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1.
The mineralogy of slightly metamorphosed manganese ore at the South Faizulino hydrothermalsedimentary deposit in the southern Urals has been studied; 32 minerals were identified. Quartz, hausmannite, rhodochrosite, tephroite, ribbeite, pyroxmangite, and caryopilite are major minerals; calcite, kutnahorite, alleghanyite, spessartine, rhodonite, clinochlore, and parsettensite are second in abundance. This mineralic composition was formed in the process of gradual burial of ore beneath the sequence of Middle Devonian-Lower Carboniferous rocks. The highest parameters of metamorphism are T ≈ 250°C and P ≈ 2.5 kbar. The relationships between minerals and their assemblages made it possible to reconstruct the succession of ore transformation with gradually increasing temperature and pressure. Manganese accumulated in the initial sediments as oxides and a gel-like Mn-Si phase. Rhodochrosite and neotocite were formed at the diagenetic stage. In the course of a further increase in temperature and pressure, neotocite was replaced with caryopilite; ribbeite, tephroite, pyroxmangite, and other silicates crystallized afterwards. In addition to the PT parameters, the formation of various metamorphic mineral assemblages was controlled by the Mn/(Mn + Si) ratio in ore and X CO2 in pore solution. The latter parameter was determined by the occurrence of organic matter in the ore-bearing rocks. Ore veinlets as products of local hydrothermal redistribution of Mn, Si, and CO2 were formed during tectonic deformations in the Middle Carboniferous and Permian.  相似文献   

2.
Melt loss and the preservation of granulite facies mineral assemblages   总被引：29，自引：3，他引：29  
The loss of a metamorphic fluid via the partitioning of H2O into silicate melt at higher metamorphic grade implies that, in the absence of open system behaviour of melt, the amount of H2O contained within rocks remains constant at temperatures above the solidus. Thus, granulite facies rocks, composed of predominantly anhydrous minerals and a hydrous silicate melt should undergo considerable retrogression to hydrous upper amphibolite facies assemblages on cooling as the melt crystallizes and releases its H2O. The common occurrence of weakly retrogressed granulite facies assemblages is consistent with substantial melt loss from the majority of granulite facies rocks. Phase diagram modelling of the effects of melt loss in hypothetical aluminous and subaluminous metapelitic compositions shows that the amount of melt that has to be removed from a rock to preserve a granulite facies assemblage varies markedly with rock composition, the number of partial melt loss events and the P–T conditions at which melt loss occurs. In an aluminous metapelite, the removal of nearly all of the melt at temperatures above the breakdown of biotite is required for the preservation of the peak mineral assemblage. In contrast, the proportion of melt loss required to preserve peak assemblages in a subaluminous metapelite is close to half that required for the aluminous metapelite. Thus, if a given proportion of melt is removed from a sequence of metapelitic granulites of varying composition, the degree of preservation of the peak metamorphic assemblage may vary widely.  相似文献   

3.
The paper describes mineralogy of the low grade metamorphosed manganese sediments, which occur in sedimentary complexes of the Pai Khoi Ridge and the Polar Urals and volcanosedimentary complexes of the Central and South Urals. The degree of metamorphism of the rocks studied corresponds to PT conditions of the prehnite–pumpellyite (deposits of Pai Khoi and Polar and South Urals) and green schist (deposits of the Central Urals) facies. One hundred and nine minerals were identified in the manganese-bearing rocks on the basis of optical and electron microscopy, X-ray diffraction, and microprobe analysis. According to the variations in the amount of major minerals of the manganese rocks of the Urals, they are subdivided on carbonate (I), oxide–carbonate–silicate (II), and oxide–silicate (III) types. Carbonates, various Mn2 +-bearing silicates associated with oxides and carbonates, and braunite (Mn3 +-bearing silicate) are the major Mn hosts in types I, II, and III, respectively. Because of the different oxidation state of Mn, the rocks of types I and II are termed as “reduced” and the rocks of type III, as “oxidized”. The formation of a certain mineralogical type of metamorphic assemblage is controlled by the content of organic matter in the primary sediments. The sequence type I → type II → type III reflects the decrease in the amount of organic matter in metalliferous sediments. Mineralogical data indicate that manganese in the primary sediments accumulated in a silicate form (MnSi gel, glass, etc). During diagenesis, the Mn–Si phase was transformed to neotokite with subsequent formation of caryopilite and further crystallization of pyroxmangite, rhodonite, tephroite, and other silicates due to reactions involving caryopilite. The hydrated Mn-silicates (caryopilite and/or friedelite) and the spatially associated parsettensite, stilpnomelane, and other minerals are the index minerals of the low grade metamorphism. Under PT conditions of prehnite–pumpellyite facies, nearly 70% of silicate minerals are hydrous. The metamorphosed Mn-bearing sediments are characterized by the low-temperature caryopilite (or tephroite-caryopilite-pyroxmangite ± rhodonite) and the high-temperature caryopilite-free (or tephroite-pyroxmangite ± rhodonite) facies. Their PT conditions correspond to zeolite and prehnite-pumpellyite (the low-temperature) and green schist and higher grade (the high-temperature) facies.  相似文献   

