和田玉、玛纳斯碧玉和岫岩老玉的产地特征

本文用电子探针研究了和田玉、玛纳斯碧玉和岫岩老玉的矿物成分,结果表明和田玉的主要矿物成分是透闪石,玛纳斯碧玉是阳起石,而岫岩老玉则由透闪石和阳起石组成,并论述了它们的产地特征.     

Pumpellyite–actinolite facies of the Sanbagawa metamorphism

The pumpellyite–actinolite facies proposed by Hashimoto is defined by the common occurrence of the pumpellyite–actinolite assemblage in basic schists. It can help characterize the paragenesis of basic and intermediate bulk compositions, which are common constituents of various low-grade metamorphic areas. The dataset of mutually consistent thermodynamic properties of minerals gives a positive slope for the boundary between the pumpellyite–actinolite and prehnite–pumpellyite facies in P–T space. In the Sanbagawa belt in Japan, the mineral parageneses of hematite-bearing and -free basic schists, as well as pelitic schists have been well documented. The higher temperature limit of this facies is defined by the disappearance of the pumpellyite+epidote+actinolite+chlorite assemblage in hematite-free basic schists with X_Fe3+ of epidote around 0.20–0.25 and the appearance of epidote+actinolite+chlorite assemblage with X^Ep_Fe3+≤0.20. In hematite-bearing basic schists, there is a continuous change of paragenesis to higher grade, epidote–glaucophane or epidote–blueschist facies. In pelitic schists, the albite+lawsonite+chlorite assemblage does occur but only rarely, and its assemblage cannot be used to determine the regional thermal structure. The lower temperature equivalence of the pumpellyite–actinolite assemblage is not observed in the field. The Mikabu Greenstone complex and the northern margin of the Chichibu complex, which are located to the south of the Sanbagawa belt, are characterized by clinopyroxene+chlorite or lawsonite+actinolite assemblages, which are lower temperature assemblages than the pumpellyite+actinolite assemblage. These three metamorphic complexes belong to the same subduction-metamorphic complex. The pumpellyite–actinolite facies or subfacies can be useful to help reveal the field thermal structure of metamorphic complexes     

Amphibolitization of metagabbros in the Scottish Highlands

Abstract Compositions of actinolite, hornblende and cummingtonite, together with pyroxene and plagioclase, are studied in basic intrusions in the Dalradian of north-east Scotland, and the Glen Scaddle complex in the West Moine. Amphibolitization is due to influx of water from the country rocks. Pyroxene compositions are found to have adjusted to the regional metamorphic environment. Owing to the difficulty of diffusion of Al and Si, calcic amphiboles are zoned and commonly contain quartz blebs. Discontinuities in zoning give rise to actinolite-hornblende pairs. Compared with north-east Scotland, disequilibrium is less strong in the Glen Scaddle area: in the latter, plagioclase compositions have been greatly changed, Na partition between hornblende and plagioclase is close to equilibrium, the maximum Al content of hornblende is lower and zoning patterns are more consistent. The Fe/Mg ratio in calcic amphiboles varies with Al content, while approaching equilibrium partition with other minerals. Both zoning patterns and Fe/Mg partition with cummingtonite suggest that Fe/Mg of the calcic amphiboles increases more strongly with increasing (Al^vi+Fe³⁺) than can be explained simply by substitution of Al,Fe³⁺ for Mg on M2. Model reactions for amphibole formation are constructed. Cummingtonite formed at lower chemical potential of CaO than actinolite: Ca was exchanged for Mg,Fe between orthopyroxene-derived and clinopyroxene-derived local systems. Both cummingtonite and actinolite were formed because of kinetic constraints, as intermediate reaction products: actinolite-hornblende pairs represent disequilibrium. This work suggests that many occurrences of actinolite with hornblende, where the minerals are zoned, may also be due to diffusion kinetics.     

