Actividad de fluidos hidrotermales del Neoproterozoico tardío en el cinturón de Tandilia, Argentina

In the Barker - Villa Cacique area, Tandilia belt, alteration mineral assemblages were studied by petrography, XRD and EMPA at three different stratigraphic levels: (1) a phyllic alteration at the unconformity palaeoproterozoic basement-neoproterozoic sedimentary succession (TLPU); (2) an advanced argillic alteration in the Las Águilas Formation (middle level); and (3) a phyllic alteration on pyroclastic rocks of the Olavarría Formation (upper level). Special emphasize was placed on the chemical characterization of K-white micas and chlorites. Secondary K-white micas of altered migmatites, from the Las Aguilas and Olavarría Formations have a low paragonite content (Na* 9.5 km) for the entire sedimentary pile. Hot fluids would rise from deep-seated realms, metamorphic and/or hidden igneous sources. A correlation with a rasiliano thermo-tectonic event is hypothesized.En el área de Barker - Villa Cacique, Tandilia, se estudiaron mediante petrografía, DRX, y microsonda electrónica, las para- génesis de minerales de alteración de tres niveles estratigráficos diferentes: (1) alteración fílica de la discordancia basamento paleoproterozoico-secuencia sedimentaria neoproterozoica (TLPU); (2) alteración argílica avanzada en la Formación Las Águilas (nivel medio); y (3) alteración fílica en rocas piroclásticas de la Formación Olavarría (nivel superior). Las micas potási- cas y cloritas, de dichos niveles de alteración, fueron caracterizadas químicamente. Las micas potásicas de migmatitas alteradas y de las formaciones Las Águilas y Olavarría tienen un bajo contenido en paragonita (Na* 9,5 km) para el total de la pila sedimentaria. Los fluidos hidrotermales habrían ascendido desde ambientes profundos con una fuente metamórfica y/o cuerpos ígneos ocultos. Una correlación con un evento termo-tectónico Brasiliano es hipotetizada.Fil: Martinez, Juan Cruz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina. Universidad Nacional del Sur; ArgentinaFil: Dristas, Jorge A.. Universidad Nacional del Sur. Departamento de Geologia. Catedra de Petrologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; ArgentinaFil: Van Den Kerkhof, Alfons M. . Geowissenschaftliches Zentrum der Universität Göttingen; AlemaniaFil: Wemmer, Klaus . Geowissenschaftliches Zentrum der Universität Göttingen; AlemaniaFil: Massonne, Hans J.. Universität Stuttgart; AlemaniaFil: Theye, Thomas. Universität Stuttgart; AlemaniaFil: Frisicale, Maria Cristina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina. Universidad Nacional del Sur; Argentin

Dating protracted fault activities: microstructures, microchemistry and geochronology of the Vaikrita Thrust, Main Central Thrust zone, Garhwal Himalaya, NW India

The timing of shearing along the Vaikrita Thrust, the structurally upper boundary of the Main Central Thrust zone (MCTz), was constrained by combined microstructural, microchemical and geochronological investigations. Three different biotite-muscovite growth and recrystallisation episodes were observed: a relict mica-1; mica-2 along the main mylonitic foliation; mica-3 in coronitic structures around garnet during its breakdown. Analyses of biotite by electron microprobe show chloritization, and bimodal composition of biotite- 2 in one sample. Muscovite-2 and muscovite-3 differ in composition from each other. Biotite and muscovite 39Ar-40Ar age spectra from all samples give both inter-sample and intra- sample discrepancies. Biotite step ages range between 8.6 and 16 Ma, muscovite step ages between 3.6 and 7.8 Ma. These ages cannot be interpreted as "cooling ages", as samples from the same outcrop cooled simultaneously. Instead, Ar systematics reflect sample-specific recrystallisation markers. Intergrown impurities were diagnosed by Ca/K ratios. Age data of biotite were interpreted as a mixture of true biotite-2 (9.00±0.10 Ma) and two alteration products. The negative Cl/K-age correlation identifies a Cl-poor muscovite-2 (>7 Ma) and a Cl-rich, post-deformational, coronitic muscovite-3 grown at ≤5.88±0.03 Ma. The Vaikrita Thrust was active at least from 9 to 6 Ma around 600 °C; its movement ceased by 6 Ma

