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About: Geochronology is a(n) research topic. Over the lifetime, 8784 publication(s) have been published within this topic receiving 231299 citation(s). more

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Journal ArticleDOI
Paul W.O. Hoskin1, Urs SchalteggerInstitutions (1)
Abstract: Zircon is the main mineral in the majority of igneous and metamorphic rocks with Zr as an essential structural constituent. It is a host for significant fractions of the whole-rock abundance of U, Th, Hf, and the REE (Sawka 1988, Bea 1996, O’Hara et al. 2001). These elements are important geochemically as process indicators or parent isotopes for age determination. The importance of zircon in crustal evolution studies is underscored by its predominant use in U-Th-Pb geochronology and investigations of the temporal evolution of both the crust and lithospheric mantle. In the past decade an increasing interest in the composition of zircon, trace-elements in particular, has been motivated by the effort to better constrain in situ microprobe-acquired isotopic ages. Electron-beam compositional imaging and isotope-ratio measurement by in situ beam techniques—and the micrometer-scale spatial resolution that is possible—has revealed in many cases that single zircon crystals contain a record of multiple geologic events. Such events can either be zircon-consuming, alteration, or zircon-forming and may be separated in time by millions or billions of years. In many cases, calculated zircon isotopic ages do not coincide with ages of geologic events determined from other minerals or from whole-rock analysis. To interpret the geologic validity and significance of multiple ages, and ages unsupported by independent analysis of other isotopic systems, has been the impetus for most past investigations of zircon composition. Some recent compositional investigations of zircon have not been directly related to geochronology, but to the ability of zircon to influence or record petrogenetic processes in igneous and metamorphic systems. Sedimentary rocks may also contain a significant fraction of zircon. Although authigenic zircon has been reported (Saxena 1966, Baruah et al. 1995, Hower et al. 1999), it appears to be very rare and may in fact be related to … more

3,143 citations


Journal ArticleDOI
27 Jul 2001-Science
TL;DR: The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more, and current models of early terrestrial differentiation need revision. more

Abstract: Well-defined constants of radioactive decay are the cornerstone of geochronology and the use of radiogenic isotopes to constrain the time scales and mechanisms of planetary differentiation. Four new determinations of the lutetium-176 decay constant (lambda176Lu) made by calibration against the uranium-lead decay schemes yield a mean value of 1.865 +/- 0.015 x 10(-11) year(-1), in agreement with the two most recent decay-counting experiments. Lutetium-hafnium ages that are based on the previously used lambda176Lu of 1.93 x 10(-11) to 1.94 x 10(-11) year(-1) are thus approximately 4% too young, and the initial hafnium isotope compositions of some of Earth's oldest minerals and rocks become less radiogenic relative to bulk undifferentiated Earth when calculated using the new decay constant. The existence of strongly unradiogenic hafnium in Early Archean and Hadean zircons implies that enriched crustal reservoirs existed on Earth by 4.3 billion years ago and persisted for 200 million years or more. Hence, current models of early terrestrial differentiation need revision. more

1,993 citations

Book ChapterDOI
01 Jan 1997-

1,932 citations

Journal ArticleDOI
Abstract: The transition from Laramide syntectonic sedimentation of the lower Eocene Willwood Formation to the post-Laramide volcanogenic sedimentation of the middle Eocene Wapiti Formation was studied in the upper South Fork Shoshone River Valley, Wyoming. To better understand the regional age, paleogeography, and provenance of volcaniclastic sandstones in the lower stratified member of the Wapiti Formation, we sampled three units for detrital zircon U/Pb geochronology (n=241). The maximum depositional age for the sandstone units within the lower-most, middle, and upper-most units are 49.03 Ma, 49.44 Ma, and 48.99 Ma, respectively, which is consistent with previous geochronologic and paleontologic studies. These ages also are consistent with rocks deposited immediately prior to the emplacement of the Heart Mountain slide. Detrital-zircon age spectra show a transition from a mixed (recycled?) provenance, consistent with drainage from the west, composed of minor primary Eocene volcanic contributions to one dominated by primary Eocene and Archean contributions from the northern Absaroka volcanoes and the Laramide Beartooth Uplift. Thus, uplift and unroofing of the Beartooth Plateau was occurring during the deposition of the oldest members of the Wapiti Formation. more

966 citations

Journal ArticleDOI
Fu-Yuan Wu1, Deyou Sun2, Wen-Chun Ge2, Yanbin Zhang1  +3 moreInstitutions (4)
Abstract: Northeast (NE) China is characterized by immense volumes of granitic rocks, exposed over an area of ∼200,000 km 2 . Although the precise geochronological framework was not clear, it was considered that most of them were emplaced during the Paleozoic, when numerous tectonic blocks amalgamated. Over the past decade, we have selected 370 samples for zircon U–Pb dating in order to constrain the spatial and temporal distribution of granitoids in the area. These data, combined with 63 ages obtained by other researchers, indicate that Paleozoic granitoids are not as widely distributed in the area as previously thought. In the eastern part of the area, granitoids in the Zhangguangcai Range were mostly emplaced during the Jurassic (150–190 Ma) with a small amount in the Paleozoic, whereas granitoids in the Nadanhada Terrane, the easternmost part of NE China, have an emplacement age of ∼115 Ma. In the west, granitoids exposed in the Great Xing’an Range were mainly formed during the Early Cretaceous (120–135 Ma) with some in the Paleozoic, and those in the Erguna Massif, the westernmost part of NE China, were emplaced during the Jurassic (160–190 Ma). Based on the temporal–spatial distribution of these granitic rocks, it is suggested that the Paleozoic granitoids were formed during various stages from oceanic subduction to block amalgamation in the Central Asian Orogenic Belt (CAOB). It is proposed that the Jurassic granitoids in the Zhangguangcai Range were probably related to Paleo-Pacific plate subduction west of the Jiamusi Massif (block). This subduction resulted in regional lithospheric thickening, and subsequent delamination of the thickened lithosphere due to its gravity instability in the Early Cretaceous. Unlike other areas in the Central Asian Orogenic Belt, NE China was significantly affected by subduction of the Paleo-Pacific ocean, and can be considered as one of the most important areas of the eastern Asian active continental margin during the Mesozoic. more

951 citations

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Topic's top 5 most impactful authors

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