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

Abstract

documented along the western margin of the Adriatic plate. The ~160 Ma age population postdates the activity of all known rift-related structures within the Adriatic margin, but coincides with extensive gabbroic magmatism and exhumation of sub-continental mantle to the floor of the Alpine Tethys, west of the Ivrea Zone. We propose that this ~160 Ma early post-rift age population records regional cooling following episodic heating of the distal Adriatic margin, likely related to extreme lithospheric thinning and associated advection of the asthenosphere to shallow levels. The partial preservation of the ~175 Ma age cluster suggests that the post-rift (~160 Ma) heating pulse was of short duration. The regional consistency of the data presented here, which is in contrast to many other thermochronometers in the IVZ, demonstrates the value of the rutile U-Pb technique for probing the thermal evolution of high-grade metamorphic terrains. In the IVZ, a significant decoupling between Zr-in-rutile temperatures and U-Pb ages of rutile is observed, with the two systems recording events ~120 Ma apart.

Zircon U‐Pb Dating of a Lower Crustal Shear Zone: A Case Study From the Northern Sector of the Ivrea‐Verbano Zone (Val Cannobina, Italy)

“…(a) Geological sketch map of the central and northern IVZ (modified after Ewing et al, ). The locations of high‐temperature shear zones are after Rutter et al ().…”

“…According to several authors, after the early Permian thermal peak, the whole crustal section underwent cooling and exhumation (e.g., Brodie et al, ; Siegesmund et al, ). Recent studies suggest that the cooling and exhumation history of the IVZ was interrupted by discrete Triassic‐Jurassic heating events, as documented by zircon, monazite, and rutile U‐Pb dating (Ewing et al, ; Langone et al, ; Schaltegger et al, ; Smye & Stockli, ; Vavra et al, ; Vavra & Schaltegger, ; Zanetti et al, , ). Based on the U‐Pb dating of rutile from the high‐grade metamorphic rocks (granulites) of the central and southern part of the IVZ, some authors suggest that discrete regional‐scale thermal pulses affected the lower structural levels of the IVZ in response to the Mesozoic hyperextension associated with rift/post‐rift processes at the Adriatic margin (Ewing et al, ; Smye & Stockli, ).…”

“…Recent studies suggest that the cooling and exhumation history of the IVZ was interrupted by discrete Triassic‐Jurassic heating events, as documented by zircon, monazite, and rutile U‐Pb dating (Ewing et al, ; Langone et al, ; Schaltegger et al, ; Smye & Stockli, ; Vavra et al, ; Vavra & Schaltegger, ; Zanetti et al, , ). Based on the U‐Pb dating of rutile from the high‐grade metamorphic rocks (granulites) of the central and southern part of the IVZ, some authors suggest that discrete regional‐scale thermal pulses affected the lower structural levels of the IVZ in response to the Mesozoic hyperextension associated with rift/post‐rift processes at the Adriatic margin (Ewing et al, ; Smye & Stockli, ). While a network of conjugate, high‐temperature, low‐angle shear zones that developed at granulite to amphibolite facies conditions has been recognized (Rutter et al, ; Rutter et al, ), it remains unclear if these are directly related to the proposed Mesozoic heating associated with rifting and exhumation.…”

A crustal‐scale view at rift localization along the fossil Adriatic margin of the Alpine Tethys preserved in NW Italy

“…This estimate is consisted with the crystallization of titanite at 173 ± 4 Ma in the footwall of the shear zone, interpreted to record retrogression arising from cooling [ Mulch et al ., ]. Cooling of the Ivrea Zone to T < 500°C through extensional unroofing is also supported by the oldest U‐Pb ages preserved in rutile, which fall in the 185–175 Ma interval [ Zack et al ., ; Smye and Stockli , ; Ewing et al ., ]. Furthermore, a recent U‐Pb geochronological study on rutile also suggests that the Ivrea Zone underwent a short‐lived heating‐cooling cycle at 160 ± 7 Ma [ Ewing et al ., ].…”

Anatexis and fluid regime of the deep continental crust: New clues from melt and fluid inclusions in metapelitic migmatites from Ivrea Zone (NW Italy)

“…The Ivrea Zone (NW Italy) is a world-renowned Permian mid to lower crustal section. Crustal rocks have been widely investigated through many approaches, such as field observations (e.g., Quick et al, 2003;Redler et al, 2012Redler et al, , 2013Zingg, 1980), phase relationships (e.g., Schmid & Wood, 1976), whole rock geochemistry (major and trace elements and isotopes; e.g., Sighinolfi & Gorgoni, 1978; | 965 Baker, 1988;Schnetger, 1994;Henk et al, 1997;Barboza et al, 1999;Bea & Montero, 1999;Alessio et al, 2018), conventional thermobarometry (e.g., Barboza & Bergantz, 2000;Bea & Montero, 1999;Demarchi, Quick, Sinigoi, & Mayer, 1998;Henk et al, 1997;Schmid & Wood, 1976;Sills, 1984;Zingg, 1980), geochronology (Ewing, Rubatto, Beltrando, & Hermann, 2015;Ewing et al, 2013;Klötzli et al, 2014;Köppel, 1974;Kunz, Regis, & Engi, 2018;Kunz, Manzotti, et al, 2018;Vavra et al, 1999), trace element thermometry (Ewing et al, 2013;Kunz, Regis, & Engi, 2018;Kunz, Manzotti, et al, 2018;Luvizotto & Zack, 2009) and modern phase equilibria modelling (Bartoli, 2018;Redler et al, 2012Redler et al, , 2013. De Negri and Touret (1978) described CO 2 fluid inclusions from Val Strona di Omegna.…”