The metamorphic complexes of the Patagonian and Fuegian Andes

The Patagonian and Fuegian Andes are made up in part by late Paleozoic to Mesozoic metamorphic complexes. The mostly low grade late Paleozoic Eastern Andes Metamorphic Complex (EAMC) crops out to the East of the Meso-Cenozoic South Patagonian batholith (SPB), which intruded the metamorphic complexes. The protholit of the EAMC was likely deposited in a passive margin setting and at the Puerto Edén area underwent Late Jurassic sillimanite grade and migmatite local metamorphic conditions. It is suspected, but not proven, that the Cordillera Darwin Metamorphic Complex is a higher grade metamorphic complex equivalent of the EAMC. West of the SPB, paleo subduction complexes occur and are represented by the allochtonous Madre de Dios terrane. This terrane is composed of the ocean floor lithologies of the Denaro Complex topped by the Tarlton limestones that represent a guyot assemblage. The low grade continent derived Duque de York complex was deposited down top of the ocean floor lithologies. Further west, the blueschist bearing Middle Jurassic Diego de Almagro Complex, with psammopelitic, mafic and siliceous volcanic rock protoliths, evolved deep in a subduction zone during the Cretaceous. The possibility that the Antarctic Peninsula was located west of the present margin of South America is discussed

Mineral inclusions in rutile: A novel recorder of HP-UHP metamorphism

The ability to accurately constrain the secular record of high- and ultra-high pressure metamorphism on Earth is potentially hampered as these rocks are metastable and prone to retrogression, particularly during exhumation. Rutile is among the most widespread and best preserved minerals in high- and ultra-high pressure rocks and a hitherto untested approach is to use mineral inclusions within rutile to record such conditions. In this study, rutiles from three different high- and ultrahigh-pressure massifs have been investigated for inclusions. Rutile is shown to contain inclusions of high-pressure minerals such as omphacite, garnet and high silica phengite, as well as diagnostic ultrahigh-pressure minerals, including the first reported occurrence of exceptionally preserved monomineralic coesite in rutile from the Dora–Maira massif. Chemical comparison of inclusion and matrix phases show that inclusions generally represent peak metamorphic assemblages; although rare prograde phases such as titanite, omphacite and corundum have also been identified implying that rutile grows continuously during prograde burial and traps mineralogic evidence of this evolution. Pressure estimates obtained from mineral inclusions, when used in conjunction with Zr-in-rutile thermometry, can provide additional constraints on the metamorphic conditions of the host rock. This study demonstrates that rutile is an excellent repository for high- and ultra-high pressure minerals and that the study of mineral inclusions in rutile may profoundly change the way we investigate and recover evidence of such events in both detrital populations and partially retrogressed samples

Complex geophysical investigations under extreme P,T–conditions at zentralinstitut für physik der erde (Zipe) (1970–1990)

The development of the geophysical high pressure research in the former German Democratic Republic (GDR) is described here. The GDR was a German state established in 1949 at the territory of the Soviet occupation zone. The different experimental investigations under extreme pressure and temperature conditions and their industrial applications, including the pilot manufacture of synthetic diamonds are explained. A review of the research topics pursued including experiments on lunar material and Earth core/mantle material is described

A new alligatoroid from the Eocene of Vietnam highlights an extinct Asian clade independent from extant Alligator sinensis

