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41.
中国东部新生代玄武岩及其地幔包体的氧逸度 总被引:1,自引:1,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
42.
G. Franz D. Pudlo G. Urlacher U. Haussmann A. Boven K. Wemmer 《International Journal of Earth Sciences》1994,83(3):614-623
Field investigations, K-Ar age determinations and chemical data were used to describe the development of an intraplate volcanic province, the Darfur Dome, Sudan. Magmatism started 36 Ma ago at a small subvolcanic complex (Jebel Kussa) in the center of the dome and was active in the same area between 26 and 23 Ma. Two major volcanic fields (Marra Mountains and Tagabo Hills) developed between 16 and 10 Ma. Volcanism started again at 6.8 Ma with a third volcanic field (Meidob Hills) and at 4.3 Ma in the Marra Mountains and with the reactivation of the center. Activity then continued until the late Quaternary. Having started in the center of the Darfur Dome, volcanism moved in 36 Ma 200 km towards the NNE and 100 km SSW No essential difference in the alkaline magma types (basanitic to phonolitic-trachytic, with different amounts of assimilation of crustal material) in the different fields, was observed. Magmatism is thought to have been produced by a rising mantle plume and volcanism was triggered by stress resolution along the Central African Fault Zone. 相似文献
43.
板块运动是地幔对流的主要证据之一.同时,作为地球动力系统中一个相对独立部分,板块自身的存在和运动对地幔内部物质的流动形态有巨大影响.地幔内部的流动由两部分组成:一是由内部非绝热温度差异造成的自由对流解;另一部分是由在地表运动的板块所激发.作为系列工作的第一部分,本文研究球腔中的自由热对流问题.得到了对地幔对流研究有实际意义的下边界为自由、上边界为刚性情况下的临界瑞利数值,不同的瑞利数时球腔内流场和温度场的分布形态等. 相似文献
44.
45.
地幔地球化学研究综述 总被引:2,自引:0,他引:2
系统地介绍了近二十年来地幔地球化学在全球及区域地幔平均化学组成,地幔的化学不均一性及区域太产分布,地幔交代作用,化学地球动力学,地幔物理化学环境等五个方面的研究现状与进展。 相似文献
46.
1989年以来,在北天山重点监视区设立了6个地热观测站(3个热水井,3个温泉),采用分辨率为0.0001℃,精度为±0.005℃的石英数字温度计连续记录水温的动态变化。观测结果表明:水温有两类正常动态类型,即稳定动态和年周期动态。4次中强地震前后水温出现明显的异常变化,震后变化更为剧烈。地热前兆异常形态各异,因井泉不同而不同。认为,深入研究活动断裂带和地热异常区的热信息不仅对寻找地震前兆,而且对地震危险区判定具有重要作用。 相似文献
47.
伊通地堑上地幔剪切带 总被引:3,自引:1,他引:3
通过研究糜棱岩型幔源包体的变形显微构造、位错亚构造及组构特征,确定它是上地幔剪切带的代表物质。该带形成温度为729~828℃、压力为1.10~1.38GPa、差异应力为97~150MPa、应变速率为IO ̄(-14)~1O ̄(-12)s ̄(-1)、等效粘滞度为10~1000EPa·s和深度为37~45km。这是一种与地幔底辟作用有关的规模较小的缓倾斜剪切带,也是应变集中带,能导致上地幔地震波速各向异性,并与地震活动有关 相似文献
48.
Sonja Aulbach William L. Griffin Norman J. Pearson Suzanne Y. O’Reilly Buddy J. Doyle 《Contributions to Mineralogy and Petrology》2007,154(4):409-427
Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the
mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate
positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr2O3 contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are
high at a given Al2O3 content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high
olivine Mg# and major-element relationships of FeO-poor peridotites (<7.5 wt%) indicative of melt loss at pressures >3 GPa
(residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration
(∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a
residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites
(>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these
rocks, which are characterised by low SiO2 contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of
melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced
olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by
lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6). 相似文献
49.
