Calcite–graphite isotope thermometry in amphibolite facies marble, Bancroft, Ontario

This study presents calcite–graphite carbon isotope fractionations for 32 samples from marble in the northern Elzevir terrane of the Central Metasedimentary Belt, Grenville Province, southern Ontario, Canada. These results are compared with temperatures calculated by calcite–dolomite thermometry (15 samples), garnet–biotite thermometry (four samples) and garnet–hornblende thermometry (three samples). Δ_cal‐gr values vary regularly across the area from >6.5‰ in the south to 4.0‰ in the north, which corresponds to temperatures of 525 °C in the south to 650 °C in the north. Previous empirical calibration of the calcite–graphite thermometer agrees very well with calcite–dolomite, garnet–biotite and garnet–hornblende thermometry, whereas, theoretical calibrations compare less well with the independent thermometry. Isograds in marble based on the reactions rutile + calcite + quartz =titanite and tremolite + calcite + quartz = diopside, span temperatures of 525–600 °C and are consistent with calculated temperature–X(CO₂) relations. Results of this study compare favourably with large‐scale regional isotherms, however, local variation is greater than that revealed by large‐scale sampling strategies. It remains unclear whether the temperature–Δ_cal‐gr relationship observed in natural materials below 650 °C represents equilibrium fractionations or not, but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble.     

膨胀石墨化学氧化法制备技术研究进展

膨胀石墨是石墨的重要深加工产品之一.目前膨胀石墨工业生产用的最多和最成熟的方法是化学氧化法,具有很多优点.由于这种工艺生产过程存在环境污染,产品在应用中对设备有腐蚀,高温抗氧化性及强度不高等原因,限制了其进一步发展.介绍了近年来围绕化学氧化法制备工艺及产品性能改进问题国内外研究的主要进展.讨论了利用低品位和细鳞片石墨原料,降低或消除生产过程中的NOX、重金属离子的污染,降低产品的含硫量和腐蚀性,提高产品的膨胀倍数、抗氧化性和强度,改进产品的膨化工艺等方面的技术措施及应用效果.指出了化学氧化法进一步发展的方向和应用前景.     

Calc-silicate reactions and bedding-controlled isotopic exchange in the Notch Peak aureole, Utah: implications for differential fluid fluxes with metamorphic grade

Fluid compositions and bedding‐scale patterns of fluid flow during contact metamorphism of the Weeks Formation in the Notch Peak aureole, Utah, were determined from mineralogy and stable isotope compositions. The Weeks Formation contains calc‐silicate and nearly pure carbonate layers that are interbedded on centimetre to decimetre scales. The prograde metamorphic sequence is characterized by the appearance of phlogopite, diopside, and wollastonite. By accounting for the solution properties of Fe, it is shown that the tremolite stability field was very narrow and perhaps absent in the prograde sequence. Unshifted oxygen and carbon isotopic ratios in calcite and silicate minerals at all grades, except above the wollastonite isograd, show that there was little to no infiltration of disequilibrium fluids. The fluid composition is poorly constrained, but X(CO₂)_fluid must have been >0.1, as indicated by the absence of talc, and has probably increased with progress of decarbonation reactions. The occurrence of scapolite and oxidation of graphite in calc‐silicate beds of the upper diopside zone provide the first evidence for limited infiltration of external aqueous fluids. Significantly larger amounts of aqueous fluid infiltrated the wollastonite zone. The aqueous fluids are recorded by the presence of vesuvianite, large decreases in δ¹⁸O values of silicate minerals from c. 16‰ in the diopside zone to c. 10‰ in the wollastonite zone, and extensive oxidation of graphite. The carbonate beds interacted with the fluids only along margins where graphite was destroyed, calcite coarsened, and isotopic ratios shifted. The wollastonite isograd represents a boundary between a high aqueous fluid‐flux region on its higher‐grade side and a low fluid‐flux region on its lower‐grade side. Preferential flow of aqueous fluids within the wollastonite zone was promoted by permeability created by the wollastonite‐forming reaction and the natural tendency of fluids to flow upward and down‐temperature near the intrusion‐wall rock contact.     