During systematic paleontological surveys in the Na Duong Basin in North Vietnam between 2009 and 2012, well-preserved fossilized cranial and postcranial remains belonging to at least 29 individuals of a middle to late Eocene (late Bartonian to Priabonian age (39–35 Ma)) alligatoroid were collected. Comparative anatomical study of the material warrants the diagnosis of a new taxon, Orientalosuchus naduongensis gen. et sp. nov. The combined presence of an enlarged fifth maxillary tooth, prominent preorbital ridges, a large supraoccipital exposure on the skull table, a palatine-pterygoid suture anterior to the posterior end of the suborbital fenestra, and a pterygoid forming a neck surrounding the choana is unique to this species. Unlike previous phylogenies, our parsimony analysis recovers a monophyletic Late Cretaceous to Paleogene East to Southeastern Asian alligatoroid group, here named Orientalosuchina. The group includes Orientalosuchus naduongensis, Krabisuchus siamogallicus, Eoalligator chunyii, Jiangxisuchus nankangensis and Protoalligator huiningensis, all of them sharing a medial shifted quadrate foramen aerum. The recognition of this clade indicates at least two separate dispersal events from North America to Asia: one during the Late Cretaceous by Orientalosuchina and one by the ancestor of Alligator sinensis during the Paleogene or Neogene, the timing of which is poorly constrained

Konzeptionelle Betrachtungen zu divergierenden Konstruktionen des Studienerfolgs

Das Konstrukt „Studienerfolg“ wird von verschiedenen Akteuren/-innen der Hochschullandschaft unterschiedlich verstanden. Insbesondere zwischen Universitäten und Fachhochschulen sowie dualen Hochschulen bestehen divergierende Auffassungen. Der Beitrag zeigt exemplarisch die Multidimensionalität des Konstrukts Studienerfolg mit seinen verschiedenen Ursachen auf und benennt Implikationen, die diese Multidimensionalität für Erfolgsmessung und -bewertung in der Innen- und Außenwirkung hat. Der Fokus liegt auf Unterschieden zwischen den Hochschularten hinsichtlich des Studienverlaufs und der Berufsfähigkeit

The composition of subduction zone fluids and the origin of the trace element enrichment in arc magmas

<jats:title>Abstract</jats:title><jats:p>The partitioning of major and trace elements between eclogite and aqueous fluids with variable salinity was studied at 700–800 °C and 4–6 GPa in piston cylinder and multi anvil experiments. Fluid compositions were determined using the diamond trap technique combined with laser ablation ICP-MS measurements in the frozen state. In addition to NaCl, SiO<jats:sub>2</jats:sub> is the main solute in the fluids. The fluid/eclogite partition coefficients of the large ion lithophile elements (LILE), such as Rb, Cs, Sr, and Ba as well as those of the light rare earths (LREE), of Pb, and of U increase by up to three orders of magnitude with salinity. These elements will therefore be efficiently transported by saline fluids. On the other hand, typical high field strength elements, such as Ti, Nb, and Ta, are not mobilized even at high salinities. Increasing temperature and pressure gradually increases the partitioning into the fluid. In particular, Th is mobilized by silica-rich fluids at 6 GPa already at low salinities. We show that we can fully reproduce the trace element enrichment pattern of primitive arc basalts by adding a few percent of saline fluid (with 5–10 wt% Cl) released from the basaltic slab to the zone of melting in the mantle wedge. Assuming 2 wt% of rutile in the eclogite equilibrated with the saline fluid produces a negative Nb Ta anomaly that is larger than in most primitive arc basalts. Therefore, we conclude that the rutile fraction in the subducted eclogite below most arcs is likely < 1 wt%. In fact, saline fluids would even produce a noticeable negative Nb Ta anomaly without any rutile in the eclogite residue. Metasomatism by sediment melts alone, on the other hand, is unable to produce the enrichment pattern seen in arc basalts. We, therefore, conclude that at least for primitive arc basalts, the release of hydrous fluids from the basaltic part of the subducted slab is the trigger for melting and the main agent of trace element enrichment. The contribution of sediment melts to the petrogenesis of these magmas is likely negligible. In the supplementary material, we provide a “Subduction Calculator” in Excel format, which allows the calculation of the trace element abundance pattern in primitive arc basalts as function of fluid salinity, the amount of fluid released from the basaltic part of the subducted slab, the fluid fraction added to the source, and the degree of melting.</jats:p&gt

Trace element signatures in rutile: characterization of standards and applications to accessory mineral behavior in metamorphic rocks

