Sphene: Uranium-Lead Ages

Tilton, G. R.; Grünenfelder, M.

doi:10.1126/science.159.3822.1458

Cited by 82 publications

(17 citation statements)

References 21 publications

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“…Tilton and Grunenfelder 1968;Catanzaro and Hanson 1971), but may become a closed system at lower temperatures than does zircon, thus recording a slightly lower age3. Finally, apatite, a mineral that is relatively susceptible to resetting (e.g.…”

Section: Discussionmentioning

confidence: 99%

U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism

Mattinson¹

1977

Can. J. Earth Sci.

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U–Pb measurements on minerals from the Burlington Peninsula indicate that volcanic rocks of the Grand Cove Group and the probably cogenetic Cape Brule porphyry have primary crystallization ages of 475 ± 10 Ma (Early Ordovician). Later intrusive rocks, including the Dunamagon granite, the Burlington granodiorite and the Seal Island Bight syenite were intruded between 445 and 435 Ma ago. The Grand Cove Group and the Cape Brule porphyry completely predate deformation and metamorphism of the eastern division of the Fleur de Lys Supergroup; the Seal Island Bight syenite, Burlington granodiorite, and Dunamagon granite were evidently emplaced during the early stages of this orogeny. The new age results therefore suggest that the orogeny is Taconic in the classic sense. Some of the isotope systems show evidence of a strong thermal event about 340 Ma ago (Early Carboniferous, Acadian). This event may have caused resetting of some of the Rb–Sr isochron ages recently reported for this area.

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Section: Discussionmentioning

confidence: 99%

U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism

Mattinson¹

1977

Can. J. Earth Sci.

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“…Tilton and Grunenfelder (1968) analyzed a sphene from one of the rocks, Lawson's (1913) unit 11, mica-syenite gneiss from Rocky Islet Bay, near the entrance to Rice Bay, which gave concordant results: Pb 206 /U 238 , 2,720 m.y. ; Pb 207 /U 235 , 2,725 m.y.…”

Section: U-th-pb Datingmentioning

confidence: 99%

Geochronology of the Rainy Lake Region, Minnesota-Ontario

Peterman

Goldich²,

Hedge³

et al. 1972

Geological Society of America Memoirs

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The Rainy Lake region on the boundary between Ontario and Minnesota is a classical Precambrian area in which two periods of folding and igneous activity, Laurentian and Algoman, were recognized by Lawson. Early efforts to resolve the two orogenic periods on the basis of K-Ar and Rb-Sr age determinations on micas were not successful. More sophisticated whole-rock Rb-Sr and zircon and sphene U-Pb studies likewise have not been wholly successful, but the U-Pb data suggest that all the early Precambrian events, including the Laurentian and Algoman igneous activity, probably occurred within the interval from 2,700 to 2,750 m.y. ago.Whole-rock Rb-Sr isochron studies, however, give younger ages as follows: Coutchiching Series Keewatin Series . Algoman granites Ontario Minnesota . . . 2,615 ± 50 m.y. 2,595 ± 45 m.y. 2,540 ± 90 m.y. 2,680 ± 95 m.y. 193 on June 18, 2015 memoirs.gsapubs.org Downloaded from 194 PETERMAN AND OTHERSMineral ages and a rock-mineral isochron clearly indicate that both the Rb-Sr and the K-Ar systems were affected by subsequent events, but it is not certain that the isochron ages date the time of specific events. It is more likely that the determined ages mark the end of periods of retrograde metamorphism, faulting, and shearing. The different apparent ages of stabilization of the Rb-Sr system probably resulted from differences in rock composition, in water content, and in local heat flow.

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“…Firstly, titanite U-Pb age was obtained using conventional isotope dilution thermal ionization mass spectrometry (ID-TIMS) method [13]. The ID-TIMS U-Pb dating method usually gives the ages with high precision.…”

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confidence: 99%

In situ U-Pb dating of titanite by LA-ICPMS

Sun

Yang

et al. 2012

Chin. Sci. Bull.

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Titanite is an ideal mineral for U-Pb isotopic dating because of its relatively high U, Th and Pb contents. Here, we developed a technique for U-Pb dating of titanite using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. Standards of titanite (BLR-1 and OLT-1) and zircon (91500 and GJ-1) were dated using single spot and line raster scan analytical methods. To check the matrix effect, titanite (BLR-1) and zircon (91500) standards were analyzed as the external standards. The weighted mean 206 Pb/ 238 U ages of OLT-1 titanite are 1015±5 Ma (2, n=24) and 1017±6 Ma (2, n=24) by single spot and line raster scan analyses, respectively, using BLR-1 titanite as the external standard. These ages are consistent with its reference age of about 1014 Ma. However, using 91500 zircon as the external standard, the weighted mean 206 Pb/ 238 U ages are 917±4 Ma (2, n=24) and 927±5 Ma (2, n=24) for BLR-1 titanite, and 891±4 Ma (2, n=24) and 901±5 Ma (2, n=24) for OLT-1 titanite by single spot and line raster scan analyses, respectively. It is evident that these ages are ~12% younger than their reference values. Our results reveal that significant matrix effect does exist between different kinds of minerals during LA-ICPMS U-Pb age determination, whereas it is insignificant between same minerals. Therefore, same mineral must be used as the external standard for fractionation corrections during in situ LA-ICPMS U-Pb age analysis. In addition, we determined U-Pb ages for titanites from the Early Cretaceous Fangshan pluton, which indicates a rapid cooling history of this pluton. Isotopic geochronology is the key to understand the temporal and special evolution of geological bodies and their related geodynamics. There are many analytical methods to date isotopic ages of geological bodies, while the most commonly used is U-Pb dating of accessory minerals [1]. Minerals such as zircon and monazite have high uranium concentration and U-Pb closure temperature (T c(zircon) >800°C[2]; T c(Monazite)~7 50°C [3]) with low common lead, which makes them to be the preferred target for U-Pb dating. However, zircon and monazite are relatively stable and cannot be reset by the later thermal and chemical processes, due to its physical and chemical resistance. Thus, they are hardly used to constrain the later metamorphic ages of metamorphosed and hydrothermally altered rocks [4,5].Furthermore, some rocks (e.g. ultramafic rocks) do not contain zircon and monazite. Titanite (CaTiSiO 5 ) is one of the common accessory minerals in igneous rocks, and also occurring in metamorphic, hydrothermal and some sedimentary rocks [5][6][7][8]. It usually has relatively high U content (10-100 ppm [7]), which is commonly hold in its crystal lattice. It also has a relatively high U-Pb closure temperature of 650-700°C [9,10], making it an attractive phase as a geochronometer. Moreover, different with zircon and monazite, titanite is mainly composed by major elements of rocks, which easily exchange with other minerals and react with fluid and melt. ...

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Sphene: Uranium-Lead Ages

Cited by 82 publications

References 21 publications

U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism

U–Pb ages of some crystalline rocks from the Burlington Peninsula, Newfoundland, and implications for the age of Fleur de Lys metamorphism

Geochronology of the Rainy Lake Region, Minnesota-Ontario

In situ U-Pb dating of titanite by LA-ICPMS

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