶结构的石榴石 单斜辉石 斜长石 角闪石±碱性长石±石英±钛铁矿组合,其中可见残斑单斜辉石±石榴石组合。它们的全岩化学成分相当于橄榄拉斑-石英拉斑玄武岩,具LREE平坦到富集的稀土配分形式(LaN/YbN=0.98-9.47),且Eu异常不明显(Eu/Eu=0.95-1.11)由细粒变晶矿物组合所计算的温压条件是765-890℃和1.25-1.59GPa(相当于存在深达52km的厚地壳)。麻粒岩的计算波速(Vp)和密度(D)分别为7.04-7.56km/s和3.05-3.30g/cm3。全岩143Nd/144Nd测试值为0.512267-0.512700,εNd(T)为-5.72至 1.01,Nd模式年龄(TDM)为1.8-1.9Ga。由这些高压基性麻粒岩所反映的华北南缘早中生代下地壳,其初始物质可能形成于早元古代的基性岩浆底侵作用,并受扬子板块俯冲碰撞作用的影响。它们在晚第三纪玄武岩喷发前大部分发生了拆沉作用。  相似文献   

扬子地块东段大陆岩石圈地幔的物质成分   总被引：4，自引：0，他引：4  

支霞臣  杨瑞瑛 《大地构造与成矿学》1995,19(1):17-34

根据苏皖地区新生代碱性玄武岩中的尖晶石二辉橄榄岩包体的化学成分，讨论了扬子地块东段大陆岩石圈地幔的物质成分。以包体的平均成分代表该区岩石圈地幔的平均成分，依照地幔地球化学演化趋势，估计了该区岩石圈地幔的原始组成。采用最近提出的二辉石地质温度计，计算了包体的平衡温度，讨论了该区岩石圈地幔物质成分在垂向上的分布和变化，上地幔橄榄岩中的玄武质组分在垂向上由上而下亏损程度逐渐减小。包体中稀土元素丰度模式反映了该区岩石圈地幔演化的多阶段性。除了程度不同的部分熔融作用外，局部地段曾有隐性地幔交代作用发生，造成了地幔橄榄岩中主量成分和稀土元素的解耦现象。  相似文献   

福建明溪大洋窠幔源包体橄榄石的位错结构特征          下载免费PDF全文

董火根  闵茂中  张富生  洪建明 《岩石矿物学杂志》1993,12(1):45-50

本文介绍了采用透射电子显微镜观察研究福建明溪大洋窠上第三系玻基玄武岩中的包体橄榄石的位错结构。研究表明,该地幔源包体橄榄石中存在位错壁、自由位错、位错弓弯和位错环等,它们是该橄榄石在上地幔的高温低应力条件下发生复杂蠕变的产物。根据该地包体橄榄石中自由位错密度(统计值为2.0×10~8cm~(-2)和共生辉石的化学成分,估算出福建明溪大洋窠玻基玄武岩中幔源包体的变形条件为:温度(T)为1070℃;压力(P)为2480MPa;深度(Z)为79.3km;流变应力(σ_1-σ_3)为136MPa;流变速率(ε)为7.6×10~(-13)s~(-1);粘稠度(η)为0.8×10~(20)poise。  相似文献   

Characteristics of Lower Crustal Granulite Xenoliths from the East Qinling Orogenic Belt and Their Tectonic Significance     

Sun Yong  Yu Zaiping  A. Kröner 《中国地球化学学报》1994,13(3):202-211

The Tongbai granulites are present mainly as xenoliths in granodioritic gneisses. The xenoliths with a zircon age of 470Ma are older than the host rocks of granodioritic gneisses which yield a zircon age of 435Ma. It is suggested that the granulites were transported from the lower crust to the upper level along with granodioritic magma. Geothermometrical and geobarometrical studies based on the coexisting minerals (Opx-Cpx and Opx-Gar) show that the granulites were crystallized at 818 –840 °C and 9.5−9.8 × 10⁸ Pa corresponding to the lower crust. Tectonically, the Shangdan suture zone constitutes the boundary between the North China and Yangtze plates. The zone is char acterized by the occurrence of ophiolites in the western part and by that of granulites in the eastern part. So the western part marks the upper crustal level of the Qinling belt, while the eastern part represents the exposure of a deeper level. The results of isotopic dating and the geochemical characteristics of the xenoliths are consistent with those of metatholeiites of the ophiolites in the western part. Therefore, it is assumed that both ophiolites found in the west and granulites found in the east all represent the remnants of the ancient Qinling ocean plate. The difference is that the ophiolites are pieces of obducted fragments from the ocean floor during the subduction in the Early Palaeozoic. However, in the Tongbai area, when the ocean floor was subducting towards the lower crust, it underwent a granulite fades metamorphism. Subsequently, granodioritic magma formed by partial melting trapped some fragments of granulite upwards. This project was jointly granted by the National Natural Science Foundation of China and Stiftung Volkswagenwerk of Germany  相似文献   

