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S. Sinigoi

Publications and source records attributed to S. Sinigoi.

5 recordsLinked to original sources
USGS2007

Duration of a large Mafic intrusion and heat transfer in the lower crust: A SHRIMP U-Pb zircon Study in the Ivrea-Verbano Zone (Western Alps, Italy)

The Ivrea-Verbano Zone in the western Italian Alps contains one of the world's classic examples of ponding of mantle-derived, mafic magma in the deep crust. Within it, a voluminous, composite mafic pluton, the Mafic Complex, intruded lower-crustal, high-grade paragneiss of the Kinzigite Formation during Permian-Carboniferous time, and is now exposed in cross-section as a result of Alpine uplift. The age of the intrusion is still debated because the results of geochronological studies in the last three decades on different rock types and with various dating techniques range from 250 to about 300 Ma. Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon age determinations on 12 samples from several locations within the Mafic Complex were performed to better constrain the age of the igneous event. The results indicate a long history of magma emplacement and cooling, which reconciles the spread in previously published ages. The main intrusive phase took place at 288 ?? 4 Ma, causing a perturbation of the deep-crustal geotherm, which relaxed to the Sm-Nd closure temperature in garnet-free mafic rocks after about 15-20 Myr of sub-solidus cooling at c. 270 Ma. These results suggest that large, deep crustal plutons, such as those identified geophysically at depths of 10-20 km within extended continental crust (e.g. Yellowstone, Rio Grande Rift, Basin and Range) may have formed rapidly but induced a prolonged thermal perturbation. In addition, the data indicate that a significant thermal event affected the country rock of the Mafic Complex at about 310 Ma. The occurrence of an upper amphibolite- to granulite-facies thermal event in the Kinzigite Formation prior to the main intrusive phase of the Mafic Complex has been postulated by several workers, and is corroborated by other geochronological investigations. However, it remains uncertain whether this event (1) was part of a prolonged perturbation of the deep-crustal geotherm, which started long before the onset of intrusion of the Mafic Complex, or (2) corresponded to the intrusion of the first sills of the Mafic Complex, or (3) was related to an earlier, independent thermal pulse. ?? The Author 2007. Published by Oxford University Press. All rights reserved.

Journal of Petrology↗
USGS1999

Development of a deep-crustal shear zone in response to syntectonic intrusion of mafic magma into the lower crust, Ivrea-Verbano zone, Italy

A 1 to 1.5 km-thick, high-temperature shear zone is localized in wall rocks subparallel to the eastern intrusive contact of the Permian Mafic Complex of the Ivrea-Verbano zone (IVZ), Italy. The shear zone is characterized by concentrated ductile deformation manifested by a penetrative foliation subparallel to the intrusive contact and a northeast-plunging sillimanite lineation. Evidence of noncoaxial strain and transposition is widespread in the shear zone including such features as rootless isoclinal folds, dismemberment of competent layers, and scattered kinematic indicators. The metasedimentary rocks in the shear zone are migmatitic, and the accumulation of leucosome is variable within the shear zone. Near the intrusive contact with the Mafic Complex leucosome forms ~20 vol% of the wall rock, whereas leucosome concentrations may locally reach ~60 vol% of the wall rock near the outer limits of the shear zone. This variation in vol% leucosome suggests melt/magma migration from the inferred site of anatexis along the intrusive contact to lower-strain regions within and near the margins of the shear zone. The leucosome accumulations chiefly occur as layer-parallel concentrations, but are also folded and boudined, and locally are associated with tension gashes and fracture arrays. Networks of granitic dikes and small plutons in the eastern IVZ suggest that some magmas migrated out of the high-temperature shear zone. Some magma apparently migrated laterally along the strike of the shear zone and concentrated in areas of lower strain where the intrusive contact takes a major westward bend. The high-temperature shear zone is interpreted as a 'stretching fault' (or stretching shear zone) after Means [W.D. Means, Stretching faults, Geology 17 (1989) 893-896], whereupon the metasedimentary wall rocks and associated leucosome deformed synchronously with the multistage emplacement and deformation flow of the Mafic Complex. The recognition of a high-temperature shear zone associated with the emplacement of mafic igneous rocks into the deep crust is an example of the progressive stratification of the lower crust during magmatic under- or intraplating that has consequences for seismic imaging and its interpretation.

Earth and Planetary Science Letters↗
USGS1996

Influence of stretching and density contrasts on the chemical evolution of continental magmas: An example from the Ivrea-Verbano Zone

The southern Ivrea-Verbano Zone of the Italian Western Alps contains a huge mafic complex that intruded high-grade metamorphic rocks while they were resident in the lower crust. Geologic mapping and chemical variations of the igneous body were used to study the evolution of underplated crust. Slivers of crustal rocks (septa) interlayered with igneous mafic rocks are concentrated in a narrow zone deep in the complex (Paragneiss-bearing Belt) and show evidence of advanced degrees of partial melting. Variations of rare-earth-element patterns and Sr isotope composition of the igneous rocks across the sequence are consistent with increasing crustal contamination approaching the septa. Therefore, the Paragneiss-bearing Belt is considered representative of an “assimilation region” where in-situ interaction between mantle- and crust-derived magmas resulted in production of hybrid melts. Buoyancy caused upwards migration of the hybrid melts that incorporated the last septa and were stored at higher levels, feeding the Upper Mafic Complex. Synmagmatic stretching of the assimilation region facilitated mixing and homogenization of melts. Chemical variations of granitoids extracted from the septa show that deep septa are more depleted than shallow ones. This suggests that the first incorporated septa were denser than the later ones, as required by the high density of the first-injected mafic magmas. It is inferred that density contrasts between mafic melts and crustal rocks play a crucial role for the processes of contamination of continental magmas. In thick under plated crust, the extraction of early felsic/hybrid melts from the lower crust may be required to increase the density of the lower crust and to allow the later mafic magmas to penetrate higher crustal levels.

Contributions to Mineralogy and Petrology↗
USGS1992

Synmagmatic deformation in the underplated igneous complex of the Ivrea-Verbano zone

The Ivrea-Verbano zone, northern Italy, contains an igneous complex up to 10 km thick that is thought to have been intruded near the interface between the continental crust and mantle during the late Paleozoic. New data indicate that this complex is pervasively deformed and concentrically foliated. Widespread deformation under hypersolidus conditions is indicated by growth of undeformed poikilitic phases across the foliation and segregation of late-stage melts into high-temperature faults and pressure shadows of boudins. The presence of analogous features in ophiolitic gabbros suggests that emplacement of the Ivrea- Verbano zone plutonic rocks involved large-scale flow of crystal mush in a dynamic, and possibly extensional, tectonic environment.

Geology↗