Early Andean subduction-related magmatism, northern Chile (~26.5 degrees south): Geochronology (e.g. uranium-lead), isotopic geochemistry (hafnium) and iron oxide copper-gold mineralization .
Published: 2006
Language: eng
Number of pages: 221
ISBN-13: 9780494218709
Description: Most of the studied Late Jurassic to Early Cretaceous plutonic units in the area host massive magnetite. The age of massive magnetite mineralization overlaps the age of plutons with which they are spatially associated. U-Pb (titanite) and 40Ar/39Ar (actinolite) ages for two massive tabular magnetite bodies, La Suerte and Bolaco (&sim;154 Ma and 152 Ma, respectively), indicate previously unreported, upper Jurassic massive magnetite mineralization. A precise apatite-magnetite U-Pb isochron age for the Carmen massive magnetite deposit shows that magnetite-apatite dykes crystallized at the same time as quartz diorites that partially host mineralization at &sim;131 Ma. Pb isotopic correspondence, combined with the temporal and spatial association between magnetite-apatite mineralization and dioritic-quartz dioritic magmatism, suggests a genetic relationship between early Andean continental arc magmatism, massive magnetite-apatite deposits and IOCG mineralization. Although the origin of the massive magnetite bodies has not been fully tested, the genetic hypothesis for derivation from Fe-P oxide melts is reasonable. Hydrothermal IOCG mineralization is spatially associated with massive magnetite-apatite mineralization, and postdates it.Early Andean (Jurassic-Early Cretaceous) arcs developed in extension on a continental crust composed of Permo-Triassic granitoids, Paleozoic metasedimentary rocks and unexposed Proterozoic rocks. The La Negra basaltic to dacitic volcanic unit occur in a &sim;1000 km belt in the Coastal Cordillera of northern Chile from &sim;18&deg;S to &sim;28&deg;S and represent the first recorded magmatic activity in the Andean cycle. The base of the La Negra Formation &sim;26&deg;S has been dated at 193.0 +/- 0.6 Ma (single zircon U-Pb). This lower Jurassic age for the onset of Andean magmatism is supported by ages obtained for the Flamenco pluton (191.3 +/- 0.4 Ma).The La Negra Formation is intruded by a series of epizonal plutonic units that range in age from &sim;160 Ma &sim;125 Ma, and show a systematic migration of the magmatic locus to the east at an average rate of &sim;460 m/Myr. Hf isotopic compositions of zircons show that the early Andean magmas were mainly mantle-derived with partial assimilation of enriched (Ho crustal rocks. They reveal a progressive change of the lower crust from less to more radiogenic crust (Hf).
Notes: Source: Dissertation Abstracts International, Volume: 68-01, Section: B, page: 0160.

Thesis (Ph.D.)--University of Toronto, 2006.

Electronic version licensed for access by U. of T. users.