4.
A mineralogical investigation of metamorphosed manganese rocks was carried out at ore deposits related to the Devonian volcanic complexes of the Magnitogorsk paleovolcanic belt of the South Urals. The mineralogical appearance of these rocks is determined by three consecutively formed groups of mineral assemblages: (1) assemblages occupying the main volume of orebodies and formed during low-grade regional metamorphism (T = 200−250°C, P = 2–3 kbar); (2) assemblages of segregated and metasomatic veinlets that fill the systems of late tectonic fractures; and (3) assemblages of near-surface supergene minerals. Sixty-one minerals have been identified in orebodies and crosscutting hydrothermal veinlets. The major minerals are quartz, hematite, hausmannite, braunite, tephroite, andradite, epidote, rhodonite, caryopilite, calcite, and rhodochrosite. The mineral assemblages of metamorphosed manganese rocks (metamanganolites) are characterized. Chemical compositions of braunite, epidote-group minerals, piemontite, pyroxenes, rhodonite, pyroxmangite, and winchite are considered. The bibliography on geology and mineralogy of the South Ural manganese deposits is given.  相似文献   

5.
Abstract Dehydration-melting reactions, in which water from a hydrous phase enters the melt, leaving an anhydrous solid assemblage, are the dominant mechanism of partial melting of high-grade rocks in the absence of externally derived vapour. Equilibria involving melt and solid phases are effective buffers of aH2,o. The element-partitioning observed in natural rocks suggests that dehydration melting occurs over a temperature interval during which, for most cases, aH2o is driven to lower values. The mass balance of dehydration melting in typical biotite gneiss and metapelite shows that the proportion of melt in the product assemblage at T± 850°C is relatively small (10–20%), and probably insufficient to mobilize a partially melted rock body. Granulite facies metapelite, biotite gneiss and metabasic gneiss in Namaqualand contain coarse-grained, discordant, unfoliated, anhydrous segregations, surrounded by a finer grained, foliated matrix that commonly includes hydrous minerals. The segregations have modes consistent with the hypothesis that they are the solid and liquid products of the dehydration-melting reactions: Bt + Sil + Qtz + PI = Grt ° Crd + Kfs + L (metapelite), Bt + Qtz + Pl = Opx + Kfs + L (biotite gneiss), and Hbl + Qtz = Opx + Cpx + Pl + L (metabasic gneiss). The size, shape, distribution and modes of segregations suggest only limited migration and extraction of melt. Growth of anhydrous poikiloblasts in matrix regions, development of anhydrous haloes around segregations and formation of dehydrated margins on metabasic layers enclosed in migmatitic metapelites all imply local gradients in water activity. Also, they suggest that individual segregations and bodies of partially melted rock acted as sinks for soluble volatiles. The preservation of anhydrous assemblages and the restricted distribution of late hydrous minerals suggest that retrograde reaction between hydrous melt and solids did not occur and that H2O in the melt was released as vapour on crystallization. This model, combined with the natural observations, suggests that it is possible to form granulite facies assemblages without participation of external fluid and without major extraction of silicate melt.  相似文献   

