1,721,110 research outputs found
Trapped minerals under stress
Full text linkResearch Focus on the problem of entrapment pressure estimation for mineral inclusions under residual pressure
Propagation of analytical errors in single-clinopyroxene geobarometry and implications on estimated mantle palaeogeotherms
No full textTowards a digital key to the lichens of Italy
No full textWork is in progress for the completion of a computer-aided key to all lichens known to occur in Italy, which will be freely available online, and as a free application for mobile devices. A first example, concerning the lichens of Northern Italy (2.339 infrageneric taxa), is already available online for testing. A computer-generated but manually edited dichotomous key is invoked for all species previously filtered via a multi-entry interface, where several selected characters can be specified in a single step. To optimize the two query interfaces, two different datasets are used, one for the dichotomous, the other for the multi-entry interface
Garnet and spinel in the upper mantle: Results from thermodynamic modeling in fertile and depleted compositions
No full textGarnet and spinel in fertile and depleted mantle: Insights from thermodynamic modelling
No full textWe performed thermodynamic calculations based on model and natural peridotitic compositions at pressure and temperature conditions relevant to the Earth's upper mantle, using well-established free energy minimization techniques. The model is consistent with the available experimental data in Cr-bearing peridotitic systems and can therefore be used to predict phase relations and mineral compositions in a wide range of realistic mantle compositions. The generated phase diagrams for six different bulk compositions, representative of fertile, depleted and ultra-depleted peridotitic mantle, shown that the garnet + spinel stability field is always broad at low temperatures and progressively narrows with increasing temperatures. In lithospheric sections with hot geotherms (ca. 60 mW/m 2 ), garnet coexists with spinel across an interval of 10-15 km, at ca. 50-70 km depths. In colder, cratonic, lithospheric sections (e.g. along a 40 mW/m 2 geotherm), the width of the garnet-spinel transition strongly depends on bulk composition: In fertile mantle, spinel can coexist with garnet to about 120 km depth, while in an ultra-depleted harzburgitic mantle, it can be stable to over 180 km depth. The formation of chromian spinel inclusions in diamonds is restricted to pressures between 4.0 and 6.0 GPa. The modes of spinel decrease rapidly to less than 1 vol % when it coexists with garnet; hence, spinel grains can be easily overlooked during the petrographical characterization of small mantle xenoliths. The very Cr-rich nature of many spinels from xenoliths and diamonds from cratonic settings may be simply a consequence of their low modes in high-pressure assemblages; thus, their composition does not necessarily imply an extremely refractory composition of the source rock. The model also shows that large Ca and Cr variations in lherzolitic garnets in equilibrium with spinel can be explained by variations of pressure and temperature along a continental geotherm and do not necessarily imply variations of bulk composition. The slope of the Cr# [i.e. Cr/(Cr + Al)mol] isopleths in garnet in equilibrium with spinel changes significantly at high temperatures, posing serious limitations to the applicability of empirical geobarometric methods calibrated on cratonic mantle xenoliths in hotter, off-craton, lithospheric mantle sections. © 2013 Springer-Verlag Berlin Heidelberg
A revision of the Ni-in-garnet geothermometer with special regard to its pressure dependence
Full text linkWe have explored the effect of temperature (T) and pressure (P) on Ni partitioning between garnet and olivine in well-equilibrated mantle xenoliths from on-craton, marginal-craton and off-craton settings and in high-P–T experiments at natural Ni abundance. Contrary to previous evaluations, the xenolith and experimental data indicate that the P effect is not negligible, consistent with the significant volume change of the garnet–olivine Mg-Ni exchange reaction. The recognition of a P effect satisfactorily resolves the discrepancies observed using previous calibrations of the Ni-in-Grt geothermometer and provides a solution to the long-standing controversy as to which Ni-in-Grt geothermometer is best applied to natural chromian pyrope compositions. A recalibrated, P-dependent Ni-in-garnet geothermometer reproduces the pyroxene T estimates for the xenoliths and the T conditions of the experiments with a standard error of estimate of 44 °C. The P dependence (ca. 40 °C/GPa) is comparable to that of the garnet–olivine Fe–Mg exchange geothermometer. A small tendency to overestimate at T < 900 °C relative to two-pyroxene thermometry is observed, which is unrelated to garnet compositional parameters. A set of simplified, geotherm-referenced calibrations permit traditional use of the Ni-in-garnet geothermometer as a single-mineral method, provided the local geotherm is known or can be estimated or inferred
Match algorithms for scientific names in floritaly, the portal to the flora of Italy
Full text linkScientific names are not part of everyday language in any modern country, and their input as strings in a query system can be easily associated with typographical errors. While globally unique identifiers univocally address a taxon name, they can hardly be used for querying a database manually. Thus, matching algorithms are often used to overcome misspelled names in query systems in several data repositories worldwide. In order to improve users’ experience in the use of FlorItaly, the Portal to the Flora of Italy, a near match algorithm to resolve misspelled scientific names has been integrated in the query systems. In addition, a novel tool in FlorItaly, capable of rapidly aligning any list of names to the nomenclatural backbone provided by the national checklists, has been developed. This manuscript aims at describing the potential of these new tools
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