TY - JOUR A1 - Terbishalieva, Baiansuluu A1 - Timmerman, Martin Jan A1 - Mikolaichuk, Alexander A1 - Altenberger, Uwe A1 - Slama, Jiri A1 - Schleicher, Anja Maria A1 - Sudo, Masafumi A1 - Sobel, Edward A1 - Cichy, Sarah Bettina T1 - Calc-alkaline volcanic rocks and zircon ages of the late Tonian BT - Early Cryogenian arc-related Big Naryn Complex in the Eastern Djetim-Too Range, Middle Tianshan block, Kyrgyzstan JF - International journal of earth sciences N2 - The Big Naryn Complex (BNC) in the East Djetim-Too Range of the Kyrgyz Middle Tianshan block is a tectonized, at least 2 km thick sequence of predominantly felsic to intermediate volcanic rocks intruded by porphyric rhyolite sills. It overlies a basement of metamorphic rocks and is overlain by late Neoproterozoic Djetim-Too Formation sediments; these also occur as tectonic intercalations in the BNC. The up to ca. 1100 m thick Lower Member is composed of predominantly rhyolites-to-dacites and minor basalts, while the at least 900 m thick pyroclastic Upper Member is dominated by rhyolitic-to-dacitic ignimbrites. Porphyric rhyolite sills are concentrated at the top of the Lower Member. A Lower Member rhyolite and a sill sample have LA-ICP-MS U-Pb zircon crystallization ages of 726.1 +/- 2.2 Ma and 720.3 +/- 6.5 Ma, respectively, showing that most of the magmatism occurred within a short time span in the late Tonian-early Cryogenian. Inherited zircons in the sill sample have Neoarchean (2.63, 2.64 Ga), Paleo- (2.33-1.81 Ga), Meso- (1.55 Ga), and Neoproterozoic (ca. 815 Ma) ages, and were derived from a heterogeneous Kuilyu Complex basement. A 1751 +/- 7 Ma Ar-40/Ar-39 age for amphibole from metagabbro is the age of cooling subsequent to Paleoproterozoic metamorphism of the Kuilyu Complex. The large amount of pyroclastic rocks, and their major and trace element compositions, the presence of Neoarchean to Neoproterozoic inherited zircons and a depositional basement of metamorphic rocks point to formation of the BNC in a continental magmatic arc setting. KW - Tianshan orogenic belt KW - Big Naryn complex KW - Tonian–Cryogenian KW - magmatic arc KW - calc-alkaline KW - Kuilyu complex Y1 - 2021 U6 - https://doi.org/10.1007/s00531-020-01956-z SN - 1437-3254 SN - 1437-3262 VL - 110 IS - 1 SP - 353 EP - 375 PB - Springer CY - New York ER - TY - JOUR A1 - Rötzler, Jochen A1 - Timmerman, Martin Jan T1 - Geochronological and petrological constraints from the evolution in the Saxon Granulite Massif, Germany, on the Variscan continental collision orogeny JF - Journal of metamorphic geology N2 - Controversy over the plate tectonic affinity and evolution of the Saxon granulites in a two- or multi-plate setting during inter- or intracontinental collision makes the Saxon Granulite Massif a key area for the understanding of the Palaeozoic Variscan orogeny. The massif is a large dome structure in which tectonic slivers of metapelite and metaophiolite units occur along a shear zone separating a diapir-like body of high-Pgranulite below from low-Pmetasedimentary rocks above. Each of the upper structural units records a different metamorphic evolution until its assembly with the exhuming granulite body. New age and petrologic data suggest that the metaophiolites developed from early Cambrian protoliths during high-Pamphibolite facies metamorphism in the mid- to late-Devonian and thermal overprinting by the exhuming hot granulite body in the early Carboniferous. A correlation of new Ar-Ar biotite ages with publishedP-T-tdata for the granulites implies that exhumation and cooling of the granulite body occurred at average rates of similar to 8 mm/year and similar to 80 degrees C/Ma, with a drop in exhumation rate from similar to 20 to similar to 2.5 mm/year and a slight rise in cooling rate between early and late stages of exhumation. A time lag ofc. 2 Ma between cooling through the closure temperatures for