Bart Willem Hendrik Hendriks

Pattern and timing of the post-Caledonian denudation of northern Scandinavia constrained by apatite fission-track thermochronology

Abstract Apatite fission-track thermochronology has been used to study the post-Caledonian denudation history of northern Scandinavia. Post-orogenic denudation progressively shifted from the interior of the continent towards the North Atlantic margin. The present-day area of maximum elevation in the Northern Scandes mountain range has experienced continuous denudation at least since Jurassic time. In Jurassic-Cretaceous time, the area north and east of this region experienced either no denudation at all or some denudation followed by a transient thermal event with a peak temperature in late Cretaceous time. Final denudation of the area to the east of the Northern Scandes probably started in late Cretaceous-Paleogene time and possibly accelerated in Neogene time. The denudation history of northern Scandinavia can be explained by scarp retreat of an uplifted rift flank. The pattern and timing of denudation of the Northern Scandes is different from that of the Southern Scandes, which experienced domal-style, late-stage postrift uplift in Neogene time. Geomorphological observations, offshore data from the Atlantic and Barents Sea margins, and scarce stratigraphical information from the mainland are in general agreement with the new thermochronological data.

Palaeoposition of the Seychelles microcontinent in relation to the Deccan Traps and the Plume Generation Zone in Late Cretaceous-Early Palaeogene time

Abstract The Early Palaeogene magmatic rocks of North and Silhouette Islands in the Seychelles contain clues to the Cenozoic geodynamic puzzle of the Indian Ocean, but have so far lacked precise geochronological data and palaeomagnetic constraints. New 40Ar/39Ar and U–Pb dates demonstrate that these rocks were emplaced during magnetochron C28n; however, 40Ar/39Ar and palaeomagnetic data from Silhouette indicate that this complex experienced a protracted period of cooling. The Seychelles palaeomagnetic pole (57.55°S and 114.22°E; A9512.3°, N=14) corresponds to poles of similar ages from the Deccan Traps after being corrected for a clockwise rotation of 29.4°±12.9°. This implies that Seychelles acted as an independent microplate between the Indian and African plates during and possibly after C27r time, confirming recent results based on kinematic studies. Our reconstruction confirms that the eruption of the Deccan Traps, which affected both India and the Seychelles and triggered continental break-up, can be linked to the present active Reunion hotspot, which is being sourced as a deep plume from the Plume Generation Zone. Supplementary material: Experimental data are available at http://www.geolsoc.org.uk/SUP18482.

Tectonic evolution and paleogeography of the Kırşehir Block and the Central Anatolian Ophiolites, Turkey

In Central and Western Anatolia two continent-derived massifs simultaneously underthrusted an oceanic lithosphere in the Cretaceous and ended up with very contrasting metamorphic grades: high pressure, low temperature in the Tavsanli zone and the low pressure, high temperature in the Kirsehir Block. To assess why, we reconstruct the Cretaceous paleogeography and plate configuration of Central Anatolia using structural, metamorphic, and geochronological constraints and Africa-Europe plate reconstructions. We review and provide new 40Ar/39Ar and U/Pb ages from Central Anatolian metamorphic and magmatic rocks and ophiolites and show new paleomagnetic data on the paleo-ridge orientation in a Central Anatolian Ophiolite. Intraoceanic subduction that formed within the Neotethys around 100–90 Ma along connected N-S and E-W striking segments was followed by overriding oceanic plate extension. Already during suprasubduction zone ocean spreading, continental subduction started. We show that the complex geology of central and southern Turkey can at first order be explained by a foreland-propagating thrusting of upper crustal nappes derived from a downgoing, dominantly continental lithosphere: the Kirsehir Block and Tavsanli zone accreted around 85 Ma, the Afyon zone around 65 Ma, and Taurides accretion continued until after the middle Eocene. We find no argument for Late Cretaceous subduction initiation within a conceptual “Inner Tauride Ocean” between the Kirsehir Block and the Afyon zone as widely inferred. We propose that the major contrast in metamorphic grade between the Kirsehir Block and the Tavsanli zone primarily results from a major contrast in subduction obliquity and the associated burial rates, higher temperature being reached upon higher subduction obliquity.

Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia recorded in the Ayhan-Büyükkışla basin

The configuration and evolution of subduction zones in the Eastern Mediterranean region in Cretaceous time accommodating Africa–Europe convergence remain poorly quantitatively reconstructed, owing to a lack of kinematic constraints. A recent palaeomagnetic study suggested that the triangular Central Anatolian Crystalline Complex (CACC) consists of three blocks that once formed an ~N–S elongated continental body, underthrusted below ophiolites in Late Cretaceous time. After extensional exhumation and upon Palaeogene collision of the CACC with the Pontides of the southern Eurasian margin, the CACC broke into three fragments that rotated and converged relative to each other. Here, we date the extension and contraction history of the boundary between two of the rotating massifs of the CACC by studying the Upper Cretaceous–Palaeogene Ayhan–Büyükkışla basin. We report an 40Ar/39Ar age of an andesite at the base of the sequence to show that the deposition started in an E–W extensional basin around 72.11 ± 1.46. The basin developed contemporaneously with regional exhumation of the CACC metamorphics. The lower basin sedimentary rocks were unconformably covered by mid-Eocene limestones and redbeds, followed by intense folding and thrust faulting. Two balanced cross-sections in the study area yield a minimum of 17–27 km of post-mid-Eocene ~N–S shortening. We thus demonstrate the Cenozoic compressional nature of the Kırşehir–Niğde-Hırkadağ block boundary and show that the extensional exhumation of the CACC predates collision-related contraction. A plate kinematic scenario is required to explain these observations that involves two Late Cretaceous–Palaeogene subduction zones to the north and south of the CACC, for which we show a possible plate boundary configuration.

Compilation and appraisal of geochronological data from the North Atlantic Igneous Province (NAIP)

Abstract The North Atlantic Igneous Province (NAIP), composed of volcanic sequences and intrusive rocks, occurs onshore in Greenland, the Faeroe Islands, the UK and Ireland, and offshore surrounding these areas as well as the west coast of Norway. Geochronological data have been published for Cenozoic igneous and volcanic rocks for much of the province, and provide valuable information to analyse the evolution of the province and magmatic processes more broadly. As part of the NE Atlantic Geosciences (NAG) cooperation, we examined approximately 700 dates from over 70 published studies and created a comprehensive database to facilitate ready access to this important information. This includes U–Pb, Rb–Sr, Re–Os, 40Ar/39Ar and K–Ar ages presented relative to the Geological Time Scale 2012. 40Ar/39Ar and K–Ar ages have been recalculated to a common reference. The complete database includes data that range from approximately 177 to 0.19 Ma. Our evaluation shows that variable sample quality, ambiguous data-handling methods, inadequate data reporting and data interpretation should preclude the use of data for purposes of rigorous geochronological analysis. Through a series of filtering techniques described here, we suggest excluding >500 dates as being of too poor a quality to use in age determinations. Our analysis highlights the need for published geochronological studies to include sufficient information to allow critical assessment of ages and interpretations. We present an ‘optimized’ dataset containing 130 ages that range from approximately 64 to 13 Ma. The filtered dataset emphasizes the need for firm chronological benchmarks and suggests that some sub-provinces in the NAIP would greatly benefit from renewed research attention. Supplementary material: The full NAG-TEC Geochronological Database 001 and Data Evaluation 002 are available at https://doi.org/10.6084/m9.figshare.c.3554472

Reply to the Comment by Côme Lefebvre on the paper: ‘Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia recorded in the Ayhan-Büyükkışla basin’ by Advokaat et al. 2014

Reply to the Comment by Come Lefebvre on the paper: ‘Late Cretaceous extension and Palaeogene rotation-related contraction in Central Anatolia recorded in the Ayhan-Buyukkisla basin’ by Advokaat et al. 2014 Eldert L. Advokaat, Douwe J.J. van Hinsbergen, Nuretdin Kaymakci, Reinoud L.M. Vissers & Bart W.H. Hendriks a Department of Earth Sciences, University of Utrecht, Utrecht, The Netherlands b SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, UK c Department of Geological Engineering, Middle East Technical University, Ankara, Turkey d Palaeomagnetic Laboratory ‘Fort Hoofddijk’, Department of Earth Sciences, University of Utrecht, Utrecht, The Netherlands e Centre for Geodynamics, Geological Survey of Norway (NGU), Trondheim, Norway Published online: 01 Apr 2015.