6.
Mn silicate-carbonate rocks at Parseoni occur as conformable lenses within metapelites and calc-silicate rocks of the Precambrian Sausar Group, India. The host rocks are estimated to have been metamorphosed at uppermost P-T conditions of 500–550°C and 3–4 kbar. The Mn-rich rocks contain appreciable Fe, reflected in the occurrence of magnetite(1) (MnO 1%), magnetite(2) (MnO 15%) and magnetite(3) (MnO 10%). Two contrasting associations of pyroxmangite, with and without tephroite, developed in the Mn silicate-carbonate rocks under isothermal-isobaric conditions. The former assemblage formed in relatively Fe-rich bulk compositions and equilibrated with a metamorphic fluid having a low X CO 2 (<0.2), and the latter equilibrated with a CO2-rich fluid. Rhodochrosite+magnetite(1)+quartz protoliths produced the observed mineral assemblages on metamorphism. Partitioning of major elements between coexisting phases is somewhat variable. Fe shows preference for tephroite over pyroxmangite at the ambient physical conditions of metamorphism. Oxygen fugacity during metamorphism was monitored at or near the QFM buffer in tephroite bearing domains, and the fluid composition was buffered by mineral reactions in respective domains. As compared to other metamorphosed Mn deposits of the Sausar Group, the Mn silicate-carbonate rocks at Parseoni were, therefore, metamorphosed at much lower f O 2 through complex mineral-fluid interactions.  相似文献   

7.
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8.
Granite- and gabbrodiorite-associated skarn deposits of NW Iran   总被引：1，自引：0，他引：1  
Field and laboratory studies show that there are two types of skarn deposits in NW Iran: granite-associated (type I) and gabbrodiorite-associated (type II). Granite-associated deposits are accompanied by Cu and Fe mineralisation, whereas Mn and Fe are the main ore metals in gabbrodiorite-associated skarn deposits. There are some differences in the mineralogy of these skarn deposits. Bixbyite, piemontite and Cr-bearing garnet are found only in gabbrodiorite-associated skarns, whereas idocrase occurs only in granite-associated deposits. Type II skarns show exoskarn features, whereas some type I skarns have developed endoskarn as well. Evidence of boiling of hydrothermal fluid can be seen in both types and seems to be a common mechanism of mineral deposition. Gabbrodiorite-associated skarns show higher fO2 than granite-associated deposits. Based on mineralogical and textural evidence, mineralisation in both groups has started from about 550 °C. Early formed anhydrous minerals have begun to be replaced by hydrous minerals from about 400 °C.It seems that due to low fluid content in the gabbrodioritic magma, heated meteoritic water in the surrounding volcanoclastic and tuffaceous rocks was the main source of hydrothermal solution in the gabbrodiorite-associated skarn system.  相似文献   

9.
Based on mineral assemblages and compositions in metamorphic marly rocks of the Western Hohe Tauern, the effect of Fe-Mg substitution on previously deduced phase relations in a simplified marly rock system (Hoschek 1980) is estimated. Fe-Mg partitioning in coexisting minerals is influenced, amongst others, by the F-OH substitution. Calculations with extrapolated mean K D Fe-Mg values for F-free minerals and with the assumption of ideal Fe-Mg solid solution show similar effects of the Fe-Mg and the F-OH substitution on phase relations. The consideration of the Fe2+ and F distribution leads to a better compatibility between experimentally determined mineral stabilities and observed mineral assemblages in the marly rocks of the Western Hohe Tauern.  相似文献   

10.
The metabasites were originally minor intrusions which are now characterised by wholly metamorphic textures and mineral assemblages diagnostic of an amphibolite-granulite facies transition. Two forms of chemical variation can be distinguished: (1) an igneous-type differentiation, involving tholeiitic iron enrichment accompanied by increases in some incompatible elements, and decreases in the transition trace elements; (2) metamorphic fractionation effects resulting in deficiencies in K, Rb, Sr, Ba, Zr, and enhancement in Na in the highest grade rocks. These distributions closely parallel those in the host acid-intermediate charnockitic gneisses. The data preclude the possibility that the deficiencies were caused by removal of melts from the granulites. The metamorphism closely followed intrusion, and it is unlikely that the fractionations were caused by secondary dehydration of once hydrous assemblages. The preferred model involves intrusion and crystallisation directly under high-grade conditions, possibly with CO2-rich fluids playing an important role in suppressing the formation of hydrous minerals.  相似文献   

