Isotopic U-Pb ages of monazites and zircons from the crust-mantle transition and adjacent units of the ivrea and ceneri zones (Southern Alps, Italy)

Köppel, V.

doi:10.1007/bf00384652

Cited by 106 publications

(23 citation statements)

References 6 publications

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“…Samples were collected along a profile crossing the Cossato-Mergozzo-Brissago (CMB) fault which separates the above tectonic units (Boriani and others, 1981). The observed decrease of the monazite ages from about 450 Ma to 300 Ma was also confirmed by lower intercept ages on discordant zircons (Koppel, 1974). In this study we present U-Pb zircon and monazite results from additional samples collected along, as well as across, the CMB-fault and discuss them together with the previously obtained age data.…”

Section: Most Of This High-temperature Deformation Appears To Have Ocsupporting

confidence: 79%

“…We suggest that the addition of cumulates by underplating was compensated in part by symmetric rifting and that the Mafic Complex may be thought of as filling a giant "tension gash" near the base of the crust. To obtain more detailed knowledge about the metamorphic history of the Ivrea zone and the adjacent Serle dei Laghi (Strona-Ceneri) U-Pb ages-on zircons and monazites have been determined (Koppel, 1974). Samples were collected along a profile crossing the Cossato-Mergozzo-Brissago (CMB) fault which separates the above tectonic units (Boriani and others, 1981).…”

Section: Most Of This High-temperature Deformation Appears To Have Ocmentioning

confidence: 99%

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Ivrea-Verbano Zone workshop, 1992

Sinigoi¹

1992

Circular

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Section: Most Of This High-temperature Deformation Appears To Have Ocsupporting

confidence: 79%

Section: Most Of This High-temperature Deformation Appears To Have Ocmentioning

confidence: 99%

Ivrea-Verbano Zone workshop, 1992

Sinigoi¹

1992

Circular

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“…This Late PermianrEarly Triassic age is somewhat younger than ages obtained from zircon in diorite near the top of Ž . the Basic Formation 285 Ma; Pin, 1986 and from Ž monazite in paragneiss 270-275 Ma; Koppel, 1974; . Koppel and Grunenfelder, 1979 .…”

Section: Field Relationsmentioning

confidence: 99%

Growth of subcontinental lithosphere: evidence from repeated dike injections in the balmuccia lherzolite massif, Italian Alps

Mukasa

Shervais

1999

Composition, Deep Structure and Evolution of Continents

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The Balmuccia alpine lherzolite massif is a fragment of subcontinental lithospheric mantle emplaced into the lower crust 251 Ma ago during the final, extensional phase of the Hercynian orogeny. The Balmuccia massif consists largely of lherzolite, with subordinate harzburgite and dunite, and an array of dike rocks formed in the mantle before crustal emplacement. Dike rocks include websterite and bronzitite of the Cr-diopside suite, spinel clinopyroxenite and spinel-poor websterite of the Al-augite suite, gabbro and gabbronorite of the late gabbro suite, and hornblendite of the hydrous vein suite. The dike rocks display consistent intrusive relationships with one another, such that Cr-diopside suite dikes are always older than dikes and veins of the Al-augite suite, followed by dikes of the late gabbro suite and veins of the hydrous vein Ž . suite. Phlogopite phl veinlets that formed during interaction with the adjacent crust are the youngest event. There are at least three generations of Cr-diopside suite dikes, as shown by crosscutting relations. Dikes of the Al-augite suite form a polybaric fractionation series from spinel clinopyroxenite to websterite and feldspathic websterite, which crystallized from aluminous alkaline magmas at relatively high pressures. The late gabbro suite of dikes intruded at lower pressures, where plagioclase saturation occurred before significant mafic phase fractionation. Hornblendite veins have distinct compositional and isotopic characteristics, which show that they are not related to either the Al-augite suite or to the late gabbro dike suite. Cr-diopside suite dikes have Nd and Sr isotopic compositions similar to those of the host lherzolite and within the range of compositions defined by ocean-island basalts. The Al-augite dikes and the hornblendite veins have Sr and Nd isotopic compositions similar to those of Cr-diopside suite lherzolite and websterite. There is overlap in the data between the Cr-diopside suite and the Al-augite and hydrous vein suites, with the exception that the Cr-diopside websterite dikes have more radiogenic Pb than any of the other samples. In Pb-Pb space as well, the late gabbro suite has the least radiogenic isotopic compositions, reflecting a change in magma source region during uplift. These data show that tectonic thinning of subcontinental lithospheric mantle during Ž . extension caused a change in the source regions of mantle-derived magmas from an ocean island basalt OIB -like lithosphere to the underlying MORB asthenosphere. They also demonstrate that the upper mantle acquires its heterogeneous isotopic character through several different processes, including in situ radiogenic growth, addition of asthenospheric melts, ) Corresponding author. Fax: q1-313-763-4690; E-mail: mukasa@umich.edu 0024-4937r99r$ -see front matter q 1999 Elsevier Science B.V. All rights reserved.Ž . PII: S 0 0 2 4 -4 9 3 7 9 9 0 0 0 3 3 -X ( ) S. B. Mukasa, J.W. SherÕaisr Lithos 48 1999 287-316 288 dike-wall rock ionic exchange, redistribution of the lithosphe...

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“…A significant amount of initial Pb or Pb-loss, if present, would deviate the line from the origin. Initial Pb correction through the chemical Th-U-total Pb isochron method was tested with data obtained from accurate isotopic analysis of monazite from rocks of the Ivrea-Ceneri zones, Southern Alps, Italy (Koppel, 1974) and zircon from rocks of the Hida terrane, Japan (Ishizaka and Yamaguchi, 1969). The monazite from the Ivrea-Ceneri zones contains 2-13 ppm initial Pb, and gives 268-316 Ma 207Pb /206 Pb ages and 259 301 Ma 208Pb/232Th ages (Table 3).…”

Section: Geological Setting and Sample Descriptionmentioning

confidence: 99%

“…Williams et al, 1974;Corfu, 1988), and gives essentially concordant U-Pb and Th-Pb ages (e.g. Burger et al, 1965;Koppel and Grunenfelder, 1971;Grauert et al, 1974;Koppel, 1974), it may be useful for pro viding reliable chronological information. Monazite, once formed, does not lose significant portions of its radiogenic Pb even at tempera tures above 600°C (e.g.…”

Section: Introductionmentioning

confidence: 99%