TY  - JOUR
A1  - Franz, Gerhard
A1  - Sudo, Masafumi
A1  - Khomenko, Vladimir
T1  - 40Ar/39Ar dating of a hydrothermal pegmatitic buddingtonite–muscovite assemblage from Volyn, Ukraine
JF  - European journal of mineralogy : EJM : an international journal on mineralogy, petrology, geochemistry, and related sciences
N2  - We determined Ar-40/Ar-39 ages of buddingtonite, occurring together with muscovite, with the laser-ablation method. This is the first attempt to date the NH4-feldspar buddingtonite, which is typical for sedimentary-diagenetic environments of sediments, rich in organic matter, or in hydrothermal environments, associated with volcanic geyser systems. The sample is a hydrothermal breccia, coming from the Paleoproterozoic pegmatite field of the Korosten Plutonic Complex, Volyn, Ukraine. A detailed characterization by optical methods, electron microprobe analyses, backscattered electron imaging, and IR analyses showed that the buddingtonite consists of euhedral-appearing platy crystals of tens of micrometers wide, 100 or more micrometers in length, which consist of fine-grained fibers of <= 1 mu m thickness. The crystals are sector and growth zoned in terms of K-NH4-H3O content. The content of K allows for an age determination with the Ar-40/Ar-39 method, as well as in the accompanying muscovite, intimately intergrown with the buddingtonite. The determinations on muscovite yielded an age of 1491 +/- 9 Ma, interpreted as the hydrothermal event forming the breccia. However, buddingtonite apparent ages yielded a range of 563 +/- 14 Ma down to 383 +/- 12 Ma, which are interpreted as reset ages due to Ar loss of the fibrous buddingtonite crystals during later heating. We conclude that buddingtonite is suited for Ar-40/Ar-39 age determinations as a supplementary method, together with other methods and minerals; however, it requires a detailed mineralogical characterization, and the ages will likely represent minimum ages.
Y1  - 2022
U6  - https://doi.org/10.5194/ejm-34-7-2022
SN  - 0935-1221
SN  - 1617-4011
VL  - 34
IS  - 1
SP  - 7
EP  - 18
PB  - Copernicus
CY  - Göttingen
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  - Bachmann, Raik
A1  - Oncken, Onno
A1  - Glodny, Johannes
A1  - Seifert, Wolfgang
A1  - Georgieva, Viktoria
A1  - Sudo, Masafumi
T1  - Exposed plate interface in the European Alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone
N2  - We present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central Alps of Europe related to Late Cretaceous-early Tertiary subduction and accretion of the South Penninic lower plate underneath the Adriatic upper plate. The material forming the exposed plate interface zone has experienced flow and fracturing over an extended period of time followed by syncollisional exhumation, thus reflecting a multistage evolution. Fabric formation and metamorphism, however, chiefly record the deformation conditions of the precollisional setting along the plate interface. We identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200 and 300 degrees C. This zone coincides with a domain of intense veining in the subduction melange with mineral growth into open cavities, indicating fast, possibly seismic, rupture. Evidence for transient near-lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear zones continues into the region below the occurrence of pseudotachylytes, possibly reflecting a zone of conditionally stable slip. The zone above the unstable slip area is devoid of veins but displays ample evidence of fluid-assisted processes similar to the deeper zone: solution-precipitation creep and dehydration reactions in the melange matrix, hydration, and sealing of the base of the upper plate. Seismic rupture here is possibly expressed by ubiquitous localized deformation zones. We hypothesize that trenchward sealing of parts of the plate interface as well as reaction-enhanced destruction of upper plate permeability is an important component, localizing the unstable slip zone. This relation may result from the competition of the pervasive, presumably interseismic, pressure solution creep destroying permeability and building elevated fluid pressure until the strength threshold is reached with seismic failure.
Y1  - 2009
UR  - http://www.agu.org/journals/jb/
U6  - https://doi.org/10.1029/2008jb005927
SN  - 0148-0227
ER  - 
TY  - JOUR
A1  - Guzman, S.
A1  - Petrinovic, I. A.
A1  - Brod, J. A.
A1  - Hongn, Fernando D.
A1  - Seggiaro, R. E.
A1  - Montero, C.
A1  - Carniel, Roberto
A1  - Dantas, E. L.
A1  - Sudo, Masafumi
T1  - Petrology of the Luingo caldera (SE margin of the Puna plateau) a middle Miocene window of the arc-back arc configuration
JF  - Journal of volcanology and geothermal research
N2  - We describe the petrographic characteristics, whole-rock geochemistry and mineral chemistry of rocks from the Pucarilla-Cerro Tipillas Volcanic Complex with emphasis on the rocks belonging to the middle Miocene Luingo caldera, located in the south-eastern portion of the Central Volcanic Zone (CVZ) of the Andes. We modelled the petrogenesis of the Luingo caldera rocks as a mixture of ca. 20% crustal magmas and 80% of mantle magmas by AFC with recharge processes. A comparison of Luingo geochemical data with the composition of Miocene-Pliocene volcanic rocks from the broad area, points to major thickening events during the middle Miocene for the western portion and during the upper Miocene for the eastern portion of the Southern CVZ. In the eastern sector (similar to 66 degrees W) the mantle source appears to change from a spinel-lherzolite type for the middle Miocene to a garnet-lherzolite type for the upper Miocene-Pliocene magmas. The areal distribution of the volcanic products led to the recognition of approximately equivalent areas covered by volcanic rocks both in the eastern and in the western Puna borders. This indicates a broad arc, which was structurally controlled at the proto-Puna/Puna margins, whose geochemical differences are related with variations in crustal thicknesses and heterogeneous mantle sources from west to east.
