Search results for "gon"
showing 10 items of 6445 documents
Detrital footprint of the Mozambique ocean: U–Pb SHRIMP and Pb evaporation zircon geochronology of metasedimentary gneisses in eastern Madagascar
2003
Abstract The southern East African Orogen is a collisional belt where the identification of major suture zones has proved elusive. In this study, we apply U–Pb isotopic techniques to date detrital zircons from a key part of the East African Orogen, analyse their possible source region and discuss how this information can help in unravelling the orogen. U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) and Pb evaporation analyses of detrital zircons from metasedimentary rocks in eastern Madagascar reveal that: (1) the protoliths of many of these rocks were deposited between ∼800 and 550 Ma; and (2) these rocks are sourced from regions with rocks that date back to over 3400 Ma, with…
Archean and Proterozoic ancestry in late Precambrian to early Paleozoic crustal elements of southern Turkey as revealed by single-zircon dating
1990
Detrital zircon ages and paleontology limit the age of the oldest known metasedimentary rocks in the Menderes-Taurus block of southwestern Turkey to between 657 {plus minus}5 Ma and Middle Cambrian (ca. 533 Ma). A mylonitic granite, also part of the basement, yielded a date of intrusion of 543 {plus minus}7 Ma. The scatter of both detrital and xenocryst zircon ages between 612 {plus minus}6 and 3,140 {plus minus}2 Ma virtually precludes northeastern Africa and Arabia as their provenance, but is compatible with a source in the Angara craton of Siberia. These results suggest that the Pan-African evolution in the Middle East may have ended by Angara's collision with Gondwana in the Early Cambr…
Electron Spin Resonance and Thermoluminescence dating of shells and sediments from Sambaqui (shell mound) Santa Marta II, Brazil
2020
In Tupi, the word Sambaqui means “mound of shells”. These archaeological sites are cultural vestiges left by the prehistoric occupation of the Brazilian coast from five to six thousand years ago. Mollusks, fishes, and other marine edible foods were important for the survival of this population. The remains of foods, mainly shells, were heaped up, giving a mound of different proportions, which became part of the landscape of the Brazilian coastal plain. Due to the large number of Sambaquis in Brazil and considering that Sambaqui Santa Marta II, Laguna, SC, has not yet been dated, Electron Spin Resonance (ESR) measurements were performed in aragonite shells collected from different layers of …
The Adamawa-Yadé domain, a piece of Archaean crust in the Neoproterozoic Central African Orogenic belt (Bafia area, Cameroon)
2017
Abstract New field observations, ages and geochemical data are presented for the Adamawa-Yade domain, forming part of Central African Orogenic Belt in Cameroon. This belt delineates the northern margin of the Congo craton and is part of the Braziliano/Pan-African orogenic system, which was formed during amalgamation of the West Gondwana continent at the end of the Neoproterozoic. U–Pb dating indicates that the protoliths of some orthogneisses from the Adamawa-Yade domain were emplaced during three distinct periods. Tonalite-Trondhjemite-Granodiorite (TTG) suites in the Makenene area intruded at ca. 3.0–2.5 Ga, and were affected by partial melting at ca. 2.08–2.07 Ga, during the Eburnean oro…
NO EXCESSIVE CRUSTAL GROWTH IN THE CENTRAL ASIAN OROGENIC BELT: FURTHER EVIDENCE FROM FIELD RELATIONSHIPS AND ISOTOPIC DATA
2017
Abstract We provide new field observations and isotopic data for key areas of the Central Asian Orogenic Belt (CAOB), reiterating our previous assessment that no excessive crustal growth occurred during its ca. 800 Ma long orogenic evolution. Many Precambrian blocks (microcontinents) identified in the belt are exotic and are most likely derived from the northern margin of Gondwana, including the Tarim craton. Ocean opening in the Palaeo-Asian Ocean, arc formation and accretionary processes began in the latest Mesoproterozoic along the southern margin of the Siberian craton and continued into the Neoproterozoic, giving rise to tectono-metamorphic terranes distinct from the exotic microcontin…
Multi-component gas emission measurements of the active lava lake of Nyiragongo, DR Congo
2017
Between 2007 and 2011 four measurement campaigns (June 2007, July 2010, June 2011, and December 2011) were carried out at the crater rim of Nyiragongo volcano, DR Congo. Nyiragongo is one of the most active volcanoes in Africa. The ground-based remote sensing technique Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS), which uses scattered sunlight, the in-situ Multi-Component Gas Analyzer System (Multi-GAS) and alkaline impregnated filter were simultaneously applied during all field trips. The bromine monoxide to sulfur dioxide (BrO/SO2) and carbon dioxide to sulfur dioxide (CO2/SO2) molar ratios were determined, among other ratios. During the different field trips variati…
Reply to J. Berger's comment on the article “Discovery of metamorphic microdiamonds from the parautochthonous units of the Variscan French Massif” by…
2015
International audience
How to make a transverse triple junction—New evidence for the assemblage of Gondwana along the Kaoko-Damara belts, Namibia
2016
T-shaped orogenic triple junctions between mobile belts usually form in two unrelated stages by subsequent and oblique continental collisions separated by a significant time span. Besides these “oblique triple junctions”, another type, named “transverse triple junctions”, may exist. Such junctions are created by a more complex mechanism of partly contemporaneous convergence of three cratons in a restricted time frame, involving strike slip. The Neoproterozoic–Cambrian Kaoko-Damara junction between the Rio de la Plata, Congo, and Kalahari cratons in Namibia is an example of such a transverse orogenic triple junction, formed by at least four subsequent but partly related deformation events. I…
Moroccan speleothem and tree ring records suggest a variable positive state of the North Atlantic Oscillation during the Medieval Warm Period
2013
We present a magnesium (Mg) and strontium (Sr) record from an aragonitic speleothem (Grotte de Piste, Morocco, 34°N; 04°W) providing a reconstruction of effective rainfall from 619 to 1962 AD. The corresponding drip site was monitored over 2 yr for drip water Mg/Ca and Sr/Ca ratios. Results show evidence for prior aragonite precipitation, which can explain negative correlations between speleothem Mg and Sr concentrations. The data shown here have important climate implications concerning the evolution of the North Atlantic Oscillation (NAO). A comparison of the stalagmite data from Grotte de Piste with an updated tree ring based drought reconstruction from Morocco and other NAO related pro…
LA-ICP-MS analyses on coral growth increments reveal heavy winter rain in the Eastern Mediterranean at 9 Ma
2009
Abstract Sediment particles incorporated into coral skeletons reflect variation in composition and amount of suspended material in ambient water during coral growth. They can be used to identify periods of enhanced storm frequency and associated freshwater discharge. Tortonian (Late Miocene) Porites corals from Crete (Aegean Sea, Eastern Mediterranean) show pronounced annual density bands in X-ray photographs. δ18O compositional variability reflects the annual banding equivalent with a ~ 7 °C annual sea surface temperature (SST) cycle over a seven-year period. Fine sediment particles are concentrated in layers with skeletal porosity parallel to growth increments. Variations in the chemical …