Search results for "GEOCHRONOLOGY"
showing 10 items of 60 documents
Geochronology of an archaean tonalitic gneiss dome in Northern Finland and its relation with an unusual overlying volcanic conglomerate and komatiiti…
1981
Archaean gneiss-greenstone relationships are still unresolved in many ancient cratonic terrains although there is growing evidence that most of the late Archaean greenstone assemblages were deposited on older tonalitic crust.
Rhenium‑osmium geochronology of the Toarcian Posidonia Shale, SW Germany
2019
Abstract Black shale samples from sedimentary layers below and between the Unterer Stein, Oberer Stein, Inoceramus Bank, and Nagelkalk horizons from the Dormettingen quarry, SW Germany were analysed for their Re and Os isotope composition and content. The ~12-m-thick sedimentary sequence of the Posidonia Shale Formation, composed of multiple layers of black shale and intercalated limestone beds, was deposited during the Early Jurassic (Toarcian), a time during which black shale sedimentation was ubiquitous in Western Europe during a widespread oceanic anoxic event. Both the marl and shale layers beneath the black shales and adjacent to the Oberer Stein limestone layer show signs of bioturba…
Zircon M127 - A Homogeneous Reference Material for SIMS U-Pb Geochronology Combined with Hafnium, Oxygen and, Potentially, Lithium Isotope Analysis
2016
Faculty of Geosciences, Geography and Astronomy, University of Vienna; Beijing SHRIMP Centre, Chinese Academy of Geological Sciences; European Commission [MEXC-CT-2005-024878]; FWF Austrian Science Fund [P20028-N10, P24448-N19]; U.S. National Science Foundation [EAR 1524336]
Age and metasomatic alteration of the Mt Neill Granite at Nooldoonooldoona Waterhole, Mt Painter Inlier, South Australia
2001
Quartz feldspar augen gneisses, quartz augen schists and trondhjemites outcrop at Nooldoonooldoona Waterhole in the southwestern corner of the Proterozoic Mt Painter Inlier, northern Flinders Ranges, South Australia. These rocks were previously interpreted as having different origins and ages. However, we argue that all rock types were the result of deformation and strong metasomatic alteration of one common precursor: the Mt Neill Granite. Our conclusion is based on field observations that show that the different lithologies grade into each other and that intrusive contacts are lacking. Whole rock major and trace element analyses also point to a common protolith. Finally, Pb/Pb dating of m…
Geochemistry, Isotope Geochemistry and Geochronology: Application to Field Studies
1990
Structural studies make it possible to reconstruct the metamorphic and deformation history of a rock body but do not provide information on the absolute timing of these processes. Likewise, field observations and structural work alone may not unambiguously identify the protoliths of many high-grade gneisses or the compositional changes associated with migmatisation, anatexis and the general action of fluid and/or vapour phases in a rock. Geochemical research can answer many of these problems but, as most of this research is laboratory-oriented, we limit ourselves to some general outlines of the possible lines of research, so that these can be borne in mind during fieldwork.
Geochronology and Nd-Sr systematics of Lusatian granitoids: significance for the evolution of the Variscan orogen in east-central Europe
1994
A variety of pre-Variscan granitoids and two Variscan monzogranites occurring in the central and western parts of the Lusatian Granodiorite Complex (LGC), Saxonia were dated by the single zircon evaporation method, complemented by whole rock Nd isotopic data and Rb —Sr whole rock and mineral ages. The virtually undeformed pre-Variscan granitoids constitute a genetically related, mostly peraluminous magmatic suite, ranging in composition from two-mica granodiorite, muscovite-bearing biotite quartz diorite (tonalite) and granodiorite to biotite granodiorite and monozogranite.
Sm-Nd dating of Fig Tree clay minerals of the Barberton greenstone belt, South Africa.
1994
Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, South Africa, form a linear array corresponding to an age of 3102 +/- 64 Ma, making these minerals the oldest dated clays on Earth. The obtained age is 120-160 m.y. younger than the depositional age determined by zircon geochronology. Nd model ages for the clays range from approximately 3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the …
The role of geochronology in understanding continental evolution
2010
Geochronology has become one of the most essential tools in reconstructing processes of continental growth and evolution, and in situ dating of minerals has become common practice through the development of high-resolution ion microprobes and laser ablation inductively coupled plasma mass spectrometry techniques. Zircon has established itself as the most robust and reliable mineral to record magmatic and metamorphic processes. The combination of mineral ages with Sm–Nd, Lu–Hf and O isotopic systematics constrains magma sources and their evolution, and a picture is emerging that supports the beginning of modern-style plate tectonics in the early Archaean. Major fields for future research in …
Late palaeozoic magmatism in the basement rocks Southwest of Mt. Olympos, Central Pelagonian zone, Greece: Remnants of a permo-carboniferous magmatic…
2001
We dated basement rocks from several localities southwest of Mt. Olympos, as well as from a locality near the top of the mountain using the single zircon Pb/Pb evaporation technique. For the samples southwest of the mountain, the ages obtained range from ca. 280 to 290 Ma, with only a few zircon grains being around 300 Ma. By contrast, the sample from near the top of the mountain appears to be slightly younger, with ca. 270 Ma. These ages imply that the granitoids crystallized during Late Carboniferous - Early Permian times, and are therefore younger than the basement gneisses of other regions of the Pelagonian zone, which yielded zircon ages of around 300 Ma (e.g. Yarwood & Aftalion 19…
Rb-Sr geochronology in favour of polymetamorphism in the Pan African Damara belt of Namibia (South West Africa)
1978
New Rb-Sr whole rock age data are reported from two metasedimentary sequences of the Damara Supergroup in the central Pan African Damara belt of Namibia (South West Africa).