Exhumation of the Dayman dome metamorphic core complex, eastern Papua New Guinea

The ～750 km² Dayman dome of the Late Cretaceous Suckling‐Dayman massif, eastern Papua New Guinea, is a domed landform that rises to an elevation of 2850 m. The northern edge of the dome is a fault scarp >1000 m high that is now part of an active microplate boundary separating continental crust of the New Guinea highlands from continental and oceanic crust of the Woodlark microplate. Previous work has shown that a parallel belt of eclogite‐bearing core complexes north‐east of the Dayman dome were exhumed from up to 24–28 kbar in the last few millions of years. The remarkably fresh and lightly eroded scarp of the Dayman dome exposes shallowly‐dipping mylonitic (S1) metabasite rocks (500 m thick) on the northern flank of Mount Dayman. Field relationships near the base of this scarp show a cross cutting suite of ductile and brittle meso‐structures that includes: (i) rare ductile S2 folia with a shallowly ESE‐plunging mineral elongation lineation defined by sodic‐calcic blue amphibole; (ii) narrow steeply‐dipping ductile D2 shear zones; and (iii) semi‐brittle to brittle fault zones. Pumpellyite‐actinolite facies assemblages reported by previous workers to contain local aragonite, lawsonite and/or glaucophane are found in the core of the complex at elevations greater than 2000 m. These assemblages indicate peak metamorphic pressures of 6–9.5 kbar, demonstrating exhumation of the core of the Dayman dome from depths of 20–30 km. The S1 metamorphic mineral assemblage in metabasite includes actinolite‐chlorite‐epidote‐albite‐quartz‐calcite‐titanite, indicative of greenschist facies conditions for the main deformation. New mineral equilibria modelling suggests that this S1 assemblage evolved at 5.9–7.2 kbar at ～425 °C. Modelling variable Fe³⁺ indicates that the sodic‐calcic blue amphibole (D2) formed under a higher oxidation state compared with the S1 assemblage, probably at <4.5 kbar. A SE‐dipping, Mio‐Pliocene sedimentary sequence (Gwoira Conglomerate) forms a hangingwall block juxtaposed by low‐angle fault contact with the metabasite footwall. Prehnite‐bearing D3 brittle fault zones separate the two blocks and likely accommodated the final exhumation of the S1 greenschist facies assemblage in the footwall. These results indicate that the extensive Mt Dayman fault surface coincides with a domed S1 greenschist facies foliation that was last active at >20 km depth. Exhumation of this foliation must therefore be controlled by brittle faults of the active microplate boundary that are largely not observed in the study area. The structural record of the final exhumation of the Dayman dome to the surface was likely lost as a result of erosion, poor exposure or wide spacing of semi‐brittle to brittle fault zones.     

A thermodynamic model for Ca–Na clinoamphiboles in Na2O–CaO–FeO–MgO–Al2O3–SiO2–H2O–O for petrological calculations

A calibration is presented for an activity–composition model for amphiboles in the system Na₂O–CaO–FeO–MgO–Al₂O₃–SiO₂–H₂O–O (NCFMASHO), formulated in terms of an independent set of six end‐members: tremolite, tschermakite, pargasite, glaucophane, ferroactinolite and ferritschermakite. The model uses mixing‐on‐sites for the ideal‐mixing activities, and for the activity coefficients, a macroscopic multicomponent van Laar model. This formulation involves 15 pairwise interaction energies and six asymmetry parameters. Calibration of the model is based on the geometrical constraints imposed by the size and shape of amphibole solvi inherent in a data set of 71 coexisting amphibole pairs from rocks, formed over 400–600 °C and 2–18 kbar. The model parameters are calibrated by combining these geometric constraints with qualitative consideration of parameter relationships, given that the data are insufficient to allow all the model parameters to be determined from a regression of the data. Use of coexisting amphiboles means that amphibole activity–composition relationships are calibrated independently of the thermodynamic properties of the end‐members. For practical applications, in geothermobarometry and the calculation of phase diagrams, the amphibole activity–composition relationships are placed in the context of the stability of other minerals by evaluating the properties of the end‐members in the independent set that are in internally consistent data sets. This has been performed using an extended natural data set for hornblende–garnet–plagioclase–quartz, giving the small adjustments necessary to the enthalpies of formation of tschermakite, pargasite and glaucophane for working with the Holland and Powell data set.     

Experimental Investigation of the Upper Thermal Stability of Mg-rich Actinolite; Implications for Kiruna-Type Iron Deposits

