AN UNUSUAL CARBONATE BAND IN THE EAST PENNINE COALFIELD (ENGLAND)

A combined petrographical and geochemical study has been made on a per- sistent carbonate horizon from the Mansfield Marine Band, an important marker horizon in the Westphalian Coal Measures of the east Pennines. The composition of this carbonate is unusual for it normally consists of ankerite, but in some localities the carbonate is siderite and not ankerite. The position of the carbonate in the sedimentary cycle is discussed and the conclusion drawn that physicochemical conditions were suitable for the precipitation of CaC03 to occur. Furthermore the detrital material in the carbonate band continued to accumulate at a similar rate to the shales above and below the carbonate. The alteration of the CaC03 is thought to have been a diagenetic effect and the result of a change in the physicochemical environment. Variations in the concentration of dissolved sulphur species and their effect on the solubilities of iron and manganese provide an adequate mechanism to explain how CaC03 may alter to siderite on the one hand or ankerite on the other.     

Martian basalt (shergottite) Queen Alexandra Range 94201 and lunar basalt 15555: A tale of two pyroxenes

Abstract— We present here ion microprobe analyses of rare earth and other selected trace and minor elements in pyroxenes of shergottite Queen Alexandra Range 94201 and lunar basalt 15555. Pyroxene zonation patterns record the crystallization histories of these two basaltic samples from Mars and the Moon, respectively, and allow a comparison of mafic melt evolution on these two planetary bodies. Elemental abundances and trends in pyroxenes of these two rocks indicate that their minerals formed by continuous, closed system fractional crystallization of their respective parent melts. This further supports the idea that QUE 94201 closely represents the composition of a true Martian basaltic melt (McSween et al., 1996). The main differences in pyroxene elemental zonation patterns in these two objects are attributed to earlier crystallization of whitlockite in QUE 94201 (i.e., before the Fe-rich pyroxenes) than in 15555 (after the Fe-rich pyroxenes). The size of Eu anomalies in pyroxenes of QUE 94201 is intermediate between that in pyroxenes of 15555 and the other shergottites and may imply that fO₂ conditions during crystallization of this Martian basalt were significantly more reducing than for other shergottites, although not quite as reducing as for lunar basalts. Cerium anomalies appear to be less prevalent in pyroxenes of QUE 94201 than other Antarctic shergottites and could be indicative of lesser degree of weathering in the Antarctic.     

Quantitative Simulation of the Hydrothermal Systems of Crystallizing Magmas on the Basis of Transport Theory and Oxygen Isotope Data: An analysis of the Skaergaard Intrusion

Application of the principles of transport theory to studiesof magma-hydrothermal systems permits quantitative predictionsto be made of the consequences of magma intruding into permeablerocks. Transport processes which redistribute energy, mass,and momentum in these environments can be represented by a setof partial differential equations involving the rate of changeof extensive properties in the system. Numerical approximationand computer evaluation of the transport equations effectivelysimulates the crystallization of magma, cooling of the igneousrocks, advection of chemical components, and chemical and isotopicmass transfer between minerals and aqueous solution. Numerical modeling of the deep portions of the Skaergaard magma-hydrothermalsystem has produced detailed maps of the temperature, pressure,fluid velocity, integrated fluid flux, ¹⁸O-values in rock andfluid, and extent of nonequilibrium exchange reactions betweenfluid and rock as a function of time for a two-dimensional cross-sectionthrough the pluton. An excellent match was made between calculated¹⁸O-values and the measured ¹⁸O-values in the three principalrock units, basalt, gabbro, and gneiss, as well as in xenolithsof roof rocks that are now embedded in Layered Series; the latterwere evidently depleted in ¹⁸O early in the system's coolinghistory, prior to falling to the bottom of the magma chamber.The best match was realized for a system in which the bulk rockpermeabilities were 10^–13 cm² for the intrusion, 10^–11cm² for basalt, and 10^–16 cm² for gneiss; reaction domainsizes were 0.2 cm in the intrusion and gneiss and 0.01 cm inthe basalts, and activation energy for the isotope exchangereaction between fluid and plagioclase was 30 kcal/mole. The calculated thermal history of the Skaergaard system wascharacterized by extensive fluid circulation that was largelyrestricted to the permeable basalts and to regions of the plutonstratigraphically above the basalt-gneiss unconformity. Althoughfluids circulated all around the crystallizing magma, fluidflow paths were deflected around the magma sheet during theinitial 130,000 years. At that time, crystallization of thefinal sheet of magma and fracture of the rock shifted the circulationsystem toward the center of the intrusion, thereby minimizingthe extent of isotope exchange between rocks near the marginof the intrusion at this level. For comparison, similar calculationswere also made for pure conductive cooling; it was found thatthe rate of crystallization of the magma body was not changed.The solidified pluton cooled by a factor of about 2 faster inthe presence of a hydrothermal system. Transport rates of thermal energy out of the intrusion and oflow-¹⁸O fluids into the intrusion controlled the overall isotopeexchange process. During the initial 150,000 years, temperatureswere high and reaction rates were fast; thus, fluids flowinginto the intrusion quickly equilibrated with plagioclase. However,the temperature decreased between 120,000 and 175,000 yearsand caused a decrease in reaction rates and an increase in theequilibrium fractionation factor between plagioclase and fluid.Consequently, during this time period fluids in the intrusiontended to be out of equilibrium with plagioclase. After 175,000years temperatures had decreased sufficiently that reactionrates became insignificant, but convection rates were largeenough to redistribute fluid and enlarge the regions where fluidand plagioclase were out of equilibrium. By 400,000 years, thepluton had cooled to approximately ambient temperatures, andthe final ¹⁸O values were ‘frozen in’. Reactionsbetween hydrothermal fluid and the intrusion occurred over abroad range in temperature, 1000-200 °C, but 75 per centof the fluid circulated through the intrusion while its averagetemperature was >480 °C. This relatively high temperatureis consistent with the observation that only minor amounts ofhydrothermal alteration products were formed in the naturalsystem, even where several per mil shifts in ¹⁸O were detected. The relative quantities of fluid to rock integrated over theentire cooling history were 0.52 for the upper part of intrusion,0.88 for the basalt, 0.003 for the gneiss, and 0.41 for theentire domain. Almost all of the fluid flowed into the intrusionfrom the basalt host rocks that occur adjacent to the side contactsof the intrusion. Convection transferred about 20 per cent ofthe total heat contained in the gabbro upward into the overlyingbasalts; the remaining 80 per cent of the heat was transferredby conduction.     