云南马关地区碧玄岩中单辉橄榄岩包体的成因   总被引：10，自引：0，他引：10  

舒小辛 《岩石矿物学杂志》1995,14(1):47-51

云南马关地区分布有许多碧玄岩岩管，其中有些岩管含有地幔橄榄岩包体、笔者在该区工作时着重对含角闪石单辉橄榄岩包体进行了研究，并从地球化学和热力学角度探讨了此类包体的成因机制。  相似文献   

中国东部新生代玄武岩及其他幔包体的氧逸度   总被引：1，自引：0，他引：1  

张毅刚  鄂莫岚 《岩石学报》1994,10(2):161-170

地幔环境的氧逸度与温度和压力一样，是控制许多地幔过程的一个重要参数。本文计算了中国东部几个具有代表性地区的玄武岩和尖晶石二辉橄榄岩的氧逸度，尖晶石二辉橄榄岩的氧逸度变化不大，均位于１ｏｇ（ｆｏ２）＝ｌｏｇ（ｆｏ２ＦＭＱ）＋０．０左右，而各地区玄武岩的氧逸度却变化很大，其平均值从尚志地区的ｌｏｇ（ｆｏ２ＦＭＱ＋０．６到长白山地区的ｌｏｇ（ｆｏ２ＦＭＱ）＋３．３左右（其中东北地区钾质玄武岩的氧逸度比除尚志以外其它地区的低），并且总体具有比地幔橄榄岩高得多的氧逸度。推测钾质玄武岩和尚志地区破性玄武岩的氧逸度比中国东部其它地区玄武岩的氧逸度低的可能原因是，前二个地区的玄武岩来源于更深部的（金云母）石榴石二辉橄榄岩，而其它地区的玄武岩来源于略浅部的尖晶石二辉橄榄岩。  相似文献   

内蒙古集宁新生代玄武岩中橄榄岩包体和巨晶的发现及意义   总被引：5，自引：0，他引：5  

杜蔚韩宝福  张文慧刘志强 《岩石矿物学杂志》2006,25(1):13-24

内蒙古集宁新生代玄武岩产于华北克拉通北缘，属于广义的“汉诺坝玄武岩”。首次在三义堂附近的碱性玄武岩中发现了大量的橄榄岩包体、辉石和长石以及少量的含钛磁铁矿巨晶。包体主要是尖晶石二辉橄榄岩，造岩矿物为橄榄石＋斜方辉石＋单斜辉石＋尖晶石，辉石巨晶主要为透辉石和普通辉石，长石巨晶主要是歪长石和少量斜长石。1．5GPa条件下，尖晶石二辉橄榄岩样品所记录的平衡温度与汉诺坝相近，集中于950℃左右，大体上反映了华北克拉通北缘大陆岩石圈地幔尖晶石相部分的温度状态。单斜辉石巨晶的结晶温压大于幔源包体的平衡温压，表明巨晶的来源深度可能大于包体。包体的结构及矿物成分分析表明，这些包体是玄武质岩浆上升过程中偶然捕获岩石圈地幔的岩石碎块。二辉橄榄岩包体中橄榄石高Mg#值（89．5～91．7）和较高的NiO含量（0．29％～0．55％），暗示集宁玄武岩中的橄榄岩包体来自较高熔融程度的岩石圈地幔。  相似文献   

云南六合霓辉正长斑岩中特殊包体岩石的发现及其意义     

刘显凡  卢秋霞  宋祥峰  陶专  龙训荣 《矿物学报》2007,27(3):249-254

在六合霓辉正长斑岩中广泛发育的各类包体岩石中，新近发现了三类特殊包体。通过岩相学、岩石化学、电子探针和扫描电镜分析研究表明，纯方解石包晶（体）和含石英的黄玉伟晶岩包体是地幔流体在运移过程中发生去气作用的产物；黑色微晶富铁硅酸盐熔融包体是地幔流体伴随去气作用的分离产物，其主要矿物组成为石英、绿泥石和富铁的柱状和片状硅酸盐矿物，特征矿物有自然铁、磷灰石和锆石；据全岩化学成分和矿物组成特征及结晶状态分析，表明该包体岩石不是常规岩浆作用产物，尤其自然铁的存在进一步证明该微晶熔融包体是还原条件或缺氧环境下的地幔流体物质。通过对特殊包体岩石的研究，为该区不同岩性和地层中的多金属成矿提供了重要的深部过程地球化学背景。  相似文献