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111.
Lithospheric composition and structure beneath the northern margin of the Qinling orogenic belt 总被引:1,自引:0,他引:1
Swarms of mafic-intermediate volcaniclastic bodies occur in the Minggang region of Henan Province, a tectonic boundary between
the North Qinling and the North China Block, and emplaced at (178.31±3.77) Ma. These volcanic rocks are subalkaline basaltic
andesites and contain abundance of lower crust and mantle xenoliths. Thus this area is an ideal place to reveal the lithospheric
composition and structure beneath the northern margin of the Qinling orogenic belt. Geochemical data indicate that these mafic
granulites, eclogites and metagabbros have trace elemental and Pb isotopic characteristics very similar to those rocks from
the South Qinling Block, representing the lower part of lower crust of the South Qinling which subducted beneath the North
China Block. Talcic peridotites represent the overlying mantle wedge materials of the North China Block, which underwent the
metasomatism of the acidic melt/fluid released from the underlying lower crust of the South Qinling Block. Deep tectonic model
proposed in this paper is that after the Late Paleozoic South Qinling lithosphere subducted northward and decoupled, the upper
part of the lithosphere emplaced under the North Qinling and the lower part continuously subducted northward under the North
China Block. In Early Mesozoic, the North Qinling Block obducted northward and the North China Block inserted into the Qinling
orogenic belt in a crocodile-mouth shape. 相似文献
112.
The oceanic substratum of Northern Luzon: Evidence from xenoliths within Monglo adakite (the Philippines) 总被引:2,自引:0,他引:2
Betchaida D. Payot Sebastien Jego Rene C. Maury Mireille Polve Michel Gregoire Georges Ceuleneer Rodolfo A. Tamayo Jr Graciano P. Yumul Jr Herve Bellon Joseph Cotten 《Island Arc》2007,16(2):276-290
Abstract A 8.65 Ma adakitic intrusive sheet exposed near Monglo village in the Baguio District of Northern Luzon contains a suite of ultramafic and mafic xenoliths including in order of abundance: spinel dunites showing typical mantle-related textures, mineral and bulk rock compositions, and serpentinites derived from them; amphibole-rich gabbros displaying incompatible element patterns similar to those of flat or moderately enriched back-arc basin basalt magmas; and amphibolites derived from metabasalts and/or metagabbros of identical affinity. A single quartz diorite xenolith carrying a similar subduction-related geochemical signature has also been sampled. One amphibolite xenolith provided a whole-rock K–Ar age of 115.6 Ma (Barremian). We attribute the origin of this suite to the sampling by ascending adakitic magmas of a Lower Cretaceous ophiolitic complex located at a depth within the 30–35 km thick Luzon crust. It could represent an equivalent of the Isabela-Aurora and Pugo-Lepanto ophiolitic massifs exposed in Northern Luzon. 相似文献
113.
Layered Lithospheric Mantle Beneath the Ontong Java Plateau: Implications from Xenoliths in Alnoite, Malaita, Solomon Islands 总被引:1,自引:0,他引:1
A varied suite of mantle xenoliths from Malaita, Solomon Islands,was investigated to constrain the evolution of the mantle beneaththe Ontong Java Plateau. Comprehensive petrological and thermobarometricstudies make it possible to identify the dominant processesthat produced the compositional diversity and to reconstructthe lithospheric stratigraphy in the context of a paleogeotherm.PT estimates show that both peridotites and pyroxenitescan be assigned to a shallower or deeper origin, separated bya garnet-poor zone of 10 km between 90 and 100 km. This zoneis dominated by refractory spinel harzburgites (Fo9192),indicating the occurrence of an intra-lithospheric depletedzone. Shallower mantle ( 相似文献
114.
