Cordilleran-type batholiths are built by prolonged arc activity along active continental margins and provide detailed magmatic records of the subduction system evolution. They complement the stratigraphic record from the associated forearcs and backarcs. We performed in-situ U-Pb geochronology and Hf isotope measurements on zircon grains from a large set of plutonic rocks from the Coastal Batholith in southern Peru. This batholith emplaced into the Precambrian basement and the Mesozoic sedimentary cover. We identify two major periods of voluminous arc activity, during the Jurassic (200-175Ma) and the Late Cretaceous-Paleocene (90-60Ma). Jurassic arc magmatism mainly resulted in the emplacement of a dominantly mafic suite with εHf values ranging from -9.5 to +0.1. Published ages south of the Arequipa area suggest that the arc migrated southwestward out of the study area during the Middle Jurassic. After a magmatic gap of 85Ma, arc activity abruptly resumed 90Ma ago in Arequipa. Intrusive bodies emplaced into both basement and older Jurassic intrusions and strata. This activity culminated between 70 and 60Ma with the emplacement of very large volumes of dominantly quartz-dioritic magmas. This last episode may be considered as a flare-up event, characterized by intense magmatic transfers into the crust and rapid relief creation. The Late Cretaceous-Paleocene initial εHf are shifted toward positive values (up to +3.3 and +2.6) compared to the Jurassic ones, indicating either a larger input of juvenile magmas, a lesser interaction with the ancient crust, or an increase of re-melting of young mantle-derived mafic lower crust. These magmatic fluxes with juvenile component are coeval with the onset of the crustal thickening at 90Ma and represent a significant contribution to the formation of the continental crust in this area.
|Number of pages||18|
|State||Published - 5 Dec 2012|
Bibliographical noteFunding Information:
The Sociedad Minera Cerro Verde S.A.A has allowed a significant part of the field studies. The project was supported by the IRD (Institut de Recherche pour le Développement) and INSU (Institut National des Sciences de l'Univers-CNRS) SYSTER program . We would like to thank José Berropsi from IRD for the field logistical support in Peru, Mireille Besairie for the mineral separations in LMV (Clermont Ferrand), Norman Pearson for his help during Hf analysis, and Flora Boekhout for her careful rereading. The constructive comments of the two reviewers, M. Poujol and M. Parada, were very useful for the improvement of the manuscript. This is contribution 214 from the ARC Centre of Excellence for Core to Crust Fluid Systems ( http://www.ccfs.mq.edu.au ) and 852 in the GEMOC Key Centre ( http://www.gemoc.mq.edu.au ). The Hf analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS, industry partners and Macquarie University.
- Crustal growth