![Hier klicken, um den Treffer aus der Auswahl zu entfernen](images/unchecked.gif) |
Titel |
Using titanite petrochronology to monitor CO2-degassing episodes from the Himalayas |
VerfasserIn |
Giulia Rapa, Chiara Groppo, Franco Rolfo, Maurizio Petrelli, Pietro Mosca |
Konferenz |
EGU General Assembly 2017
|
Medientyp |
Artikel
|
Sprache |
en
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250143305
|
Publikation (Nr.) |
EGU/EGU2017-7011.pdf |
|
|
|
Zusammenfassung |
Metamorphic degassing from active collisional orogens supplies a significant fraction of CO2 to the atmosphere, playing a fundamental role in the long-term (> 1 Ma) global carbon cycle (Gaillardet & Galy, 2008). The petro-chronologic study of the CO2-source rocks (e.g. calc-silicate rocks) in collisional settings is therefore fundamental to understand the nature, timing, duration and magnitude of the orogenic carbon cycle. So far, the incomplete knowledge of these systems hindered a reliable quantitative modelling of metamorphic CO2 fluxes.
A detailed petrological modelling of a clinopyroxene + scapolite + K-feldspar + plagioclase + biotite + zoisite ± calcite calc-silicate rock from central Nepal Himalaya allowed us to identify and fully characterize - for the first time - different metamorphic reactions that led to the simultaneous growth of titanite and production of CO2. These reactions involve biotite (rather than rutile) as the Ti-bearing reactant counterpart of titanite. The results of petrological modelling combined with Zr-in-Ttn thermometry and U-Pb geochronology suggest that in the studied sample, most titanite grains grew during two nearly continuous episodes of titanite formation: a near-peak event at 730-740°C, 10 kbar, 25.5±1.5 Ma, and a peak event at 740-765°C, 10.5 kbar, 22±3 Ma. Both episodes of titanite growth are correlated to specific CO2-producing reactions, thus allowing to constrain the timing, duration and P-T conditions of the main CO2-producing events, as well as the amounts of CO2 produced. Assuming that fluids released at a depth of ca. 30 km are able to reach the Earth’s surface ~10 Ma after their production, it is therefore possible to speculate on the role exerted by the Himalayan orogenesis on the climate in the past.
Gaillardet J. & Galy A. (2008): Himalaya-carbon sink or source? Science, 320, 1727–1728. |
|
|
|
|
|