4. Ordovician Orogeny and Jurassic Low-Lying Orogen in the Santander Massif, Northern Andes (Colombia)

The metamorphic crystalline core of the Santander Massif recorded an early Paleozoic peak metamorphism that reached the granulite facies with temperatures above the wet pelite solidus and an overprinting Jurassic low-pressure metamorphism. The early Paleozoic metamorphism occurred during the Ordovician and produced greenschist to amphibolite facies rocks (Silgará Schist) in the outer and upper parts of the orogen and migmatitic granulite facies rocks (Bucaramanga Gneiss and Berlín Orthogneiss) as observed in the deepest exhumed parts of the orogen. The location of the highest recorded metamorphic PT conditions and the S_n+1 foliation geometry hints at a dome-like structure. The overprinting Jurassic low-pressure metamorphism affected middle to late Paleozoic sedimentary sequences and is related to a N-S Triassic-Jurassic magmatic belt of a low-lying orogen. The plutonic belt is composed mainly of granites and tonalites with a range in ages from 172 to 210 Ma and is interpreted to belong to a low-lying orogen (low-lying Triassic-Jurassic magmatic arc). Present structures in the massif imprint a geometry characterized by converging faults toward the core of the massif giving the appearance of compressional horsts similar to the known back thrust and shortcut thrust geometry. The most important structural features are the Bucaramanga fault toward the west and the Pamplona-Cubogón-Mercedes system toward the east; additionally, there are numerous structures with contrasting cinematic behavior. Some of those faults have been interpreted to represent reactivated and inverted normal faults. It is still unclear if these reactivated faults operated during the Triassic-Jurassic as the boundaries of extensional basins.