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1.
The proposed PT grid of mineral facies of metamorphic rocks, which retains the commonly adopted nomenclature (greenschist, epidote-amphibolite, amphibolite, granulite, glaucophane-schist, and eclogite facies), is based on original calculations and the published calculated and experimental data on mineral equilibria. To validate the facies and subfacies PT boundaries, the mineral equilibria in metapelitic and metabasic rocks have been used.  相似文献   

2.
The paper presents authors’ data on mineral assemblages in rocks of olistostrome melange in the northern part of the Vardar zone in the Fruška Gora Range, Serbia, Balkan Peninsula, which were affected by metamorphism to low grade of the glaucophane-schist facies in relation to Late Jurassic-Early Cretaceous subduction. The olistostrome is dominated by phengite-chlorite-quartz metasandstones and glaucophane-bearing metabasalts, with the latter rocks containing an equilibrium association of zonal riebeckite-glaucophane amphibole, chlorite, pumpellyite, actinolite, and epidote. The Na-amphibole is commonly zonal and has riebeckite cores and glaucophane outermost zones. The metasandstones contain phengite rich in Si (3.45 f.u.) and Mg (0.40 f.u.), which can be formed only under high pressures. The composition of the phengite and the position of glaucophane-pumpellyite-bearing mineral assemblages from the Fruška Gora Range in the P-T grid for low-temperature metabasites indicate that the culmination of subduction-related metamorphism occurred at T − 340–350°C, P = 4−8 kbar, which corresponded to a depth of 14–29 km. Comparison with certain typical glaucophane-bearing complexes shows that the Rbk → Gln zoning of the Na-amphiboles develops in the course of prograde metamorphism. The zoning of Na and Na-Ca amphiboles of the riebeckite-glaucophane-winchite-barroisite series is proved to be, along with zonal garnet crystals, a sensitive indicator of prograde high-pressure transformations in metabasites in the low-temperature region and can be utilized to distinguish between metamorphic zones and subfacies in glaucophane schist complexes.  相似文献   

3.
After the integration of petrographic study, geothermobarometry and Gibbs method, the synthetic P-T paths for the rocks from different geological profiles in the North Qilian, China, have been derived. The composite P-T paths from different methods indicate that all the high-pressure rocks in the Qilian area recorded P-T paths with clockwise loops starting at the blueschist facies, later reaching peak metamorphism at the blueschist facies, eclogite fades or epidote-amphibolite facies and ending up with the greenschist facies. The incremental Ar-Ar dating shows that the plateau ages for the high-pressure rocks range from 410 to 443 Ma. The plateau ages could be used as a minimum age constraint for the subduction that resulted in the formation of these high-pressure rocks in the Qilian area. It is proposed that the late-stage decompressional and cooling P-T paths with ends at the greenschist facies for these high-pressure rocks probably reflect the uplift process which could occur after shifting the arc-t  相似文献   

4.
Rocks of the glaucophane-schist facies are widely though irregularly developed in the Franciscan formation of California. Minerals critical of the facies are lawsonite, aragonite, jadeite and omphacitic pyroxenes associated with quartz; amphiboles of the glaucophane-crossite series are almost ubiquitous. The most widely distributed rock, occurring over areas of many square kilometers, is jadeite-lawsonite metagraywacke, commonly veined with aragonite. More spectacular, but occurring mainly in isolated blocks are coarse-grained glaucophane-lawsonite Schists of many kinds. Commonly, but by no means invariably, they are closely associated with bodies of serpentinite. Also common in the vicinity of serpentinite masses are blocks of amphibolite and eclogite.All the metamorphic rocks are considered to be Franciscan sediments and basic volcanics metamorphosed and metasomatized in the deep levels of a folded geosynclinal prism. Experimental data on the stability fields of jadeite-quartz, aragonite, and lawsonite show that the glaucophane-schist facies represents metamorphism at pressures of between 5 and 10 kb and temperatures of 150–300° C. Such conditions could develop at depths greater than 15 km provided a very low geothermal gradient (10°/km) were maintained. The metagray-wackes are considered to represent a regional response to such conditions.The role of serpentinites in glaucophane-schist metamorphism is discussed in terms of a tentatively proposed model: — In very deep levels — perhaps at depths as great as 30 km, bodies of hot ultramafic magma develop restricted aureoles' in which temperatures of 400–600° C are maintained fer perhaps 100–1000 years. The products of metamorphism, which also involves desilication under the influence of the ultramafic magma, are eclogite and amphibolite. Later, and perhaps at higher levels serpentinization of the now solid ultramafic masses (near 400° C), causes renewed metamorphism at lower grades. Marginal development of glaucophane Schists and prehnite and hydrogarnet rocks, and retrogressive alteration of eclogite and amphibolite to glaucophane-schist assemblages is attributed to this period.  相似文献   

