高压基性麻粒岩与榴辉岩的抬升转换作用--信阳超镁铁质火山角砾岩管的捕虏体研究   总被引：3，自引：0，他引：3  

郑建平  路凤香  钟增球  孙敏 《地球科学》1999,24(4):400-404

通过对华北地块与秦岭-大别造山带结合部位豫南信阳北超基性火山角砾岩管中基性麻粒岩、榴辉岩和石榴石辉石岩捕虏体的岩相学、矿物化学成分的初步研究和对比,发现这些基性岩石捕虏体中大多存在着因抬升降压而发生的转换反应作用.这些转换反应可能与华北地块和秦岭-大别造山带相互作用过程中的抬升过程有关.  相似文献   

中国的榴辉岩   总被引：4，自引：3，他引：1  

徐少康 《化工矿产地质》2004,26(4):193-204

自20世纪90年代,对中国大别山造山带等地榴辉岩的研究,已成为国际地学界关注的热点。榴辉岩形成于高一超高压地质环境,其分布、地质产状、矿物组合、地球化学特征、成岩温压、成岩年龄及相关矿产等具有自身的特点,对其成因尚有地幔捕获说、岩浆说、变质说等不同认识。  相似文献   

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite,Granulitgebirge, Germany     

Alessia Borghini  Silvio Ferrero  Patrick J. O’Brien  Oscar Laurent  Christina Günter  Martin A. Ziemann 《Journal of Metamorphic Geology》2020,38(3):207-234

Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.  相似文献   

Petrogenesis and mantle source characteristics of the late Cenozoic Baekdusan (Changbaishan) basalts,North China Craton     

《Gondwana Research》2020

Late Cenozoic intraplate basaltic rocks in northeastern China have been interpreted as being derived from a mantle source composed of DMM and EM1 components. To constrain the origin of the enriched mantle component, we have now determined the geochemical compositions of basaltic rocks from the active Baekdusan volcano on the border of China and North Korea. The samples show LREE-enriched patterns, with positive Eu and negative Ce anomalies. On a trace element distribution diagram, they show typical oceanic island basalt (OIB)-like LILE enrichments without significant Nb or Ta depletions. However, compared with OIB, they show enrichments in Ba, Rb, K, Pb, Sr, and P. The Nb/U ratios are generally within the range of OIB, but the Ce/Pb ratios are lower than those of OIB. Olivine phenocrysts are characterized by low Ca and high Ni contents. The radiogenic isotopic characteristics (⁸⁷Sr/⁸⁶Sr = 0.70449 to 0.70554; ε_Nd = −2.0 to +1.8; ε_Hf = −1.7 to +6.1; ²⁰⁶Pb/²⁰⁴Pb = 17.26 to 18.12) suggest derivation from an EM1-like source together with an Indian MORB-like depleted mantle. The Mg isotopic compositions (δ²⁶Mg = −0.39 ± 0.17‰) are generally lower than the average upper mantle, indicating carbonates in the source. The ⁸⁷Sr/⁸⁶Sr ratios decrease with decreasing δ²⁶Mg values whereas the ¹⁴³Nd/¹⁴⁴Nd and (Nb/La)_N ratios increase. These observations suggest the mantle source of the Baekdusan basalts contained at least two components that resided in the mantle transition zone (MTZ): (1) recycled subducted ancient (∼2.2–1.6 Ga) terrigenous silicate sediments, possessing EM1-like Sr–Nd–Pb–Hf isotopic signatures and relatively high values of δ²⁶Mg; and (2) carbonated eclogites with relatively MORB-like radiogenic isotopic compositions and low values of δ²⁶Mg. These components might have acted as metasomatizing agents in refertilizing the asthenosphere, eventually influencing the composition of the MTZ-derived plume that produced the Baekdusan volcanism.  相似文献   

Coexisting different types of zoned garnet in kyanite‐quartz eclogites from the Sanbagawa metamorphic belt: Evidence of deformation‐induced lithological mixing during prograde metamorphism     

Masaki Enami  Jun‐Ichi Kimura  Motohiro Tsuboi  Yui Kouketsu  Takayoshi Nagaya  Shuaimin Huang 《Island Arc》2019,28(1)

