This rifting possibly also extended farther west into Crete and mainland Greece. In contrast, the Nd isotopic composition in clay- to silt-size fractions of one bulk sediment sample is similar to within 0. The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian—Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. They display a homogeneous deformation pattern characterized by a generally steeply dipping foliation and a near-horizontal to gently plunging mineral stretching lineation, indicating a strike-slip tectonic regime of deformation. The Middle Palaeozoic subduction and accretion events mark the evolutionary history along an active convergent margin between the Indochina and South China blocks, possibly related to the amalgamation of the Pangaea supercontinent. High-pressure mafic granulites containing granoblastic garnet, quartz, and minor hornblende have been found from the Song Ma Suture zone in northern Vietnam, regarded as a microcontinental boundary between the South China and Indochina blocks.
Therefore, the Luang Prabang Basin documents a magmatic arc in a good agreement with the recent recognition of neighboring ophiolitic rocks in the Luang Prabang area. The isotopic results other than potassium-argon K-Ar , namely rubidium-strontium Rb-Sr , samarium-neodymium Sm-Nd and lead-lead Pb-Pb , were used to calculate ages for the rock formation utilizing isochrons. To be able to distinguish the relative ages of rocks from such old material, and to get a better time resolution than that available from long-lived isotopes, short-lived isotopes that are no longer present in the rock can be used. However, local eruptions of or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. Growth of titanite, occurring between 1789 and 1814 Ma in the underthrust Archean basement of the Paleoproterozoic Ungava orogen northern Quebec , is associated with retrograde metamorphism during underthrusting of the Archean basement Approx. ? The inhomogeneous distribution of Lu and Hf in granitic rocks and their sensitivity to alteration during metamorphism create reproducibility problems for the Lu-Hf model. The U-Pb age distribution pattern of detrital zircon in the Nam Co Complex is compatible with that of the South China craton rather than that of the Indochina craton.
It is also necessary to assume that no isotopes were gained or lost over time and that the rate of radioactive decay has remained constant at the very slow rate measured today. Paleo-Tethyan remnants were largely exposed as dismembered mafic- ultramafic serpentinized fragments in close relationship to oceanic sedimentary rocks and mélange suites Hutchison, 1994. This field is known as or thermochronometry. But is a great resource. In Vietnam, the Triassic Indosinian collision affected coevally the Truong Son belt and the Kontum Massif,which were not independent tectonic units, but parts of the same Gondwana-derived Indochina continental block. The use of radiometric dating was first published in 1907 by and is now the principal source of information about the of rocks and other , including the age of or the itself, and can also be used to date a wide range of natural and.
A Shorter 146Sm Half-Life Measured and Implications for 146Sm-142Nd Chronology in the Solar System. Then, in 1896, radioactivity was discovered. Neodymium isotopes in the Colorado Front Range and crust — mantle evolution in the Proterozoic. This suture zone was finally re-shaped by the indentation between the active margin of Indochina and the irregular passive continental margin of South China during the Late Triassic as well as displacement along the Red River fault zone during the Cenozoic. After Turner and Cadogan 1974. Considering this petrotectonic information, we suggest that the serpentinite body of the Song Ma fault zone represents a remnant of paleo-oceanic lithosphere between the Indochina and South China blocks.
Within the Indochina plate, internal collisions occurred coevally in the Early Triassic, as along the Poko suture, at the western border of the Kontum Massif. The intersection between these two evolution lines then indicates the crustal formation age. The Song Ma Anticlinorium displays evidence for four deformations, the first two accompanied by high-grade to greenschist facies metamorphism, and the third by production of syn-low-grade metamorphic sheath folds. This causes induced fission of 235U, as opposed to the spontaneous fission of 238U. The collision along Song Ma follows the northwards subduction of Indochina beneath South China and the subsequent development of the Song Da zone which in turn was affected by the Late Triassic Indosinian phase of shortening.
To northwest of the Ailaoshan tectonic zone is the Jinshajiang tectonic zone Wang et al. Conversion to a foreland basin reflected collision between the South China and Indochina blocks. They are SiO2- and TiO2-poor, Al2O3-rich mafic rocks. Journal Journal of Asian Earth Sciences — Elsevier Published: Jan 1, 2006. Thus, the Kham Duc complex is interpreted as a tectonic mélange formed during a collisional orogeny that subsequently underwent crustal melting giving rise to the migmatites. On the basis of U—Pb ages, the Hf isotopic characteristics of zircons and the geochemical composition of granitoids, a two-stage magmatic evolution process of the Song Ma zone at ~290—260 and ~245—230 Ma can be proposed. This complex is structurally characterized by an antiformal metamorphic core consisting of two distinct metamorphic zones: inner garnet and outer biotite zones.
Sometimes, however, numerous discordant dates from the same rock will plot along a line representing a chord on the Concordia diagram. Our diabase sample L03-1 and coarse-grained basalt L04-2 yield zircon U—Pb weighted mean ages of 335. The two elements are joined in a parent—daughter relationship by the of 147Sm to 143Nd with a of 1. The dashed profile in Fig. Relative to the present-day coordinates, a northward-directed subduction of a slab attached to the Indochina plate has been proposed e.
Earth and Planetary Science Letters. The downcore variation in Sr and Nd isotopic composition indicates climatically induced changes in sediment provenance from two isotopically distinct end-members: 1 Eurasian shelf sediments as a distal source; and 2 Svalbard bedrock as a proximal source that coincide with a change in transport mechanism from sea ice to glacial ice. The Song Ma zone and Song Chay ophiolitic melange represent two ophiolitic sutures. So far, the oldest rock found is a tonalitic Gneiss metamorphic rock rock from the Northwest Territories, Canada, with an age of 3. Is this the age of the Earth? A synthesis of these data indicates that the Permian ~280-260 Ma and Late Triassic ~230-220 Ma felsic igneous rocks in northern Laos were generated in arc and post-collisional settings, respectively, with a transition from subduction to collision occurring at ~250 Ma Fig. According to you reply, did you mean that I may not have a meaningful Sm-Nd isochron age of this sample. The Swedish National Heritage Board.