40Ar--39Ar dating of volcanogenic products from the AND-2A core (ANDRILL Southern McMurdo Sound Project, Antarctica): correlations with the Erebus Volcanic Province and implications for the age model of the core

The AND-2A drillcore (Antarctic Drilling Program – ANDRILL) was successfully completed in late 2007 on the Antarctic continental margin (southern McMurdo Sound, Ross Sea) with the aim of tracking ice-proximal to shallow marine environmental fluctuations and to document the 20-Ma evolution of the Erebus Volcanic Province. Lava clasts and tephra layers from the AND-2A drillcore were investigated from a petrographic and stratigraphic point of view and analyzed by the 40Ar–39Ar laser technique in order to constrain the age model of the core and to gain information on the style and nature of sediment deposition in the Victoria Land Basin since Early Miocene. Ten out of 17 samples yielded statistically robust 40Ar–39Ar ages, indicating that the AND-2A drillcore recovered !230 m of Middle Miocene (~128–358 meters below sea floor, ~11.5–16.0 Ma) and >780 m of Early Miocene (~358–1093 48 meters below sea floor, ~16.0–20.1 Ma). Results also highlight a nearly continuous stratigraphic record from at least 358 meters below sea floor down hole, characterized by a mean sedimentation rate of ~19 cm/ka, possible oscillations of no more than a few hundreds of ka and a break within ~17.5–18.1 Ma. Comparison with available data from volcanic deposits on land, suggests that volcanic rocks within the AND-2A core were supplied from the south, possibly with source areas closer to the drill site for the upper core levels, and from 358 meters below sea floor down hole, with the “proto-Mount Morning” as the main source

Dating minerals by ID-TIMS geochronology at times of in situ analysis: selected case studies from the CPGeo-IGc-USP laboratory

Since 1964, the Center for Geochronological Research - CPGeo, one of the interdepartmental centers of the Instituto de Geociências (IG) of São Paulo University, has developed studies related to several geological processes associated with different rock types. Thermal Ionization Mass Spectrometry Isotopic Dilution (ID-TIMS) has been the technique widely used in the CPGeo U-Pb Laboratory. It provides reliable and accurate results in age determination of superposed events. However, the open-system behavior such as Pb-loss, the inheritance problem and metamictization processes allow and impel us to a much richer understanding of the power and limitations of U-Pb geochronology and thermochronology. In this article, we present the current methodology used at the CPGeo-IGc-USP U-Pb laboratory, the improvements on ID-TIMS method, and report high-precision U-Pb data from zircon, monazite, epidote, titanite, baddeleyite and rutile from different rock types of several domains of the Brazilian south-southeast area, Argentina and Uruguay.O Centro de Pesquisas Geocronológicas (CPGeo), um dos centros interdepartamentais do Instituto de Geociências (IG) da Universidade de São Paulo (USP), desde 1964 desenvolve estudos relacionados a diversos processos geológicos que se associam a diferentes tipos de rochas. A técnica amplamente utilizada no Laboratório U-Pb é a diluição isotópica por espectrometria de massa termo ionizada (ID-TIMS). Esta sistemática proporciona resultados bastante confiáveis e precisos na determinação das idades de eventos geológicos superpostos. Entretanto, o comportamento de sistema aberto como perda de Pb, problemas de herança isotópica e processos de metamictização, nos permite o entendimento do poder e limitação da geocronologia e termocronologia U-Pb. Neste artigo apresentamos a metodologia atualmente utilizada no Laboratório U-Pb do CPGeo-IGc-USP, as melhorias atingidas na técnica ID-TIMS e alguns dados obtidos em zircão, epídoto, titanita, baddeleyita e rutilo de diferentes tipos de rochas de alguns domínios da região sul-sudeste brasileira e da Argentina e Uruguai.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

SHRIMP ion probe zircon geochronology and Sr and Nd isotope geochemistry for southern Longwood Range and Bluff Peninsula intrusive rocks of Southland, New Zealand