The occurrence of actinolite in magnetite deposits of possiblemagmatic origin has prompted an experimental investigation ofthe upper thermal stability of Mg-rich actinolite to determinehow the stability of actinolite changes with increasing Fe content.Experiments were carried out primarily on the compositionalre-equilibration of natural tremolite [molar Fe/(Fe + Mg) =Fe-number = 0·014] in the presence of synthetic clinopyroxene(Ca_0·80Fe_0·67Mg_0·54Si_2·00O₆), syntheticpigeonite/orthopyroxene (Ca_0·08Fe_1·19Mg_0·70Si_2·02O₆),quartz, and water to a more Fe-rich actinolite over the rangeof 600–880°C, 1 and 4 kbar, at the Ni–NiO oxygenbuffer, for durations of 1–2 weeks. The bulk compositionof the mineral mixture is close to actinolite with Fe-number= 0·5. These experiments constitute a half-reversal ofthe amphibole composition, which, when approached from a Mg-richstarting composition, provides information on the minimum Fecontent of actinolite at a given temperature. Compositionalchanges were monitored by electron microprobe analysis of amphibolerim compositions and/or overgrowths on the original tremolite.At 4 kbar and 880–800°C, tremolite shows strong re-equilibrationwith overgrowths of an Fe-rich but low-Ca (1·7 > Ca> 1·4) actinolite; Fe-rich cummingtonite (Ca <0·7)begins to nucleate at 860°C. At 800–700°C, tremoliteshows weak compositional re-equilibration but strong nucleationof Fe-rich cummingtonite. Similar results were observed at 1kbar, with tremolite showing strong re-equilibration to low-Caactinolite at 790–600°C with cummingtonite nucleationat 800°C and below. The wide variation in Ca contents ofthe re-equilibrated amphiboles was unexpected. Additional univariantreversal experiments were carried out on the thermal decompositionof a natural actinolite (Fe-number = 0·22) from PleitoMelón, Chile, indicating the breakdown of actinoliteto clinopyroxene, orthopyroxene, quartz, and water at 780°Cand 1 kbar, and 850°C and 4 kbar. Considering only amphiboleswith Ca >1·7 a.p.f.u., the thermal stability of actinoliteis observed to decrease in a linear manner over the P–Trange investigated with a dT/dFe-number slope of –372°C/Fe-numberat 1 kbar and –546°C/Fe-number at 4 kbar. The highthermal stabilities (750–900°C) of actinolites withFe-numbers in the range of 0–0·4 overlap with therange of water-saturated melting for a typical andesite or tonalite.These conditions also overlap the field of experimental Fe–P-richmelt formation, suggesting that actinolite may have an igneousorigin in Kiruna-type ore deposits. KEY WORDS: actinolite; mineral stability; Kiruna deposits, thermodynamic values; cummingonite     

秘鲁马尔科纳铁矿区北部TA-02勘查区铜多金属矿地质特征及成矿类型

秘鲁马尔科纳(Marcona)铁矿区北部TA-02勘查区蕴含丰富的铜矿和铁矿资源,并伴生锌、钴等矿产资源。TA-02勘查区处于环太平洋构造-岩浆活动带的东侧,西南部发育有圣尼古拉斯(San Nicolás)岩基,胡斯塔(Justa)断裂控制了区内的铁、铜矿化及阳起石化蚀变带,是勘查区内(铁)铜矿体的主要控矿构造;胡斯塔断裂内常充填磁铁矿体、铜矿体及不同种类的脉岩,矿体形态以脉状为主;矿石中含铜矿物主要为黄铜矿,伴生/共生金属矿物主要为磁铁矿、赤铁矿、钴矿物、闪锌矿等,铜矿化与铁矿化具有高度的一致性,共/伴生关系密切,二者呈正相关关系,因此铜矿区呈现较高的磁异常;此外,矿体穿切地层,赋矿围岩无专属性,围岩蚀变以阳起石化蚀变为特征。研究认为,TA-02勘查区铜多金属矿属于IOCG型(氧化铁型铜-金)矿床。     

Parageneses and compositions of amphiboles from Franciscan jadeite–glaucophane type facies series metabasites at Cazadero, California

