Pressure Gradient and Original Orientation of A Lower‐Crustal Intrusion in the Ivrea‐Verbano Zone, Northern Italy

Abstract

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 TThe southern Ivrea-Verbano Zone of the western Italian Alps contains a huge complex of mafic to intermediate plutonic rocks that intruded the lower continental crust during the Permian. Recent geologic mapping of the complex has characterized the effects of Alpine deformation and has demonstrated that the complex contains an arcuate internal structure. Building on this geologic foundation, we report a thermobarometric study of the plutonic and associated metamorphic rocks that was performed to better constrain the depth and orientation of the complex at the time of intrusion. The results demonstrate a continuous increase in equilibration pressure from 5 Ϯ 1 kb along the eastern intrusive contact of the complex to 8 Ϯ 1 kb near the western limit of the complex. After correcting for the effects of Alpine faulting, the observed pressure gradient ranges from 0.32 to 0.38 kb/km. Given the large uncertainties inherent in the geobarometric calculations relative to the narrow pressure range recorded in the complex, we conclude that the observed gradient is indistinguishable from a normal, vertical pressure gradient in the lower crust. It appears that, following intrusion and equilibration at a depth of 15 to 25 km, the complex was uplifted and rotated approximately 90°. The data also demonstrate that the internal arcuate structure formed in the complex before the observed pressure gradient was established. This result reinforces models for the growth of the complex by synmagmatic deformation and large-scale necking during crustal extension and excludes the possibility that the arcuate structure was produced during the more recent Alpine uplift.

Production of hybrid granitic magma at the advancing front of basaltic underplating: Inferences from the Sesia Magmatic System (south-western Alps, Italy)

“…Fountain (1976) first proposed on the basis of their geophysical properties that these two lithostratigraphic belts collectively comprise a section through the continental crust of northwest Italy that has been exposed tectonically along the Insubric Line. Consistent with exposure of progressively deeper crustal levels to the west, observations assembled over the last 35 years support Fountain's interpretation, among the most compelling of which are the increase in metamorphic grade and equilibration pressures (Demarchi et al, 1998;Ewing et al, 2013;Redler et al, 2012Redler et al, , 2013Zingg, 1980Zingg, , 1983 and the decrease in cooling ages (Siegesmund et al, 2008;Wolff et al, 2012) approaching the Insubric Line.…”

“…b) Upper Mafic Complex, showing the fields of Main Gabbro (light blue) and Upper Zone (light purple), and the average composition computed as 70% Main Gabbro and 30% Upper Zone. Rivalenti et al, 1975;Sinigoi et al, 1991Sinigoi et al, , 2011, which intruded the deep crust at depths between 25 and 17 km (Barboza and Bergantz, 2000;Barboza et al, 1999;Demarchi et al, 1998). Rotation of the Mafic Complex by approximately 90°from its original orientation is indicated by a subvertical foliation and a progressive increase in equilibration pressures from east to west (Demarchi et al, 1998).…”

U and Th content in the Central Apennines continental crust: A contribution to the determination of the geo-neutrinos flux at LNGS

“…Upper and Lower Crust (UC and LC respectively) material does not outcrop around the studied area. Samples were thus taken from the LC-UC section of Ivrea-Verbano Zone from granulitic rocks of Val Strona, Val Sessera and Val Sesia to amphibolitic schists of Serie dei Laghi and related intrusives (Hunziker and Zingg, 1980;Borghi, 1988;Boriani et al, 1990;De Marchi et al, 1998;Quick et al, 1992;2003;Franz and Romer, 2007). To complete the UC section, the low grade metamorphic philladic rocks outcropping in Valsugana, and related intrusive rocks of Caoria and Cima d'Asta complexes were also sampled (Dal Piaz and Martin, 1998;D'Amico et al, 1971;Sassi et al, 2004).…”

Constraints on the thermal evolution of the Adriatic margin during Jurassic continental break-up: U–Pb dating of rutile from the Ivrea–Verbano Zone, Italy

“…Boriani et al 1990;Demarchi et al 1998;Handy et al 1999;Quick et al 1994;Sinigoi et al 1996;Zingg et al 1990; Fig. 1).…”