KW  - Luingo caldera
KW  - Central Andes
KW  - Miocene volcanism
KW  - Southern Central Volcanic Zone
KW  - crustal thickness
Y1  - 2011
U6  - https://doi.org/10.1016/j.jvolgeores.2010.12.008
SN  - 0377-0273
VL  - 200
IS  - 3-4
SP  - 171
EP  - 191
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Carrapa, Barbara
A1  - DeCelles, Peter G.
A1  - Reiners, Peter W.
A1  - Gehrels, George E.
A1  - Sudo, Masafumi
T1  - Apatite triple dating and white mica Ar-40/Ar-39 thermochronology of syntectonic detritus in the Central Andes : a multiphase tectonothermal history
N2  - We applied apatite U-Pb, fission track, and (U-Th)/He triple dating and white mica Ar-40/Ar-39 thermochronology to syntectonic sedimentary rocks from the central Andean Puna plateau in order to determine the source-area geochronology and source sedimentary basin thermal histories, and ultimately the timing of multiple tectonothermal events in the Central Andes. Apatite triple dating of samples from the Eocene Geste Formation in the Salar de Pastos Grandes basin shows late Precambrian-Devonian apatite U-Pb crystallization ages, Eocene apatite fission track (AFT), and Eocene-Miocene (U-Th)/He (ca. 8-47 Ma) cooling ages. Double dating of cobbles from equivalent strata in the Arizaro basin documents early Eocene (46.2 +/- 3.9 Ma) and Cretaceous (107.6 +/- 7.6, 109.5 +/- 7.7 Ma) AFT and Eocene-Oligocene (ca. 55-30 Ma) (U-Th)/He ages. Thermal modeling suggests relatively rapid cooling between ca. 80 and 50 Ma and reheating and subsequent diachronous basin exhumation between ca. 30 Ma and 5 Ma. The Ar-40/Ar-39 white mica ages from the same samples in the Salar de Pastos Grandes area are mainly 400-350 Ma, younger than apatite U-Pb ages, suggesting source- terrane cooling and exhumation during the Devonian-early Carboniferous. Together these data reveal multiple phases of mountain building in the Paleozoic and Cenozoic. Basin burial temperatures within the plateau were limited to <80 degrees C and incision occurred diachronously during the Cenozoic.
Y1  - 2009
UR  - http://geology.gsapubs.org/
U6  - https://doi.org/10.1130/G25698a.1
SN  - 0091-7613
ER  - 
TY  - JOUR
A1  - Vasquez, Mónica
A1  - Altenberger, Uwe
A1  - Romer, Rolf L.
A1  - Sudo, Masafumi
A1  - Moreno-Murillo, Juan Manuel
T1  - Magmatic evolution of the Andean Eastern Cordillera of Colombia during the Cretaceous : Influence of previous tectonic processes
N2  - The Eastern Cordillera of the Colombian Andes represents an inverted Cretaceous basin where Cretaceous magmatism is characterized by rare mafic dykes and sills. We use Ar-40/Ar-39, Sr-Nd-Pb isotopes, as well as major and trace elements analyses of Cretaceous intrusions from both flanks of the Eastern Cordillera in combination with structural data to document the complex evolution of the basin. Magmatism, which is diachronous and geochemically diverse, seems to be related to mantle melting beneath the most subsiding segments of each sub-basin during enhanced extensional tectonics. The mafic intrusions display two different compositional series: an alkaline one with OIB-like pattern and a tholeiitic one with MORB-like features. This indicates at least two diverse mantle sources. Trace-element patterns suggest that the intrusions were emplaced in an extensional setting. Ar-40/Ar-39 dating on primary plagioclase and hornblende provides plateau ages between similar to 136 and similar to 74 Ma. The geochemical and temporal diversities show that the emplacement of the magmas was tectonically controlled, each sub-basin reflecting an individual subsidence event.
Y1  - 2010
UR  - http://www.sciencedirect.com/science/journal/08959811
U6  - https://doi.org/10.1016/j.jsames.2009.02.003
SN  - 0895-9811
ER  - 
TY  - JOUR
A1  - Ozawa, Ayako
A1  - Tagami, Takahiro
A1  - Listanco, Eddie L.
A1  - Arpa, Carmencita B.
A1  - Sudo, Masafumi
T1  - Initiation and propagation of subduction along the Philippine Trench : evidence from the temporal and spatial distribution of volcanoes
N2  - K-Ar ages of 37 samples collected from the Bicol peninsula, the Luzon island, Philippines, were determined by the unspiked sensitivity method in order to constrain the timing of initiation of subduction along the Philippine Trench. The measured K-Ar ages range from 0 to 7 Ma with two old outliers of 27 and 43 Ma. Together with K-Ar ages previously reported on volcanics in Leyte and eastern Mindanao, subduction volcanism has likely propagated from north to south: similar to 6.6 Ma in Bicol and similar to 3.5 Ma in Leyte and its vicinity. The temporal and spatial distribution suggests that the subduction volcanism started earlier in the north than in the south. This is consistent with the southern propagation of subduction along the Philippine Trench from similar to 8 Ma. (C) 2003 Elsevier Ltd. All rights reserved
Y1  - 2004
SN  - 1367-9120
ER  - 
TY  - JOUR
A1  - Ozawa, Ayako
A1  - Tagami, T.
