Emeralds in the Eastern Cordillera of Colombia: Two tectonic settings for one mineralization

Abstract

Colombian emeralds are formed through a hydrothermal-sedimentary process. On the western side of the Eastern Cordillera, the deposits are linked by tear faults and associated thrusts developed during a compressive tectonic phase that occurred at the time of the Eocene-Oligocene boundary, prior to the major uplift of the Cordillera during the Andean phase (middle Miocene). On the eastern side of the Cordillera, emerald mineralization occurred earlier, at the time of the Cretaceous-Tertiary boundary, during a thin-skinned extensional tectonic event linked to evaporite dissolution. This event predates the Andean phase, during which this part of the chain was folded and thrust over the Llanos foreland.

An integrated analysis of an orogen-sedimentary basin pair: Latest Cretaceous-Cenozoic evolution of the linked Eastern Cordillera orogen and the Llanos foreland basin of Colombia

“…Flexural deformation induced: (1) erosion of Paleocene-upper Cretaceous strata in the Llanos foothills and Llanos Basin, (2) westward thickening of unconformity-bounded Maastrichtian-Paleocene syntectonic sequences, (3) increased input of lithic fragments in upper Paleocene strata and northward dispersal of detritus, (4) amalgamation of fl uvial-to-estuarine channel structures during the early and middle Eocene, (5) change of subsidence rates in the latest Cretaceous and late Paleocene, and (6) slow tectonic subsidence regimes during the early-middle Eocene in the axial Eastern Cordillera and Llanos foothills. These phases of deformation are constrained in the hinterland by: (1) zircon fi ssiontrack data from the Santander massif ; (2) geochronological data from micas fi lling normal faults associated with fl exural extension during the latest Cretaceous (Branquet et al, 1999); and (3) angular unconformities in the Magdalena Valley (Gómez et al, 2003(Gómez et al, , 2005b. Geodynamic analysis allows us to infer that equivalent tectonic loads for these phases were less that 3 km high, less than 100 km wide, and wider in the northern than in the central part of the study area.…”

“…6-3 Ma triggered rapid denudation and shortening rates of the eastern fl ank of the Eastern Cordillera . Reported geochronological data from green muscovite crystallized on emeraldbearing vein wall rocks (Ar/Ar and K/Ar) indicate a fi rst extensional event at 65 ± 3 Ma on the eastern fl ank and a compressional event on the western fl ank between 32 and 38 Ma (Branquet et al, 1999). A regional shift from marine to continental depositional environments at the end of the Cretaceous was coeval with accretion of oceanic terranes west of the Romeral fault system (e.g., Etayo-Serna et al, 1983;McCourt et al, 1984).…”

“…11 and 12E). Apatite FT ages (Toro, 1990) Apatite FT ages Figure 13 Zircon FT ages Micas filling normal faults (Branquet et al, 1999) Forebulge Litharenites; source areas less than 100 km Paleorelief controlled northward dispersion of detritus Amalgamated sandstones = very low subsidence Flexural subsidence causes abrupt change of thickness, incipient development of structures Apatite FT ages (Toro, 1990) Apatite FT ages (Hossack et al, 1999) Apatite FT ages La TN C-BA Pesca F.…”

Uplift history of the Central and Northern Andes: A review

“…In the Late Cretaceous-Paleocene, a volcanic arc collided with the South American margin from northern Peru to Colombia; remnants of the arc are preserved in the Western Cordillera of Ecuador and Colombia (Dengo and Covey, 1993). This event caused compressional deformation of the Western and Central Cordilleras and foreland deposition in the area of the Eastern Cordillera (Cooper et al, 1995;Branquet et al, 1999). Some folding and thrusting in the middle Magdalena Valley and western Eastern Cordillera occurred in the middle Eocene (Branquet et al, 1999), perhaps associated with collision of the Piñon-Macuchi terrane (Toussaint and Restrepo, 1994).…”

“…This event caused compressional deformation of the Western and Central Cordilleras and foreland deposition in the area of the Eastern Cordillera (Cooper et al, 1995;Branquet et al, 1999). Some folding and thrusting in the middle Magdalena Valley and western Eastern Cordillera occurred in the middle Eocene (Branquet et al, 1999), perhaps associated with collision of the Piñon-Macuchi terrane (Toussaint and Restrepo, 1994). The Panama-Choco island arc collided with the northwest margin of the South American plate from 12 to 6 Ma (Dengo and Covey, 1993;Kellogg and Vega, 1995); this event is associated with deformation in the Eastern Cordillera region.…”