Permian–Jurassic ultramafic to felsic intrusive complexes at Bluff Peninsula and in the southern Longwood Range along the Southland coast represent a series of intraoceanic magmatic arcs with ages spanning a time interval of 110 m.y. New SHRIMP U-Pb zircon data for a quartz diorite from the Flat Hill complex, Bluff Peninsula, yield an age of 259 ± 4 Ma, consistent with other geochronological and paleontological evidence confirming a Late Permian age. The new data are consistent with an age of c. 260 Ma for the intrusive rocks of the Brook Street Terrane. SHRIMP U-Pb zircon ages for the southern Longwood Range confirm that intrusions become progressively younger from east to west across the complex. A gabbro at Oraka Point (eastern end of coastal section) has an age of 245 ± 4 Ma and shows virtually no evidence of zircon inheritance. The age is significantly different from that of the Brook Street Terrane intrusives. Zircon ages from the western parts of the section are younger and more varied (203–227 Ma), indicating more complex magmatic histories. A leucogabbro dike from Pahia Point gives the youngest emplacement age of 142 Ma, which is similar to published U-Pb zircon ages for the Anglem Complex and Paterson Group on Stewart Island

40Ar–39Ar dating of volcanogenic products from the AND-2A core (ANDRILL Southern McMurdo Sound Project, Antarctica): correlations with the Erebus Volcanic Province and implications for the age model of the core

The AND-2A drillcore (Antarctic Drilling Program—ANDRILL) was successfully completed in late 2007 on the Antarctic continental margin (Southern McMurdo Sound, Ross Sea) with the aim of tracking ice proximal to shallow marine environmental fluctuations and to document the 20-Ma evolution of the Erebus Volcanic Province. Lava clasts and tephra layers from the AND-2A drillcore were investigated from a petrographic and stratigraphic point of view and analyzed by the 40Ar–39Ar laser technique in order to constrain the age model of the core and to gain information on the style and nature of sediment deposition in the Victoria Land Basin since Early Miocene. Ten out of 17 samples yielded statistically robust 40Ar–39Ar ages, indicating that the AND-2A drillcore recovered ≤230 m of Middle Miocene (∼128–358 m below sea floor, ∼11.5–16.0 Ma) and >780 m of Early Miocene (∼358–1093 m below sea floor, ∼16.0–20.1 Ma). Results also highlight a nearly continuous stratigraphic record from at least 358 m below sea floor down hole, characterized by a mean sedimentation rate of ∼19 cm/ka, possible oscillations of no more than a few hundreds of ka and a break within ∼17.5–18.1 Ma. Comparison with available data from volcanic deposits on land, suggests that volcanic rocks within the AND-2A core were supplied from the south, possibly with source areas closer to the drill site for the upper core levels, and from 358 m below sea floor down hole, with the “proto-Mount Morning” as the main source

Posets pluton: a geochronological piece in the puzzle of the Axial Zone of the Pyrenees

[EN]A detailed geochronological study was conducted on zircons from a diorite sample of the Posets pluton (Axial Zone, Pyrenees). The extracted igneous zircons constrain the emplacement of the pluton to 302 +/- 2 Ma and 301 +/- 3 Ma, by means of U-Pb sensitive high-resolution ion microprobe (SHRIMP) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses, respectively. Considering the syn- to late-tectonic emplacement of the Posets pluton during the main Variscan deformation event (D-2), the obtained ages constrain the long-lasting D-2, associated with the dextral transpression registered through the Axial Zone of the Pyrenees.This work was supported by grants EHUA13/03 and GIU20/017 from the University of the Basque Country (UPV/EHU) and CGL2017-82976 from the Ministerio de Economia, Industria y Competitividad / Agencia Estatal de Investigacion / Fondo Europeo de Desarrollo Regional, European Union. E. Druguet, Y. Denele, an anonymous reviewer and the editor Olivier Lacombe are thanked for reviews and discussions that improved the final manuscript

Exploring the Base of the Volcano: A Case Study of an Active Stratovolcano, Mt. Zao, NE Japan

It is very important to explore the base of large volcanoes because older volcanoes with distinct petrological characteristics are sometimes hidden behind them. Such older volcanoes provide keys to investigate the change of magma genesis and tectonic setting during geological time. We newly found an older volcano in southern part of Zao volcano, located in Japan. We have investigated in detail the eruptive products outcropping in its southern part and found that some eruptive rocks with peculiar features form a new stratovolcano which is different from Zao volcano. We call this newly found volcano, the Hiyamizuyama volcano. We have performed K-Ar dating on the representative rocks, obtaining an old age of approximately 1.45 My. The rocks are calcalkaline andesites to dacites, having distinct chemical compositional features with respect to any other calcalkaline rock of the stages 2–6 of Zao volcano. Megacrystals and plutonic intrusions represent a distinct character of the eruptive rocks of the Hiyamizuyama volcano. The finding of this older volcano is also important in order to consider the long-term temporal variation of volcanism and magmatism in the northeastern sector of Japan