沉积物中元素碳的提取、鉴定及其古气候环境意义

通过化学氧化方法提取沉积物中元素碳物质,采用拉曼光谱对其进行分析鉴定,实验结果表明:元素碳是介于单晶石墨碳和无定形碳之间的一系列物质,是一种操作上的定义;化学氧化法提取沉积物中元素碳是可靠的,控制好氧化条件和时间,则能有效去除有机碳,保留元素碳成份。鉴于目前不同工作者由于不同的实验条件和方法下得到了不同结果,我们认为确定标准样及其浓度,统一实验方法是亟待解决的问题,进而统一这种碳微粒的名称,明确其定义,以利于相关研究的横向对比和深入。而在纵向研究方面,我们利用该实验流程提取灵台黄土剖面长时间序列黄土—古土壤样的元素碳,并进行元素碳含量的测定,结果表明元素碳记录能有效揭示古气候环境变化。在不同时间尺度上,元素碳记录有不同的气候指示意义,并且与其他气候环境指标能进行较好的对比,元素碳记录为古气候环境变化提供一新的指标。     

悬浮液进样石墨炉原子吸收光谱法测定环境样品中痕量铅

提出了悬浮液进样石墨炉原子吸收光谱法测定环境样品中痕量铅的分析方法.讨论了悬浮颗粒粒径、悬浮液浓度、悬浮稳定剂、基体改进剂等因素对测定结果的影响.实验结果表明: 样品粒径 < 38μm, 以0.2g/L的Triton - 100为悬浮剂, 3g/L的(NH₄)₂HPO₄为基体改进剂, 电磁搅拌进样可简便快速地测定地质样品中的痕量铅, 方法的检出限为0.10ng/g, 精密度为3.31% (n =10).43GSD标样测定结果与推荐值一致      

集安市复兴屯—金厂沟一带晶质石墨矿地质特征及找矿标志

集安晶质石墨矿产于古元古界集安群荒岔沟组变质岩系中,矿体严格受地层层位控制,矿石质量好且易选。集安群在通化一集安一带广泛发育,为一套含石墨的火山一沉积建造,是晶质石墨矿找矿的重点区域。     

内蒙古大乌淀石墨矿地质特征与成因探讨

大乌淀石墨矿是近年来在狼山—白云鄂博裂谷带内新发现的超大型石墨矿床,矿体赋存于白云鄂博岩群尖山岩组一段。文章在分析成矿地质背景、矿床地质特征、矿石矿物赋存状态及特征等基础上,对矿床成因进行了探讨,并总结其成矿模式。研究表明:大乌淀石墨矿含矿岩性,主要为各类红柱石石墨片岩;碳质来源为生物有机碳;矿床成因为经区域浅变质后又叠加接触变质的多成因层控矿床。大乌淀石墨矿的成矿作用可概括为原生碳沉积富集,无定型碳热变质转变为石墨核晶;碳硅有机热液交代石墨核晶形成鳞片状石墨的成矿作用过程。     

Phase equilibria constraints on melting of stromatic migmatites from Ronda (S. Spain): insights on the formation of peritectic garnet

