Preservation of high‐P rocks coupled to rock composition and the absence of metamorphic fluids

Eclogites, blueschists and greenschists are found in close proximity to one another along a 1‐km coastal section where the Cyclades Blueschist Unit (CBU) is exposed on SE Syros, Greece. Here, we show that the eclogites and blueschists experienced the same metamorphic history: prograde lawsonite blueschist facies metamorphism at 1.2–1.9 GPa and 410–530°C followed, at 43–38 Ma, by peak blueschist/eclogite facies metamorphism at 1.5–2.1 GPa and 520–580°C. We explain co‐existence of eclogites and blueschists by compositional variation probably reflecting original compositional layering. It is also shown that the greenschists record retrogression at 0.34 ± 0.21 GPa and T = 456 ± 68°C. This was spatially associated with a shear zone on a scales of 10–100‐m and veins on a scale of 1–10‐cm. Greenschist facies metamorphism ended at (or shortly after) 27 Ma. We thus infer a period of metamorphic quiescence after eclogite/blueschist facies metamorphism and before greenschist facies retrogression which lasted up to 11–16 million years. We suggest that this reflects an absence of metamorphic fluid flow at that time and conclude that greenschist facies retrogression only occurred when and where metamorphic fluids were present. From a tectonic perspective, our findings are consistent with studies showing that the CBU is (a) a high‐P nappe stack consisting of belts in which high‐P metamorphism and exhumation occurred at different times and (b) affected by greenschist facies metamorphism during the Oligocene, prior to the onset of regional tectonic extension.     

Cl/Br of scapolite as a fluid tracer in the earth's crust: insights into fluid sources in the Mary Kathleen Fold Belt,Mt. Isa Inlier,Australia

A combination of analytical methods, including trace element analysis of Br in scapolite by LA‐ICP‐MS, was employed to unravel the fluid–rock interaction history of the Mary Kathleen Fold Belt of northern Australia. Halogen ratios in the metamorphic and hydrothermally derived scapolite from a range of rock‐types record interaction between the host rocks and magmatic‐hydrothermal fluids derived from granite plutons and regional metamorphism. The results show that halite‐dissolution supplied at best only minor chlorine to fluids in the Fold Belt. Chlorine/bromine ratios in metamorphic scapolite indicate that fluids were dominantly derived from basinal brines formed from sub‐aerial evaporation of seawater beyond the point of halite saturation. This bittern fluid infiltrated the underlying sedimentary sequences prior to regional metamorphism. Zoned scapolite in a major late metamorphic mineralized shear‐zone records three discrete pulses of magmatic and metamorphic fluid, and it is suggested that fluid mixing may have assisted mineralization along and around this shear‐zone. As a crucial prerequisite for halogen fluid tracer studies using scapolite, we find in our samples that Cl and Br do not fractionate when incorporated in scapolite. Furthermore, unaltered rims of heavily retrogressed scapolite show indistinguishable Cl/Br signatures compared with fresh grains from the same sample indicating retrograde metamorphism did not significantly affect Cl and Br signatures in scapolite group minerals.     

Impact of experimental parameters for manometric equipment on CO2 isotherms measured: Comment on “Inter-laboratory comparison II: CO2 isotherms measured on moisture-equilibrated Argonne premium coals at 55°C and up to 15 MPa” by Goodman et al. (2007)

Modelling the sorption properties of coals for carbon dioxide under supercritical conditions is necessary for accurate prediction of the sequestering ability of coals in seams. We present recent data for sorption curves of three dry Argonne Premium coals, for carbon dioxide, methane and nitrogen at two different temperatures at pressures up to 15 MPa. The sorption capacity of coals tends to decrease with increasing temperature. An investigation into literature values for sorption of nitrogen and methane by charcoal also show sorption capacities that decrease dramatically with increasing temperature. This is inconsistent with expectations from Langmuir models of coal sorption, which predict a sorption capacity that is independent of temperature. We have successfully fitted the isotherms using a modified Dubinin–Radushkevich equation that uses gas density rather than pressure. A simple pore-filling model that assumes there is a maximum pore width that can be filled in supercritical conditions and that this maximum pore width decreases with increasing temperature, can explain this temperature dependence of sorption capacity. It can also explain why different supercritical gases give apparently different surface sorption capacities on the same material. The calculated heat of sorption for these gases on these coals is similar to those found for these gases on activated carbon.     