This study focuses on the trace element composition of rutile, a frequent accessory mineral in various rock types (mafic, pelitic and felsic protoliths; common at blueschist-, eclogite- and granulite-facies conditions) and one of the most stable minerals in sedimentary environments. Rutile is an important carrier of highly charged elements, such as Ti, V, Cr, Zr, Nb, Sn, Sb, Hf, Ta and W. Due to these characteristics rutile has attracted significant interest in various fields of geology, e.g., as a likely controller of Nb and Ta budgets in subduction zones. Furthermore, it is useful as a geothermometer (Zr incorporation is strongly temperature dependent in quartz- and zircon-bearing systems), and as a geochronological tool (U-Pb and (U-Th)/He dating), and to assess the nature of an initial source rock in sediment provenance studies (Nb and Cr contents can de used to distinguish between mafic and felsic sources). An increasing number of today’s geochemical studies, which include the investigations presented here, are based on microanalysis of trace elements, several of which are carried out in-situ. All of these techniques depend on calibration using a homogeneous material with well documented chemical concentration. In this sense, having a rutile standard is a key issue. A set of rutile crystals were investigated in order to find rutiles suitable for use as mineral standards. Trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Pb and Hf isotope data are presented for four large (centimeter size) and relatively homogeneous rutile grains. Analytical techniques used are SIMS, EMP, LA–ICP–MS, ID–MC–ICP–MS and TIMS. For most elements, homogeneity is usually within ±10% and variations are occasionally less than (±5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the element and agreement between techniques, are presented for Zr, Nb, Sn, Sb, Hf, Ta, W and U. One of the studied grains has a relatively high U concentration (ca. 30 ppm) and rather constant U–Pb ages (1085.1 to 1096.2 Ma, 207Pb/235U ages and 1086.3 to 1096.6 Ma, 206Pb/238U ages), favoring its application as an age standard for U-Pb rutile dating. The studied rutiles are useful as mineral standards in for in-situ rutile measurements, particularly for Zr–in–rutile thermometry, quantitative provenance studies (Nb and Cr concentrations as an index of source rock type) and U–Pb dating. The efforts in characterizing a set of rutile standards are not only relevant for the scientific community. It also provides the analytical background for the results presented here. Following the characterization of standards, textural observations and in-situ analyses were used to investigate trace element behavior during prograde and retrograde metamorphic reactions involving rutiles. The investigated samples derive from two well studied localities: the Ivrea-Verbano Zone (Italy) and the Erzgebirge (Germany). The Ivrea-Verbano Zone is a classic granulite area and rocks from the Strona and d’Ossola Valleys are an example of the amphibolite to granulite facies transition, where rutile growth is associated with the breakdown of high-Ti biotite. Rutile bearing rocks show a rich inventory of textures that allow for the investigation of trace element behavior in response to prograde rutile growth, and the effect of postpeak processes on rutile chemistry. Nb concentrations in rutile from lower grade samples show a larger spread (from 500 to 5000 ppm within one sample) when compared to those from higher grades. This pattern can be modeled using prograde rutile growth formed from biotite breakdown. Zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution. Maximum Zr concentrations increase according to the general metamorphic gradient known for this area. Temperatures (from Zr-in-rutile thermometry), although feasible, are considerably higher than previous calculations (increasing from ca. 850 to 930°). A second cluster of Zr concentrations in rutile occurs at rather constant concentrations (ca. 1000 ppm) for all localities and is interpreted to be related to intense fluid influx at high temperature and/or to post-peak diffusional resetting favored by slow cooling rates. Alteration textures, characterized by a complex network of microveins, are evidence for the late fluid influx. The fluid strongly affected the rutiles, which is evidenced by corrosion of older rutile grains and the formation of rutile veinlets. In the Ezgebirge, metamorphic texture support prograde rutile growth from ilmenite in low- to medium-grade (430-630C° metasedimentary rocks. Newly crystallized rutiles occur as polycrystalline aggregates that mimic the shape of the ilmenites. In-situ trace element data show that rutiles from the lowest grade samples (ca 480C° mirror the Nb/Ti ratio of ilmenite. Under these conditions, rutile did not equilibrate its chemistry with the remaining ilmenites. In higher grade samples, rutiles show a larger scatter in Nb and have Nb/Ti ratios higher than relict ilmenite. In these rocks, the Nb pattern can be modeled using prograde rutile growth from ilmenite, in a model similar to the one applied to granulites from the the Ivrea- Verbano Zone. Results indicate that rutiles from these rocks were able to reequilibrate its chemistry with the remaining ilmenites. Newly formed rutiles yield temperatures (from 500 to 630C° that are in agreement with the metamorphic conditions published for the studied rocks. Detrital rutile grains, identified by their distinct chemical composition (high Zr and Nb contents) and textures (single grains surrounded by fine grained ilmenites), occur in quartzites from the medium-grade rocks (ca 530C°. This confirms models in which detrital rutiles survive in quartzites to higher metamorphic grade compared to rutiles in metapelites. Preliminary calculations based on the grain size distribution of rutiles in the studied rocks show that quartzites are probably the main source of rutiles in sediments derived from low-grade metamorphic sequences, even if the occurrence of quartzite is minor. Part of the data obtained during the development of this thesis contributed to other publications related, directly or indirectly, to its topic. For example, to evaluate how well the Zr-in-rutile thermometer can be applied to eclogites; to evaluate the applicability of rutile trace element geochemistry to provenance studies; and to characterize the occurrence and stability of coesite-bearing tourmaline in ultra-high pressure metamorphic rocks