argon diffusion in hornblende and biotite indicates a cooling rate of 90 degrees C/Ma when all units had assembled into the massif. A two-plate model of the Variscan orogeny in which the above evolution is related to a short-lived intra-Gondwana subduction zone conflicts with the oceanic affinity of the metaophiolites and the timescale ofc. 50 Ma for the metamorphism. Alternative models focusing on the internal Variscan belt assume distinctly different material paths through the lower or upper crust for strikingly similar granulite massifs. An earlier proposed model of bilateral subduction below the internal Variscan belt may solve this problem. KW - geochronology KW - granulite KW - high-Pmetamorphism KW - metaophiolite KW - Variscan KW - orogeny Y1 - 2020 U6 - https://doi.org/10.1111/jmg.12559 SN - 0263-4929 SN - 1525-1314 VL - 39 IS - 1 SP - 3 EP - 38 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Krmíček, Lukáš A1 - Timmerman, Martin Jan A1 - Ziemann, Martin Andreas A1 - Sudo, Masafumi A1 - Ulrych, Jaromir T1 - 40Ar/39Ar step-heating dating of phlogopite and kaersutite megacrysts from the Železná hůrka (Eisenbühl) Pleistocene scoria cone, Czech Republic JF - Geologica Carpathica N2 - (40)A/Ar-39 step-heating of mica and amphibole megacrysts from hauyne-bearing olivine melilitite scoria/tephra from the Zelezna hurka yielded a 435 +/- 108 ka isotope correlation age for phlogopite and a more imprecise 1.55 Ma total gas age of the kaersutite megacryst. The amphibole megacrysts may constitute the first, and the younger phlogopite megacrysts the later phase of mafic, hydrous melilitic magma crystallization. It cannot be ruled out that the amphibole megacrysts are petrogenetically unrelated to tephra and phlogopite megacrysts and were derived from mantle xenoliths or disaggregated older, deep crustal pegmatites. This is in line both with the rarity of amphibole at Zelezna hurka and with the observed signs of magmatic resorption at the edges of amphibole crystals. KW - Bohemian Massif KW - Zelezna hurka KW - Eisenbuhl KW - argon dating KW - mica KW - amphibole KW - melilitite Y1 - 2020 U6 - https://doi.org/10.31577/GeolCarp.71.4.6 SN - 1335-0552 SN - 1336-8052 VL - 71 IS - 4 SP - 382 EP - 387 PB - Veda CY - Bratislava 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 - 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 - 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 - Motuza, Gediminas A1 - Sliaupa, Saulius A1 - Timmerman, Martin Jan T1 - Geochemistry and Ar-40/Ar-39 age of Early Carboniferous dolerite sills in the southern Baltic Sea JF - Estonian journal of earth sciences N2 - The Early Carboniferous magmatic event in the southern Baltic Sea is manifested by dolerite intrusions. The presumable area in which the dolerite intrusions occur ranges from 30 to 60 km in east-west direction, and is about 100 km in north-south direction. The dolerites were sampled in well D1-1 and investigated by applying chemical analysis and Ar-40/Ar-39 step-heating dating. Dolerites are classified as alkali and sodic, characterized by high TiO2 (3.92, 3.99 wt%) and P2O5 (1.67, 1.77 wt%) and low MgO (4.89, 4.91 wt%) concentrations, enriched in light rare earth elements, originated from an enriched mantle magma source and emplaced in a continental rift tectonic setting. The 351 +/- 11 Ma Ar-40/Ar-39 plateau age for groundmass plagioclase indicates a considerable age gap with the 310-250 Ma magmatism in southern Scandinavia and northern Germany. The magmatic rocks in the Baltic Sedimentary Basin are coeval with alkaline intrusions of NE Poland. Both magmatic provinces lie in the northwestward prolongation of the Pripyat-Dnieper-Donetsk Rift (370-359 Ma) and may constitute a later phase of magmatic activity of this propagating rift system. KW - dolerite KW - rifting KW - Carboniferous KW - argon dating KW - Baltic Sea Y1 - 2015 U6 - https://doi.org/10.3176/earth.2015.30 SN - 1736-4728 SN - 1736-7557 VL - 64 IS - 3 SP - 233 EP - 248 PB - Estonian Academy Publ. CY - Tallinn 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 - JOUR A1 - Lago, M. A1 - de la Horra, R. A1 - Ubide, T. A1 - Gale, C. A1 - Galan-Abellan, B. A1 - Barrenechea, J. F. A1 - Lopez-Gomez, J. A1 - Benito, M. I. A1 - Arche, A. A1 - Alonso-Azcarate, J. A1 - Luque, F. J. A1 - Timmerman, Martin Jan T1 - First report of a Middle-Upper Permian magmatism in the SE Iberian Ranges characterisation and comparison with coeval magmatisms in the western Tethys JF - Journal of Iberian geology N2 - A multiple basic to intermediate sill is reported for the first time in the south-eastern Iberian Ranges. It is composed of several tabular to irregular levels intercalated within the fluvial sediments of the Alcotas Formation (Middle-Upper Permian). The sill could represent the youngest Paleozoic subvolcanic intrusion in the Iberian Ranges. The igneous rocks are classified as basaltic andesites. They show a subophitic microstructure constituted by plagioclase (An62 - An6), augite (En48Wo44Fs7 - En46Wo39Fs15), pseudomorphosed olivine, minor amounts of oxides (magnetite and ilmenite) and accessory F-apatite. According to the mineralogy and whole-rock composition, their geochemical affinity is transitional from subalkaline to alkaline. Radiometric dating of the sill is not feasible due to its significant alteration. Field criteria, however, suggest an emplacement coeval to the deposition of the Alcotas Formation (Middle-Upper Permian). This hypothesis is supported by the transitional affinity of these rocks, similar to other Middle-Upper Permian magmatisms in the western Tethys, e.g., from the Pyrenees. Taking into account their isotopic signature (epsilon(Sr) : -6.8 to -9.2; epsilon(Nd) : + 1.7 to + 8.3), an enriched mantle source with the involvement of a HIMU component has been identified. This interpretation is supported by the trace element contents. Some of these HIMU characteristics have been recognised in the Middle-Upper Permian magmatisms of the Central Pyrenees (Anayet Basin) and the High Atlas (Argana Basin). However, none of these source features are shared with other Middle-Upper Permian magmatisms of the western Tethys (Catalonian Coastal Ranges, Corsica-Sardinia and southern France), nor with the Lower Permian magmatism of the Iberian Ranges. These differences support the presence of a heterogeneous mantle in the western Tethys during the Permian. KW - sill KW - peperite KW - subalkaline to alkaline magmatism KW - Middle-Upper Permian KW - Iberian Basin Y1 - 2012 U6 - https://doi.org/10.5209/rev_JIGE.2012.v38.n2.40462 SN - 1698-6180 VL - 38 IS - 2 SP - 331 EP - 348 PB - Instituto de Geología Económica, Consejo Superior de Investigaciones Científicas, Universidad Complutense Madrid CY - Madrid ER - TY - JOUR A1 - Faithfull, J. W. A1 - Timmerman, Martin Jan A1 - Upton, B. G. J. A1 - Rumsey, M. S. T1 - Mid-Eocene renewal of magmatism in NW Scotland the Loch Roag Dyke, outer hebrides JF - Journal of the Geological Society N2 - Amonchquite dyke, in the vicinity of Loch Roag, Lewis, Outer Hebrides has an unusually enriched chemistry, and contains a unique assemblage of megacrysts and xenoliths from the lithosphere of the Hebridean craton. A Ar-40/Ar-39 plateau age of 45.2 +/- 0.2 Ma (2 sigma) of a phlogopite megacryst from the dyke overlaps an earlier reported K-Ar age, and confirms that the British Palaeogene Igneous Province extended into the Eocene. Similar late low-volume melts were erupted in the Eocene and Oligocene in West and East Greenland, suggesting that such late-stage magmatic rejuvenescence is a widespread feature across the North Atlantic Igneous Province. Y1 - 2012 U6 - https://doi.org/10.1144/0016-76492011-117 SN - 0016-7649 VL - 169 IS - 2 SP - 115 EP - 118 PB - Geological Soc. Publ. House CY - Bath ER -