PALEOMAGNETISM, MAGNETIC FABRIC, AND GEOCHRONOLOGY OF THE DIPILTO BATHOLITH (NICARAGUA): EARLY TO LATE CRETACEOUS TECTONIC EVOLUTION OF THE CHORTIS BLOCK AND SW NORTH AMERICAN PLATE

The Dipilto batholith is one of the largest plutonic complexes in Central America (~1,200 km²), located in the meridional region of the Chortis block, northwestern Nicaragua. This plutonic body is mainly composed of Bt-Amp granodiorite, and I- and S-type granites, and it is cut by quartz diorite, microdiorite, diabase, and leucogranite dikes. The Dipilto batholith intrudes the Nueva Segovia Schist of presumed Paleozoic to Middle Jurassic age (?). The origin and tectonic relationship of this batholith in Central America is a dimly understood topic.

Paleomagnetic, rock magnetic, and magnetic fabric results from 34 sites, as well as four U-Pb (zircon) isotopic ages, are presented. Our results indicate that the intrusive suites of the Dipilto batholith are of the Ilmenite-series, with magnetic susceptibilities less than 700 x10^-6SI, whose main magnetic carrier is Ti-rich titanomagnetite. Paleomagnetic results shows 101° counterclockwise rotation and 28.7°N paleolatitude from 16 selected sites. The anisotropy of magnetic susceptibility, at room and high temperature, indicates two main directions of K_max of 47/05 and 225/14 (i.e., NE-SW), with magnetic fabric dominated by paramagnetic minerals. The U-Pb isotopic ages range from 119.08 ± 0.37 and 112.69 ± 0.44 Ma.

Altogether, location, composition, age, and magnetic fabric suggest that the Dipilto batholith was formed during the collision of the Siuna intraoceanic arc against the southern part of the Chortis block. Several paleomagnetic studies support the rotation and accommodation of the Chortis block, which are consistent with the evolution of the southwestern North American plate during the Aptian-Albian. The results of our study permit to propose an arc-continent collision model to explain the accretion and shortening of the Guerrero Terrane and the closure of the Arperos Basin.