Post-supereruption recovery at Toba Caldera

Large calderas, or supervolcanoes, are sites of the most catastrophic and hazardous events on Earth, yet the temporal details of post-supereruption activity, or resurgence, remain largely unknown, limiting our ability to understand how supervolcanoes work and address their hazards. Toba Caldera, Indonesia, caused the greatest volcanic catastrophe of the last 100 kyr, climactically erupting ~74 ka. Since the supereruption, Toba has been in a state of resurgence but its magmatic and uplift history has remained unclear. Here we reveal that new 14 C, zircon U-Th crystallization and (U-Th)/He ages show resurgence commenced at 69.7±4.5 ka and continued until at least ~2.7 ka, progressing westward across the caldera, as reflected by post-caldera effusive lava eruptions and uplifted lake sediment. The major stratovolcano north of Toba, Sinabung, shows strong geochemical kinship with Toba, and zircons from recent eruption products suggest Toba's climactic magma reservoir extends beneath Sinabung and is being tapped during eruptions

Thermal history of the central Gotthard and Aar massifs, European Alps: Evidence for steady state, long-term exhumation

International audienceQuantifying long-term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces. Here we reconstruct the exhumation history of the central Aar and Gotthard external crystalline massifs in the European Alps using apatite and zircon fission track and apatite (U-Th)/He data. Age-elevation relationships and time-temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of ∼0.5 km/Ma since ∼14 Ma. A slightly accelerated rate (∼0.7 km/Ma) occurred from 16 to 14 Ma and again from 10 to 7 Ma. Faster exhumation between 16 and 14 Ma is most likely linked to indentation of the Adriatic wedge and related thrusting along the Alpine sole thrust, which, in turn, caused uplift and exhumation in the external crystalline massifs. The data suggest nearly steady, moderate exhumation rates since ∼14 Ma, regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 Ma or orogen-perpendicular extension initiated in Pliocene times. Recent uplift and denudation rates, interpreted to be the result of climate fluctuations and associated increase in erosional efficiency, are nearly twice this ∼0.5 km/Ma paleoexhumation rate

Tephrochronology

Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly

Rapid cooling and geospeedometry of granitic rocks exhumation within a volcanic arc: A case study from the Central Slovakian Neovolcanic Field (Western Carpathians)

U-Pb Sensitive High-Resolution Ion MicroProbe (SHRIMP) dating of zircon in combination with (U-Th)/He dating of zircon and apatite is applied to constrain the emplacement and exhumation history of the youngest granitic rocks in the Western Carpathians collected in the Central Slovakian Neovolcanic Field. Two samples of diorite from the locality Banky, and granodiorite from Banská Hodruša yield the U-Pb zircon concordia ages of 15.21 ±0.19 Ma and 12.92 ±0.27Ma, respectively, recording the time of zircon crystallization and the intrusions' emplacement. Zircon (U-Th)/He ages of 14.70 ±0.94 (Banky) and 12.65 ±0.61Ma (Banská Hodruša), and apatite (U-Th)/He ages of 14.45 ±0.70Ma (diorite) and 12.26 ±0.77Ma (granodiorite) are less than 1Myr younger than the corresponding zircon U-Pb ages. For both diorite and granodiorite rocks their chronological data thus document a simple cooling process from magmatic crystallization/solidification temperatures to near-surface temperatures in the Middle Miocene, without subsequent reheating. Geospeedometry data suggest for rapid cooling at an average rate of 678 ±158 °C/Myr, and the exhumation rate of 5mm/year corresponding to active tectonic-forced exhumation. The quick cooling is interpreted to record the exhumation of the studied granitic rocks complex that closely followed its emplacement, and was likely accompanied by a drop in the paleo-geothermal gradient due to cessation of volcanic activity in the area

Crustal-scale folding: Palaeozoic deformation of the mt painter inlier, South Australia

The Mt Painter Inlier (Northern Flinders Ranges, South Australia) was exhumed in the Yankaninna Anticline, in the hanging wall of the major NE-SW-running Paralana Fault System. Regional north-south compression resulted in SE-directed oblique and lateral ramping on to the rigid Curnamona Province. Formation of the crustal-scale anticline caused exhumation of up to 15 km of basement rocks in the core of the anticline. Currently exposed rocks reached the surface in Permian times. Folding and thrusting commenced between c. 500 and c. 450 Ma and lasted until the Permian Period. Contrary to previous studies, only a minor part of the deformation can be attributed to the c. 500 Ma Delamerian Orogeny, with most of the tectonic activity being contemporaneous with the Alice Springs and Lachlan Orogenies. New Permo-Triassic zircon and apatite (U-Th)/He ages, as well as a titanite fission-track age point to a long-lived nearsurface hydrothermal event that overprinted the basement and cover rocks. Hydrothermal reheating and burial below the Mesozoic Eromanga Basin sediments, to a depth of no more than 2 km, resulted in partial or full rejuvenation of the apatite (U-Th)/He system