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Search Results: 1 - 10 of 5728 matches for " U/Pb "
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Slope Year for the U-Pb Dating Method and Its Applications  [PDF]
Jie Yuan
Open Journal of Geology (OJG) , 2015, DOI: 10.4236/ojg.2015.55032
Abstract: The slope year tslope for the U-Pb dating method is given as \"\", where λ238 and λ235 are the decay constants for 238U and 235U, respectively, and k is the slope of the tangent line at a point on either the Concordia or Discordia line. These two lines are determined by the
Basement Lithology Characteristics and Forming Age of Bongor Basin Chad

张明瑜, 宋柏荣, 田志彬, 张乃丹, 施玉华, 王奇
Open Journal of Nature Science (OJNS) , 2016, DOI: 10.12677/OJNS.2016.41009
乍得Bongor盆地基底为早寒武世之前形成的一套结晶基岩,该套岩石富含油气,因此,对盆地基底岩石类型及形成时代的研究越显重要。本文主要以岩心观察、描述为基础,采用岩石薄片鉴定、单颗粒锆石U-Pb同位素测定等方法,对乍得Bongor盆地基底岩性进行鉴定和划分,并对其形成和演化时代进行分析。结果认为:岩性为由变质岩和岩浆岩组成的杂岩体,岩性包括2大类14个亚类;单锆石测年年龄集中在550~600 Ma,变质岩原岩年龄主要集中在616 ± 6~526.5 ± 2.7 Ma,最老的原岩年龄1006 ± 12~946 ± 5 Ma,变质年龄在553 ± 19~464 ± 5 Ma,岩浆岩的年龄主要集中在621 ± 16~525.3 ± 2.5 Ma。由于岩石类型、性质及形成时代的差异,造成后期地质作用改造和储层的发育程度不同。
The basement of the Bongor basin Chad is formed by a set of crystalline basement rocks before the Early Cambrian, which is rich in oil and gas. Therefore, it is more important to study the type of basement rocks and the formation age of the basin. This paper is mainly based on the core observation and description, by identification of rock slice, single grain zircon U-Pb isotope determination, Chad Bongor basin’s basement lithology of identification and delineation, and the formation and evolution of era were analyzed. The results show that the lithology is composed of metamorphic rocks and magmatic rocks, which are composed of 14 kinds of 2 sub categories; Single Zircon dating was concentrated in the age of 550 - 600 Ma, the age of metamorphic rocks was mainly con- centrated in 616 ± 6 - 526.5 ± 2.7 Ma, the oldest old rock age was 1006 ± 12 - 946 ± 5 Ma, metamorphic age was 553 ± 19 - 464 ± 5 Ma, the age of magmatic rock was mainly concentrated in 621 ± 16 - 525.3 ± 2.5 Ma. Because of the difference of the rock type, nature and the age of formation, the transformation of the geological function and the development of the reservoir are different in the later stage.
SHRIMP zircon age of the high aeromagnetic anomaly zone in central Tarim Basin and its geological implications  [PDF]
Guanghui Wu, Zhiyong Chen, Tailai Qu, Yanlong Xu, Chengze Zhang
Natural Science (NS) , 2012, DOI: 10.4236/ns.2012.41001
Abstract: In order to get the correct isotopic age, SHRIMP U-Pb zircon date of Precambrian hornblende granite in Well TD2, located in the central aeromagnetic belt in the eastern of the Tarim basin, was carried out. The result showed a dependable age of 1908.2 ± 8.6 Ma, which demonstrated that the granite pluton is the result of the magmatic activity in early Palaeoproterozoic. It is indicated that the central aeromagnetic belt across Tarim basin, divided it into north and south block, is formed before Neoproterozoic by a large scale tectonothermal events based on the seismic and drilling date. The Tarim continent may have different age and type basements formed the united crystalline basement in Precambrian. This result has yielded new intraplate evidence to constrain the relation between the Tarim plate and the Colombia supercontinent.
SHRIMP zircon U-Pb dating of the mafic and felsic intrusive rocks of the Saza area in the Lupa goldfields, southwestern Tanzania: Implication for gold mineralization  [PDF]
Shukrani Manya
Natural Science (NS) , 2012, DOI: 10.4236/ns.2012.49096
Abstract: The Lupa Goldfield (LGF) is one of the eight structural terranes in the NW – SE striking Ubendian Belt of SW Tanzania. The LGF is comprised of granitic gneisses with bands of amphibolites which are intruded by mafic intrusions including gabbros, granodiorites, diorites; and various granites as well as metavol-canics. These rocks are cross-cut by narrow mafic dykes and aplites. SHRIMP zircon U-Pb data are presented for the granodiorite and a mafic dyke that cross-cut the granodiorites in the Saza area of the LGF, with the aim of constraining the mafic and felsic magmatism and their implication to gold mineralization. The zircon U-Pb data shows that the Saza granodiorites were emplaced at 1924 ± 13 Ma (MSWD = 2.6) whereas the cross-cutting mafic dyke yielded a zircon U-Pb age of 1758 ± 33 Ma (MSWD = 0.88). The dated granodiorite sample was in sheared contact with an altered mafic intrusive rock, most likely a diorite, along which an auriferous quartz vein occurs. The 1924 ± 13 Ma age of granodiorites is within error of the reported molybdenite Re-Os age of 1937 Ma determined for the gold mineralization event in Lupa Goldfields. Although auriferous quartz veins are younger than the granodiorites, the more or less similar ages between the emplacement of granodiorites and the mineralizing event indicate that the granodiorites might be the heat source (or driver) of hydrothermal fluids responsible for gold mineralization in the Lupa goldfields. This would further suggest that gold mineralization in the LGF is intrusion-related type. The mafic dykes represent the youngest rocks to have been emplaced in the area and hence the 1758 ± 33 Ma age of the mafic dykes conclude the magmatic evolution in the Lupa goldfields during the Palaeoproterozoic.
U-Pb Geochronology of the Jebba Granitic Gneiss and Its Implications for the Paleoproterozoic Evolution of Jebba Area, Southwestern Nigeria  [PDF]
C. T. Okonkwo, V. Y. Ganev
International Journal of Geosciences (IJG) , 2012, DOI: 10.4236/ijg.2012.35107
Abstract: Jebba area southwestern Nigeria forms part of the Nigerian basement complex which lies in the Neoproterozoic PanAfrican mobile belt. It is underlain by several lithological units among which is a polydeformed granitic gneiss. This rock has been dated by LA-ICP-MS yielding a concordant U-Pb zircon age of 2207 ± 20 Ma indicating the crystallization age of the granite protolith. This early Rhyacian age and its affinity with within-plate granites indicates emplacement during crustal extension and rifting presceding the main phase of the Eburnean orogeny. The strong, early, shear fabric, S1, in the rock is interpreted to be also of Paleoproterozoic age i.e. imprinted during the Eburnean orogeny. The Jebba granitic gneiss is thus correlatable with the widely abundant Paleoproterozoic granitic magmatism now represented by many orthogneisses and documented in other parts of southwestern Nigeria, the West African craton, the Borborema Province, the Gurupi Belt, Sao Luis craton and Sao Francisco craton in Brazil.
New detrital zircon U-Pb ages from BIF-related metasediments in the Ntem Complex (Congo craton) of southern Cameroon, West Africa  [PDF]
Nelson N. Chombong, Emmanuel C. Suh, Charles D. C. Ilouga
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.57101

