TY - JOUR A1 - Timmerman, Martin Jan T1 - Timing, geodynamic setting and character of Permo-Carboniferous magmatism in the foreland of the Variscan Orogen, NW Europe Y1 - 2004 SN - 1-86239-152-1 ER - TY - GEN A1 - Fairey, Brenton J. A1 - Timmerman, Martin Jan A1 - Sudo, Masafumi A1 - Tsikos, Harilaos T1 - The role of hydrothermal activity in the formation of Karst-hosted manganese deposits of the Postmasburg Mn Field, Northern Cape Province, South Africa T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - The Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, sérandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 966 KW - manganese ore KW - Postmasburg manganese field KW - hydrothermal KW - karst KW - South Africa Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-473304 SN - 1866-8372 IS - 966 ER - TY - JOUR A1 - Fairey, Brenton J. A1 - Timmerman, Martin Jan A1 - Sudo, Masafumi A1 - Tsikos, Harilaos T1 - The role of hydrothermal activity in the formation of Karst-hosted manganese deposits of the Postmasburg Mn Field, Northern Cape Province, South Africa JF - Minerals N2 - The Postmasburg Manganese Field (PMF), Northern Cape Province, South Africa, once represented one of the largest sources of manganese ore worldwide. Two belts of manganese ore deposits have been distinguished in the PMF, namely the Western Belt of ferruginous manganese ores and the Eastern Belt of siliceous manganese ores. Prevailing models of ore formation in these two belts invoke karstification of manganese-rich dolomites and residual accumulation of manganese wad which later underwent diagenetic and low-grade metamorphic processes. For the most part, the role of hydrothermal processes and metasomatic alteration towards ore formation has not been adequately discussed. Here we report an abundance of common and some rare Al-, Na-, K- and Ba-bearing minerals, particularly aegirine, albite, microcline, banalsite, serandite-pectolite, paragonite and natrolite in Mn ores of the PMF, indicative of hydrothermal influence. Enrichments in Na, K and/or Ba in the ores are generally on a percentage level for most samples analysed through bulk-rock techniques. The presence of As-rich tokyoite also suggests the presence of As and V in the hydrothermal fluid. The fluid was likely oxidized and alkaline in nature, akin to a mature basinal brine. Various replacement textures, particularly of Na- and K- rich minerals by Ba-bearing phases, suggest sequential deposition of gangue as well as ore-minerals from the hydrothermal fluid, with Ba phases being deposited at a later stage. The stratigraphic variability of the studied ores and their deviation from the strict classification of ferruginous and siliceous ores in the literature, suggests that a re-evaluation of genetic models is warranted. New Ar-Ar ages for K-feldspars suggest a late Neoproterozoic timing for hydrothermal activity. This corroborates previous geochronological evidence for regional hydrothermal activity that affected Mn ores at the PMF but also, possibly, the high-grade Mn ores of the Kalahari Manganese Field to the north. A revised, all-encompassing model for the development of the manganese deposits of the PMF is then proposed, whereby the source of metals is attributed to underlying carbonate rocks beyond the Reivilo Formation of the Campbellrand Subgroup. The main process by which metals are primarily accumulated is attributed to karstification of the dolomitic substrate. The overlying Asbestos Hills Subgroup banded iron formation (BIF) is suggested as a potential source of alkali metals, which also provides a mechanism for leaching of these BIFs to form high-grade residual iron ore deposits. KW - manganese ore KW - Postmasburg manganese field KW - hydrothermal KW - karst KW - South Africa Y1 - 2019 U6 - https://doi.org/10.3390/min9070408 SN - 2075-163X VL - 9 IS - 7 PB - MDPI CY - Basel ER - TY - JOUR A1 - Wilke, Franziska Daniela Helena A1 - O'Brien, Patrick J. A1 - Gerdes, Axel A1 - Timmerman, Martin Jan A1 - Sudo, Masafumi A1 - Khan, M. Ahmed T1 - The multistage exhumation history of the Kaghan Valley UHP series, NW Himalaya, Pakistan from U-Pb and Ar-40/Ar- 39 ages N2 - Amphibole and mica Ar-40/Ar-39 ages as well as zircon, rutile and titanite U-Pb geochronology of eclogites and associated host rocks from the Higher Himalayan Crystalline Nappes (Indian Plate) in the Upper Kaghan Valley, Pakistan allow distinction of a multistage exhumation history. An Eocene age for peak-pressure metamorphism has been obtained by phengite Ar-40/Ar-39 (47.3 +/- 0.3 Ma) and zircon U-Pb (47.3 +/- 0.4 and 47.4 +/- 0.3 Ma) ages from cover and basement gneisses. A very short-lived metamorphic peak and rapid cooling is documented by an amphibole Ar-40/Ar-39 age of 46.6 +/- 0.5 Ma and a rutile U-Pb age of 44.1 +/- 1.3 Ma from eclogites. Phengite and biotite ages from cover and basement sequences metamorphosed during the Himalayan orogeny are 34.5 +/- 0.2 to 28.1 +/- 0.2 Ma whereas youngest biotites, yielding 23.6 +/- 0.1 and 21.7 +/- 0.2 Ma, probably reflect argon partial resetting. The amphibole age, together with those derived from phengite and zircon demonstrate a