Enikő Bali Alberto Zanetti Csaba Szabó David W. Peate Tod E. Waight 《Contributions to Mineralogy and Petrology》2008,155(2):165-179
Mantle xenoliths in Neogene alkali basalts of the Bakony–Balaton Highland Volcanic Field (Western Hungary) frequently have
melt pockets that contain silicate minerals, glass, and often carbonate globules. Textural, geochemical and thermobarometric
data indicate that the melt pockets formed at relatively high pressure through breakdown of mainly amphibole as a result of
temperature increases accompanied, in most cases, by the influx of external metasomatic agents. New elemental and Sr–Nd–Pb
isotope data show that in several xenoliths the external agent was either a LIL-enriched aqueous fluid or a CO2-rich fluid, whereas in other xenoliths the melt pockets were additionally enriched in LREE and sometimes HFSE, suggesting
metasomatism by a silicate melt. The compositional character of the external agents might have been inherited by melting of
a hydrated and probably carbonated deeper lithospheric component, which itself was metasomatized by melts with significant
slab-derived components.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
115.
辽西中生代晚期岩石圈地幔的性质:来自玄武岩和地幔捕虏体的证据 总被引:19,自引:4,他引:19
辽西中生代玄武岩中幔源气榄岩捕虏体的岩石学、矿物学和地球化学研究表明,中生代岩石圈地幔是由古老富集型的岩石圈地幔和新增生的岩石圈地幔所组成。前者以角闪尖晶二辉橄榄岩为代表,它经历了富钠质的地幔交代作用。橄榄岩类捕虏体富含轻稀土元素,并具有较高的ω(^87Sr)/ω(^86Sr)比值;后者以二辉石岩为代表,具典型堆积结构,与本区尖晶石二辉橄榄岩相比,具有较高的稀土元素丰度。在矿物成分和稀土元素丰度上,本区辉石岩捕虏体类似于中国东部新生代玄武岩中幔源辉石岩捕虏体,这意味着辉石岩捕虏体可能是上地幔中更早期的岩浆堆积体。 相似文献
116.
LIU Xianfan SONG Xiangfeng LU Qiuxi TAO Zhuan LONG Xunrong ZHAO Fufeng 《《地质学报》英文版》2009,83(2):258-265
Three special types of xenoliths have recently been found in an aegirine–augite syenite porphyry in Liuhe, Yunnan, China. Petrographical, petrochemical, electron microprobe, and scanning electron microscopy studies indicate that pure calcite xenocrysts and quartz-bearing topaz pegmatite xenoliths result from the degassing of mantle fluids during their migration, and that black microcrystalline iron-rich silicate-melt xenoliths are the product of the extraction of mantle fluids accompanying degassing and are composed dominantly of quartz, chlorite, and iron-rich columnar and sheet silicate minerals with characteristic minerals, such as native iron, apatite, and zircon. According to the bulk-rock chemical and mineral compositions and crystallization states, the microcrystalline melt xenoliths are not the product of conventional magmatism, and especially the existence of native iron further proves that the xenoliths were mantle fluid materials under reduction or anoxic conditions. The study of the special xenoliths furnishes an important deep-process geochemical background of polymetallic mineralization in different rocks and strata in the study area. 相似文献
117.
中国东部几个地区新生代玄武岩中单斜辉石—熔体平衡温压—兼论幔源包体的成因 总被引:4,自引:1,他引:4
以中国东部宽甸、汉诺坝和明溪含有幔源包体的新生代玄武岩中的单斜辉石斑(巨)晶为研究对象,采用最新的单斜辉石-熔体平衡温压计对单斜辉石斑(巨)晶-熔体进行了平衡温压计算。结果表明,碱性玄武岩中的单斜辉石斑晶结晶温度和压力高于共生的亚碱性玄武岩中的单斜辉石斑晶,单斜辉石巨晶的结晶温度和压力高于单斜辉石斑晶。这说明碱性玄武岩的形成深度大于亚碱性玄武岩,单斜辉石巨晶是更高压力下的结晶产物,单斜辉石斑晶在岩浆上升的不同深度均有晶出。回归分析表明,尽管携带幔源包体的玄武岩浆上升速度较快,但并不是绝热上升。单斜辉石斑(巨)晶的结晶温压条件与同一地点幔源包体平衡温压条件的对比表明,单斜辉石巨晶和碱性玄武岩中的部分单斜辉石斑(巨)晶的结晶温压大于幔源包体的平衡温压,表明了包体寄主岩浆的来源深度大于包体的深度。因此,幔源包体是寄主岩浆上升途中捕虏的上地幔碎块,而非寄主岩浆形成源区的残留体。 相似文献
118.
119.
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
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
120.
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
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