The evolution of excess argon in alpine biotites — A40Ar-39Ar analysis

Roddick, J. C.; Cliff, R. A.; Rex, D. C.

doi:10.1016/0012-821x(80)90181-8

Cited by 282 publications

(94 citation statements)

References 32 publications

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“…Plateau ages reported in section 4.2 were calculated using the approach recommended by Fleck et al [1977], and their quoted uncertainties are based on the standard error of the weighted mean age of increments on the plateau. Isochron ages were derived from linear regression fits to sample increments plotted on the 39Ar/4øAr versus 36Ar/4øAr inverse isochron diagram [Roddick et al, 1980]. Fitting procedures followed those recommended by York [1969], and the quoted uncertainties in isochron ages and derived 4øAr/36Ar ratios include contributions from the error in J, the data scatter about the best fit line, and analytical uncertainties.…”

Section: Summary Of Muscovite 4øar/39ar Resultsmentioning

confidence: 99%

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

Godin¹,

Parrish²,

Brown³

et al. 2001

Tectonics

241

255

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Section: Summary Of Muscovite 4øar/39ar Resultsmentioning

confidence: 99%

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

Godin¹,

Parrish²,

Brown³

et al. 2001

Tectonics

241

255

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“…The formula corresponding to p is that of Berger and York (1970), which takes into account the error in the 40 Ar*/ 39 Ar ratio of the monitor but not the error in its age. The criteria we used to define a plateau are those of Feraud et al (1986): (1) (Roddick et al, 1980).…”

Section: Analytical Techniquesmentioning

confidence: 99%

K-Ar and 40Ar/39Ar Ages of Central Kerguelen Plateau Basalts

Whitechurch¹,

Montigny²,

Sevigny³

et al. 1992

Proceedings of the Ocean Drilling Program

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Conventional K-Ar and 40 Ar/ 39 Ar analyses on whole-rock samples are reported for basaltic samples retrieved on the Central and Southern Kerguelen plateaus during Ocean Drilling Program Leg 120. Sites 747, 749, and 750 recovered basalts from the plateau basement, whereas Site 748 drilled a lava flow interbedded with sediments of probable Albian age.The freshest core basalts from the basement yielded dates falling in the 110-100 m.y. interval. Sample 120-749C-15R-3 (26-31 cm) gave conventional K-Ar, total fusion, and plateau ^Ar/^Ar ages that are closely concordant: 111.5 ± 3.2 m.y., 109.9 ± 1.2 m.y., and 109.6 ± 0.7 m.y., respectively. Sample 120-750B-15R-5 (54-60 cm), when taking into account the analytical uncertainties, yields conventional K-Ar and 40 Ar/ 39 Ar plateau ages that can be considered similar: 101.2 ± 7.5 and 118.2 ± 5 m.y., respectively. Inspection of the 39 Ar/ 40 Ar vs. 36 Ar/ 40 Ar diagram does not reveal the occurrence of an initial argon component of radiogenic composition in the two samples. Accordingly, our results suggest that the formation of the basement of the Central Kerguelen Plateau was closed at 110 m.y.. Furthermore, these results are in agreement with a K-Ar age of 114 ± 1 m.y. mentioned in the literature for a basalt dredged in the 77°E Graben.The still scant amount of data indicates that the outpourings of the Central Kerguelen Plateau correspond rather well with widespread continental magmatism in Gondwanaland that is believed to mark the incipient opening of the eastern Indian Ocean. This implies a huge head for the mantle plume at the source of these liquids. Nevertheless, on land and at sea the exact duration of magmatism remains unknown. Therefore, a catastrophic pattern similar to that currently invoked for the Deccan Traps at the end of the Cretaceous, though possible, is not yet required by present geochronologic data.

