The evolution of the Sesia Zone (Western Alps) from Carboniferous to Cretaceous: insights from zircon and allanite geoch
- PDF / 13,906,193 Bytes
- 33 Pages / 595.276 x 790.866 pts Page_size
- 78 Downloads / 173 Views
Swiss Journal of Geosciences
Open Access
ORIGINALPAPER
The evolution of the Sesia Zone (Western Alps) from Carboniferous to Cretaceous: insights from zircon and allanite geochronology Alice Vho1* , Daniela Rubatto1,2 , Pierre Lanari1 and Daniele Regis3
Abstract Microscale dating of distinct domains in minerals that contain relics of multiple metamorphic events is a key tool to characterize the polyphase evolution of complex metamorphic terranes. Zircon and allanite from five metasediments and five metaintrusive high-pressure (HP) rocks from the Eclogite Micaschist Complex of the Sesia Zone were dated by SIMS and LA-ICP-MS. In the metasediments, zircon systematically preserves detrital cores and one or two metamorphic overgrowths. An early Permian age is obtained for the first zircon rim in metasediments from the localities of Malone Valley, Chiusella Valley and Monte Mucrone (292 ± 11, 278.8 ± 3.6 and 285.9 ± 2.9 Ma, respectively). In the Malone Valley and Monte Mucrone samples, the early Permian ages are attributed to high-temperature metamorphism and coincide with the crystallization ages of associated mafic and felsic intrusions. This implies that magmatism and metamorphism were coeval and associated to the same tectono-metamorphic extensional event. In the Malone Valley, allanite from a metasediment is dated at 241.1 ± 6.1 Ma and this age is tentatively attributed to a metasomatic/metamorphic event during Permo-Triassic extension. Outer zircon rims with a late Cretaceous age (67.4 ± 1.9 Ma) are found only in the micaschist from Monte Mucrone. In metagabbro of the Ivozio Complex, zircon cores yield an intrusive age for the protolith of 340.7 ± 6.8 Ma, whereas Alpine allanite are dated at 62.9 ± 4.2 and 55.3 ± 7.3 Ma. The Cretaceous ages constrain the timing of the HP metamorphic stage. The presence of zircon overgrowth only in the central area of the Eclogite Micaschist Complex is attributed to local factors such as (1) multiple fluid pulses at HP that locally enhanced zircon dissolution and recrystallization, and (2) slightly higher temperatures reached in this area during HP metamorphism. Keywords: U-Th-Pb dating, SIMS, LA-ICP-MS, Permian metamorphism, Alpine subduction 1 Introduction The Sesia Zone (SZ) in the Italian Western Alps represents a slice of Adriatic continental crust that underwent blueschist to eclogite facies metamorphism during convergence between the African and European plates. Since more than 50 years, extensive structural and petrological studies have been focused on unravelling the pressure–temperature (P–T) evolution of the SZ during the Editorial handling: Paola Manzotti. *Correspondence: [email protected] 1 Institute of Geological Sciences, University of Bern, Baltzerstrasse 1+3, CH‑3012 Bern, Switzerland Full list of author information is available at the end of the article
subduction, exhumation and continental collision of the Alpine orogenic cycle (e.g. Dal Piaz et al. 1972; Compagnoni 1977; Pognante et al. 1980; Oberhänsli et al. 1985; Zucali et al. 2004; Regis et a
Data Loading...