A1  - Sudo, Masafumi
T1  - K-Ar geochronology of the temporal change of eruptive style in the eastern Izu peninsula, central Japan
N2  - A recent K-Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3-0.2 Ma. To narrow down the time of change, we determined 10 K-Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26- 0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29-0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism
Y1  - 2004
SN  - 1038-4871
ER  - 
TY  - JOUR
A1  - Pourteau, Amaury
A1  - Sudo, Masafumi
A1  - Candan, Osman
A1  - Lanari, P.
A1  - Vidal, O.
A1  - Oberhänsli, Roland
T1  - Neotethys closure history of Anatolia - insights from Ar-40-Ar-39 geochronology and P-T estimation in high-pressure metasedimentary rocks
JF  - Journal of metamorphic geology
N2  - The multiple high-pressure (HP), low-temperature (LT) metamorphic units of Western and Central Anatolia offer a great opportunity to investigate the subduction-and continental accretion-related evolution of the eastern limb of the long-lived Aegean subduction system. Recent reports of the HP-LT index mineral Fe-Mg-carpholite in three metasedimentary units of the Gondwana-derived Anatolide-Tauride continental block (namely the Afyon Zone, the Oren Unit and the southern Menderes Massif) suggest a more complicated scenario than the single-continental accretion model generally put forward in previous studies. This study presents the first isotopic dates (white mica Ar-40-Ar-39 geochronology), and where possible are combined with P-T estimates (chlorite thermometry, phengite barometry, multi-equilibrium thermobarometry), on carpholite-bearing rocks from these three HP-LT metasedimentary units. It is shown that, in the Afyon Zone, carpholite-bearing assemblages were retrogressed through greenschist-facies conditions at c. 67-62 Ma. Early retrograde stages in the Oren Unit are dated to 63-59 Ma. In the Kurudere-Nebiler Unit (HP Mesozoic cover of the southern Menderes Massif), HP retrograde stages are dated to c. 45 Ma, and post-collisional cooling to c. 26 Ma. These new results support that the Oren Unit represents the westernmost continuation of the Afyon Zone, whereas the Kurudere-Nebiler Unit correlates with the Cycladic Blueschist Unit of the Aegean Domain. In Western Anatolia, three successive HP-LT metamorphic belts thus formed: the northernmost Tavsanli Zone (c. 88-82 Ma), the Oren-Afyon Zone (between 70 and 65 Ma), and the Kurudere-Nebiler Unit (c. 52-45 Ma). The southward younging trend of the HP-LT metamorphism from the upper and internal to the deeper and more external structural units, as in the Aegean Domain, points to the persistence of subduction in Western Anatolia between 93-90 and c. 35 Ma. After the accretion of the Menderes-Tauride terrane, in Eocene times, subduction stopped, leading to continental collision and associated Barrovian-type metamorphism. Because, by contrast, the Aegean subduction did remain active due to slab roll-back and trench migration, the eastern limb (below Southwestern Anatolia) of the Hellenic slab was dramatically curved and consequently teared. It therefore is suggested that the possibility for subduction to continue after the accretion of buoyant (e.g. continental) terranes probably depends much on palaeogeography.
KW  - Ar-40-Ar-39 geochronology
KW  - Anatolia
KW  - chlorite-phengite thermobarometry
KW  - high-pressure metasedimentary rocks
Y1  - 2013
U6  - https://doi.org/10.1111/jmg.12034
SN  - 0263-4929
SN  - 1525-1314
VL  - 31
IS  - 6
SP  - 585
EP  - 606
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Willner, Arne P.
A1  - Massonne, Hans-Joachim
A1  - Ring, Uwe
A1  - Sudo, Masafumi
A1  - Thomson, Stuart N.
T1  - P-T evolution and timing of a late Palaeozoic fore-arc system and its heterogeneous Mesozoic overprint in north-central Chile (latitudes 31-32 degrees S)
JF  - Geological magazine
N2  - In the late Palaeozoic fore-arc system of north-central Chile at latitudes 31-32 degrees S (from the west to the east) three lithotectonic units are telescoped within a short distance by a Mesozoic strikeslip event (derived peak P-T conditions in brackets): (1) the basally accreted Choapa Metamorphic Complex (CMC; 350-430 degrees C, 6-9 kbar), (2) the frontally accreted Arrayan Formation (AF; 280-320 degrees C, 4-6 kbar) and (3) the retrowedge basin of the Huentelauquen Formation (HF; 280-320 degrees C, 3-4 kbar). In the CMC, Ar-Ar spot ages locally date white-mica formation at peak P-T conditions and during early exhumation at 279-242 Ma. In a local garnet mica-schist intercalation (570-585 degrees C, 11-13 kbar) Ar-Ar spot ages refer to the ascent from the subduction channel at 307-274 Ma. Portions of the CMC were isobarically heated to 510-580 degrees C at 6.6-8.5 kbar. The age of peak P-T conditions in the AF can only vaguely be approximated at >= 310 Ma by relict fission-track ages consistent with the observation that frontal accretion occurred prior to basal accretion. Zircon fission-track dating indicates cooling below similar to 280 degrees C at similar to 248 Ma in the CMC and the AF, when a regional unconformity also formed. Ar-Ar white-mica spot ages in parts of the CMC and within the entire AF and HF point to heterogeneous resetting during Mesozoic extensional and shortening events at similar to 245-240 Ma, similar to 210-200 Ma, similar to 174-159 Ma and similar to 142-127 Ma. The zircon fission-track ages are locally reset at 109-96 Ma. All resetting of Ar-Ar white-mica ages is proposed to have occurred by in situ dissolution/precipitation at low temperature in the presence of locally penetrating hydrous fluids. Hence syn-and postaccretionary events in the fore-arc system can still be distinguished and dated in spite of its complex heterogeneous postaccretional overprint.
