Petrographic interpretation of a complex seismic crust–mantle transition in the central-eastern Alps

Musacchio, Gemma; Zappone, Alba; Cassinis, R.; Scarascia, S.

doi:10.1016/s0040-1951(98)00094-8

Cited by 11 publications

(7 citation statements)

References 27 publications

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“…First-cycle detritus from the South Alpine crustal section provides a unique opportunity to test the use of the SRD index as an estimator of average source rock density. The comparison with direct density measurements of basement bedrock samples (Burke and Fountain 1990;Sinigoi et al 1995;Musacchio et al 1998;Khazanehdari et al 2000;Mazzoli et al 2002;Boriani et al 2003) shows that discrepancies result to be ≤1% for most metamorphic and plutonic source rocks and somewhat larger only for granulitic gabbros (fig. 5).…”

Section: Mineralogy Profilementioning

confidence: 94%

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The Continental Crust as a Source of Sand (Southern Alps Cross Section, Northern Italy)

Garzanti¹,

Andó²,

Vezzoli³

2006

The Journal of Geology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to The Journal of Geology. A B S T R A C TAll tectonostratigraphic levels of the continental crust, from carbonate platforms in the Dolomites to granulites in the Ivrea Zone, are exposed along strike in the world-famous Southern Alps cross section. In this extraordinary natural laboratory, we studied the composition of modern stream sands shed by each distinct type of source rock in order to improve on existing models of sediment provenance and specifically to reconstruct the step-by-step changes of detrital signatures ideally produced during unroofing of a continental block. Detritus from progressively deeper crustal levels of the Southern Alps changes systematically from lithic sedimentaclastic (unmetamorphosed cover sequences) to lithoquartzose, quartzolithic, and quartzofeldspathic metamorphiclastic (greenschist facies to amphibolite facies basement units) and finally to feldspathoquartzose and feldspathic composition (granulite facies basement units). Six progressively richer types of heavy mineral assemblages (ZTR-brookite, garnet-chloritoid, garnet-staurolite, blue/green hornblende-kyanite, green/brown hornblende-fibrolitic sillimanite, and garnet-brown hornblende-prismatic sillimanite) faithfully reflect the increasing grade of metamorphic source rocks. Hypersthene-brown hornblende and olivine-enstatite assemblages characterize detritus from lower crustal gabbros and mantle peridotites. In alpine settings undergoing rapid erosion and minor chemical weathering, the mineralogy of detrital sediments faithfully mirrors the mineralogy of their parent rocks. Therefore, our database can be used to integrate direct measurements of physical and chemical properties of exposed bedrock and to reconstruct an ideally complete mineralogy and density profile from the base to the top of the South Alpine crust. This shows a progressive upward increase in quartz and muscovite at the expense of plagioclase and heavy minerals and an effective density stratification from lower crustal (3.10-3.00 g/cm 3 ) to middle crustal (∼2.85 g/cm 3 ) and upper crustal levels (2.75-2.70 g/cm 3 ). Sharp jumps in average rock density observed across major structural discontinuities (e.g., Cossato-Mergozzo-Brissago Line) mirror the fact that the South Alpine basement is the extensional stack of several slivers that followed distinct metamorphic and exhumation paths during the multistage tectonic evolution linking the Carboniferous Variscan Orogeny with the Jurassic opening of the Alpine Tethys.

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Section: Mineralogy Profilementioning

confidence: 94%

“…2C). Because of only incipient phyllosilicate recrystallization in these supra- Burke and Fountain (1990), Sinigoi et al (1995), Musacchio et al (1998), Khazanehdari et al (2000), Mazzoli et al (2002), and Boriani et al (2003). of muscovite and then of biotite in source rocks, stronalite sands yield few micas ( fig.…”

Section: Micas and MImentioning

confidence: 96%

The Continental Crust as a Source of Sand (Southern Alps Cross Section, Northern Italy)

Garzanti¹,

Andó²,

Vezzoli³

2006

The Journal of Geology

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“…, 1992). Below the Tertiary Bergell intrusion seismic reflectors outline a discontinuity between the European and Adriatic Moho, where anomalously low seismic velocities (6.2–6.5 km s −1 ; Musacchio et al. , 1998) and gravity anomalies (Holliger and Kissling, 1992) suggest the presence of European lower crust delaminated from the upper crust and coupled with the subducted European slab.…”