Banded Iron Formations (BIFs) were formed by contemporaneous events of active sediments supply and the venting of a hydrothermal fluid source at the Mid-Ocean-Ridge. BIFs within the Ntem Complex at the northern edge of the Congo Craton are intercalated with metasandstones and siltstones. SHRIMP U-Pb analysis on detrital zircons obtained from these metasediments gave variable ages from over 3000 Ma to 1000 Ma with the maximum age of deposition clustered around 1200 Ma and the peak of deposition at 1800 Ma. This age range suggested that the sub-basin was opened sometime in the Archean and remained active up till the Neoproterozoic. Zircons with Archean ages have a provenance linked to the charnockitic suite and the high-K granites within the Ntem Complex. The Paleoproterozoic ages are attributed to clastic inputs from the neigbouring Nyong Series west of the Ntem Complex. Also the peak of deposition in the Proterozoic could probably be explained by the globally recognized intense crust-forming processes in the Early Proterozoic time. The provenance of the younger Neoproterozoic ages is tied to various lithologies within the northern mobile belts of the Adamawa-Yade massifs and correlates with Neoproterozoic sedimentation ages in the Yaoundé, Lom and Poli series. The Neoproterozoic ages obtained are comparable to those obtained from metasediments of the Amazonian Craton and provide evidence of Pre-Gondwana assemblage of the Congo and the S?o Francisco Cratons.