KW  - Ar-Ar white-mica dating
KW  - zircon fission-track dating
KW  - accretionary prism
KW  - frontal accretion
KW  - basal accretion
KW  - thermal overprint
KW  - age resetting
Y1  - 2012
U6  - https://doi.org/10.1017/S0016756811000641
SN  - 0016-7568
VL  - 149
IS  - 2
SP  - 177
EP  - 207
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Willner, Arne P.
A1  - Sepúlveda, Fernando A.
A1  - Hervé, Francisco
A1  - Massonne, Hans-Joachim
A1  - Sudo, Masafumi
T1  - Conditions and timing of pumpellyite-actinolite-facies metamorphism in the early Mesozoic frontal accretionary prism of the Madre de Dios Archipelago (latitude 50 degrees 20'S; Southern Chile)
N2  - The Madre de Dios Metamorphic Complex (MDMC) in southern Chile is a fossil frontal accretionary prism, which is mainly composed of metapsammopelitic rocks, intercalations of oceanic rocks (greenstone and metachert) and platform carbonate. We concentrated on the metabasite to decipher the metamorphic evolution. This rock type contains assemblages of the pumpellyite-actinolite facies: pumpellyite +/- actinolite-chlorite +/- grandite +/- phengite +/- epidote-albite- quartz-titanite +/- K-feldspar +/- calcite. The metamorphic phases mainly grew by prograde hydration reactions during various episodes of restricted fluid influx. Fundamental phase relations of the pumpellyite-actinolite facies and adjacent facies were reproduced by pseudosections calculated for the system K2O-Na2O-CaO-FeO-O-2-MgO-Al2O3-TiO2-SiO2-H2O- CO2 at 200-400 degrees C and 1-9 kbar. The calculated stability fields of the metamorphic assemblages as realized in the MDMC metabasite indicate highest metamorphic conditions restricted to 290-310 degrees C, 4-6 kbar for the MDMC, presumably as a result of the main fluid influx at these conditions. Nevertheless, earlier local equilibria are still preserved as a result of strongly kinetically controlled mineral reactions and a lack of recrystallization and compositional homogenization at thin-section scale. Hence, thermodynamic calculations of local multivariant mineral equilibria using the entire compositional variation of minerals in the MDMC show that the prograde PT path evolved from 4 +/- 1 kbar, 200-220 degrees C to 5 +/- 1 kbar, 290-330 degrees C. The prograde PT path reflects nearly horizontal particle paths after reaching the maximum depth typical for frontal accretionary prisms. Long residence at maximum depth resulted in thermal re-equilibration. Ar-40/Ar-39 spot ages were measured by in situ UV laser ablation of local phengite concentrations in a deformed metapelite at 233 center dot 2 +/- 1 center dot 8 Ma and in an undeformed metabasite at 200 center dot 8 +/- 2 center dot 4 Ma. Whereas the first age represents an age of accretion, the latter age can be attributed to mineral growth either during a younger stage of accretion or during a retrograde stage. Ar-40/Ar-39 isotopic analyses of two further metabasite samples reflect a prominent resetting of ages at 152 center dot 0 +/- 2 center dot 2 Ma and white mica growth during external fluid access triggered by either a local intrusion or a late Jurassic extensional episode.
Y1  - 2009
UR  - http://petrology.oxfordjournals.org/
U6  - https://doi.org/10.1093/petrology/egp071
SN  - 0022-3530
ER  - 
TY  - JOUR
A1  - Beyene, Yonas
A1  - Katoh, Shigehiro
A1  - Wolde Gabriel, Giday
A1  - Hart, William K.
A1  - Uto, Kozo
A1  - Sudo, Masafumi
A1  - Kondo, Megumi
A1  - Hyodo, Masayuki
A1  - Renne, Paul R.
A1  - Suwa, Gen
A1  - Asfaw, Berhane
T1  - The characteristics and chronology of the earliest. Acheulean at Konso, Ethiopia
JF  - Proceedings of the National Academy of Sciences of the United States of America
N2  - The Acheulean technological tradition, characterized by a large (>10 cm) flake-based component, represents a significant technological advance over the Oldowan. Although stone tool assemblages attributed to the Acheulean have been reported from as early as circa 1.6-1.75 Ma, the characteristics of these earliest occurrences and comparisons with later assemblages have not been reported in detail. Here, we provide a newly established chronometric calibration for the Acheulean assemblages of the Konso Formation, southern Ethiopia, which span the time period similar to 1.75 to <1.0 Ma. The earliest Konso Acheulean is chronologically indistinguishable from the assemblage recently published as the world's earliest with an age of similar to 1.75 Ma at Kokiselei, west of Lake Turkana, Kenya. This Konso assemblage is characterized by a combination of large picks and crude bifaces/unifaces made predominantly on large flake blanks. An increase in the number of flake scars was observed within the Konso Formation handaxe assemblages through time, but this was less so with picks. The Konso evidence suggests that both picks and handaxes were essential components of the Acheulean from its initial stages and that the two probably differed in function. The temporal refinement seen, especially in the handaxe forms at Konso, implies enhanced function through time, perhaps in processing carcasses with long and stable cutting edges. The documentation of the earliest Acheulean at similar to 1.75 Ma in both northern Kenya and southern Ethiopia suggests that behavioral novelties were being established in a regional scale at that time, paralleling the emergence of Homo erectus-like hominid morphology.
