榴辉岩的熔融实验及其地质意义     

韩宗珠  谢鸿森  刘振云  盛兴土 《海洋科学》1991,15(1):39-43

在25kb,1300—1400℃条件下对榴辉岩进行的24次熔融实验研究表明,在25kb时榴辉岩的起始熔融温度为1300℃±,从初熔到完全熔融所需的温度间隔小于100℃;随着熔融程度的增高,熔体中SiO_2,TiO_2,K_2O含量显著降低,Al_2O_3含量略有降低,FeO~*(全铁),MgO,CaO含量明显增加。当熔融 程度小于5％时,熔体成分相当于流纹岩;当熔融程度为10—50％时,熔体成分相当于英安岩-安山岩;当熔融程度大于50％时,熔体成分相当于安山玄武岩-玄武岩。推测环太平洋安山岩线的成因及大陆内部安山岩-玄武岩的形成与地幔榴辉岩的熔融有关。  相似文献   

Phase relations and formation of sodium-rich majoritic garnet in the system Mg3Al2Si3O12–Na2MgSi5O12 at 7.0 and 8.5 GPa     

A. V. Bobrov  Yu. A. Litvin  L. Bindi  A. M. Dymshits 《Contributions to Mineralogy and Petrology》2008,156(2):243-257

The pseudo-binary system Mg₃Al₂Si₃O₁₂–Na₂MgSi₅O₁₂ modelling the sodium-bearing garnet solid solutions has been studied at 7 and 8.5 GPa and 1,500–1,950°C. The Na-bearing garnet is a liquidus phase of the system up to 60 mol% Na₂MgSi₅O₁₂ (NaGrt). At higher content of NaGrt in the system, enstatite (up to ∼80 mol%) and then coesite are observed as liquidus phases. Our experiments provided evidence for a stable sodium incorporation in garnet (0.3–0.6 wt% Na₂O) and its control by temperature and pressure. The highest sodium contents were obtained in experiments at P = 8.5 GPa. Near the liquidus (T = 1,840°C), the equilibrium concentration of Na₂O in garnet is 0.7–0.8 wt% (∼6 mol% Na₂MgSi₅O₁₂). With the temperature decrease, Na concentration in Grt increases, and the maximal Na₂MgSi₅O₁₂ content of ∼12 mol% (1.52 wt% Na₂O) is gained at the solidus of the system (T = 1,760°С). The data obtained show that most of natural diamonds, with inclusions of Na-bearing garnets usually containing <0.4 wt% Na₂O, could be formed from sodium-rich melts at pressures lower than 7 GPa. Majoritic garnets with higher sodium concentrations (>1 wt% Na₂O) may crystallize at a pressure range of 7.0–8.5 GPa. However the upper pressure limit for the formation of naturally occurring Na-bearing garnets is restricted by the eclogite/garnetite bulk composition.  相似文献   

Petrogenesis and structural petrology of high-pressure metabasalt pods,Sivrihisar, Turkey     

Peter B. Davis  Donna L. Whitney 《Contributions to Mineralogy and Petrology》2008,156(2):217-241

Lawsonite eclogite pods ranging in size from 3 cm to 6 m occur in lawsonite blueschist and eclogite facies metasedimentary and metabasaltic rocks in the Sivrihisar Massif, Turkey. Some pods have a core of lawsonite eclogite surrounded by alternating, centimeter-scale layers of lawsonite blueschist, eclogite, and transitional eclogite–blueschist, all with similar basaltic bulk composition. These pods also contain texturally late lawsonite-rich veins and layers. Most eclogites and blueschists within the pods lack reaction textures, but some blueschists near pod margins contain texturally complex garnet as well as glaucophane rims on omphacite, suggesting retrogression of eclogite to blueschist. Phase diagrams (pseudosections) calculated for the lawsonite eclogite core of a meter-scale pod indicate that the eclogite equilibrated at ∼22–24 kbar, ∼520°C. Lawsonite eclogite and blueschist at the tectonized margin of the same pod equilibrated at similar temperatures and slightly lower pressures. The composite eclogite–blueschist pod is foliated, lineated, and folded. An earlier generation of lineated omphacite in the pod core has a different spatial orientation than the lineation at the pod margin, although electron backscattered diffraction data show that core and rim omphacite have similar lattice preferred orientation patterns. Petrologic and structural data are consistent with mechanical formation of pods by folding and dissection of eclogite layers at high-P, and localized retrogression at pod margins during initial stages of exhumation at P–T conditions >425°C, 16 kbar.  相似文献   