A new late Eocene alligatoroid crocodyliform from Transylvania

Here we describe a new eusuchian crocodyliform, collected 130 years ago from a shallow marine limestone of the late Eocene (Priabonian) fossil locality of Cluj-Manastur, Transylvania, Romania. Diplocynodon kochi n. sp. is represented by a three-dimensionally preserved incomplete skull that may have belonged to a mature individual. The new taxon possesses a relatively narrow and elongated snout and a mediolaterally shallow but anteroposteriorly wide premaxillary-maxillary notch, strengthened by a prominent bony ridge. The nasals are excluded from the naris and the anterior tip of the frontal forms a broad, complex sutural contact with the nasals. Diplocynodon kochi n. sp. possesses, similarly to other members of the genus, 16-17 maxillary alveoli of which the fourth and fifth alveoli are enlarged and confluent; the lacrimal is longer than the prefrontal; the ectopterygoid is situated dose to the posteriormost maxillary tooth alveoli, the dorsal margin of the infratemporal fenestra is bordered by the quadratojugal, preventing the quadrate from reaching the fenestra, and the foramen aereum is situated on the dorsal surface of the quadrate. The occurrence of D. kochi n. sp. in the Priabonian of the eastern part of Central Europe suggests that the genus was still present and probably widespread across the continent that contributed probably to its survival (at least locally) across the Eocene/Oligocene boundary. | Nous décrivons ici un nouveau crocodyliforme eusuchien découvert il y a environ 130 ans dans un calcaire marin peu profond de la localité de Cluj-Mănăștur (Transylvanie, Roumanie), datant de l’Éocène supérieur (Priabonien). Diplocynodon kochi n. sp. est représenté par un crâne incomplet, préservé en trois dimensions, appartenant à un individu vraisemblablement mature. Le nouveau taxon possède un museau de type platyrostre, relativement étroit et allongé et une encoche prémaxillaire- maxillaire médio-latéralement peu profonde, mais antéropostérieurement longue, renforcée par une crête osseuse proéminente. L’os nasal est exclu des narines et l’extrémité antérieure du frontal forme un contact sutural grand et complexe avec l’os nasal. Diplocynodon kochi n. sp. possède, comme les autres membres du genre, 16-17 alvéoles sur le maxillaire, dont les quatrième et cinquième alvéoles sont grands et confluents ; le lacrymal est plus long que le préfrontal ; l’ectoptérygoïde est positionné près des alvéoles des maxillaires les plus postérieures ; la marge dorsale de la fenêtre infra-temporale est bordée par le quadratojugal, séparant ainsi le carré de la fenêtre infratemporale ; et le foramen aëreum est situé sur la surface dorsale du carré. La présence de D. kochi dans le Priabonien de la partie orientale de l’Europe centrale suggère que le genre était encore présent et probablement largement distribué sur le continent, ce qui a probablement contribué à sa survie (au moins localement) au-delà de la limite Éocène/Oligocène