5.
聂树人  贾紫宸 《现代地质》1991,5(1):41-50,T001
本文论述了北祁连含蓝闪石岩的岩石类型、原岩类型、特征矿物组合及产态.区内含蓝闪石岩的原岩包括优地槽内发育的各类富钠火山岩、含富钠火山质的沉积岩。在含蓝闪石岩分布区,岩石的变质相有葡萄石-绿纤石相、蓝闪石—绿片岩相、绿帘石-角闪岩相、铁铝榴石—角闪岩相等,未发现高压低温矿物组合.岩石应属区域动力变质作用产物,并对其形成环境进行了探讨.  相似文献   

6.
Eclogite fades rocks in this area are diverse in rock type. The field occurrence and rock-chemistry reflect theirin-situ origin. Based on their regional geology and field occurrence, two groups of eclogites are divided in terms of their peak temperature of metamorphism. Medium-temperature eclogites (MT), as Group B, occur in the Dabie Group. They were formed from epidote-amphibolite facies. The metamorphism of eclogite facies has two stages: the coesite eclogite facies stage (the peak condition:T = 600 -700°C,P = 2.7-3.0 GPa) and the glaucophane eclogite facies stage (the pressure decreases, may be lower than 2.5 GPa while the temperature has little change). Low temperature eclogites (LT), as Group C, occur in the Qijiaoshan Formation. They were formed from blue schist facies (the peak condition:T = 490–560°C,P< 1.5 GPa). The appearance of hydrous minerals in the eclogites indicates the important role of water in metamorphism. Medium-temperature eclogites are different from low-temperature ones in metamorphism. At last, the evolution of the high-pressure metamorphic belt is discussed as well. This research project was financially supported by the National Natural Science Foundation of China (No. 49372100).  相似文献   

7.
石永红  林伟  王清晨 《地质科学》2007,42(3):518-531
依据对大别山太湖地区宿松变质杂岩中的石榴斜长角闪岩的岩相学、矿物成份分析和P-T条件评价,将变质作用分为Ⅰ、Ⅱ、Ⅲ和Ⅳ4个阶段,其中Ⅰ、Ⅱ阶段经历了绿帘角闪岩相的变质;Ⅲ阶段为峰期变质,变质条件为T=580℃,P=1.31GPa,为角闪石—榴辉岩相变质;Ⅳ阶段为绿片岩相变质。构建的P-T轨迹显示了顺时针的演化特征,反映了宿松变质杂岩分阶段的、不等速的俯冲和折返过程:早期短暂的迅速俯冲→峰期缓慢俯冲→晚期可能的相对缓慢抬升。研究表明宿松变质杂岩的峰期变质条件偏离“俯冲梯度”线,显示了大幅增温、压力变化轻微的特征,这一增温可能是由于受到扰动的热结构恢复所致。结合前人对高压榴辉岩的峰期变质条件的研究,认为宿松变质杂岩与高压-超高压榴辉岩单元至少有0.5GPa的压力差,约15km厚的地壳损失,两者为太湖—马庙断层(F2)所分隔。  相似文献   