大别山碧溪岭石榴橄榄岩—榴辉岩体的原岩性质及同位素年代学的启示   总被引：33，自引：5，他引：33  

刘若新  李惠民 《岩石学报》1995,11(3):243-256

碧溪岭橄榄岩一榴辉岩体的原岩为形成於岛弧环境并经受结晶分离作用的镁铁－超镁铁质侵入体。它们形成于２２１０±３９Ｍａ或更早，于８００～１０００Ｍａ时经受超高压变质之后上升于壳幔边界附近，并经受多期次高压退变质作用及韧性变形（６６０～４１０Ｍａ），于２１０～２５０Ｍａ时折返上升至地壳并伴随发生石榴石的重结晶以及随后在地壳条件下榴辉岩的角闪岩化。  相似文献   

安徽岳西碧溪岭榴辉岩及伴生石榴石橄榄岩的岩石学和地球化学   总被引：5，自引：1，他引：5  

韩宗珠  袁棨林  盛兴土 《岩石学报》1989,5(4)

本文对安徽岳西碧溪岭榴辉岩-石榴石橄榄岩伴生岩体作了岩相学、岩石化学、矿物化学及稀土元素地球化学研究。利用湿法化学分析完成了13个榴辉岩和8个石榴石橄榄岩的成分分析,利用电子探针分析了15个石榴石,14个单斜辉石、2个斜方辉石、4个橄榄石的化学组成,利用等离子光谱完成了5个榴辉岩和2个石榴石橄榄岩的稀土元素含量测定,利用地质温压计估算了榴辉岩和石榴石橄榄岩的成岩温度和压力,最后讨论了其物质来源和形成条件。  相似文献   

山东荣城大疃榴辉岩成因岩石学研究   总被引：19，自引：8，他引：19  

叶凯  徐平 《岩石学报》1992,8(1):27-39,T001

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Garnet pyroxenite and eclogite in the Bohemian Massif: geochemical evidence for Variscan recycling of subducted lithosphere   总被引：6，自引：0，他引：6  

L. G. Medaris Jr  B. L. Beard  C. M. Johnson  J. W. Valley  M. J. Spicuzza  E. Jelínek  Z. Mísâr 《International Journal of Earth Sciences》1995,84(3):489-505

High-temperature, high-pressure eclogite and garnet pyroxenite occur as lenses in garnet peridotite bodies of the Gföhl nappe in the Bohemian Massif. The high-pressure assemblages formed in the mantle and are important for allowing investigations of mantle compositions and processes. Eclogite is distinguished from garnet pyroxenite on the basis of elemental composition, with mg number <80, Na₂O > 0.75 wt.%, Cr₂O₃ < 0.15 wt.% and Ni < 400 ppm. Considerable scatter in two-element variation diagrams and the common modal layering of some eclogite bodies indicate the importance of crystal accumulation in eclogite and garnet pyroxenite petrogenesis. A wide range in isotopic composition of clinopyroxene separates [_Nd, +5.4 to –6.0; (⁸⁷Sr/⁸⁶Sr)_i, 0.70314–0.71445; ¹⁸O_SMOW, 3.8–5.8%o] requires that subducted oceanic crust is a component in some melts from which eclogite and garnet pyroxenite crystallized. Variscan Sm-Nd ages were obtained for garnet-clinopyroxene pairs from Dobeovice eclogite (338 Ma), Úhrov eclogite (344 Ma) and Nové Dvory garnet pyroxenite (343 Ma). Gföhl eclogite and garnet pyroxenite formed by high-pressure crystal accumulation (±trapped melt) from transient melts in the lithosphere, and the source of such melts was subducted, hydrothermally altered oceanic crust, including subducted sediments. Much of the chemical variation in the eclogites can be explained by simple fractional crystallization, whereas variation in the pyroxenites indicates fractional crystallization accompanied by some assimilation of the peridotite host.  相似文献   