KW  - chronostratigraphy
KW  - Early Pleistocene
KW  - lithic technology development
Y1  - 2013
U6  - https://doi.org/10.1073/pnas.1221285110
SN  - 0027-8424
VL  - 110
IS  - 5
SP  - 1584
EP  - 1591
PB  - National Acad. of Sciences
CY  - Washington
ER  - 
TY  - JOUR
A1  - Ogasawara, Masatsugu
A1  - Fukuyama, Mayuko
A1  - Horie, Kenji
A1  - Sumii, Tomoaki
A1  - Takehara, Mami
A1  - Sudo, Masafumi
T1  - SHRIMP U-Pb age of SoriZ93 zircon from the Sori Granodiorite, Northeast
 Japan: a potential reference zircon of Late Cretaceous age
JF  - ISLAND ARC
N2  - SoriZ93 zircon was separated from residual mineral fraction after the preparation of the SORI93 biotite standard from the Sori Granodiorite in the Ashio Mountains, Northeast Japan, and analyzed for its U-Pb age using a sensitive high resolution ion microprobe (SHRIMP). The zircon grains of SoriZ93 are prismatic with pyramidal ends or broken prismatic fragments. Most zircons are 100-250m long and 50-150m wide. The zircons are clear crystals and colorless to pale yellow, although some grains are brown with optically low transparency. Cathodoluminescence (CL) imaging of the SoriZ93 zircons showed a fine oscillatory zoning, which is a typical characteristic of zircons in granitic rocks. A xenocrystic core was not present in the zircons. Although some mineral inclusions were present in the zircons, it is possible to select a typical analytical area with a dimension of 30m necessary for the microbeam technique. The analytical results of the colorless zircons provided a weighted mean Pb-207 corrected Pb-206/U-238 age of 93.9 +/- 0.6Ma (95% confidence, MSWD=0.97). This Pb-206/U-238 age is 1.3m.y. older than the K-Ar age of the SORI93 biotite, indicating that the granodiorite cooled to a closure temperature of the K-Ar biotite system within a short time interval. Although some grains of the SoriZ93 zircons show high U concentration, a selection of colorless zircons provided the precise age to be used for the calibration and reference for zircons of the Late Cretaceous.
KW  - Late Cretaceous
KW  - SHRIMP U-Pb dating
KW  - Sori Granodiorite
KW  - SoriZ93
KW  - zircon standard
Y1  - 2013
U6  - https://doi.org/10.1111/iar.12041
SN  - 1038-4871
VL  - 22
IS  - 3
SP  - 306
EP  - 317
PB  - WILEY-BLACKWELL
CY  - HOBOKEN
ER  - 
TY  - JOUR
A1  - Van der Meer, Q. H. A.
A1  - Scott, James M.
A1  - Waight, T. E.
A1  - Sudo, Masafumi
A1  - Schersten, A.
A1  - Cooper, Alan F.
A1  - Spell, Terry L.
T1  - Magmatism during Gondwana break-up: new geochronological data from Westland, New Zealand
JF  - New Zealand journal of geology and geophysics : an international journal of pacific rim geosciences
N2  - Newly determined Late Cretaceous Ar-40/Ar-39 ages on megacrystic kaersutite from four lamprophyre dikes, and a U-Pb zircon age on a trachyte, from central and north Westland (New Zealand) are presented. These ages suggest that the intrusion of mafic dikes (88-86 and 69 Ma) was not necessarily restricted to the previously established narrow age range of 80-92 Ma. The younger lamprophyre and trachyte dikes (c. 68-70 Ma) imply that tensional stresses in the Western Province were either renewed at this time, or that extension and related magmatism continued during opening of the Tasman Sea. Extension-related magmatism in the region not only preceded Tasman seafloor spreading initiation (starting at c. 83 Ma, lasting to c. 53 Ma), but may have sporadically continued for up to 15 Ma after continental break-up.
KW  - Gondwana break-up
KW  - geochronology
KW  - lamprophyre
KW  - central Westland
KW  - Fraser Complex
Y1  - 2013
U6  - https://doi.org/10.1080/00288306.2013.826699
SN  - 0028-8306
SN  - 1175-8791
VL  - 56
IS  - 4
SP  - 229
EP  - 242
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Wiederkehr, Michael
A1  - Sudo, Masafumi
A1  - Bousquet, Romain
A1  - Berger, Alfons
A1  - Schmid, Stefan M.