蔡家营铅—锌—银矿床的稳定同位素地球化学研究

河北蔡家营矿床是大型中温热液充填－交代脉型铅－锌－银矿床。其硫化物的δ＾３４Ｓ值为２．２‰－７．８‰，同世代共存的１０个硫化物对的Δ＾３４Ｓ值表明，Ｆｅ－（Ｚｎ、Ｐｂ）－Ｓ系统的硫同位素非平衡分馏占主导，硫是岩浆（为主）与老变质岩层硫的混合来源。石英及其流体包裹体的δ＾１８ＯＳＭＯＷ和δＤＳＭＯＷ值（‰）按混合模式计算表明，成矿流体为混合的岩浆和大气降水，早期成矿流体以岩浆为主，尔后则变为以大气降     

Seismicity of the Koyna region and regional tectonomagmatism of the Western Margin (India)

Recent findings on the Meso-Cenozoic tectonomagmatism and deep-seated anomalous geophysical structures suggest a close linkage between the seismicity of the Koyna region, the Westernghat uplift (WG-U) and associated thermomechanical and fluid activities. The WG-U seems to be the result of late Cretaceous thermal mobilization, erosion of the Deccan trap cover and superposition of compressional stress. The association of seismicity with uplift seems to result from movement of deep-seated heat and fluids/volatiles along the edges (or boundary faults) of the uplift; because the force required for crustal deformation depends on the relief. Observed gradients in relief may be attributed to the differential erosion-rates and heat inputs, due to the time gap of 50 Ma in the break-ups and plume activities on the eastern and western sides and consequence magmatism. Further, the geology and tectonics strongly indicate that the western margin (WM) is a relic of a mobile arm (MA), that included Madagascar, and which formed a part of the Proterozoic mobile belt of greater India (fort>85 Ma). The mobile nature of the WM facilitates mantle upwellings and transient elevation of isotherms at depth, raising the possibility of intermittent metamorphism and greater deformation.Superposition of the ongoing compression and uplift-induced forces make local permeability and pore-fluid pressure vital in triggering the seismic slip over the Peninsular shield. Certain representative model calculations have been carried out to estimate change in the e.m. induction characteristics caused by an intermittent hydraulic connectivity. The results show a drop in the resistivity which could be a useful monitoring index. The close connection of uplift and fluid activity as discussed here seems applicable for other active parts of the South Indian Shield (SIS) also.     

Petrology, geothermobarometry and C-O-H-S fluid compositions in the environs of Rampura-Agucha Zn-(Pb) ore deposit, Bhilwara District, Rajasthan

The massive Zn-(Pb) sulfide ore body at Rampura-Agucha in Bhilwara district, Rajasthan, occurs within graphitic metapelites surrounded by garnet-biotite-sillimanite gneiss containing concordant bodies of amphibolite. These rocks and the sulfide ores have been studied to estimate the pressure, temperature and fluid composition associated with upper amphibolite facies metamorphism. Geothermobarometric calculations involving garnet-biotite and garnet-hornblende pairs, as well as sphalerite-hexagonal pyrrhotite-pyrite and garnet-plagioclase-sillimanite-quartz assemblages indicate that the most pervasive P-T condition during peak of regional metamorphism was 650°C and 6 kb, and was attained between the first and second deformations in the region. Some temperature-pressure estimates also cluster around 500°C–5.1 kb which probably represent retrograde cooling during unloading. Consideration of devolatilization equilibria in the C-O-H-S system at the pervasive metamorphic conditions mentioned above shows that the metamorphic fluid was H₂O-rich ( ) but also had a substantial component of . and were the other important phases in the fluid. CO (X_CO = 0.002) and were the minor phases in the fluid. It is probable that a part of this aqueous fluid was consumed by re-/neocrystallization of hydrous silicate phases like chlorite during the retrogressive metamorphic path, so that fluid entrapped in quartz below 450°C was rendered CO₂-rich (Holleret al 1996).     

超临界水的特性及其对地球深部物质研究的意义

水在超临界状态下有着与标准状态明显不同的行为，超临界水具有许多的特殊性质，如强烈的氧化作用，很强的溶解性能，以及通过温度和压力变化控制其密度在类似蒸汽到类似液体的密度之间等。水在约４００℃的超临界温度下，几乎有的氢键都裂解了，超临界水的这一性质很可能是超临界水具有许多特殊性质的主要原因，超临状态地幔水的存在，不仅对球物理场的性质有重要影响，崦且对于地质构造演化、地球化学动力学、成矿作用，以及深部地     