8.
《地学前缘(英文版)》2018,9(6):1795-1807
The high-to ultrahigh-pressure metamorphic rocks of the Atbashy complex were petrologically investigated. The eclogites of the Choloktor Formation show a prograde evolution from epidote-blueschist facies(P = 17-21 kbar and T = 450-515 ℃) to peak eclogite-UHP conditions(P = 26-29 kbar and T = 545-615 ℃) with a subsequent epidote-amphibolite and greenschist facies overprint. The micaschists of the Choloktor Formation also show a clockwise P-T path from blueschist/epidote-blueschist facies conditions through peak eclogite facies conditions(P = 21-23 kbar and T = 530-580 ℃) to retrograde epidote-amphibolite and greenschist facies stages. A comparison of the P-T paths in the eclogites and mica-schists of Choloktor Formation reveal that they may have shared their P-T history from peak to retrograde stages. The mica-schists of the Atbashy Formation record peak metamorphism of P = 10-12 kbar and T = 515-565 ℃, which indicates that the highest grade of regional metamorphism in the Atbashy Ridge was epidote-amphibolite facies.The newly obtained P-T conditions for the mica-schists of Choloktor Formation indicate that sheets of sedimentary rocks were brought to great depths along the subduction zone and they metamorphosed under eclogite facies HP conditions. The eclogite blocks were amalgamated with mica-schists of Choloktor Formation in the eclogite facies HP conditions and together they experienced isothermal decompression to ～40 km. During this path, the eclogites and mica-schists of Choloktor Formation docked with mica-schists of Atbashy Formation at 10-12 kbar and 515-565 ℃, and from this depth(～40 km) the whole sequence was exhumed together. These new results improve our understanding of high-pressure metamorphism in subduction-related accretionary prism zones and the exhumation processes of deeply-seated rocks in the Atbashy HP-UHP complex.  相似文献   

9.
The Ordovician volcanic rocks in the Mayaxueshan area have been pervasively altered or metamorphosed and contain abundant secondary minerals such as albite, chlorite, epidote, prehnite, pumpellyite, actinolite, titanite, quartz, and/or calcite. They were denoted as spilites or spilitic rocks in terms of their petrographic features and mineral assemblages. The metamorphic grades of the volcanic rocks are equivalent to that of the intercalated metaclastic rocks. This indicates that both the spilitic volcanic rocks and metaclastic rocks in the Mayaxueshan area have formed as a result of Caledonian regional metamorphism. We suggest that the previously denoted spilitic rocks or altered volcanic rocks should be re-denoted as metabasalts or metabasaltic rocks. The metamorphic grade of the volcanic rocks increases with their age: prehnite-pumpellyite facies for the upper part of the Middle Ordovician volcanic rocks, prehnite-pumpeilyite to lower greenschist facies for the lower part of the Middle Ordovician vol  相似文献   

10.
Paragonite- and garnet-bearing high-grade epidote-amphibolite (PGEA) in the Ise area of the Hida Mountains, Japan is characterized by the high-pressure (HP) epidote-amphibolite facies parageneses (M1), garnet + hornblende + clinozoisite + paragonite + quartz + rutile. Paragonite and garnet of the peak M1 stage are locally replaced by retrograde albite (+ oligoclase) and chlorite (M2), respectively. Phase equilibria constrain peak metamorphic conditions of P = 1.1–1.4 GPa and T = 530–570 °C, and a decompressional P–T path for this rock. Mineral parageneses of prograde epidote-amphibolite facies are comparable to some HP rocks from the Hongan region of western Dabie, but differ from other HP mafic schists with cooling ages of c. 330 Ma in the Hida Mountains. New paragonite K–Ar dating for the PGEA yields a Triassic cooling event at 210 Ma that is coeval with regional cooling and exhumation of the Sulu–Dabie–Qinling (SDQ) belt. Both petrological and geochronological data of the Triassic HP epidote-amphibolite in Hida Mountains support our earlier hypothesis that the SDQ belt extends across the Korean Peninsula to SW Japan.  相似文献   