Tidal deposits in the Early Miocene Central Paratethys: the Vučji Jarek and Čemernica members of the Macelj formation (NW Croatia)

The Macelj formation is an informal Eggenburgian-early Ottnangian lithostratigraphic unit that is established in the area of the Hrvatsko Zagorje Basin, which represented a marginal zone of the Early Miocene Central Paratethys Sea. Modern studies, as a part of the Geologic Map of the Republic of Croatia 1:50 000 project, yielded new data that improves the knowledge of the depositional and stratigraphic characteristics of the formation. The sedimentological research within this study was focused on the two older lithostratigraphic units of the Macelj formation: the Vučji Jarek member and the Čemernica member. The Vučji Jarek mb. is represented by three facies. The Facies of horizontally bedded sandstones is characterized by mostly medium-grained, moderately sorted sandstones that reflect deposition on the foreshore to the upper shoreface. The facies of horizontally and cross-bedded glauconitic sandstones is composed of fine- to coarsegrained, well-sorted sandstones that indicate foreshore to shoreface deposition under tidal influence. The Facies of horizontally and cross-bedded pyroclastics consists of tuff, pumice, lapilli and large blocks, showing a chaotic structure in places. Deposition occurred at the shoreface under tidal influence. The Čemernica mb. is represented by the Facies of structureless clayey-silty sands that are poorly sorted and bioturbated, and indicates deposition below the fairweather wavebase, in the offshore-transition zone. Deposits of the members include marine macro- and microfossil associations.K-Ar dating of separated glauconite mineral fractions yielded an early Eggenburgian age for the Vučji Jarek mb. glauconitic sandstones (19.2±0.64 Ma) which is in accordance with biostratigraphical analyses. Sedimentological characteristics of the Eggenburgian Macelj fm., especially those that reflect the tidal influence, fit the general characteristics of the Central Paratethys Sea in the Early Miocene

Cytomegalovirus-specific T-cell responses and viral replication in kidney transplant recipients

<p>Abstract</p> <p>Background</p> <p>Cytomegalovirus (CMV) seronegative recipients (R-) of kidney transplants (KT) from seropositive donors (D+) are at higher risk for CMV replication and ganciclovir(GCV)-resistance than CMV R(+). We hypothesized that low CMV-specific T-cell responses are associated with increased risk of CMV replication in R(+)-patients with D(+) or D(-) donors.</p> <p>Methods</p> <p>We prospectively evaluated 73 consecutive KT-patients [48 R(+), 25 D(+)R(-)] undergoing routine testing for CMV replication as part of a preemptive strategy. We compared CMV-specific interferon-γ (IFN-γ) responses of CD4+CD3+ lymphocytes in peripheral blood mononuclear cells (PBMC) using three different antigen preparation (CMV-lysate, pp72- and pp65-overlapping peptide pools) using intracellular cytokine staining and flow cytometry.</p> <p>Results</p> <p>Median CD4+ and CD8+T-cell responses to CMV-lysate, pp72- and pp65-overlapping peptide pools were lower in D(+)R(-) than in R(+)patients or in non-immunosuppressed donors. Comparing subpopulations we found that CMV-lysate favored CD4+- over CD8+-responses, whereas the reverse was observed for pp72, while pp65-CD4+- and -CD8+-responses were similar. Concurrent CMV replication in R(+)-patients was associated with significantly lower T-cell responses (pp65 median CD4+ 0.00% vs. 0.03%, p = 0.001; CD8+ 0.01% vs. 0.03%; p = 0.033). Receiver operated curve analysis associated CMV-pp65 CD4+ responses of > 0.03% in R(+)-patients with absence of concurrent (p = 0.003) and future CMV replication in the following 8 weeks (p = 0.036). GCV-resistant CMV replication occurred in 3 R(+)-patients (6.3%) with pp65- CD4+ frequencies < 0.03% (p = 0.041).</p> <p>Conclusion</p> <p>The data suggest that pp65-specific CD4+ T-cells might be useful to identify R(+)-patients at increased risk of CMV replication. Provided further corroborating evidence, CMV-pp65 CD4+ responses above 0.03% in PBMCs of KT patients under stable immunosuppression are associated with lower risk of concurrent and future CMV replication during the following 8 weeks.</p