Stromatic metatexites occurring structurally below the contact with the Ronda peridotite (Ojén nappe, Betic Cordillera, S Spain) are characterized by the mineral assemblage Qtz+Pl+Kfs+Bt+Sil+Grt+Ap+Gr+Ilm. Garnet occurs in low modal amount (2–5 vol.%). Very rare muscovite is present as armoured inclusions, indicating prograde exhaustion. Microstructural evidence of melting in the migmatites includes pseudomorphs after melt films and nanogranite and glassy inclusions hosted in garnet cores. The latter microstructure demonstrates that garnet crystallized in the presence of melt. Re‐melted nanogranites and preserved glassy inclusions show leucogranitic compositions. Phase equilibria modelling of the stromatic migmatite in the MnO–Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂–O₂–C (MnNCaKFMASHOC) system with graphite‐saturated fluid shows P–T conditions of equilibration of 4.5–5 kbar, 660–700 °C. These results are consistent with the complete experimental re‐melting of nanogranites at 700 °C and indicate that nanogranites represent the anatectic melt generated immediately after entering supersolidus conditions. The P–T estimate for garnet and melt development does not, however, overlap with the low‐temperature tip of the pure melt field in the phase diagram calculated for the composition of preserved glassy inclusions in garnet in the Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O (NCKFMASH) system. A comparison of measured melt compositions formed immediately beyond the solidus with results of phase equilibria modelling points to the systematic underestimation of FeO, MgO and CaO in the calculated melt. These discrepancies are present also when calculated melts are compared with low‐T natural and experimental melts from the literature. Under such conditions, the available melt model does not perform well. Given the presence of melt inclusions in garnet cores and the P–T estimates for their formation, we argue that small amounts (<5 vol.%) of peritectic garnet may grow at low temperatures (≤700 °C), as a result of continuous melting reactions consuming biotite.     

湖南新化地区煤变形变质与构造环境特征

采用煤质化验、XRD、SEM等测试手段,分析煤的化学组分、结构特征、显微构造等特征,结合古应力估算值、古温度和应变速率等结果,探讨了湖南新化地区煤变形变质特征与构造环境的关系。结果表明：煤样的d₀₀₂值为3.36~3.39 nm,受天龙山构造挤压的局部应力场及叠加岩浆构造热的作用,煤逐渐转变为隐晶质石墨,结晶颗粒是由细小的鳞片组成的集合体,粒径集中在50~250 nm;石墨3R型含量随着煤化程度升高,石墨晶体开始增加,Rh相的数量减少;构造变形环境属于低温低围压高应变速率的浅层脆性-韧脆性构造域;天龙山岩体提供了构造热源,侧向挤压应力使寒婆坳向斜煤大分子结构有序化,层面间距减小,形成隐晶质石墨。     

Significance of graphite inclusion occurrence in the minerals of the San Miguel skarn for the Palaeoproterozoic basement of Tandilia Belt (Argentina) and for the Río de la Plata Craton

Graphite in Archaean-Palaeoproterozoic rocks has been a subject of interest since it could represent an evidence of early life on Earth. In the Palaeoproterozoic basement of the Tandilia Belt, graphite was found both in fluid inclusions (FI) hosted in the San Miguel skarn calc-silicate minerals, and as solid inclusions in calcite crystals from the protolithic marble (a¹³C enriched carbonate from the “Lomagundi-Jatuli event”). FI microthermometry and oxygen stable isotope ratios indicated the skarn minerals formation within the range of 630–650 °C (at ∼5 kbars) and ∼642–654 °C, respectively. Also, the characterisation of the metasomatic fluid (of a low salinity <7 wt% NaCl eq. NaClH₂O/NaClKClH₂O aqueous system) pointed out that the zonal crystallisation pattern shown by the skarn minerals (wollastonite-vesuvianite, grossular-diopside-calcite and diopside-calcite zones in the exoskarn, and grossular-diopside and diopside-calcic plagioclase zones in the endoskarn) responds to the increase of the involved cation activity gradients (Ca²⁺-Si⁴⁺-Mg²⁺-Fe^2+/3+-Al³⁺) and not to significant changes in the temperature or concentration of CO₂ in the system. Variation in the crystallinity degree of the graphite hosted in the skarn minerals and in marble calcite, shown by Raman spectroscopy, would indicate that the graphite could have been formed from the ripening of organic matter present in the sedimentary rocks during the metamorphic-metasomatic event (Transamazonian Orogeny). In this sense, the increase of the organic carbon productivity in the oceans during the Palaeoproterozoic, represented by the “Lomagundi-Jatuli event”, would support this graphite origin and also the possible existence of a marine sedimentary basin in the previous stages of the Río de la Plata amalgamation (Siderian-Rhyacian), in the San Miguel area of the Tandilia Belt.