TY - JOUR

T1 - Organic metamorphism as a key for reconstructing tectonic processes: a case study from the Austroalpine unit (Eastern Alps)

AU - Rantitsch, Gerd

AU - Iglseder, Christoph

AU - Schuster, Ralf

AU - Hollinetz, Marianne Sophie

AU - Huet, Benjamin

AU - Werdenich, Manuel

N1 - Publisher Copyright: © 2020, The Author(s).

PY - 2020/7/3

Y1 - 2020/7/3

N2 - At the northwestern margin of the Gurktal Alps (Eastern Alps), Eoalpine (Cretaceous) thrusting of carbonaceous material (CM) bearing metasediments formed a very low- to low-grade metamorphic nappe stack above higher-grade metamorphic basement nappes. Sedimentary burial as well as progressive metamorphism transformed the enclosed CM to anthracite, metaanthracite and semigraphite. In a kinematically well-constrained section at the northwestern frontal margin of the nappe stack, this transformation has been investigated by vitrinite reflectance measurements and Raman spectroscopy of carbonaceous materials (RSCM). Automated, interactive fitting of Raman spectra estimates the metamorphic peak temperatures in a complete section through the upper part of the Upper Austroalpine unit. A RSCM trend indicates a temperature profile of ca. 250–600 °C. The top part of the gradient is reconstructed by one-dimensional thermal modeling. The certainty of ca. ± 25 °C at a confidence level of 0.9 resembles the data variability within a sample location. Due to the large calibration range, the method is able to reconstruct a thermal crustal profile in space and time. The study highlights the versatility of RSCM, which characterizes almost 250 Ma of a complex and polyphase tectonic history. RSCM data characterize the Variscan metamorphic grade in nappes now imbricated in the Eoalpine nappe stack. They additionally constrain a numerical model which emphasizes the significance of an increased thermal gradient in a continental margin towards the western Neotethyan ocean during Permo-Triassic lithospheric extension. It finally characterizes the Eoalpine metamorphic gradient during nappe stacking and a significant metamorphic jump related to exhumation and normal faulting.

AB - At the northwestern margin of the Gurktal Alps (Eastern Alps), Eoalpine (Cretaceous) thrusting of carbonaceous material (CM) bearing metasediments formed a very low- to low-grade metamorphic nappe stack above higher-grade metamorphic basement nappes. Sedimentary burial as well as progressive metamorphism transformed the enclosed CM to anthracite, metaanthracite and semigraphite. In a kinematically well-constrained section at the northwestern frontal margin of the nappe stack, this transformation has been investigated by vitrinite reflectance measurements and Raman spectroscopy of carbonaceous materials (RSCM). Automated, interactive fitting of Raman spectra estimates the metamorphic peak temperatures in a complete section through the upper part of the Upper Austroalpine unit. A RSCM trend indicates a temperature profile of ca. 250–600 °C. The top part of the gradient is reconstructed by one-dimensional thermal modeling. The certainty of ca. ± 25 °C at a confidence level of 0.9 resembles the data variability within a sample location. Due to the large calibration range, the method is able to reconstruct a thermal crustal profile in space and time. The study highlights the versatility of RSCM, which characterizes almost 250 Ma of a complex and polyphase tectonic history. RSCM data characterize the Variscan metamorphic grade in nappes now imbricated in the Eoalpine nappe stack. They additionally constrain a numerical model which emphasizes the significance of an increased thermal gradient in a continental margin towards the western Neotethyan ocean during Permo-Triassic lithospheric extension. It finally characterizes the Eoalpine metamorphic gradient during nappe stacking and a significant metamorphic jump related to exhumation and normal faulting.

UR - http://www.scopus.com/inward/record.url?scp=85087455369&partnerID=8YFLogxK

U2 - 10.1007/s00531-020-01897-7

DO - 10.1007/s00531-020-01897-7

M3 - Article

VL - 109.2020

SP - 2235

EP - 2253

JO - International journal of earth sciences : Geologische Rundschau : GR ; Geologische Rundschau

JF - International journal of earth sciences : Geologische Rundschau : GR ; Geologische Rundschau

SN - 1437-3254

IS - 6

ER -