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| Titel |
Cross correlation of chemical profiles in minerals: insights into the architecture of magmatic reservoirs |
| VerfasserIn |
Line Probst, Luca Caricchi, Martin Gander, Glenn Wallace |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250126952
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| Publikation (Nr.) |
 EGU/EGU2016-6748.pdf |
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| Zusammenfassung |
| Analysis of chemical zoning in minerals offers the opportunity to reconstruct the pre-eruptive
conditions and the temporal evolution of magmatic reservoirs. The chemical composition of
minerals is a function of the thermodynamic conditions of the reservoir from which they grow
and therefore minerals record the evolution and variation of residual melt chemistry and
intensive parameters within the magmatic system. A quantitative approach is required to
determine if similar crystals actually shared a portion of their crystallisation history. These
analyses are in many cases extremely time consuming and rather expensive. Therefore, it is
not always possible to analyse a statically significant number of crystals, especially within
their textural context in thin sections and that is the main reason to build automated
methods. We are presenting a numerical cross-correlation method that compares the
zonation pattern of minerals to identify if they share the totality or part of their
growth history. We modified the method first developed by Wallace and Bergantz
(2004) to compare profiles in minerals also from samples collected in different
outcrops and that can be used for any dataset (i.e. geochemical proxies in stratigraphic
sections).
The main purpose of this method is to objectively compare chemical profiles in minerals
(collected by electron microprobe, LA-ICP-MS or cathodoluminescence images) and
quantify their degree of similarity. For this purpose, we use a well-known mathematical tool:
the cross correlation which is a way of quantifying the difference between two given signals
at a given position. Once our program was built, we performed tests using a set of synthetic
profiles, profiles acquired along different transects of the same mineral and also on different
minerals.
Finally we applied our program to about 100 zircons from Kilgore Tuff, Heise Volcanic
Field (USA) collected at different stratigraphic levels in two different outcrops. The
correlation shows that two populations of zircons can be identified on the base of the
variations of grey-scale intensity of catholuminescence of their outer rims. The relative
proportion of zircons from the two population is different in the investigated sections, which
are locate at two extreme of the Heise caldera. No correlation was found between the cores of
these zircons. These results suggest, in agreement with recent zircon isotopic studies that
several isolated pockets of eruptible magma merged just before the eruption (e.g. Wotzlaw et
al., 2014).
References
[1] WALLACE, G.S. and BERGANTZ, G.W., 2004. Reconciling heterogeneity in crystal
zoning data : An application of shared characteristic diagrams at Chaos Crags, Lassen
Volcanic Center, California. Contributions to Mineralogy and Petrology, vol. 149, pp.
98-112.
[2] WOTZLAW, J.F., BINDEMAN, I.N., WATTS, K.E., SCHMITT, A.K., CARICCHI, L. and
SCHALTEGGER, U., 2014. Linking rapid magma reservoir assembly and eruption trigger
mechanisms at evolved Yellowstone-type supervolcanoes. Geology published online as
doi:10.1130/G35979.1. |
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