11.
The Motuo area is located in the east of the Eastern Himalayan Syntaxis. There outcrops a sequence of high-grade metamorphic rocks, such as metapelites. Petrology and mineralogy data suggest that these rocks have experienced three stages of metamorphism. The prograde metamorphic mineral assemblages(M1) are mineral inclusions(biotite + plagioclase + quartz ± sillimanite ± Fe-Ti oxides) preserved in garnet porphyroblasts, and the peak metamorphic assemblages(M2) are represented by garnet with the lowest XSps values and the lowest XFe# ratios and the matrix minerals(plagioclase + quartz ± Kfeldspar + biotite + muscovite + kyanite ± sillimanite), whereas the retrograde assemblages(M3) are composed of biotite + plagioclase + quartz symplectites rimming the garnet porphyroblasts. Thermobarometric computation shows that the metamorphic conditions are 562–714°C at 7.3–7.4 kbar for the M1 stage, 661–800°C at 9.4–11.6 kbar for the M2 stage, and 579–713°C at 5.5–6.6 kbar for the M3 stage. These rocks are deciphered to have undergone metamorphism characterized by clockwise P-T paths involving nearly isothermal decompression(ITD) segments, which is inferred to be related to the collision of the India and Eurasia plates.  相似文献   

12.
翟明国  从柏林 《岩石学报》1995,11(3):257-272
蓝晶石在大别山含柯石英和不含柯石英的榴辉岩、高压变质的副片麻岩、非高压变质的宿松群的变质沉积岩中都是重要的变质矿物。它们多有冠状或其它的变质反应结构，形成多样化的退变质反应矿物。有些退变质反应是十分罕见的。本文报道了８种蓝晶石的矿物组合和退变质反应，推测和计算了变质反应的温度－压力条件，从而探讨了它们代表的近等温降压、升温降压和流体为重要因素的降温降压的不同的动力学过程。这些数据与用其它变质矿物所得到的温度压力条件和ＰＴｔ演化基本一致。为探讨大别山超高压变质带的构造演化提供了新的依据。  相似文献   

13.
陈仁旭  郑永飞  龚冰 《岩石学报》2011,27(2):451-468
对超高压变质岩中含水矿物和名义上无水矿物的地球化学研究,极大地深化了我们对大陆碰撞带地壳俯冲和折返过程中流体体制的认识。就流体体制和化学地球动力学来说,有关研究在大别-苏鲁造山带进行的最为详细,因此已经成为研究大陆俯冲带变质的典型地区。本文以大别-苏鲁造山带为对象,从矿物水含量的角度,结合稳定同位素论述了大陆俯冲带流体活动。超高压变质岩中名义上无水矿物含有大量的水,以结构羟基和分子水形式存在。名义上无水矿物中结构羟基和分子水出溶与含水矿物分解共同构成了折返过程中退变质流体的主要来源。名义上无水矿物所释放的水以富集轻的氢氧同位素为特征,而含水矿物分解则提供了富集D的流体来源。折返过程中,名义上无水矿物降压脱水存在亏损D的分子水的优先丢失和不同形式水之间的相互转化。不同岩性的水含量差异导致了它们在折返过程中不同的流体活动行为。大陆板块俯冲和折返过程中,在不同矿物、不同岩性以及板片不同部位之间存在水的再分配;板片的一部分作为富水流体的源,而另一部分可能作为汇。  相似文献   

14.
A detailed petrological analysis of the marble assemblages observed within the M2 metamorphic complex on Naxos is presented. Two distinct periods of mineral growth are documented; the first is associated with prograde M2 metamorphism and the second with retrograde M2 metamorphism occurring during ductile extensional thinning of the complex. The textural and miner-alogical characteristics and the carbon and oxygen isotope compositions of each generation are described, and the P-T-X CO 2 conditions at which these two mineral generations were stable, and the compositions of the fluids present during metamorphism are characterised. Whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution, the retrograde mineral generation is shown to have grown as a result of the infiltration of a water-rich fluid phase that transported silica, Al2O3, Na2O and FeO into the host rocks. This observation, together with the stable isotope compositions of the retrograde calcite, and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas (T>600° C) of the metamorphic complex, suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures. The existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on Naxos, because many of the unusually low 18O compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde M2 fluids, rather than with prograde fluids.  相似文献   