11.
Gumer Galn  Alberto Marcos 《Lithos》2000,54(3-4):139-171
The high pressure mafic granulites of the Bacariza Formation outcrop in the two uppermost structural units of the Cabo Ortegal Complex (La Capelada unit and Cedeira unit) were separated by a Variscan thrust. In both cases, they appear as heterogeneous metabasites in normal contact between ultramafic rocks and other more homogeneous and less differentiated metabasic rocks, also affected by catazonal metamorphism. The main difference between the mafic granulites in the two units is the degree of deformation, which is higher in the underlying Cedeira unit. Petrologic and mineralogical data indicate that the high-pressure (HP) granulites (Gt-Cpx±Amp-Pl±Qtz±Scp-Rt±Ilm-Czo) are already retrograde (M2 Stage), post-dating an earlier eclogite facies metamorphism (M1 Stage) characterised by the mineral associations: Gt-Cpx±Amp±Ky±Qtz-Rt and Gt-Cpx±Amp±Qtz±Zo-Rt. The main structure related to the exhumation processes is the development of a general mylonitic foliation that, although initiated in granulite facies conditions, was mainly equilibrated in amphibolite facies (M3 Stage). This foliation was affected by isoclinal folds, which led to the formation of the Variscan thrusts responsible for the present stacking position. Thrust conditions were transitional between amphibolite and greenschist facies (M4 Stage). Thermobarometric data point to different P–T exhumation paths in the two units. Estimated P–T conditions were higher in La Capelada unit during M1 (P≥13 kbar; 860°C) and M2 (15 kbar; 800°C) than in the Cedeira unit (M1: P≥11 kbar, 770°C; M2: 12 kbar; 750°C). Temperatures for the M3 stage were comparable (720°C) in both units but rocks from the Cedeira unit show a much bigger drop in pressure. This resulted in an isothermal decompression type path for the Cedeira unit, while both P and T decreased more steadily in La Capelada rocks. These were always located at deeper level than the Cedeira rocks before the Variscan stacking. The difference in the two paths is related to different exhumation rates; higher in rocks from the Cedeira unit than in those from La Capelada. Exhumation processes coeval with underthrusting, and a different location of the rocks with respect to the main shear zone responsible for the exhumation would account for the distinct paths.  相似文献   

12.
Four metasedimentary zircon populations from different tectonometamorphic units of the Central and the Northern Schwarzwald (Variscan belt, SW-Germany) were investigated using SEM, cathodoluminescence and SHRIMP dating. Despite partially strong modifications of primary internal morphologies during Variscan metamorphism at amphibolite (750 °C, 0.4–0.6 GPa) and granulite-facies conditions (950–1,000 °C, 1.4–1.8 GPa), many grains show well-preserved protolith ages. The detritus indicates a northern Gondwana origin and different Palaeozoic episodes of sediment deposition and consolidation. Two of the studied sediments were deposited in Cambrian/early-Ordovician times and consolidated in positions close to northern Gondwana. Late Ordovician and rare Devonian detritus from sediments of two other tectonometamorphic units indicates much later sedimentation close to the leading edge of Gondwana or a terrane assemblage during northern drift towards Laurussia. Subsolidus growth of new zircon due to Variscan granulite facies metamorphism of one of the tectonometamorphic units is precisely dated at 335±2 Ma.Editorial responsibility: J. Hoefs  相似文献   

13.
羌塘中部的高压变质带位于龙木错—双湖—澜沧江板块缝合带之上,由榴辉岩、蓝片岩和石榴石白云母片岩组成。其形成过程对探讨板块缝合带的构造演化具有重要意义。2008年笔者在果干加年山地区的展金岩群湖南山岩组中发现了硬玉石榴石二云母片岩这种新的高压变质岩石类型,文中以其为研究对象,做了较为详细的岩石学、矿物学以及变质作用的研究,认为硬玉石榴石二云母片岩至少经历了二期的变质作用:第一期早期绿片岩相,形成了片理S1,其pT条件为T=425～434℃,p=300～500MPa;第二期主期蓝片岩相高压变质作用,形成岩石主期片理S2,其pT条件为T=472～481℃,p=1200～1700MPa。硬玉石榴石二云母片岩是榴辉岩折返过程中构造事件的产物,这期折返事件形成了218～220Ma的一期蓝片岩相变形-变质作用。  相似文献   