Garnet grains in Sanbagawa quartz eclogites from the Besshi region, central Shikoku commonly show a zoning pattern consisting of core and mantle/rim that formed during two prograde stages of eclogite and subsequent epidote–amphibolite facies metamorphism, respectively. Garnet grains in the quartz eclogites are grouped into four types (I, II, III, and IV) according to the compositional trends of their cores. Type I garnet is most common and sometimes coexists with other types of garnet in a thin section. Type I core formed with epidote and kyanite during the prograde eclogite facies stage. The inner cores of types II and III crystallized within different whole‐rock compositions of epidote‐free and kyanite‐bearing eclogite and epidote‐ and kyanite‐free eclogite at the earlier prograde stage, respectively. The inner core of type IV probably formed during the pre‐eclogite facies stage. The inner cores of types II, III, and IV, which formed under different P–T conditions of prograde metamorphism and/or whole‐rock compositions, were juxtaposed with the core of type I, probably due to tectonic mixing of rocks at various points during the prograde eclogite facies stage. After these processes, they have shared the following same growth history: (i) successive crystal growth during the later stage of prograde eclogite facies metamorphism that formed the margin of the type I core and the outer cores of types II, III, and IV; (ii) partial resorption of the core during exhumation and hydration stage; and (iii) subsequent formation of mantle zones during prograde metamorphism of the epidote–amphibolite facies. The prograde metamorphic reactions may not have progressed under an isochemical condition in some Sanbagawa metamorphic rocks, at least at the hand specimen scale. This interpretation suggests that, in some cases, material interaction promoted by mechanical mixing and fluid‐assisted diffusive mass transfer probably influences mineral reactions and paragenesis of high‐pressure metamorphic rocks.  相似文献   

CCSD超高压榴辉岩中的水:红外光谱分析     

徐薇  刘祥文  金振民 《地球科学》2006,31(6):830-838

超高压变质岩中名义上无水矿物(NAMs) 在板块俯冲过程中可以携带一部分地表水进入上地幔, 这些水储存于地球深部并对地幔动力学有着重要的影响.对中国大陆科学钻探主孔榴辉岩中的绿辉石和石榴石进行了详细的显微傅立叶变换红外光谱(Micro-FTIR) 分析, 结果显示所有绿辉石和石榴石颗粒都含有结构水, 其水含量范围分别在68~29μg/g和20~75μg/g.榴辉岩全岩的水含量为150~300μg/g.绿辉石和石榴石结构水含量的分布出现2种情况: (1) 颗粒内部的均一分布; (2) 不均匀分布, 表现为水含量从核部到幔部到边部随之增加或水含量核部、边部低而幔部高.电子探针结果表明水含量分布不均与矿物化学成分无直接关系.位错分布不均匀可能导致了颗粒内部结构水分布的不均匀.   相似文献   

榴辉岩型钛矿化的地球化学制约   总被引：1，自引：0，他引：1  

胡建  邱检生  王汝成  李晨曦  倪培  张晓琳 《地质与勘探》2006,42(4):57-61

根据对国内外已发表的榴辉岩地球化学资料的统计分析,表明榴辉岩中TiO2含量与全铁(TFeO)具正相关性,而与MgO, 特别是MgO/(MgO TFeO)比值具负相关性.按TiO2含量的高低,可将榴辉岩区分为高钛型(TiO2＞2.0%)、中钛型(TiO2=0.60%～2.00%)和低钛型(TiO2＜0.6%)三类,文章重点讨论了高钛与低钛榴辉岩地球化学特征的差异.与低钛型榴辉岩相比,高钛型榴辉岩相对偏基性,富铁,贫镁,并具有较高的高场强元素(如Nb、Ta、Zr、Hf等)和亲铁元素(如V、Co、Ni等)含量.原岩恢复显示低钛榴辉岩的源岩有两种类型,其一为洋壳俯冲形成的蛇绿岩残片,另一为富钙质的沉积泥灰岩.高钛型榴辉岩的源岩则具OIB特征,可能为富集地幔部分熔融或上涌的软流圈地幔物质与地壳物质混染的产物.榴辉岩中的钛矿化主要受源岩因素制约,此外,岩浆结晶分异对其也有一定影响.  相似文献   

Isothermal compression of an eclogite from the Western Gneiss Region (Norway)     

Martin Simon  Pavel Pitra  Philippe Yamato  Marc Poujol 《Journal of Metamorphic Geology》2023,41(1):181-203

