Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet
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Research Article| March 01, 2007 Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet Richard O. Lease; Richard O. Lease 1Department of Earth Science, University of California-Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Douglas W. Burbank; Douglas W. Burbank 1Department of Earth Science, University of California-Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar George E. Gehrels; George E. Gehrels 2Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA Search for other works by this author on: GSW Google Scholar Zhicai Wang; Zhicai Wang 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Daoyang Yuan Daoyang Yuan 3State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China Search for other works by this author on: GSW Google Scholar Geology (2007) 35 (3): 239–242. https://doi.org/10.1130/G23057A.1 Article history received: 02 Jun 2006 rev-recd: 26 Oct 2006 accepted: 27 Oct 2006 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard O. Lease, Douglas W. Burbank, George E. Gehrels, Zhicai Wang, Daoyang Yuan; Signatures of mountain building: Detrital zircon U/Pb ages from northeastern Tibet. Geology 2007;; 35 (3): 239–242. doi: https://doi.org/10.1130/G23057A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Although detrital zircon has proven to be a powerful tool for determining provenance, past work has focused primarily on delimiting regional source terranes. Here we explore the limits of spatial resolution and stratigraphic sensitivity of detrital zircon in ascertaining provenance, and we demonstrate its ability to detect source changes for terranes separated by only a few tens of kilometers. For such an analysis to succeed for a given mountain, discrete intrarange source terranes must have unique U/Pb zircon age signatures and sediments eroded from the range must have well-defined depositional ages. Here we use ∼1400 single-grain U/Pb zircon ages from northeastern Tibet to identify and analyze an area that satisfies these conditions. This analysis shows that the edges of intermontane basins are stratigraphically sensitive to discrete, punctuated changes in local source terranes. By tracking eroding rock units chronologically through the stratigraphic record, this sensitivity permits the detection of the differential rock uplift and progressive erosion that began ca. 8 Ma in the Laji Shan, a 10-25-km-wide range in northeastern Tibet with a unique U/Pb age signature. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.Keywords:
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Abstract Zircon textures, chemistry and microstructures have been characterized in situ within Carboniferous sandstones from the Midland Valley of Scotland using back‐scattered electron and cathodoluminescence images, electron backscatter diffraction techniques and chemical analyses. The study of polished thin sections reveals a variety of zircon types including unmodified detrital zircon, zircon outgrowths and different forms of modified zircon that formed in low‐temperature conditions within the sedimentary rocks. These rocks have only experienced temperatures of <100 °C during burial; however, altered zircon is abundant and characterized by a low mean atomic number, with relatively high contents of non‐formula elements and a nano‐crystalline or microcrystalline structure. It forms by replacement of detrital zircon that subsequently became metamict. Two types of replacement mechanisms are effective in sedimentary environments and involve either dissolution–reprecipitation or solid‐state reaction, but both require fluid access to the radiation‐damaged areas. The former process appears to become the dominant replacement mechanism as temperature increases and produces highly porous, inclusion‐rich zircon. Metamict zircon is extremely reactive in near‐surface conditions and the production of low‐temperature zircon is sensitive to both parent zircon characteristics and environmental conditions. As such, the alteration of zircon has the potential to yield unique information on the diagenetic history of sedimentary rocks. Low‐temperature zircon would be unlikely to survive sedimentary transport or the rock crushing procedures that characterize many investigations of detrital zircon populations and consequently may generate severe biases in studies of this type.
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Io-ages obtained for glass-zircon pairs which were not consistent with expected ages were discussed on the basis of uranium and thorium distribution between zircon and glass. Uranium and thorium distribution between zircon and host rocks from dacites and granites were also discussed. Discordant Io-ages obtained for glass-zircon pairs with normal (Th/U)zircon/(Th/U)glass ratio are explained by early stage crysallization of the zircon in the magma. Discordant Io-ages with abnormal (Th/U)zircon/(Th/U)glass ratios suggest that the zircon was captured in the magma as xenoryst. The discrepancy between (Th/U)zircon/(Th/U)glass ratios (about 0.19) for dacites and (Th/U)zircon/(Th/U)whole rock ratios (about 0.12) for granites could be explained by crystallization of granitic zircon from liquid having chemical composition different from that of the whole rock of granite.
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Baddeleyite
Ultramafic rock
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The intrusive rocks in El Sela area can be arranged from the oldest to the youngest into: two-mica granite and postgranitic dikes which include microgranite, dolerite and bostonite dikes. Zircon is the most abundant accessory mineral. Zircon morphology and geochemical features are good indicators for evolution of rocks. The aim of the work is to determine the morphology, internal structure and chemical composition of zircon to identify the difference of zircon in various intrusive rocks. Results show that morphologically, zircon in the two-mica granite is euhedral coarse- grained with zonation. It is represented by crystals up to 125 µm and corresponds to S10 and P2. Zircon in post-granitic dikes exhibit irregular forms. Geochemically, zircon crystals have higher ZrO2 values in the core whereas HfO2 , UO2 , ThO2 increase at the peripheries of zoned crystals of the two-mica granite. Zircon of two-mica granite contains high HfO2 , UO2 , ThO2 and CaO contents but low Sc2 O3 content. HfO2 is not detected in zircon of microgranite. TiO2 in zircon of two-mica granite and bostonite dikes is under detection limits. REEs are not recorded in zircon of the studied intrusive rocks
Dike
Granitic rock
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This paper presents a systematic study on morphology,geochemistry and geochronology of a zircon population from the Danzhu granodiorite located in the southwest region of the Zhejiang province.The analysis results show that there are two types of zircons from the Danzhu granodiorite:magmatic zircon and metamorphic zircon.The former is characterized by euhedral—subhedral and long-prismatic form,incolorness,transparence,presence of magmatic and mineral inclusions,homogeneous internal structure(occasionally with oscillatory zoning)on the section of grains revealed by backscattered electron(BSE)imaging,and analogue pattern of typological indices of zircon for those from the calco-alkaline granodiorite;the latter is characterized mainly by its occurrence as overgrowth on magmatic zircon,but it also occurs very occasionally as anhedral grains,which is yellow-brown,semi-transparent,and homogeneous on the BSE imaging.These two types of zircon differ also in trace element composition,i.e.,the magmatic zircon is significantly richer in the substituent elements like as U,Th and Y than the metamorphic zircon.The zircon U-Pb dating using LA-ICPMS shows that the magmatic zircon and metamorphic zircon were formed in two different periods:at 1875±33 Ma and at 209±12 Ma respectively,demonstrating the objective response for the Zhe-Min(Zhejiang—Fujian)movement and the Indosinian movement in the southwest region of the Zhejiang province.
Petrogenesis
Geochronology
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In this article we present a compilation of U-Pb zircon ages of the whole Xolapa terrane in coastal southern Mexico (dataset 1) as a curved line, obtained from plotting individual zircon grains versus its corresponding age. We identified five low-slope segments of the curved line, each one assigned to a high zircon-production (or preservation) event (HZE). Crystallization temperatures (CT) from Ti-in-zircon geothermometer data on Xolapa rocks were estimated separately from individual zircon grains (dataset 2), in order to compare CT ranges corresponding to each HZE identified. Datasets 1 and 2 are discussed for tectonic implications in the research article "The opening and closure of the Jurassic-Cretaceous Xolapa basin, southern Mexico" Peña-Alonso et al., 2017.
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