Deformation inside a paleosubduction channel – Insights from microstructures and crystallographic preferred orientations of eclogites and metasediments from the Tauern Window,Austria     

《Journal of Structural Geology》2016

The Eclogite Zone, of the Tauern Window is an exhumed subduction channel comprising eclogites with different grades of retrogression in a matrix of high-pressure metasediments. The rocks were exposed to 600 °C and 20–25 kbars, and then retrogressed during their exhumation, first under blueschist facies and later under amphibolite facies metamorphism. To gain insights into the deformation within the subduction channel during subduction and exhumation, both fresh and retrogressed eclogites, as well as the surrounding metasediments were investigated with respect to their deformation microstructures and crystallographic preferred orientations (CPOs). Pristine and retrogressed eclogites show grain boundary migration and subgrain rotation recrystallization microstructures in omphacite. A misorientation axes analysis reveals the activity of complementary deformation mechanisms including grain boundary sliding and dislocation creep. The omphacite CPOs of the eclogites correspond to dominant SL-fabrics characteristic of plane strain deformation, though there are local variations towards flattening or constriction within the paleosubduction channel. The glaucophane CPOs in retrogressed eclogites match those of omphacite, suggesting that a constant strain geometry persisted during exhumation at blueschist facies conditions. Plastic deformation of the host high-pressure metasediments outlasted that of the eclogites, as indicated by white mica fabrics and quartz CPO. The latter is consistently asymmetric, pointing to the operation of non-coaxial deformation. The microstructures and CPO data indicate a continuous plastic deformation cycle with eclogite and blueschist facies metamorphism related to subduction and exhumation of the different rock units.  相似文献   

Geochemical signatures of Variscan eclogites from the Saxonian Erzgebirge, central Europe     

Hans-Joachim Massonne  Anita Czambor 《Chemie der Erde / Geochemistry》2007,67(1):69-83

From the abundant metre to km-sized eclogite bodies in the Variscan crystalline complex of the Saxonian Erzgebirge we have investigated 19 samples from the ultrahigh pressure area at the Saidenbach reservoir. Twenty-two samples were from the south-western Erzgebirge, and from occurrences located only some km away from the reservoir. These samples were analysed for major and trace elements using X-ray fluorescence (XRF) spectrometry and inductively coupled plasma mass spectrometry (ICP-MS).The non-Saidenbach eclogites (SiO₂=49–53 wt%) can be derived from N-mid-ocean ridge basalts (MORBs) partially transitional to P-MORBs (e.g., (Nb)_N: 3–36; (Sr)_N: 4–17; (La/Sm)_N<1.5 (in most instances <0.7) and (Sm/Yb)_N around 1.2). Eclogites from the Saidenbach reservoir (SiO₂=49–61 wt%) are characterised by (Nb)_N: 20–170; (Sr)_N: 9–43; (La/Sm)_N: 1.2–3.0; (Sm/Yb)_N: 1.4–8.8, and a clear negative Eu anomaly for the Si-rich samples, thus, being significantly different from the other investigated eclogites. These signatures point to protoliths related to within plate igneous rocks. However, we also discuss the possibilities of (1) protoliths related to a magmatic arc along an active continental margin and (2) the formation by melting of crustal material in the deep mantle and final crystallisation in the lowermost continental crust similar to the adjacent diamondiferous quartzofeldspathic rocks.Due to the specific geochemical signatures of eclogites in the Saidenbach area including other facts, this ultrahigh pressure region is believed to represent a section of lowermost crust not outcropping in other portions of the Saxonian Erzgebirge.  相似文献   

Survival of eclogite xenolith in a Cretaceous granite intruding the Central Dabieshan migmatite gneiss dome (Eastern China) and its tectonic implications   总被引：3，自引：0，他引：3  

Wei Lin  Masaki Enami  Michel Faure  Urs Schärer  Nicolas Arnaud 《International Journal of Earth Sciences》2007,96(4):707-724

Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new ⁴⁰Ar/³⁹Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.  相似文献