In the Western Gneiss Region in Norway, mafic eclogites form lenses within granitoid orthogneiss and contain the best record of the pressure and temperature evolution of this ultrahigh-pressure (UHP) terrane. Their exhumation from the UHP conditions has been extensively studied, but their prograde evolution has been rarely quantified although it represents a key constraint for the tectonic history of this area. This study focused on a well-preserved phengite-bearing eclogite sample from the Nordfjord region. The sample was investigated using phase-equilibrium modelling, trace-element analyses of garnet, trace- and major-element thermobarometry and quartz-in-garnet barometry by Raman spectroscopy. Inclusions in garnet core point to crystallization conditions in the amphibolite facies at 510–600°C and 11–16 kbar, whereas chemical zoning in garnet suggests growth during isothermal compression up to the peak pressure of 28 kbar at 600°C, followed by near-isobaric heating to 660–680°C. Near-isothermal decompression to 10–14 kbar is recorded in fine-grained clinopyroxene–amphibole–plagioclase symplectites. The absence of a temperature increase during compression seems incompatible with the classic view of crystallization along a geothermal gradient in a subduction zone and may question the tectonic significance of eclogite facies metamorphism. Two end-member tectonic scenarios are proposed to explain such an isothermal compression: Either (1) the mafic rocks were originally at depth within the lower crust and were consecutively buried along the isothermal portion of the subducting slab or (2) the mafic rocks recorded up to 14 kbar of tectonic overpressure at constant depth and temperature during the collisional stage of the orogeny.  相似文献   

Low temperature eclogite facies rocks discovered in the Eastern Himalayan Syntaxis: Poly-cyclic metamorphic evolution and implications     

Wangchao Li  Changqing Yin  Zeming Zhang  Peter A. Cawood  Shun Li  Jian Zhang  Huixia Ding  Jiahui Qian  Yanling Zhang 《Journal of Metamorphic Geology》2023,41(1):97-119

We report the first occurrence of poly-cyclic high-pressure low-temperature (HP-LT) rocks from the easternmost Indus-Yarlung suture zone, formed during subduction of Neo-Tethyan oceanic lithosphere. Petrology, mineral composition and P–T pseudosection modelling reveal two low-temperature eclogite facies metamorphic events with an initial high-pressure P–T condition of 16.4–18.7 kbar and 510–520°C, exhumation to 10.5–12.0 kbar and 580–590°C and a subsequent second high-pressure P–T condition of ~16 kbar and ~560°C and exhumation to ≤9 kbar and ≤600°C. This history implies a complex ‘yo-yo type’ P–T path. In situ monazite dating and textural relationships show that late-stage exhumation, cooling and garnet breakdown occurred at c. ~25–22 Ma. We interpret the first burial event to represent subduction of the Neo-Tethys Ocean at the eastern Indus-Yarlung suture zone. Initial exhumation, reburial and final exhumation represent material transport in a large-scale convective circulation system in the subduction channel. Convective overturn in the subduction channel evidently serves both as a mechanism to produce poly-cyclic metamorphism and to exhume LT eclogite facies rocks.  相似文献   

大别山菖蒲—碧溪岭地区高压—超高压榴辉岩相变质岩和有关岩石的岩石类型及其原岩性质   总被引：17，自引：2，他引：17       下载免费PDF全文

程裕淇  庄育勋  高天山  简平 《地质学报》2002,76(1):1-13,T001

安徽岳西菖蒲—碧溪岭地区出露两条北北西向的高压—超高压变质岩带:西带由土桥冲至菖蒲水电站,该带由层状硬玉石英岩类、大理岩及少量的石英深色榴辉岩以及浅色榴辉岩等组成;东带由小南山岭至碧溪岭,主要由层状的浅色榴辉岩系列和层状深色榴辉岩系列岩石组成。该区发育的层状浅色榴辉岩和层状的深色榴辉岩两种榴辉岩在岩石组合、矿物组合、矿物成分等方面有明显差别。浅色榴辉岩一般由硬玉质绿辉石(Jd 65～45)、+镁铝以及钙铝端元成分(Pyr+Gro,60±)的石榴子石+蓝晶石±多硅白云母±石英及次生的角闪石、绿帘石组成。其中夹有硬玉质绿辉石石英岩、富蓝晶石岩石、石榴子石岩和硬玉石榴白云片岩等岩石薄层。深色榴辉岩由绿辉石(Jd20～50)±富铁铝端元的石榴子石(Alm 50～60)+金红石±石英及次生的角闪石等组成。石英深色榴辉岩由绿辉石(Jd 40～45)+镁铝端元的石榴子石(Pyr 10～30)+石英+金红石及次生的角闪石、长石组成。深色榴辉岩与石榴橄榄岩分布上紧密相随。浅色榴辉岩的原岩为基性凝灰质沉积岩,相伴随的硬玉石英岩、硬玉岩、白云片岩的原岩大致分别为粉砂岩、长石砂岩、泥质粉砂岩;深色榴辉岩为基性凝灰质熔岩。大理岩的原岩为灰岩。同时,本文的研究表明,在相同的变质作用条件下,榴辉岩相岩石中石榴  相似文献