Trace element evolution in the Phlegrean Fields (Central Italy): fractional crystallization and selective enrichment

Trace element analysis of Phlegrean Fields volcanic products shows that they belong to a homogeneous series whose evolution is due mainly to fractional crystallization. However quantitative modelling of crystal fractionation using measured mineral/groundmass and computed bulk distribution coefficients singles out K, Sb, Cl and F as elements which are selectively enriched in the differentiation process with respect to proven hygromagmaphile (HYG) elements. This anomalous enrichment involving elements that are easily transported in a magmatic fluid phase is thought to be due to percolation of such a fluid through a stored magma body. This enrichment is strongest in products resulting from protracted differentiation (trachybasalts-latites). Isotopic data from the literature are reinterpreted in terms of this model and show good agreement. Trace elements concentrations in clinopyroxenes provide evidence that complex differentiation paths were followed to produce latitic magmas. Their origin by mixing of magmas from different parentages is not indicated by the data. However, mixing of batches of the same parentage but of different degree of evolution seems likely. Because HYG elements ratios are not modified in the evolution of the magmas, they record these ratios in the partial melting zone. For example, the Th/Ta ratio in the source areas of the magmas has apparently been quite heterogeneous.     

Serpentinization of the martian crust during Noachian

This paper proposes a model of serpentinization of the Southern martian crust that may explain the topographic dichotomy, the absence of an associated free-air gravity anomaly and the presence of strong magnetic anomalies in the Southern Hemisphere. The thermodynamical conditions for serpentinization were likely met in the lithosphere during the Noachian period. This process may have decreased the density in the Southern crust and created the topographic dichotomy. Different reactions of serpentinization that can form magnetite have been considered. Assuming an intense magnetic field (core dynamo), we obtain chemical remanent magnetizations that are in the order of the estimates deduced from martian magnetic anomaly studies. The pertinence and the implications of our model concerning the early thermal evolution of Mars are discussed, with emphasis on the intensity of the paleo-magnetic field.     

The non‐trivial problem of meteorite pairing

Abstract— Pairing is the procedure of identifying fragments of a single meteorite fall (that were separated during atmospheric passage or during terrestrial history) by establishing the similarity of two or more meteorite fragments. We argue that pairing is governed by two principles, that only a single mismatch of properties is required to refute a proposed pairing, and that virtually all pairings bear some degree of uncertainty. Using data distributions for modern falls, we take a probability approach to estimate degrees of certainty associated with proposed pairings, emphasizing the importance of unusual features. For new pairing criteria or new analytical additions to old criteria, the degree of variation within individual meteorites must be delineated and the degree of variation within meteorite classes must be quantified. Criteria for pairing can be divided into (1) parent body history indicators, (2) meteoroid space history indicators, and (3) terrestrial history indicators. Included in these categories are 11 specific criteria, including petrographic textures, mineralogy and mineral composition, terrestrial age estimates, cosmic‐ray exposure ages, and natural thermoluminescence (TL) levels. Not all criteria are applicable to all meteorite types. About 2275 pairings suggested in the literature have been subjected to this analysis. Many literature pairings, especially those involving common meteorite types, bear large uncertainties due to lack of data.     

Variably saturated groundwater modelling for optimizing managed aquifer recharge using trench infiltration

Spreading‐basin methods have resulted in more than 130 million cubic metres of recharge to the unconfined Navajo Sandstone of southern Utah in the past decade, but infiltration rates have slowed in recent years because of reduced hydraulic gradients and (or) clogging. Trench infiltration is a promising alternative technique for increasing recharge and minimizing evaporation. This paper uses a variably saturated flow model to further investigate the relative importance of the following variables on rates of trench infiltration to unconfined aquifers: saturated hydraulic conductivity, trench spacing and dimensions, initial water‐table depth, alternate wet/dry periods, and number of parallel trenches. Modelling results showed (1) increased infiltration with higher hydraulic conductivity, deeper initial water tables, and larger spacing between parallel trenches, (2) deeper or wider trenches do not substantially increase infiltration, (3) alternating wet/dry periods result in less overall infiltration than keeping the trenches continuously full, and (4) larger numbers of parallel trenches within a fixed area increases infiltration but with a diminishing effect as trench spacing becomes tighter. An empirical equation for estimating expected trench infiltration rates as a function of hydraulic conductivity and initial water‐table depth was derived and can be used for evaluating feasibility of trench infiltration in other hydrogeologic settings. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermoluminescence survey of 12 meteorites collected by the European 1988 Antarctic meteorite expedition to Allan Hills and the importance of acid washing for thermoluminescence sensitivity measurements

Abstract— Natural and induced thermoluminescence (TL) data are reported for 12 meteorites recovered from the Allan Hills region of Antarctica by the European field party during the 1988/89 field season. The samples include one with extremely high natural TL, ALH88035, suggestive of exposure to unusually high radiation doses (i.e., low degrees of shielding), and one, ALH88034, whose low natural TL suggests reheating within the last 10⁵ years. The remainder have natural TL values suggestive of terrestrial ages similar to those of other meteorites from Allan Hills. ALH88015 (L6) has induced TL data suggestive of intense shock. TL sensitivities of these meteorites are generally lower than observed falls of their petrologic types, as is also observed for Antarctic meteorites in general. Acid-washing experiments indicate that this is solely the result of terrestrial weathering rather than a nonterrestrial Antarctic—non-Antarctic difference. However, other TL parameters, such as natural TL and induced peak temperature-width, are unchanged by acid washing and are sensitive indicators of a meteorite's metamorphic and recent radiation history.     

EPR microplates, a model for the Oman Ophiolite

Structural mapping in the Southern half of the Oman ophiolite has revealed a palaeoridge organization with similarities to an EPR microplate, forming in superfast spreading conditions. A NW-trending propagator was rapidly opening in a lithosphere no more than 1 Myr older and itself created in a NE-SW ridge system. The NW-trending propagator, underlined by small mantle diapirs, was active or dying when detached as part of a future ophiolite. Local thrusting of the future ophiolite was also initiated very early, between 1 and 5 Myr after ridge accretion; it was accompanied by a 40° rotation within this time lapse. Such an activity supports the comparison of the Oman palaeoridge system with an oceanic microplate, and provides evidence to suggest the existence of thrusts at active microplates.     

Rapid changes in the nature of the H chondrites falling to Earth

Abstract— We have previously identified a subgroup of Antarctic H chondrites that are significantly different from H chondrites among the modern falls in terms of induced thermoluminescence (TL), metallographic cooling rate, and cosmogenic inert gas contents. Here we examine their terrestrial and thermal history as apparent in their natural TL and radioactive cosmogenic isotope abundances. These meteorites have a tendency towards high ²⁶Al activities and fairly short ¹⁴C and ³⁶Cl terrestrial ages (generally <100 ka). They also sometimes exhibit unusually high natural TL levels, which we have previously interpreted as indicating orbital evolution from perihelia >1.2 AU to ～1 AU within the last <10⁵ years. We suggest that the nature of the meteorites falling to Earth is not independent of time but depends on stochastic events, such as the breakup of parent bodies and recent variations in orbit.