Rapid exhumation of the Zermatt-Saas ophiolite deduced from high-precision SmNd and RbSr geochronology

Amato, Jeffrey M.; Johnson, Clark M.; Baumgartner, Lukas P.; Beard, Brian L.

doi:10.1016/s0012-821x(99)00161-2

Cited by 197 publications

(141 citation statements)

References 38 publications

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“…44-45 Ma (zircon SHRIMP-data by Rubatto et al 1998 andHermann 2003) or between 48.8±2.1 and 40.6±2.6 Ma. The latter age range (not fully consistent with the SHRIMP-data) was interpreted by Lapen et al (2003) to reflect the duration of the prograde PT path, based on their Lu-Hf data, as well as on SmNd data by Amato et al (1999).…”

Section: Geodynamic Implications and Discussionmentioning

confidence: 94%

“…It was repeatedly ascertained that zircon responds to metamorphic recrystallization only at or above T conditions corresponding to the upper amphibolite-/granulite-or high-temperature eclogite-facies (e.g., Vavra et al 1999 and references therein), unless unusually high amounts of fluids are present, in which case recrystallization may take place at lower T. Thus, the age obtained from the metamorphic domains of the zircon most probably reflects the time when the rocks were at or close to the metamorphic peak. Since the rates of exhumation are usually high (>1-2 cm/ year), as identified in several (ultra) high-pressure [(U)HP] rocks from orogens worldwide (e.g., Gebauer et al 1997;Amato et al 1999;Liati and Gebauer 1999;Cartwright and Barnicoat 2002 and references therein) the metamorphic peak refers roughly to both T and P. The relatively short time difference between T peak and P peak is commonly unresolvable within the uncertainty of the current geochronological technique. Therefore, the age data obtained from metamorphically recrystallized zircon crystals (or crystal domains) of (U)HP rocks correspond to time of peak metamorphism, with respect to both P and T. (2) In this particular case of the amphibolitized eclogite of Mottone, the presence of rutile inclusions in metamorphic zircon domains (in contrast to rutile in the matrix, which is altered to sphene) confirms this general observation (see also Sect.…”

Section: Amphibolitized Eclogite At Passo Del Mottonementioning

confidence: 99%

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Jurassic ophiolites within the Valais domain of the Western and Central Alps: geochronological evidence for re-rifting of oceanic crust

Liati

Froitzheim

Fanning

2005

Contrib Mineral Petrol

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Metabasic rocks from different parts of the Antrona ophiolites, Western Alps, as well as from the Misox zone, Central Alps, were dated using ion microprobe (SHRIMP) U-Pb analyses of zircon, in association with cathodoluminescence (CL) imaging. HP metamorphism must have affected at least the major part of the Antrona ophiolites, although HP relics are rarely preserved, probably due to the Lepontine metamorphic overprint. HP metamorphism has affected also the area of the Misox zone. The origin of the Antrona ophiolites is arguable. They were interpreted as part of both the Piemont-Ligurian (PL) and the Valais ocean, the two main oceans in the area of the Alps before Alpine convergence. SHRIMP-analyses of co-magmatic zircon domains from the Antrona ophiolites (Guggilihorn, Passo del Mottone and Quarata areas) yielded identical (within uncertainty) weighted mean 206 Pb/ 238 U ages of 155.2±1.6 Ma, 158±17 Ma (or 163.1±2.4 Ma: one analysis; 1r error) and 155.6±2.1 Ma, respectively, interpreted as the time of crystallization of the magmatic protoliths. These Late Jurassic ages fit well to the time span considered for the formation of Piemont-Ligurian oceanic crust. The metagabbro of the Misox zone (Hinterrhein area), for which a Valaisan origin is generally accepted, gave also a Late Jurassic, PL protolith age of 161.0±3.9 Ma. The metamorphic zircon domains from the amphibolitized eclogite of Mottone yielded an age of 38.5±0.7 Ma, interpreted as the time of HP metamorphism. This age is in good agreement with the time of metamorphism reported from previous zircon SHRIMP-data for eclogites and amphibolites of other parts in the Valais domain. In order to bring in line the PL protolith ages with the Valaisan metamorphic ages, we suggest a scenario involving emplacement of part of the PL oceanic crust to the north of the newly formed Brianc¸onnais peninsula, inside the Valais geotectonic domain. This paleotectonic configuration was probably established when younger Valaisan oceanic crust formed by spreading and re-rifting, partly within PL oceanic crust.

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Section: Geodynamic Implications and Discussionmentioning

confidence: 94%

Section: Amphibolitized Eclogite At Passo Del Mottonementioning

confidence: 99%

Jurassic ophiolites within the Valais domain of the Western and Central Alps: geochronological evidence for re-rifting of oceanic crust

Liati

Froitzheim

Fanning

2005

Contrib Mineral Petrol

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“…34) 0.512638ῌ0.000015 Univ. Wisconsin 35) 0.512630ῌ0.000025 Okayama Univ. 36) Unspiked and spiked isotopic analyses of 4 to 6 ng Nd aliquots (with the assumption of 85῏ recovery yields) individually separated from about 180 to 240 mg of PCC-1 were also carried out.…”