斑岩铜(钼-金)矿床的成矿流体

斑岩铜矿是主要的铜资源,是矿床研究和勘查的重要目标。斑岩铜矿按其与板块构造的关系可分为2种:俯冲带斑岩铜矿和碰撞造山带斑岩铜矿,它们在成矿流体方面有很多区别,其中较大的差别是碰撞造山带斑岩铜矿的钾化蚀变带比俯冲带斑岩铜矿的钾化蚀变带强得多,且范围也相对较宽。文章简述了这2种斑岩矿床的主要地质特征,着重从流体包裹体、蚀变作用和稳定同位素研究来探讨斑铜矿床成矿流体的主要特征,包括成矿流体的成分、形成温度和压力,氢、氧、碳和硫稳定同位素组成。这两种类型的斑岩铜矿中主要发育5种包裹体:M熔体包裹体;Ⅰ液体包裹体;Ⅱ气体包裹体;Ⅲ含子矿物的多相包裹体和CO2_H2O包裹体。Ⅱ类和Ⅲ类包裹体常共存,且均一温度相似,表明成矿流体经历了不混溶和沸腾作用。在Ⅲ类含子矿物的包裹体中发现了含金属硫化物(黄铜矿、黄铁矿)和氧化物(赤铁矿、磁铁矿)子矿物。在斑岩金矿和碰撞造山带的斑岩铜矿中出现CO2_H2O包裹体,在斑岩的斑晶和一些早期石英脉的石英中可见到熔体包裹体以及熔体_流体包裹体,它们代表斑岩岩浆的样品,说明斑岩铜矿的形成经历了岩浆和热液阶段。最近的研究表明,斑岩铜矿的初始流体是中等盐度和密度的岩浆流体。这种流体在上升过程中因压力释放而发生沸腾,形成气体包裹体和含子矿物的高盐度包裹体。     

内蒙古阿巴嘎旗必鲁甘干钼铜矿床成矿流体演化与成矿机制

必鲁甘干钼铜矿床位于内蒙古阿巴嘎旗境内,二连-东乌旗成矿带东段,自2007年发现以来,已探明钼金属量已超过16万吨,达到大型规模。矿床赋存于印支期花岗斑岩和二叠系上统林西组接触带附近,含矿带呈NNE向展布,向SE缓倾。必鲁甘干钼铜矿床成矿阶段可划分为早、主、晚三个阶段,早阶段以硅化和钾长石化蚀变及浸染状和星点状矿化为特征,矿化较强;主阶段以硅化和绢云母化蚀变和发育乳白色含矿石英脉为特征,矿化很强;晚阶段以硅化、碳酸盐化、青磐岩化和粘土化蚀变以及发育石英方解石细脉为特征,矿化较弱。石英中流体包裹体类型主要有富液相水溶液包裹体(L型)、富气相水溶液包裹体(V型)和富CO_2包裹体(C1和C2型)。早阶段发育大量L型和少量C1型包裹体,主阶段发育大量L型和C1型以及少量V型和C2型包裹体,晚阶段主要发育L型包裹体,个别样品发育少量C1型包裹体。早、主、晚阶段均一温度分别为210~354℃、182~351℃、128~312℃,盐度分别为3.6%~9.2%NaC leqv、2.6%~9.2%NaC leqv、2.8%~9.6%NaC leqv。主阶段成矿温度、压力为232~269℃、0.54~1.55kbar;三个阶段成矿深度分别约为8.1~5.8km、5.7~5.5km、3.9~2.6km。从早阶段到晚阶段,成矿流体由中温、中等盐度、富CO_2的NaCl-H_2O-CO_2体系向中低温、低盐度、贫CO_2的H_2O-NaC l体系演化。成矿流体在演化过程中由于周期性压力脉动而导致发生流体不混溶,其可能是成矿元素发生聚集、沉淀形成矿床的重要机制。由必鲁甘干钼铜矿床围岩蚀变("贫水蚀变")、成矿流体成分(NaCl-H_2O-CO_2体系)和成矿深度(主阶段成矿深度约5.7~5.5km)推测其属陆内环境斑岩矿床。     

南极冰钻钻井液应用性试验研究

钻井液的性质及性能参数对于南极科学钻探有着重要的影响。钻井液除了必须要具备合适的粘度和密度,以满足冷却钻头、平衡孔壁压力、携带冰屑、清洁孔底的要求外,钻井液的性质如导电性、导热性及其腐蚀性对于保证钻具的正常工作、输送孔内信息也有着重要的影响。根据目前已经在南极使用的钻井液类型,分别对6种介质（国产硅油-3cst、KF96硅油-2cst、丁酸乙酯、丁酸丁酯、丁酸戊酯、丙酸丙酯）在不同温度下的电导率、导热系数和对密封件的腐蚀性进行了试验测试,选出了适合南极应用的钻井液类型及在钻具中使用的密封件材质,可供极地钻探选择钻井液类型及钻具设计提供重要的参考。