T1  - Alpine orogenic evolution from subduction to collisional thermal overprint : the Ar-40/Ar-39 age constraints from the Valaisan Ocean, central Alps
N2  - The investigated HP/LT metasedimentary units of the Valaisan and adjacent European domains occupy a key position in the Alpine belt for understanding the transition from early subduction-related HP/LT metamorphism to collision-related Barrovian overprint and the evolution of mountain belts in general. The timing of high-pressure metamorphism, subsequent retrogression and following Barrow-type overprint was studied by Ar-40/Ar-39 dating of biotite and several white mica generations that are well characterized in terms of mineral chemistry, texture and associated mineral assemblages. Four distinct age populations of white mica record peak pressure conditions (42-40 Ma) and several stages of subsequent retrograde metamorphic evolution (36-25 Ma). Biotite isotopic analyses yield consistent apparent ages that cluster around 18-16 Ma for the Barrow-type thermal overprint. The recorded isotopic data reveal a significant time gap in the order of some 20 Ma between subduction-related HP/LT metamorphism and collision-related Barrovian overprint, supporting the notion of a polymetamorphic evolution associated with a bimodal P-T path.
Y1  - 2009
UR  - http://www.agu.org/journals/tc/
U6  - https://doi.org/10.1029/2009tc002496
SN  - 0278-7407
ER  - 
TY  - JOUR
A1  - Sirocko, Frank
A1  - Dietrich, Stephan
A1  - Veres, Daniel
A1  - Grootes, Pieter M.
A1  - Schaber-Mohr, Katja
A1  - Seelos, Klemens
A1  - Nadeau, Marie-Josee
A1  - Kromer, Bernd
A1  - Rothacker, Leo
A1  - Roehner, Marieke
A1  - Krbetschek, Matthias
A1  - Appleby, Peter G.
A1  - Hambach, Ulrich
A1  - Rolf, Christian
A1  - Sudo, Masafumi
A1  - Grim, Stephanie
T1  - Multi-proxy dating of Holocene maar lakes and Pleistocene dry maar sediments in the Eifel, Germany
JF  - Quaternary science reviews : the international multidisciplinary research and review journal
N2  - During the last twelve years the ELSA Project (Eifel Laminated Sediment Archive) at Mainz University has drilled a total of about 52 cores from 27 maar lakes and filled-in maar basins in the Eifel/Germany. Dating has been completed for the Holocene cores using 6 different methods (Pb-210 and Cs-137 activities, palynostratigraphy, event markers, varve counting, C-14) In general, the different methods consistently complement one another within error margins. Event correlation was used for relating typical lithological changes with historically known events such as the two major Holocene flood events at 1342 AD and ca 800 BC. Dating of MIS2-MIS3 core sections is based on greyscale tuning, radiocarbon and OSL dating, magnetostratigraphy and tephrochronology. The lithological changes in the sediment cores demonstrate a sequence of events similar to the North Atlantic rapid climate variability of the Last Glacial Cycle. The warmest of the MIS3 interstadials was GI14, when a forest with abundant spruce covered the Eifel area from 55 to 48 ka BP, i.e. during a time when also other climate archives in Europe suggested very warm conditions. The forest of this "Early Stage 3 warm phase" developed subsequently into a steppe with scattered birch and pine, and finally into a glacial desert at around 25 ka BP. Evidence for Mono Lake and Laschamp geomagnetic excursions is found in two long cores. Several large eruptions during Middle and Late Pleistocene (Ulmener Maar - 11,000 varve years BP, Laacher See - 12,900 varve years BP, Mosenberg volcanoes/Meerfelder Maar 41-45 cal ka BP, Dumpel Maar 116 ka BP, Glees Maar - 151 ka BP) produced distinct ash-layers crucial for inter-core and inter-site correlations. The oldest investigated maar of the Eifel is Ar-40/Ar-39 dated to the time older than 520 ka BP.
KW  - Eifel maar
KW  - Laminated lake sediments
KW  - Tuning
KW  - Historical events
KW  - C-14-derived chronology
KW  - Varve counting
KW  - Luminescence dating
KW  - Palynostratigraphy
KW  - (CS)-C-137 and Pb-210 dating
KW  - Palaeomagnetism
KW  - Tephrostratigraphy
KW  - Argon-Argon dating
KW  - GIS
Y1  - 2013
U6  - https://doi.org/10.1016/j.quascirev.2012.09.011
SN  - 0277-3791
VL  - 62
SP  - 56
EP  - 76
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Ozsayin, Erman
A1  - Ciner, T. Attila
A1  - Rojay, F. Bora
A1  - Dirik, R. Kadir
A1  - Melnick, Daniel
A1  - Fernandez-Blanco, David
A1  - Bertotti, Giovanni
A1  - Schildgen, Taylor F.