Section: ῃ1mentioning

confidence: 99%

Precise Isotope Determination of Trace Amounts of Nd in Magnesium-rich Samples

Shibata

Yoshikawa

2004

J. Mass Spectrom. Soc. Jpn.

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We developed a technique combining mass spectrometry with chemical separation to analyze Sm῎Nd isotopic compositions of ultramafic rock samples, which have extremely high Mg and low Nd concentrations and are always di$cult to analyze. In the case of ultramafic rocks, abundant Mg forms fluorides during decomposition by HF, and minor amounts of Sm and Nd are strongly partitioned into fluorides, which would be a significant reason of low recovery yields of these elements and obstructed to determine a reliable isotopic ratio of Nd and Sm. We introduced pre-decomposition by HCl prior to the conventional method by HF and HClO 4 that made it possible to elevate recovery yield to 85ῑ. On the other hand, replicate measurements of Nd standard solution (La Jolla) by changing the ion current of Nd ῌ and the amount of Nd indicate that reliable isotopic ratios are measured under the condition of ῐ0.04῎10῍11 A of 144 Nd ῌ ion current and ῐ2 ng of Nd. By applying our method, we analyzed 143 Nd/ 144 Nd ratio and Sm and Nd concentrations of PCC-1, which is an ultramafic standard rock sample of United States Geological Survey. The results of our analysis were 0.512226῍0.000026, 0.00551 ῍0.00041, and 0.0278῍0.0011 ppm, respectively. These results are the first report of 143 Nd/ 144 Nd ratio for PCC-1.

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“…Such leaching protocols have been successfully developed over the past few years, some developed specifically to improve precision and accuracy (e.g. Frei & Kamber 1995;Frei et al 1997;Amato et al 1999;Baxter et al 2002), others to explore the systematics of isotope behaviour in garnet and its inclusions (e.g. Zhou & Hensen 1995;Schaller et al 1997;Vance et al 1998a).…”

Section: Advances In the Chronometry Of Major Metamorphic Minerals -Pmentioning

confidence: 99%

“…The paper is primarily concerned with REE phosphates such as monazite and xenotime because sulphuric acid does not dissolve silicates. The other major problem inclusion is allanite, which is a silicate and is not amenable to separation from garnet using sulphuric acid but which has been successfully removed using dilute HF (Amato et al 1999). The advantage of the newly proposed approach is that, besides the fact that significant improvement in age precision results from the removal of inclusions of mineral phases that are near-ubiquitous in metapelitic garnets with a consequent doubling of the Sm/ Nd ratio in some cases, it involves a low-blank single-step leach.…”

Section: Advances In the Chronometry Of Major Metamorphic Minerals -Pmentioning

confidence: 99%

Geochronology: linking the isotopic record with petrology and textures — an introduction

Vance

Müller

Villa³

2003

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Abstract:One of the key aims of geochronology, and the subject of the papers in this Special Publication, is the linkage of isotopic ages to petrological and textural information. A close link between the two types of information greatly improves the constraints available from geochronology on the nature and rates of lithospheric processes such as metamorphism and deformation. There have been several key advances in this area over the past 10-20 years, relating to increased precision and accuracy of isotopic ages but also, and crucially, to the spatial resolution available to geochronologists. This resolution now approaches that on which petrological, chemical and textural information is obtained. We also, in this introduction, identify the barriers that have impeded further progress, which relate both to technical issues as well as to problems of understanding. Finally we set the papers in this volume in the context of the preceding discussion and outline the key ways in which these papers point towards further progress in the future.Time has always been recognized as a key variable in the Earth sciences, both in its own right and through the constraints that chronological information provides on the rates of, and hence the physical mechanisms for, Earth processes. In the study of the dynamics of the Earth's lithosphere during orogenesis and metamorphism, one of the key requirements of any time datum is that it is relatable in a straightforward manner to other geological information, such as data on temperature, pressure and deformation. It is only through this linkage that chronometric information can achieve its full potential in contributing to progress in understanding the dynamics of mountain belts and other metamorphic settings. This linkage is the focus of the set of papers in this volume, which emanate from a special symposium at the 2002 Goldschmidt Conference, held at Davos, Switzerland. The topic under discussion has been the subject of a review by one of us recently (Mtiller 2003). Inevitably, there is some overlap between this paper and Miiller (2003). However, the emphasis of the two papers is slightly different, with Mtiller (2003) concentrating largely on new in-situ techniques and their resulting prospects, whereas here we give a broader overview of the whole subject, with more emphasis on the dating of high temperature processes and the interrelated achievements of both modelling and experimental work in petrology. We also aim to highlight some general issues that are dealt with in specifics in the subsequent contributions. First, we give a brief account of the progress that has been made over the past two decades in our ability to extract the timing and conditions of deformation and metamorphism from minerals and in the interpretive framework in which these new data are analysed. Next we identify three key barriers that initially impeded further progress and which have been and continue to be the subjects of intensive research eflbrt. Finally, we discuss ways that are being developed to surm...

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Rapid exhumation of the Zermatt-Saas ophiolite deduced from high-precision SmNd and RbSr geochronology

Cited by 197 publications

References 38 publications

Jurassic ophiolites within the Valais domain of the Western and Central Alps: geochronological evidence for re-rifting of oceanic crust

Jurassic ophiolites within the Valais domain of the Western and Central Alps: geochronological evidence for re-rifting of oceanic crust

Precise Isotope Determination of Trace Amounts of Nd in Magnesium-rich Samples

Geochronology: linking the isotopic record with petrology and textures — an introduction

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