Project

Back to overview

Tracking crustal contributions to rhyolite formation in the Chon Aike Province ( Patagonia)

English title Tracking crustal contributions to rhyolite formation in the Chon Aike Province ( Patagonia)
Applicant Putlitz Benita
Number 175808
Funding scheme Project funding (Div. I-III)
Research institution Institut des sciences de la Terre Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Geology
Start/End 01.03.2018 - 28.02.2022
Approved amount 320'000.00
Show all

All Disciplines (2)

Discipline
Geology
Geochemistry

Keywords (7)

timescales; crustal melting; rhyolite formation; Patagonia; oxygen isotope diffusion; Chon Aike Province; diffusionchronometry

Lay Summary (German)

Lead
Wir untersuchen die Enstehung von Rhyolithen, einem sehr SiO2-reichen vulkanischen Gestein. Der Ausbruch rhyolithischer Magmen ist häufig sehr explosiv, und ein besseres Verständnis der Genese von Rhyolithen dient in der Lagen Sicht einer besseren Abschätzung der Naturgefahren.
Lay summary

Wir untersuchen die Entstehung, einer grossen magmatischen Provinz, der Chon Aike Provinz, die im Jura entstanden ist und mit dem Aufbrechen des Superkontinentes Gondwana im Zusammenhang steht. Die vulkanischen Gesteine dieser Provinz bedeckt grosse Teile Patagoniens (Argentinien). Von besonderem Interesse ist, dass diese Gesteinsserien reich an Rhyolith, einem sehr SiO2-reichen vulkanischen Gestein, sind. Die Entstehung, solcher SiO2-reicher Vulkanite ist seit nicht nur Gegenstand wissenschaftlichen Diskussion, sie sind auch von gesellschaftlichem Interesse, da ein Ausbruch rhyolithischer Magmen häufig sehr explosiv ist, und gewaltige Menge von Asche ausgeworfen werden können – oft zum Schaden von Mensch und Natur. Beispiele solcher rhyolithischer Systeme sind die Yellowstone Provinz in den USA oder auch der Vulkan Chaitén in Chile.

 

Unser Interesse gilt der Frage nach der Entstehung solcher Magmen, speziell der Frage welche Rolle die Aufschmelzung einer bereits existierenden kontinentalen Kruste z.B. alter Sedimente in der Genese von Rhyolithen spielt (im Gegensatz zur sog. fraktionierten Kristallisation aus einem basaltischen Stamm-Magma). In diesem Rahmen werden wir auch neuen Methoden testen vor allem die Diffusion von Spurenelementen (z.B. das Verhalten von Titanium in Quarz). Dies erfordert den Gebrauch moderner hochauflösender Analysetechniken (Sekundär-Ionen-Massenspektrometrie). Diese Studien zur Geospeedometrie werden uns Aufschluss über den Zeitraum der Magmenbildung geben; im Besonderen ist die mögliche Abschätzung des Zeitraumes zwischen Kristallisation eines Minerals (z.B. Quarz) und dem Auswurf an der Oberfläche interessant.

 

Neue Daten werden zu einem besseren geologischen Verständnis solcher vulkanischen Systeme führt, und damit zu einer besseren Einschätzung ihres Gefahrenpotentials.  

Direct link to Lay Summary Last update: 23.01.2018

Responsible applicant and co-applicants

Employees

Name Institute

Project partner

Abstract

I propose to study the rhyolitic volcanic rocks (s.l.) of the Chon Aike Province in Patagonia to decipher (a) the importance of crustal melting in the formation of these rhyolites and the (b) duration of magma ascent and crystallization - both important and much debated topics in igneous petrology. The Jurassic Chon Aike Province of South America and Antarctica is thought to be one of the largest silicic provinces in the world, yet the geochemical database is quite incomplete. Only a few oxygen isotope data are available, despite the fact that oxygen isotopes provide stringent constraints on crustal assimilation processes involved in magma generation. Our new oxygen isotope data show that these peraluminous rhyolites are characterized by high 18O signatures, which in turn suggest a significant crustal - most likely sedimentary - contribution in the melt formation process. This yield new and important constraints on existing petrological models. Previous studies on the Patagonian silicic volcanics did discuss crustal contributions, and while early papers advocate crustal melting, later works suggest complex crystal fractionation and assimilation processes of a mafic crust. Thus - like elsewhere - there are still many open questions with regard to the nature of the source(s) involved (mafic vs. sediment), upper vs. lower crust, and the degree of melting and assimilation, and finally how to integrated this observation into our knowledge about the Jurassic tectonic landscape. Although, wholesale crustal meting seems difficult to achieve due to the important heat flux needed, the peraluminous composition and the high 18O data, clearly suggest a major crustal influence. In this project, we propose to test the hypothesis that the Chon Aike Province is also on the regional scale largely govern by melting of a sedimentary source. We will combine field work with state-of-the-art analytical techniques. To this end, we will employ stable isotope analysis using SIMS to look at quartz and zircon, specifically their intra-crystalline variations. Laser-fluorination will be used for whole rock analysis and to further supplement the mineral data. This analysis will be embedded in classical whole rock geochemistry supplemented by radiogenic analysis. Oxygen isotope analysis of zircon will be complemented by U/Pb dating and trace element work. SIMS respectively NanoSIMS intra-crystalline (mainly quartz) analysis in combinations with trace element determinations (e.g. Ti-in quartz) can finally also be used to access time scales of rhyolite formation using diffusion chronometry. In its oxygen isotope characteristic, the Chon Aike province seems very different from the well-known silicic system of the Western US, which are dominated by a low 18O signature. Also, the Chon Aike Province is of Jurassic age, and thus much older than many other large silicic systems. Thus, by studying the Chon Aike province we have a chance to enhance our knowledge about formation of rhyolites by investigating a relatively old silicic province, which seems to be govern by melting of supracrustal material. If the S-type oxygen isotope values prove to be a large-scale signature - suggested by the fact of the peraluminous character, which is well documented all over the province - this has important consequence of how we look at (revisit) crustal melting and in turn how we interpret the tectonic-magmatic models suggested for the Jurassic. Funding is asked for one (1) PhD student for 4 years, along with support for fieldwork (3 field season) and analytical expenses.
-