A1  - Garcin, Yannick
A1  - Strecker, Manfred
A1  - Sudo, Masafumi
T1  - Plio-Quaternary extensional tectonics of the Central Anatolian Plateau  a case study from the Tuz Golu Basin, Turkey
JF  - Turkish journal of earth sciences = Türk yerbilimleri dergisi
N2  - The Tuz Golu Basin is the largest sedimentary depression located at the center of the Central Anatolian Plateau, an extensive, low-relief region with elevations of ca. 1 km located between the Pontide and Tauride mountains. Presently, the basin morphology and sedimentation processes are mainly controlled by the extensional Tuz Golu Fault Zone in the east and the transtensional Inonu-Eskisehir Fault System in the west. The purpose of this study is to contribute to the understanding of the Plio-Quaternary deformation history and to refine the timing of the latest extensional phase of the Tuz Golu Basin. Field observations, kinematic analyses, interpretations of seismic reflection lines, and Ar-40/Ar-39 dating of a key ignimbrite layer suggest that a regional phase of NNW-SSE to NE-SW contraction ended by 6.81 +/- 0.24 Ma and was followed by N-S to NE-SW extension during the Pliocene-Quaternary periods. Based on sedimentological and chronostratigraphic markers, the average vertical displacement rates over the past 5 or 3 Ma with respect to the central part of Tuz Golu Lake are 0.03 to 0.05 mm/year for the fault system at the western flank of the basin and 0.08 to 0.13 mm/year at the eastern flank. Paleo-shorelines of the Tuz Golu Lake, vestiges of higher lake levels related to Quaternary climate change, are important strain markers and were formed during Last Glacial Maximum conditions as indicated by a radiocarbon age of 21.8 +/- 0.4 ka BP obtained from a stromatolitic crust. Geomorphic observations and deformed lacustrine shorelines suggest that the main strand of the Tuz Golu Fault Zone straddling the foothills of the Sereflikochisar-Aksaray range has not been active during the Holocene. Instead, deformation appears to have migrated towards the interior of the basin along an offshore fault that runs immediately west of Sereflikochisar Peninsula. This basinward migration of deformation is probably associated with various processes acting at the lithospheric scale, such as plateau uplift and/or microplate extrusion.
KW  - Central Anatolia
KW  - Tuz Golu Basin
KW  - orogenic plateau evolution
KW  - extensional tectonics
KW  - kinematic analysis
KW  - lake shoreline
Y1  - 2013
U6  - https://doi.org/10.3906/yer-1210-5
SN  - 1300-0985
VL  - 22
IS  - 5
SP  - 691
EP  - 714
PB  - Tübitak
CY  - Ankara
ER  - 
TY  - JOUR
A1  - Willner, Arne P.
A1  - Barr, Sandra M.
A1  - Glodny, Johannes
A1  - Massonne, Hans-Joachim
A1  - Sudo, Masafumi
A1  - Thomson, Stuart N.
A1  - Van Staal, Cees R.
A1  - White, Chris E.
T1  - Effects of fluid flow, cooling and deformation as recorded by Ar-40/Ar-39, Rb-Sr and zircon fission track ages in very low- to low-grade metamorphic rocks in Avalonian SE Cape Breton Island (Nova Scotia, Canada)
JF  - Geological magazine
N2  - Ar-40/Ar-39 in situ UV laser ablation of white mica, Rb-Sr mineral isochrons and zircon fission track dating were applied to determine ages of very low- to low-grade metamorphic processes at 3.5 +/- 0.4 kbar, 280 +/- 30 degrees C in the Avalonian Mira terrane of SE Cape Breton Island (Nova Scotia). The Mira terrane comprises Neoproterozoic volcanic-arc rocks overlain by Cambrian sedimentary rocks. Crystallization of metamorphic white mica was dated in six metavolcanic samples by Ar-40/Ar-39 spot age peaks between 396 +/- 3 and 363 +/- 14 Ma. Rb-Sr systematics of minerals and mineral aggregates yielded two isochrons at 389 +/- 7 Ma and 365 +/- 8 Ma, corroborating equilibrium conditions during very low- to low-grade metamorphism. The dated white mica is oriented parallel to foliations produced by sinistral strike-slip faulting and/or folding related to the Middle-Late Devonian transpressive assembly of Avalonian terranes during convergence and emplacement of the neighbouring Meguma terrane. Exhumation occurred earlier in the NW Mira terrane than in the SE. Transpression was related to the closure of the Rheic Ocean between Gondwana and Laurussia by NW-directed convergence. The Ar-40/Ar-39 spot age spectra also display relict age peaks at 477-465 Ma, 439 Ma and 420-428 Ma attributed to deformation and fluid access, possibly related to the collision of Avalonia with composite Laurentia or to earlier Ordovician-Silurian rifting. Fission track ages of zircon from Mira terrane samples range between 242 +/- 18 and 225 +/- 21 Ma and reflect late Palaeozoic reburial and reheating close to previous peak metamorphic temperatures under fluid-absent conditions during rifting prior to opening of the Central Atlantic Ocean.
KW  - Ar-40/Ar-39 spot ages
KW  - Rb-Sr mineral isochrons
KW  - zircon fission tracks
KW  - very low-low-grade metamorphism
KW  - Avalonia
KW  - Devonian transpression
KW  - Rheic Ocean
Y1  - 2015
U6  - https://doi.org/10.1017/S0016756814000508
SN  - 0016-7568
SN  - 1469-5081
VL  - 152
IS  - 5
SP  - 767
EP  - 787
PB  - Cambridge Univ. Press
CY  - New York
ER  - 
TY  - JOUR
A1  - Willner, Arne P.
A1  - Gerdes, Axel
A1  - Massonne, Hans-Joachim
A1  - Schmidt, Alexander
A1  - Sudo, Masafumi
A1  - Thomson, Stuart N.
