PETROGRAPHIC ANALYSIS OF THE BOSQUE ENANO GRANITE IN THE SIERRA DE LAS MINAS, GUATEMALA

The Sierra de las Minas lies along the North American-Caribbean plate boundary in Guatemala. The mountains are underlain by various accretionary terranes that record multiple deformational events. The Bosque Enano (BE) granite lies to the north of Santa Rosalía along the east-west divide of the mountains. The unstudied BE granite is potentially important for Paleozoic tectonic interpretations based upon its possible relationship with the orogen-scale Baja-Verapaz shear zone. If it cuts, or is cut by the shear zone, its age could be useful in dating the structure. The goal of this pilot study was to compare the BE granite with possible regional correlatives. These include:

(1) the Ordovician Rabinal granite distinguished by its grade of deformation in minerals due to its proximity to the Cizalla Baja Verapaz fault,

(2) the Triassic Sinanjá granite, granodiorite calco-alkaline rock unit of S type origin with consistent lineation on the mineral’s crystal structure, zoning and dynamic recrystallization deformations, and

(3) the Cretaceous Matanzas stock, which shares the same characteristics as the Sinanjá granite except its monzonite composition.

The BE granite is made up of usually massive medium-grained quartz, microcline, biotite, and muscovite. Locally, the granite records low grade deformation exhibited by undulatory extinction on coarse to medium quartz crystals, sub-parallel polycrystalline quartz bands with weak foliation, and crystal fractures filled with polycrystalline quartz.

In sum, the BE granite is tentatively interpreted to be similar to the Matanzas stock, yet much larger in extent. Future studies are necessary to date and carefully interpret the structural location of the BE granite and to determine its role during Paleozoic orogenesis along the southern Laurentian margin.