The New Data on Stratigraphy of the Riphean Stratotype in the Southern Urals, Russia  [PDF]
V. N. Puchkov, A. A. Krasnobaev, N. D. Sergeeva
Journal of Geoscience and Environment Protection (GEP) , 2014, DOI: 10.4236/gep.2014.23015

A recent series of U-Pb age determinations of zircons (SHRIMP, IDTIMS) from volcanic flows of several levels permitted to refine stratigraphy of the Riphean of Bashkirian megaanticlinorium (Urals, Russia), and provide a better correlation of this straton with the International and Chinese scales of the Proterozoic.

Geochemical Characteristics and Chemical Electron Microprobe U-Pb-Th Dating of Pitchblende Mineralization from Gabal Gattar Younger Granite, North Eastern Desert, Egypt  [PDF]
Hassan A. A. Shahin
Open Journal of Geology (OJG) , 2014, DOI: 10.4236/ojg.2014.41003

Pitchblende mineralization was studied in the younger granite samples collected from Gabal Gattar, north Eastern Desert, Egypt using electron scanning microscope (ESM) and electron probe microanalyses (EPMA). This study revealed that this pitchblende contains significant Zr content reaching up to (66.80% ZrO2), which suggests that volcanic rocks were probably the source of such a deposit. High level emplaced high-K Calc-alkaline plutons as Qattar granite may have been associated with their volcanic equivalent emplaced in the surrounding area or now eroded. Lead content of the pitchblende mineralization is high and with moderate volcanics (up to 7.71% PbO). In contrast, it is low in ThO2, Y2O3 and REE2O3. High Zr and Pb content associated with pitchblende mineralization from Gattar granite indicates

Geochronological, Sedimentary, Structural, and Metallogenic Characteristics of Southeast China during the Mesozoic: A General Review  [PDF]
Pengju Li, Hongying Li
International Journal of Geosciences (IJG) , 2015, DOI: 10.4236/ijg.2015.69082
Abstract: The tectonic evolution of Southeast China during Late Mesozoic is a prominent topic. Numerous tectonic models on Late Mesozoic evolution ofSoutheast Chinahave beenpublished in the past 50 years. We synthesized many up-to-date and precise zircon U-Pb ages, sedimentary strata, and regional structures and discussed the oxygen fugacity of magmas and related ore deposits. We also analyzed the most current tectonic models published by some scholars. A multistage tectonic stress evolution history during Late Mesozoic was constructed, which included the following stages: 1) Early-Middle Jurassic (196 - 175 Ma) extension, in which many bimodal volcanics formed; 2) Middle-Late Jurassic (165 - 140 Ma) compression, which generated largescale gneissic granites, garnet-bearing granites, stratigraphic hiatus, and nappe structures; 3) Early Cretaceous (140 ± 5 - 120 Ma) extension, which formed weakly deformed or undeformed granites, alkali granites, metamorphic core complexes, graben basins, and basic dike swarms; 4) Early Cretaceous (120 - 110 Ma) compression, which generated nappe structures, volcanic hiatuses, and garnet-bearing granites; and 5) Early-Late Cretaceous (110 - 80 Ma) extension, which generated largescale bimodal volcanics, basic dike swarms, alkali granites, and graben basins. The Late Mesozoic tectonic evolution ofSoutheast Chinamay be attributed to the drifting history of the Paleo-Pacific plate. The drifting direction of the Paleo-Pacific plate has changed several times since 140 Ma, which led to major changes in the tectonicphenomena from Jurassic to Cretaceous and to the formation of Late Mesozoic mineral deposits.

Xu Ronghua,

岩石学报 , 1989,
Abstract: This paper reported the influence factors on single zircon crystal dating:the interference of T1 and Ba, the discrimination of mass, and the memory effect of U. The U blank testing for a long time indicates that the TEFLON bombs,treated with concentrated HP and aqua regia, possess the memory effect of U, Which could be eliminated by cleaning with dilute HBr. Finally its geological significance is illustrated in the paper.
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