A1  - Vujovich, Graciela
T1  - The geodynamics of collision of a microplate (Chilenia) in Devonian times deduced by the pressure-temperature-time evolution within part of a collisional belt (Guarguaraz Complex, W-Argentina)
JF  - Contributions to mineralogy and petrology
N2  - The Guarguaraz Complex in West Argentina formed during collision between the microplate Chilenia and South America. It is composed of neritic clastic metasediments with intercalations of metabasic and ultrabasic rocks of oceanic origin. Prograde garnet growth in metapelite and metabasite occurred between 1.2 GPa, 470 degrees C and 1.4 GPa, 530 degrees C, when the penetrative s(2)-foliation was formed. The average age of garnet crystallization of 390 +/- 2 Ma (2 sigma) was determined from three four-point Lu-Hf mineral isochrones from metapelite and metabasite samples and represents the time of collision. Peak pressure conditions are followed by a decompression path with slight heating at 0.5 GPa, 560 degrees C. Fluid release during decompression caused equilibration of mineral compositions at the rims and also aided Ar diffusion. An Ar-40/39 Ar plateau age of white mica at 353 +/- 1 Ma (1 sigma) indicates the time of cooling below 350-400 degrees C. These temperatures were attained at pressures of 0.2-0.3 GPa, indicative of an average exhumation rate of >= 1 mm/a for the period 390-353 Ma. Late hydrous influx at 0.1-0.3 GPa caused pervasive growth of sericite and chlorite and reset the Ar/Ar ages of earlier coarse-grained white mica. At 284-295 Ma, the entire basement cooled below 280 degrees C (fission track ages of zircon) after abundant post-collisional granitoid intrusion. The deeply buried epicontinental sedimentary rocks, the high peak pressure referring to a low metamorphic geotherm of 10-12 degrees C/km, and the decompression/heating path are characteristics of material buried and exhumed within a (micro) continent-continent collisional setting.
KW  - Albite-amphibolite facies
KW  - Geothermobarometry
KW  - Lu-Hf system
KW  - K-Ar system
KW  - Fission track (zircon)
KW  - Collision zone
KW  - Garnet
KW  - Potassic white mica
Y1  - 2011
U6  - https://doi.org/10.1007/s00410-010-0598-8
SN  - 0010-7999
VL  - 162
IS  - 2
SP  - 303
EP  - 327
PB  - Springer
CY  - New York
ER  - 
TY  - JOUR
A1  - Halama, Ralf
A1  - Konrad-Schmolke, Matthias
A1  - Sudo, Masafumi
A1  - Marschall, Horst R.
A1  - Wiedenbeck, Michael
T1  - Effects of fluid-rock interaction on Ar-40/Ar-39 geochronology in high-pressure rocks (Sesia-Lanzo Zone, Western Alps)
JF  - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society
N2  - In situ UV laser spot Ar-40/Ar-39 analyses of distinct phengite types in eclogite-facies rocks from the Sesia-Lanzo Zone (Western Alps, Italy) were combined with SIMS boron isotope analyses as well as boron (B) and lithium (Li) concentration data to link geochronological information with constraints on fluid-rock interaction. In weakly deformed samples, apparent Ar-40/Ar-39 ages of phengite cores span a range of similar to 20 Ma, but inverse isochrons define two distinct main high-pressure (HP) phengite core crystallization periods of 88-82 and 77-74 Ma, respectively. The younger cores have on average lower B contents (similar to 36 mu g/g) than the older ones (similar to 43-48 mu g/g), suggesting that loss of B and resetting of the Ar isotopic system were related. Phengite cores have variable delta B-11 values (-18 parts per thousand to -10 parts per thousand), indicating the lack of km scale B homogenization during HP crystallization.
 Overprinted phengite rims in the weakly deformed samples generally yield younger apparent Ar-40/Ar-39 ages than the respective cores. They also show variable effects of heterogeneous excess 40 Ar incorporation and Ar loss. One acceptable inverse isochron age of 77.1 +/- 1.1 Ma for rims surrounding older cores (82.6 +/- 0.6 Ma) overlaps with the second period of core crystallization. Compared to the phengite cores, all rims have lower B and Li abundances but similar delta B-11 values (-15 parts per thousand to -9 parts per thousand), reflecting internal redistribution of B and Li and internal fluid buffering of the B isotopic composition during rim growth. The combined observation of younger Ar-40/Ar-39 ages and boron loss, yielding comparable values of both parameters only in cores and rims of different samples, is best explained by a selective metasomatic overprint. In low permeability samples, this overprint caused recrystallization of phengite rims, whereas higher permeability in other samples led to complete recrystallization of phengite grains.
 Strongly deformed samples from a several km long, blueschist-facies shear zone contain mylonitic phengite that forms a tightly clustered group of relatively young apparent Ar-40/Ar-39 ages (64.7-68.8 Ma), yielding an inverse isochron age of 65.0 +/- 3.0 Ma. Almost complete B and Li removal in mylonitic phengite is due to leaching into a fluid. The B isotopic composition is significantly heavier than in phengites from the weakly deformed samples, indicating an external control by a high-delta B-11 fluid (delta B-11 = + 7 +/- 4 parts per thousand). We interpret this result as reflecting phengite recrystallization related to deformation and associated fluid flow in the shear zone. This event also caused partial resetting of the Ar isotope system and further B loss in more permeable rocks of the adjacent unit. We conclude that geochemical evidence for pervasive or limited fluid flow is crucial for the interpretation of Ar-40/Ar-39 data in partially metasomatized rocks.
Y1  - 2014
U6  - https://doi.org/10.1016/j.gca.2013.10.023
SN  - 0016-7037
SN  - 1872-9533
VL  - 126
SP  - 475
EP  - 494
PB  - Elsevier
CY  - Oxford
ER  -