Abstract Sodic amphiboles are common in Franciscan type II and type III metabasites from Cazadero, California. They occur as (1) vein-fillings, (2) overgrowths on relict augites, (3) discrete tiny crystals in the groundmass, and (4) composite crystals with metamorphic Ca–Na pyroxenes in low-grade rocks. They become coarse-grained and show strong preferred orientation in schistose high-grade rocks. In the lowest grade, only riebeckite to crossite appears; with increasing grade, sodic amphibole becomes, first, enriched in glaucophane component, later coexists with actinolite, and finally, at even higher grade, becomes winchite. Actinolite first appears in foliated blueschists of the upper pumpellyite zone. It occurs (1) interlayered on a millimetre scale with glaucophane prisms and (2) as segments of composite amphibole crystals. Actinolite is considered to be in equilibrium with other high-pressure phases on the basis of its restricted occurrence in higher grade rocks, textural and compositional characteristics, and Fe/Mg distribution coefficient between actinolite and chlorite. Detailed analyses delineate a compositional gap for coexisting sodic and calcic amphiboles. At the highest grade, winchite appears at the expense of the actinolite–glaucophane pair. Compositional characteristics of Franciscan amphiboles from Ward Creek are compared with those of other high P/T facies series. The amphibole trend in terms of major components is very sensitive to the metamorphic field gradient. Na-amphibole appears at lower grade than actinolite along the higher P/T facies series (e.g. Franciscan and New Caledonia), whereas reverse relations occur in the lower P/T facies series (e.g. Sanbagawa and New Zealand). Available data also indicate that at low-temperature conditions, such as those of the blueschist and pumpellyite–actinolite facies, large compositional gaps exist between Ca- and Na-amphiboles, and between actinolite and hornblende, whereas at higher temperatures such as in the epidote–amphibolite, greenschist and eclogite facies, the gaps become very restricted. Common occurrence of both sodic and calcic amphiboles and Ca–Na pyroxene together with albite + quartz in the Ward Creek metabasites and their compositional trends are characteristic of the jadeite–glaucophane type facies series. In New Caledonia blueschists, Ca–Na pyroxenes are also common; Na-amphiboles do not appear alone at low grade in metabasites, instead, Na-amphiboles coexist with Ca-amphiboles throughout the progressive sequence. However, for metabasites of the intermediate pressure facies series, such as those of the Sanbagawa belt, Japan and South Island, New Zealand, Ca–Na pyroxene and glaucophane are not common; sodic amphiboles are restricted to crossite and riebeckite in composition and clinopyroxenes to acmite and sodic augite, and occur only in Fe₂O₃-rich metabasites. The glaucophane component of Na-amphibole systematically decreases from Ward Creek, New Caledonia, through Sanbagawa to New Zealand. This relation is consistent with estimated pressure decrease employing the geobarometer of Maruyama et al. (1986). Similarly, the decrease in tschermakite content and increase in NaM₄ of Ca-amphiboles from New Zealand, through Sanbagawa to New Caledonia is consistent with the geobarometry of Brown (1977b). Therefore, the difference in compositional trends of amphiboles can be used as a guide for P–T detail within the metamorphic facies series.     

红外光谱-拉曼光谱无损检测技术对透闪石和阳起石鉴定特征的研究

透闪石属于角闪石族矿物,与阳起石构成完全类质同象,有关透闪石和阳起石的红外光谱和拉曼光谱的特征差异还未见有报道。本文以外观特征相似的5件广西大化黑青色阳起石样品和2件新疆塔县青玉样品为研究对象,在前期矿物成分测试的基础下,采用红外光谱和拉曼光谱进行测试和对比分析。结果表明,阳起石的红外光谱和拉曼光谱都表现为闪石类矿物的特征峰,与透闪石的特征峰存在细微差异,漫反射红外光谱的差异特征是鉴别两者最准确、快速、无损的依据,并且适用于任意形状的样品,符合珠宝玉石饰品实验室检测领域的要求,可为和田玉的分类分级和产地鉴别等提供科学依据。按照GB/T 16552-2017与GB/T 16553-2017规定,广西大化黑青色阳起石可定名为和田玉。     

Subdivision of the Sanbagawa pumpellyite–actinolite facies region in central Shikoku, southwest Japan

Abstract   The mineral assemblages of the pumpellyite–actinolite facies such as pumpellyite + actinolite + epidote + chlorite or actinolite + epidote + hematite + chlorite occur in the Sanbagawa low-grade metamorphic region, central Shikoku, southwest Japan. Chemical compositions of these minerals from the eight newly studied areas were analyzed in order to evaluate the areal extent and thermal structure of the region. In the buffered assemblage of pumpellyite + actinolite + epidote + chlorite, the Fe³⁺/(Fe³⁺ + Al) values of epidote decrease slightly with decreasing Fe²⁺/(Fe²⁺ + Mg) values for chlorite. The changes in these values show a general correlation with temperature. The presence of this relationship implies that the Fe³⁺/(Fe³⁺ + Al) values of epidote can be used to divide the Sanbagawa low-grade metamorphic region into low-, medium- and high-grade subzones. The areal distribution of these subzones indicates that: (i) the temperature seems to decrease in the same sense as envisaged by the zonal mapping of the higher-grade pelitic schists; and (ii) there is no significant gap of metamorphic conditions through the boundary between the two structural units (Besshi and Oboke units). It follows that the Sanbagawa low-grade metamorphic region decreases in temperature going up the structural section, and tectonic discontinuities have not affected the thermal structure.