We have conducted high-pressure experiments on a natural oceanic gabbro composition (Gb108). Our aim was to test recent proposals
that Sr-enrichment in rare primitive melt inclusions from Mauna Loa, Hawaii, may have resulted from melting of garnet pyroxenite
formed in the magma source regions by reaction of peridotite with siliceous, Sr-enriched partial melts of eclogite of gabbroic
composition. Gb108 is a natural, Sr-enriched olivine gabbro, which has a strong positive Sr anomaly superimposed on an overall
depleted incompatible trace element pattern, reflecting its origin as a plagioclase-rich cumulate. At high pressures it crystallises
as a coesite eclogite assemblage, with the solidus between 1,300 and 1,350°C at 3.5 GPa and 1,450 and 1,500°C at 4.5 GPa.
Clinopyroxenes contain 4–9% Ca-eskolaite component, which varies systematically with pressure and temperature. Garnets are
almandine and grossular-rich. Low degree partial melts are highly siliceous in composition, resembling dacites. Coesite is
eliminated between 50 and 100°C above the solidus. The whole-rock Sr-enrichment is primarily hosted by clinopyroxene. This
phase dominates the mode (>75 wt%) at all investigated PT conditions, and is the major contributor to partial melts of this
eclogite composition. Hence the partial melts have trace element patterns sub-parallel to those of clinopyroxene with ≈10×
greater overall abundances and with strong positive Sr anomalies. Recent studies of primitive Hawaiian volcanics have suggested
the incorporation into their source regions of eclogite, formerly gabbroic material recycled through the mantle at subduction
zones. The models suggest that formerly gabbroic material, present as eclogite in the Hawaiian plume, partially melted earlier
than surrounding peridotite (i.e. at higher pressure) because of the lower solidus temperature of eclogite compared with peridotite.
This produced highly siliceous melts which reacted with surrounding peridotite producing hybrid pyroxene + garnet lithologies.
The Sr-enriched nature of the formerly plagioclase-rich gabbro was present in the siliceous partial melts, as demonstrated
by these experiments, and was transferred to the reactive pyroxenite. These in turn partially melted, producing Sr-enriched
picritic liquids which mixed with normal picritic partial melts of peridotite before eruption. On rare occasions these mixed,
relatively Sr-rich melts were trapped as melt inclusions in primitive olivine phenocrysts.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
50.
Vadim S. Kamenetsky Andrey A. Gurenko 《Contributions to Mineralogy and Petrology》2007,153(4):465-481
The origin of compositional heterogeneities among the magmas parental to mid-ocean ridge basalts (MORB) was investigated using
a single rock piece of the olivine-phyric basalt from 43°N, Mid-Atlantic Ridge (AII D11-177). The exceptional feature of this
sample is presence of very primitive olivine crystals (90–91 mol% Fo) that are significantly variable in terms of CaO (0.15–0.35 wt%).
A population of low-Ca olivine (0.15–0.25 wt% CaO) is also notably distinct from high-Ca olivine population in AII D11-177,
and primitive MORB olivine in general, in having unusual assemblage of trapped mineral and glass inclusions. Mineral inclusions
are represented by high-magnesian (Mg# 90.7–91.1 mol%) orthopyroxene and Cr-spinel, distinctly enriched in TiO2 (up to 5 wt%, c.f. <1 wt% in common MORB spinel). Glass inclusions associated with orthopyroxene and high-Ti Cr-spinel have
andesitic compositions (53–58 wt% SiO2). Compared to the pillow-rim glass and “normal” MORB inclusions, the Si-rich glass inclusions in low-Ca olivine have strongly
reduced Ca and elevated concentrations of Ti, Na, K, P, Cl, and highly incompatible trace elements. Strong variability is
recorded among glass inclusions within a single olivine phenocrysts. We argue that the observed compositional anomalies are
mineralogically controlled, and thus may arise from the interaction between hot MORB magmas and crystal cumulates in the oceanic
crust or magma chamber. 相似文献