Intrusion and differentiation of granitic magma at a high level in the crust: the Puscao pluton, Lima Province, Peru

Regression surface techniques have been used on partial whole-rockchemical analyses from the Puscao pluton to establish the three-dimensionalnature of the chemical variations within this body, which wasemplaced at a depth of between 4 km and 8 km within the crust.Block diagrams produced by the computer program are consistentwith the hypothesis that during the period preceding the totalconsolidation of the magma, the pluton has undergone in situdifferentiation to give a layered structure. Statistical analysis confirms that there is a large scale variationwithin the pluton and that local variation, such as might beexpected to result from the contamination of the Puscao magmaby assimilated volcanic material, did not contribute significantlyto the overall variation. Evidence is presented which suggests that the layering withinthe Puscao pluton was disturbed as a result of the emplacementof the much later Cañhas pluton, and that this disturbancehas the form of a simple doming centred upon the site of thepresent Cañas intrusion.     

Tomography: A window on the role of sulfur in the structure of micrometeorites

Abstract– To determine the role played by sulfides in the formation of vesicles and FeNi metal beads, we mapped the locations and tabulated the numbers of sulfides, metal beads, and vesicles in 1583 sectioned micrometeorites (MMs) using conventional microscopy and in 190 whole MMs using synchrotron computed microtomography (SCMT). Both the section and the SCMT images show that sulfides melt, coalesce, and migrate to the MMs surface. The decomposition of sulfides may occur during all these stages. Given the sulfide morphologies and compositions that we see in section, we think the breakdown of Ni sulfides produces the FeNi beads. The SCMT images show that metal beads are common in melted MMs, >50% have them. Vesicles in porphyritic and scoriaceous MMs are also probably formed as sulfides decompose. Not only do sulfides abut the vesicles but also the temperatures at which sulfides decompose overlap those at which MM surfaces first melt and temporarily seal, suggesting that S gases could produce most of these vesicles. As the vesicle shapes and patterns of distribution differ among MM classes, tomography can be used to nondestructively screen for specific types of MMs. Tomography is a powerful tool for visualizing the three‐dimensional distribution of metal beads, sulfides, mean densities, and vesicles in MMs.     

The lunar rock and mineral characterization consortium: Deconstruction and integrated mineralogical,petrologic, and spectroscopic analyses of mare basalts

The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts.     

Origin of a metamorphosed lithic clast in CM chondrite Grove Mountains 021536

Abstract– A metamorphosed lithic clast was discovered in the CM chondrite Grove Mountains 021536, which was collected in the Antarctica by the Chinese Antarctic Research Exploration team. The lithic clast is composed mainly of Fe‐rich olivine (Fo₆₂) with minor diopside (Fs_9.7–11.1Wo_48.3–51.6), plagioclase (An_43–46.5), nepheline, merrillite, Al‐rich chromite (21.8 wt% Al₂O₃; 4.43 wt% TiO₂), and pentlandite. Δ¹⁷O values of olivine in the lithic clast vary from ?3.9‰ to ?0.8‰. Mineral compositions and oxygen isotopic compositions of olivine suggest that the lithic clast has an exotic source different from the CM chondrite parent body. The clast could be derived from strong thermal metamorphism of pre‐existing chondrule that has experienced low‐temperature anhydrous alteration. The lithic clast is similar in mineral assemblage and chemistry to a few clasts observed in oxidized CV3 chondrites (Mokoia and Yamato‐86009) and might have been derived from the interior of the primitive CV asteroid. The apparent lack of hydration in the lithic clast indicates that the clast accreted into the CM chondrite after hydration of the CM components.     