rate of initial exhumation of 86-143 mm/a i.e. an extremely rapid transport of the Indian Plate continental crust from ultra-high pressure (UHP) conditions back to crustal levels (47-46 Ma for transport from 140 to 40 km depth). Subsequent exhumation (46-41 Ma, 40-35 km) slowed to about 1 mm/a at the base of the continental crust but increased again later towards slightly higher exhumation rates of ca. 2 mm/a (41-34 Ma, 35- 20 km). This indicates a change from buoyancy-driven exhumation at mantle depths to compression forces related to continent-continent collision and accompanied crustal folding, thrusting and stacking that finally exposed the former deeply-buried rocks. Y1 - 2010 UR - http://eurjmin.geoscienceworld.org/ U6 - https://doi.org/10.1127/0935-1221/2010/0022-2051 SN - 0935-1221 ER - TY - JOUR A1 - Heeremans, Michel A1 - Timmerman, Martin Jan A1 - Kirstein, Linda A. A1 - Faleide, J. I. T1 - The late carboniferous : early permian evolution of the central North Sea Y1 - 2004 ER - TY - GEN A1 - Meere, Patrick A. A1 - Mulchrone, Kieran F. A1 - McCarthy, David J. A1 - Timmerman, Martin Jan A1 - Dewey, John F. T1 - Prelithification and synlithification tectonic foliation development in a clastic sedimentary sequence T2 - Geology Y1 - 2016 U6 - https://doi.org/10.1130/G38103Y.1 SN - 0091-7613 SN - 1943-2682 VL - 44 SP - E397 EP - E397 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Meere, Patrick A. A1 - Mulchrone, Kieran F. A1 - McCarthy, Dave J. A1 - Timmerman, Martin Jan A1 - Dewey, John F. T1 - Prelithification and synlithification tectonic foliation development in a clastic sedimentary sequence JF - Geology N2 - The current view regarding the timing of regionally developed penetrative tectonic fabrics in sedimentary rocks is that their development postdates lithification of those rocks. In this case, fabric development is achieved by a number of deformation mechanisms, including grain rigid body rotation, crystal-plastic deformation, and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal structure of cleavage in low-grade metamorphic rocks. In this study we combine field observations with strain studies to characterize considerable (>50%) Acadian crustal shortening in a Devonian clastic sedimentary sequence from southwest Ireland. Despite these high levels of shortening there is a marked absence of the domainal cleavage structure and intraclast deformation that are expected with this level of deformation. Fabrics in these rocks are predominantly a product of rigid body rotation and repacking of extraformational clasts during deformation of a clastic sedimentary sequence before lithification was complete. Y1 - 2016 U6 - https://doi.org/10.1130/G37587.1 SN - 0091-7613 SN - 1943-2682 VL - 44 SP - 291 EP - 294 PB - American Institute of Physics CY - Boulder ER - TY - JOUR A1 - Ennis, Meg A1 - Meere, Patrick A. A1 - Timmerman, Martin Jan A1 - Sudo, Masafumi T1 - Post-Acadian sediment recycling in the Devonian Old Red Sandstone of Southern Ireland JF - Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research N2 - The Upper Devonian Munster Basin of southern Ireland has traditionally been viewed as a post-orogenic molasse deposit that was sourced from the Caledonides of central Ireland and subsequently deformed by the end Carboniferous Variscan orogenic event. The basin fill is composed of super-mature quartz arenite sandstone that clearly represents a second cycle of deposition. The source of this detritus is now recognized as Lower Devonian Dingle Basin red bed sequences to the north. This genetic link is based on the degree of similarity in the detrital mica chemistry in both of these units; micas plot in identical fields and define the same trends. In addition, the two sequences show increased textural and chemical maturity up-sequence and define indistinguishable Ar-40/Ar-39 age ranges for the detrital mica grains. Partial resetting of the Ar ages can be attributed to elevated heat flow in the region caused by Munster Basin extension and subsequent Variscan deformation. The combined evidence from southwest Ireland therefore points to a Caledonian or possibly Taconian primary source area that initially shed detritus into the Lower Devonian Dingle Basin which was subsequently recycled into the Upper Devonian Munster Basin following mid-Devonian Acadian basin inversion. (C) 2014 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved. KW - Caledonian KW - Acadian KW - Variscan KW - Old Red Sandstone KW - Sediment recycling Y1 - 2015 U6 - https://doi.org/10.1016/j.gr.2014.10.007 SN - 1342-937X SN - 1878-0571 VL - 28 IS - 4 SP - 1415 EP - 1433 PB - Elsevier CY - Amsterdam ER - TY - BOOK A1 - Wilson, M. A1 - Neumann, Else Ragnhild A1 - Davies, G. R. A1 - Timmerman, Martin Jan A1 - Heeremans, Michel A1 - Larsen, Bjoern Tore T1 - Permo-carboniferous magmatism and rifting in Europe T3 - Geological Society special publication Y1 - 2004 UR - http://www.geolsoc.org.uk/template.cfm?name=bookshop_details&action=details&id=302 SN - 1-86239-152-1 VL - 223 PB - Geological Society CY - London ER - TY - JOUR A1 - Henk, A. A1 - Timmerman, Martin Jan T1 - Permian basins Y1 - 2005 ER -