Isotope Geology and Petrology
Isotope geology interprets isotopic signals to reconstruct geologic processes. These signals result from the physical and chemical separation of isotopes and from radioactive processes. Radiometric dating allows to assign an absolute age to geologic processes. This method is based on the radioactive decay of a parent isotope to a daughter isotope using the half-life (time interval after which half of the initial amount of the parent isotope has decayed) to calculate an age. Depending on the geologic setting the rock originates from, the rock´s mineral content, and the isotopic system selected for analysis the temporal succession of important geological events can be reconstructed. These events could be, for example, magmatic or metamorphic crystallization, erosion and cooling of rocks, volcanic eruptions, or deposition and diagenesis of sediments.
Current research by our group focusses on understanding the development of magmatic systems. We study minerals that are stable even at magmatic temperatures and that contain the radioactive element uranium (U) such as zircon, allanite, baddeleyite, or monazite. Some of the decay products of U are short-lived (e.g., 230Th) and others are stable (e.g., Pb and He). Using the ion probe (SIMS = secondary ion mass spectrometry) is essential to determine the duration of crystal growth over natural time scales. The isotopic fingerprint of the minerals makes it possible to resolve their origin in a geological and archaeological context, for example when dating and correlating volcanic deposits.
Rocks are archives of the geologic history of the Earth as well as witnesses of hidden processes occurring deep in the Earth which are crucial for the development of the planet. The composition, texture, and structure of rocks helps to decipher their origin in respect of the physical and chemical conditions during their formation. Geological processes such as magmatism, weathering, diagenesis, or metamorphism leave traces in the mineral components whose isotopic composition can vary in the micro- to nano-range. Therefore, petrologic research applies a variety of microscopic methods (from the petrographic microscope to the ion probe) which are available in a unique constellation at the Institute of Earth Sciences Heidelberg.
New study on the evolution of Toba caldera after the supereruption in cooperation with researchers from the US, Australia, and Indonesia
Image courtesy of NASA/GSFC/MITI/ERSDAC/JAROS, and the U.S./Japan ASTER Science Team.
Presentation of HIP - Heidelberg Ion Probe during the RIMG Shortcourse (Vienna 2017)
Publication & cover photo in the journal "Geology":
Tierney, C. R.*, Schmitt, A. K., Lovera, O. M., & de Silva, S. L. (2016). Voluminous plutonism during volcanic quiescence revealed by thermochemical modeling of zircon. Geology, 44(8), 683-686.
Student field trip to Oman:
In March a small group of geology students and professors from Heidelberg went to Oman to study the petrology of the oceanic crust and learn about geochemical and tectonic processes of the Oman-Ophiolith. The ophiolith represents a complete sequence of oceanic crust and upper mantle which is usually located in several kilometers of depth and under a few kilometers of water, well hidden from the researchers' eyes. In the Oman mountains this sequence comes up to surface and offers the rare opportunity to investigate several million year old oceanic rocks at the Earth's surface.
2015 Gondwana Research Best Paper Award for:
Robinson, Paul T., Robert B. Trumbull, Axel Schmitt, Jing-Sui Yang, Jian-Wei Li, Mei-Fu Zhou, Jörg Erzinger, Sarah Dare, and Fahui Xiong. "The origin and significance of crustal minerals in ophiolitic chromitites and peridotites." Gondwana Research 27, no. 2 (2015): 486-506.
The paper reports the surprising presence of crustal minerals in oceanic upper mantle rocks from Tibet, Oman and Russia.
Is there a strombolian eruption (photo) depicted in a 35000 year old cave painting in south-eastern France? This is what French scientists assume who dated samples of volcanic rocks from the Bas-Vivarais Region at approximately this age. In an interview with the journal NATURE Axel Schmitt from the Institute of Earth Sciences at Heidelberg University commented on the results.
Photo: Stromboli (Felix Wicke)
Publication of the Master student Wan-Ning-Wu „U-Th baddeleyite geochronology and its significance to date the emplacement of silica undersaturated magmas” presented as “Highlight and Breakthrough“ in the October edition of the journal „American Mineralogist“ (Bernal, J. P., 2015, Reaching new boundaries for in-situ U-Th geochronology. American Mineralogist, 100, 2017-2017).