西秦岭温泉钼矿床成矿作用时限及其对斑岩型钼矿床系统分类制约

斑岩系统是一个涉及岩浆和热液作用的复杂系统,建立精细的斑岩系统成因模型对于寻找更为丰富的金属矿产尤为重要,成矿作用时限是建立成因模型和指导矿产勘查的关键。温泉钼矿床是西秦岭造山带内与晚三叠世花岗岩有关的斑岩型钼矿床,其在西秦岭造山带的独特发育蕴含印支期斑岩成矿作用、大陆地壳演化及矿产勘查关键科学问题。钼矿体主要赋存于温泉复式岩体Ⅱ单元和Ⅲ单元的黑云母二长花岗斑岩和似斑状二长花岗岩中,钼以细脉和浸染状矿化形式产出。赋矿岩石单元锆石U-Pb年龄为224.6±2.5Ma到216.2±1.7Ma,Ⅱ和Ⅲ单元分别侵位于~223Ma和~217Ma,持续约8Myr。辉钼矿Re-Os年龄为212.7±2.6Ma到215.1±2.6Ma,暗示晚三叠世钼成矿作用与花岗质岩浆作用密切时空关系,且成矿年龄稍晚,反映钼矿化主要发生在岩浆作用晚期阶段。成岩、成矿作用发生于华北板块与华南板块全面对接后秦岭造山带构造体制由碰撞到后碰撞的转折阶段,响应南秦岭变质变形、勉-略洋盆闭合及大别-苏鲁超高压岩石板片折返统一地质事件。黑云母K-Ar年龄为207~226Ma,可能反映~223Ma和~208Ma的岩体冷却事件和~216Ma的岩浆-热液成矿作用。锆石U-Pb、辉钼矿Re-Os和黑云母K-Ar多元同位素定年系统准确刻画岩体侵位、热液成矿与冷却事件上有所重叠,岩浆-热液分异演化充分,且具有较高的冷却速率,精确厘定温泉斑岩系统岩浆活动的"多期性"(复式岩体)、成矿事件的"瞬时性"(~214Ma)和成矿作用的"持续性"(~8Myr)。同时,系统对比全球典型斑岩钼(铜)矿床成矿动力学背景,细化分类方案,即产于挤压背景的大洋俯冲和大陆碰撞环境矿床及产于伸展背景的后碰撞、陆缘弧后和板内裂谷环境矿床。明确在大洋俯冲→大陆碰撞→后碰撞→板内裂谷旋回的四个阶段均可以产生规模的斑岩型钼(铜)矿床,且挤压向伸展过渡的构造体制转换尤其是大型矿床形成的有利环境。     

In situ bioremediation of trichloroethylene-contaminated water by a resting-cell methanotrophic microbial filter

Abstract

An in situ microbial filter technology is being tested and developed for remediating migrating subsurface plumes contaminated with low concentrations of trichloroethylene (TCE). The current focus is the establishment of a replenishable bioactive zone (catalytic filter) along expanding plume boundaries by the injection of a representative methanotrophic bacterium, Methylosinus trichosporium OB3b. This microbial filter strategy has been successfully demonstrated using emplaced, attached resting cells (no methane additions) in a 1.1 m flow-through test bed loaded with water-saturated sand. Two separate 24 h pulses of TCE (109 ppb and 85 ppb), one week apart, were pumped through the system at a flow velocity of 15 mm h^?1; no TCE (< 0.5 ppb) was detected on the downstream side of the microbial filter. Subsequent excavation of the wet sand confirmed the existence of a TCE-bioactive zone 21 days after it had been created. An enhanced longevity of the cellular, soluble-form methane monooxygenase produced by this methanotroph is a result of the laboratory bioreactor culturing conditions. Additional experiments with cells in sealed vials and emplaced in the 1.1 m test bed yielded a high resting-cell finite TCE biotransformation capacity of about 0.25 mg per mg of bacteria; this is suitable for a planned sand-filled trench field demonstration at a Lawrence Livermore National Laboratory site.     

Preparing For Hyperseed MAC: An Observing Campaign To Monitor The Entry Of The Genesis Sample Return Capsule

The imminent return of the Genesis Sample Return Capsule (SRC) from the Earth’s L1 point on September 8, 2004, represents the first opportunity since the Apollo era to study the atmospheric entry of a meter-sized body at or above the Earth’s escape speed. Until now, reentry heating models are based on only one successful reentry with an instrumented vehicle at higher than escape speed, the 22 May 1965 NASA “FIRE 2” experiment. In preparation of an instrumented airborne and ground-based observing campaign, we examined the expected bolide radiation for the reentry of the Genesis SRC. We find that the expected emission spectrum consists mostly of blackbody emission from the SRC surface (T∼ ∼2630 K@peak heating), slightly skewed in shape because of a range of surface temperatures. At high enough spectral resolution, shock emission from nitrogen and oxygen atoms, as well as the first positive and first negative bands of N₂⁺, will stand out above this continuum. Carbon atom lines and the 389-nm CN band emission may also be detected, as well as the mid-IR 4.6-μm CO band. The ablation rate can be studied from the signature of trace sodium in the heat shield material, calibrated by the total amount of matter lost from the recovered shield. A pristine collection of the heat shield would also permit the sampling of products of ablation.