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“…Age plateau given are weighted mean plateaus which error takes the error on the J factor into account. The isochron ages are obtained in an inverse isochron diagram of 36 Ar/ 40 Ar versus 39 Ar/ 40 Ar (Roddick, 1978;Roddick et al, 1980), which allows homogeneous excess components to be individualized in many occasions. Errors on age and intercept age include individual errors on each point and linear regression by York's method (1969).…”

Section: A1 40 Ar-39 Ar Techniquesmentioning

confidence: 99%

Syn- and post-orogenic exhumation of metamorphic rocks in North Aegean

Lacassin

Arnaud

Leloup

et al. 2007

eEarth

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Abstract. The Olympos-Ossa-Pelion (OOP) ranges, in NW Aegean, encompass Greece highest summit and are located near the extremity of the North Anatolian Fault (NAF). Structural and thermochronological data gathered in the OOP ranges show that the main exhumation of metamorphic nappes occurred in the Eocene, at ca. 43-39 Ma. This early exhumation, associated with ductile, then brittle-ductile normal faulting with northeastward transport, is coeval with orogenic shortening in the close area. Cooling rates, and likely exhumation, have been low between ∼40 Ma and ∼20 Ma. 40 Ar/ 39 Ar crystallization ages (between 20 and 15 Ma) appears related to brittle-ductile normal faulting and likely associated with Neogene Aegean back-arc extension. The dating of a diabase dyke, and the geometry of associated brittle jointing, of onshore and offshore active normal faults suggest a shift in extension direction after 4Ma, possibly in relation with the propagation of the NAF in northern Aegean. IntroductionThere is some consensus on the view that Aegean continental extension ( Fig. 1) can be explained by some combination of gravitational forces in a thickened crust with pull forces associated with the retreat of the Hellenic Arc (e.g. McKenzie, 1978;Le Pichon and Angelier, 1981;Jolivet et al., 2003). It is also agreed that it postdates the compressional stacking of the Hellenic thrust-nappes, which is of upper Mesozoic to Lower-Cenozoic age in the internal part of the belt (e.g., Mercier et al., 1989;Schermer et al., 1990;Lips et al., 1998Lips et al., , 1999. However, the timing of inception of continental stretching, which is critical for constraining mechanical evoCorrespondence to: R. Lacassin (lacassin@ipgp.jussieu.fr) lution models of the Aegean lithosphere, remains poorly constrained. Estimates range from 5 Ma (e.g. McKenzie, 1978) to more than 24 Ma (e.g., Gautier and Brun, 1994;Gautier et al., 1999).Evidence for extension in the Aegean comes from separate sets of observations. One set derives from seismology and earthquake geology. It focuses on the brittle, steeplydipping normal faults that account for the present-day deformation of the upper crust. A second set, derives from observations of older (Tertiary) ductile structures. It has been inferred from the latter that large amounts of extension of the lithosphere, associated with significant amounts of shear on shallow-dipping detachments at mid-crustal levels, induced rapid exhumation of metamorphic core complexes (e.g. Lister et al., 1984;Buick, 1991;Brun et al., 1994;Jolivet et al., 1994;Gautier et al., 1999). Finally a distinctive feature of the Aegean extension derives from recent tectonic and geodetic (GPS) observations: the mechanical interaction between the Aegean extension and the North Anatolian Fault (NAF), which propagated westward and likely entered the Aegean at 5 Ma according to Armijo et al. (1996Armijo et al. ( , 1999. Right-lateral motion along the NAF induced transtension in northern Aegean (Mc Neil et al., 2004) and enhanced extension in the North Ae...

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The evolution of excess argon in alpine biotites — A40Ar-39Ar analysis

Cited by 282 publications

References 32 publications

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

K-Ar and 40Ar/39Ar Ages of Central Kerguelen Plateau Basalts

Syn- and post-orogenic exhumation of metamorphic rocks in North Aegean

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The evolution of excess argon in alpine biotites — A40Ar-39Ar analysis

Cited by 282 publications

References 32 publications

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and 40Ar/39Ar Thermochronology

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and 40Ar/39Ar Thermochronology

K-Ar and 40Ar/39Ar Ages of Central Kerguelen Plateau Basalts

Syn- and post-orogenic exhumation of metamorphic rocks in North Aegean

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Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology

Crustal thickening leading to exhumation of the Himalayan Metamorphic core of central Nepal: Insight from U‐Pb Geochronology and ⁴⁰Ar/³⁹Ar Thermochronology