14.
The Malino Metamorphic Complex (MMC) is located at the western end of the north arm of Sulawesi. It consists of mica schists and gneisses (derived from proximal turbidite and granitoid protoliths), with intercalations of greenschist, amphibolite, marble, and quartzite, forming an E-W elongated dome-like structure bounded on all sides by faults. The age of the MMC is constrained between Devonian and Early Carboniferous. This Paleozoic age, the presence of Archean and Proterozoic inherited zircons, and the isotopic signature of the mica schists and gneisses indicate that the terrane was derived from the New Guinea-Australian margin of Gondwana. Similarities with basement rocks in the Bird’s Head suggests a common origin. Greenschists forming a discontinuous selvage (metamorphic carapace) around the complex were derived from adjacent autochthonous Paleogene formations. The rocks of the MMC show a Barrovian-type progression from greenschist through epidote-amphibolite to amphibolite facies. P–T estimations suggest a depth of burial of up to 27–30 km. K/Ar and 40Ar/39Ar cooling ages of 23–11 Ma, and a 7 Ma age for unconformably overlying volcanic rocks, indicate that the complex was exhumed during the Miocene. Two tectonic scenarios are considered: 1. the continental fragment docked with Sulawesi during the Mesozoic and was exhumed as a metamorphic core complex during the Miocene; 2. it was subducted beneath the north arm during the late Oligocene and then rapidly returned back to the surface.  相似文献   

15.
The Taratash Complex (TC) in the northernmost Bashkirian Anticlinorium (Middle Urals) is unique among the pre-Uralian polymetamorphic complexes along the eastern margin of the East European Craton because it experienced granulite facies peak metamorphic conditions (850–900°C/10 kbar). Herein, we constrain the post-granulite facies polystage evolution of the complex, which records various increments of the geodynamic history of the East European continental margin. Formation of granite and migmatite associated with amphibolite facies events are dated at 2,344±29 and 2,044±8 Ma (U–Pb, zircon) in different structural units. At 1,810±41 Ma, the TC was affected by a greenschist facies retrogressive metamorphism which was probably related to a stage of granite formation in the eastern part of the East European Craton. This is confirmed by a U–Pb–zircon age of 1,848±8 Ma obtained from a sheared granite in the adjacent Alexandrovskiy Complex (AC). Greenschist facies shear zones which separate different structural units of the TC formed before 1,350 Ma. Partial re-equilibration of Rb–Sr- and K–Ar-isotope systems between 1,350 Ma and 1,200 Ma is attributed to fluid flow probably induced by anorogenic magmatism in the Bashkirian Anticlinorium. Meso- to Neoproterozoic basaltic dykes indicate that the TC had been exhumed to upper crustal levels at that time. Evidence for a Grenvillian event or for the Timanian orogeny which affected other pre-Uralian complexes in the Urals is lacking. Uralian orogenic shortening and thrusting on Devonian limestones is recorded by shear zones in the AC to the east of the TC and has been dated at 300 Ma (Rb–Sr, 40Ar/39Ar).  相似文献   

16.
豫南熊店高压变质岩块体经历了６期变形和变质作用,即从深地壳层次挤压缩短体制下的不均匀韧性剪切、榴辉岩进变质作用,到中地壳层次挤压体制下的逆冲推覆、钠长绿帘角闪岩相退变质作用,到地壳浅层伸展体制下的脆性—韧性滑脱、绿片岩相变质作用,以及更浅层次的脆性变形,动力变质作用。高压变质岩的形成与向地壳中、浅层次的大幅度抬升均是在挤压机制下韧性变形作用的结果,而高压变质岩暴露到地表是伸展滑脱、断块升降和差异抬升所致。  相似文献   

17.
Five kinds of UHP metamorphic rocks, including eclogite, orthogneiss, paragneiss, schist and quartzite are exposed in the Qinglongshan roadcut, southern Sulu orogenic belt of eastern central China. They comprise metamorphic supracrustal rocks with bimodal volcanic characteristics and continental affinity, and granitic intrusive associations. The preservation of coesite inclusions and/or its pseudomorphs in eclogite and other rocks indicate that they have been subjected to in-situ UHP metamorphism. Four stages of metamorphism were recognized by combining petrographic observations and compositions of minerals from various UHP rocks. Prograde epidote-amphibolite facies, UHP coesite–eclogite facies, post UHP quartz–eclogite facies, and retrograde amphibolite facies assemblages delineate an inferred P–T path with a clockwise trajectory and a retrograde event characterized by the coupling of decompression with a temperature decrease. Garnet porphyroblasts in UHP eclogites display a complex growth zoning and mineral distribution, and record a crucial segment of the prograde and retrograde metamorphic evolution. The preservation of growth zoning in eclogitic and gneissic garnets suggests that the UHP rocks had a short residence time before retrograde metamorphism and a very high uplift rate in order to preserve the prograde growth zoning.  相似文献   