Section: Geological Background and Available Geophysical Datamentioning

confidence: 99%

“…The European Moho has a southward dip of about 12°d own to 60 km , while the northwarddipping Adriatic Moho reaches depths of 50 km (Blundell et al, 1992). Below the Tertiary Bergell intrusion seismic reflectors outline a discontinuity between the European and Adriatic Moho, where anomalously low seismic velocities (6.2-6.5 km s )1 ; Musacchio et al, 1998) and gravity anomalies (Holliger and Kissling, 1992) suggest the presence of European lower crust delaminated from the upper crust and coupled with the subducted European slab. On the basis of gravimetric models, a highdensity body has been inferred below the axial zone of the chain.…”

Section: Introductionmentioning

confidence: 98%

Thermorheological model for the European Central Alps: brittle–ductile transition and lithospheric strength

Viganò

Martin

2007

Terra Nova

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A two‐dimensional thermorheological model of the Central Alps along a north–south transect is presented. Thermophysical and rheological parameters of the various lithological units are chosen from seismic and gravity information. The inferred temperature distribution matches surface heat flow and results in Moho temperatures between 500 and 800 °C. Both European and Adriatic lithospheres have a ‘jelly‐sandwich’ structure, with a 15–20 km thick brittle upper crust overlying a ductile lower crust and a mantle lid whose uppermost part is brittle. The total strength of the lithosphere is of the order of 0.5–1.0 × 1013 N m−1 if the upper mantle is dry, or slightly less if the upper mantle is wet. In both cases, the higher values correspond to the Adriatic indenter.

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“…Evidently, petrological information is very important for understanding the CMTZs, but rock samples originated directly from the CMTZs are rare at the surface (Behn and Kelemen 2006;Musacchio et al 1998). Fortunately, xenoliths entrained in alkaline basalts and kimberlites (Downes et al 2004;Griffin et al 1984) and enclaves in dioritic rocks (Chen and Zhou 2005;Xu et al 2008) may be from deep lithosphere so that some of them could provide important insights into the CMTZs (e.g.…”

Section: Introductionmentioning

confidence: 99%

Cumulate hornblendite enclaves in diorite–porphyrite intrusions from the Shuangyashan, Northeast China, and implications for the transition from lower crust to upper mantle in subduction setting

Zhang

Han

Wei

et al. 2009

Int J Earth Sci (Geol Rundsch)

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A suite of hornblendite (amphibole proportion C90%) enclaves were found in Late Cretaceous dioriteporphyrite stocks intruding the lower Cretaceous coal strata around the Shuangyashan City, eastern Heilongjiang Province, Northeast China. The enclaves have similar mineralogy and may be divided into clinopyroxene-bearing and clinopyroxene-free hornblendites and both of them show cumulate textures: pargasitic amphibole and clinopyroxene are cumulus and anorthitic plagioclase is intercumulus. The accumulation might have occurred in the magma chamber, minor clinopyroxene enclosed in amphibole was earlier crystallized, followed by a large amount of amphibole, and the residual melt trapped between cumulate crystals finally formed the intercumulus plagioclase. Probably, such a crystallization process could produce layered cumulates: lower part is dominated by clinopyroxene-bearing hornblendite and upper part is composed of clinopyroxene-free one. The enclaves have similar geochemistry and imply a hydrous basaltic parental magma enriched Rb, Ba, Th and other large-ion lithophile elements. The generation of the parental magma might be related to the subduction of Paleo-Pacific plate beneath eastern Eurasian continent at that time. Estimated crystallization pressure, P-wave velocity, and density for the cumulate hornblendite enclaves are generally in agreement with the values of the local crust-mantle transition zone, suggesting that these cumulates may have the origin in the transition from the lower crust to upper mantle in arc and back-arc settings.

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Petrographic interpretation of a complex seismic crust–mantle transition in the central-eastern Alps

Cited by 11 publications

References 27 publications

The Continental Crust as a Source of Sand (Southern Alps Cross Section, Northern Italy)

The Continental Crust as a Source of Sand (Southern Alps Cross Section, Northern Italy)

Thermorheological model for the European Central Alps: brittle–ductile transition and lithospheric strength

Cumulate hornblendite enclaves in diorite–porphyrite intrusions from the Shuangyashan, Northeast China, and implications for the transition from lower crust to upper mantle in subduction setting

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