15.
The Pahnavar calcic Fe-bearing skarn zone is located in the Eastern Azarbaijan (NW Iran). This skarn zone occurs along the contact between Upper Cretaceous impure carbonates and an Oligocene granodioritic batholith. The skarnification process can be categorized into two discrete stages: prograde and retrograde. The prograde stage began immediately after the initial emplacement of the granodioritic magma into the enclosing impure carbonate rocks. The effect of heat flow from the batholith caused the enclosing rocks to become isochemically marmorized in the pure limestone layers and bimetasomatized (skarnoids) in the impure clay-rich carbonates. Segregation and evolution of an aqueous phase from the magma that infiltrated to the marbles and skarnoids through fractures and micro-fractures took place during the emplacement of magma. The influx of Fe, Si and Mg from the granodiorite to the skarnoids and marbles led to the crystallization of anhydrous calc-silicates (garnet and pyroxene). The retrograde stage can be divided, in turn, into two distinct sub-stages. During earliest sub-stage, the previously formed skarn assemblages were affected by intense hydro-fracturing; in addition, Cu, Pb, Zn, along with H2S and CO2 were added. Consequently, hydrous calc-silicates (epidote and tremolite-actinolite), sulfides (pyrite, chalcopyrite, galena and sphalerite), oxides (magnetite and hematite) and carbonates (calcite) deposited the anhydrous calc-silicates. The late-retrograde sub-stage was due the incursion of colder oxidizing fluids into the skarn system, causing the alteration of the previously formed calc-silicate assemblages and the development of fine-grained aggregates of chlorite, illite, kaolinite, hematite and calcite. The lack of wollastonite in the mineral assemblage, along with the garnet-clinopyroxene paragenesis, suggests that the prograde stage formed under temperature and fO2 conditions of 430?C550°C and 10?26?C10?23, respectively.  相似文献   

16.
Garnet-bearing metapelites and amphibolites are exposed in the south and middle parts of the Zanhuang complex, which is located in the central segment of the nearly NS-striking Trans-North China Orogen. These rocks preserve three metamorphic mineral assemblages forming at the prograde, peak and post-peak decompression stages. The prograde metamorphic stage (M1) is represented by mineral inclusions within garnet porphyroblasts, the peak metamorphic stage (M2) is represented by garnet rims and matrix minerals, whereas the retrograde stage (M3) is represented by amphibole + plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite + plagioclase symplectite rimming garnet porphyroblasts in the metapelites. All garnet porphyroblasts in the metapelites preserve prograde chemical zoning except for the ubiquitous, quite narrow zones from the underwent post-peak decompression. It has been determined through thermobarometric computation that the metamorphic conditions are 650–710°C at 8.2−9.2 kbar for the M1 (inclusion) assemblages, >810°C at >12.5 kbar for the metamorphic peak M2 (matrix) assemblages, and 660–680°C at 4.4–4.5 kbar for the retrograde M3 (symplectite) assemblages. These rocks are thus determined to have undergone metamorphism with clockwise P–T paths involving nearly isothermal decompression (ITD) segments, which is inferred to be related to the amalgamation of the Eastern and Western Blocks to form the coherent basement of the North China Craton along the Trans-North China Orogen in the late Paleoproterozoic (1.88–1.85 Ga).  相似文献   

17.
The preservation of mineral assemblages that were fluid‐present during their prograde history is primarily related to the consumption of the fluid by growth of more hydrous minerals as the retrograde history begins. The range of behaviour relating to the preservation of mineral assemblages is examined using calculated phase diagrams for fluid‐saturated conditions, contoured for the H2O content of the mineral assemblage. At equilibrium, as a mineral assemblage crosses contours of decreasing H2O content along a pressure–temperature path, it dehydrates, the fluid being lost from the rock. If the assemblage crosses contours of increasing H2O content, the mineral assemblage starts to rehydrate using any fluid on its grain boundaries. When the rock has consumed its fluid, the resulting mineral assemblage is that preserved in the rock. Conditions relating to the preservation of mineral assemblages are discussed, and examples of the consequences of different pressure–temperature paths on preservation in a metapelitic and a metabasic rock composition are considered on phase diagrams calculated with thermocalc .  相似文献   