18.
This paper presents new petrologic data for high-pressure, low-temperature (HP–LT) metamorphic rocks at Juisui. We reinterpret the so-called “Tamayen block” (Yang and Wang, 1985) or “Juisui block” (Liou, 1981, Beyssac et al., 2008) as a tectonic mélange. It is not a coherent sheet but rather a mixture dominated by greenschist and pelitic schist with pods of serpentinite, epidote amphibolite, and rare blueschist. Four types of glaucophane-bearing rocks are newly recognized in this mélange. Type I is in contact with greenschist lacking glaucophane and garnet. Glaucophane is present only as rare inclusions within pargasite. This type records metamorphic evolution from epidote blueschists-, epidote amphibolite-, to greenschist-facies. Type II contains characteristic zoned amphiboles from barroisite core to Mg-katophorite mantle and glaucophane rim, implying an epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Type III includes winchite and indicates P–T conditions of about 6–8 kbar, approaching 400 °C. Type IV contains paragonite but lacks garnet; amphibole shows a Na–Ca core surrounded by a glaucophane rim. This type shows a high-pressure (?) epidote amphibolite-facies stage overprinted by an epidote blueschists-facies one. Amphibole zoning trends and mineral assemblages imply contradictory P–T paths for the four types of glaucophane-bearing rocks—consistent with the nature of a tectonic mélange. The new P–T constraints and petrologic findings differ from previous studies (Liou et al., 1975, Beyssac et al., 2008).  相似文献   

19.
HP rocks (eclogites and granulites) occur in the upper unit of the western Iberian allochthonous complexes in Spain and Portugal. This HP metamorphism was considered as Early Variscan or Ordovician in Spain and Precambrian in Portugal. We have dated eclogites retrogressed into granulites in the Bragança massif in NE Portugal by U–Pb on rutile and zircon. The upper intercept of the discordia gives 390±4 Ma that we consider as the age of the HP/HT metamorphism.  相似文献   

20.
The Nevado-Filábride complex is the lowest tectonic unit of the Betic Zone sensu stricto (ss) of the Betic Cordilleras (S.E. Spain). The upper series of this complex consists of a metamorphosed sequence intruded by basic and ultrabasic igneous rocks. High-pressure metamorphism in the eclogite and blueschist facies is recorded in the metabasites, but this was partially obliterated by further successive metamorphic stages in the almandine-amphibolite and greenschist facies.Coronitic and granoblastic eclogites appear side by side in the large stocks of basic rocks. The coronitic eclogites originate from coarse-to medium-grained olivine gabbros, and the granoblastic eclogites from fine-grained basic rocks (dolerites and porphyritic basaltic rocks). Higher chemical mobility and rate of diffusion, as well as the availability of fluids during the eclogite facies metamorphism, are responsible for the greater degree of recrystallization found in the granoblastic eclogites. The availability of fluids during this metamorphic stage was controlled by the difference in the hydration of the protolith and by variable proximity to surrounding water-rich metasediments.The minerals in the eclogites are chemically homogeneous, suggesting that they are almost completely equilibrated, even in the coronitic eclogites. The estimated equilibrium P-T conditions were found to be the same (approximately 550° C at 12 kbar pressure) in both coronitic and granoblastic eclogites, and it has, therefore, been deduced that the coronitic eclogites do not represent the first and lower-grade step of a prograde metamorphism in which the granoblastic eclogites are the higher-grade step.No relationship was found between shearing and eclogite crystallization. Nevertheless, a first fabric/foliation developed in the later blueschist facies stage, and syntectonic growth of the minerals was detected in glaucophane-bearing rocks.The further metamorphic evolution of the metabasites from high-to intermediate-pressure conditions is documented by the formation of minerals belonging to albiteepidote and almandine-amphibolite facies assemblages. The application of the amphibole zonation model, in order to deduce the P-T path, does not give realistic values.High-pressure metamorphism is related to an early subduction event in the Betic Cordilleras, with a later more-or-less isothermal uplift to shallower levels.  相似文献   

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