18.
田作林  张泽明  董昕 《岩石学报》2020,36(9):2616-2630
变质相平衡模拟是变质岩领域近几十年最重要的进展之一，它已经成为确定变质作用P-T-t轨迹和探索变质演化过程的有力工具。变质岩的矿物组合不但与其形成的温度（T）和压力（P）条件有关，而且受控于岩石的全岩成分（X）。但是变质岩通常是不均匀的并且往往保留两期以上的矿物组合，因此计算不同成分域或不同变质演化期次的有效全岩成分是模拟P-T视剖面图的核心问题之一。在中-低温变质岩中，石榴石变斑晶的生长会不断地将其核部成分"冻结"而不参与后续变质反应，这导致根据实测全岩成分计算的P-T视剖面图无法有效地模拟石榴石幔部或边部生长阶段的变质演化过程。"瑞利分馏法"和"球体积法"利用电子探针实测的石榴石成分环带可以模拟计算石榴石各个生长阶段所对应的有效全岩成分，本文推荐使用这两个方法来处理石榴石变斑晶的分馏效应问题。相比较而言，石榴石在高温变质岩中通常无法保留生长阶段的成分环带特征，这是因为石榴石成分在高温条件下会发生扩散再平衡，并同时与多数基质矿物达到热力学平衡，这时一般不需要考虑石榴石的分馏效应。但是高温变质岩通常会发生部分熔融并伴随熔体的迁移，进而改变岩石的有效全岩成分。因此，通过P-T视剖面图模拟熔体迁移前后的变质演化过程需要使用"相平衡法"计算迁移的熔体成分以及熔体迁移前后岩石的有效全岩成分。此外，后成合晶与反应边是变质岩中最常见的退变质反应结构，但是后成合晶或反应边中的矿物之间并未达到热力学平衡。这种情况需要结合岩相学观察和矿物成分，利用最小二乘法确定后成合晶或反应边中发生的平衡反应方程式，进而获取变质反应发生时的有效全岩成分并通过计算P-T视剖面图来估算退变质的温压条件。除此之外，岩石体系中三价铁（Fe2O3）和H2O含量的估算一直以来都是相平衡模拟研究中的难点，本文推荐使用P/T-X（Fe3+/Fetot，MH2O）视剖面图来确定这两个组分的含量，这是因为P/T-X图可以估算各个变质演化阶段或特定矿物组合的Fe2O3或H2O含量。  相似文献   

19.
The Archaean lode-gold deposits at Norseman, Western Australia, consist of auriferous quartz veins in dextral-reverse ductile-brittle shear zones within tholeiitic metabasalts of upper-greenschist to amphibolite facies metamorphic grade. Three types of deposits (Northern, Central, Southern) are delineated on the basis of their spatial distribution, veining style, alteration mineraloty and metamorphic grade of host rocks. Northern deposits, hosted in upper-greenschist to lower-amphibolite facies rocks, comprise massive to laminated quartz veins with selvedges of quartz-chlorite-calcite-biotite-plagioclase assemblages. Central deposits, hosted in lower-amphibolite facies rocks, consist of laminated to massive quartz veins with selvedges of quartz-actinolite-biotite-plagioclasecalcite assemblages. Southern deposits, hosted in middleamphibolite facies metabasalts, consist of banded quartz-diopside-calcite-microcline-zoisite veins. All deposits exhibit variable ductile deformation of veins and contiguous alteration haloes, consistent with a syn-deformational genesis at high temperatures. From Northern to Southern deposits, the alteration assemblages are indicative of higher temperatures of formation, and there are progressively greater degrees of dynamically recovered textures in alteration and gangue minerals. These observations imply that a thermal variation of gold-related hydrothermal alteration exists within the Norseman Terrane over a distance of 40 km, with TNorthern<TCentral<TSouthern This thermal zonation is corroborated by T−XCO 2 phase relations between vein selvedge assemblages, which signify formation temperatures of approximately 420°–475°C, 470°–495°C and >500°C for Northern, Central and Southern deposits, respectively. The sum of structural, petrographic and mineral chemistry data indicates that the alteration assemblages formed in high-temperature, open hydrothermal systems and have not been subsequently metamorphosed. The thermal differences between the deposit groups may reflect (1) a temperature gradient, at relatively constant P, corresponding to the proximity of the deposits to regional granitoid complexes, or (2) formation of the deposits at progressively deeper crustal levels from north to south. In either case the deposits represent a continuum of gold deposition from upper-greenschist to amphibolite facies, now exposed in an oblique section through the Archaean crust at Norseman.  相似文献   

20.
麻粒岩的研究进展与方法   总被引：2，自引：0，他引：2  
近年来,有关麻粒岩的研究取得了长足进展,本文讨论了4个相关问题:(1)麻粒岩的大地构造环境与P-T轨迹.麻粒岩可以形成于4种大地构造环境中:(a)碰撞造山带以形成高压麻粒岩为特征,为中压相系,包括曾位于地壳浅部的岩石经历构造埋深达到变质峰期后再折返的过程,为顺时针型P-T轨迹;也包括曾经历洋壳或陆壳俯冲形成的高压-超高...  相似文献   

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