TRACING MAJOR CHANGES IN MIDDLE MESOZOIC PLATE CONVERGENCE IN THE NORTHERN ANDES: INSIGHTS FROM THE JURASSIC MAGMATIC RECORD OF SOUTHERN COLOMBIA

Jurassic magmatism is widely distributed in the Colombian Andes. It´s exposed as a series of fault bounded blocks with discontinuous granitoids belt and volcanic sequences in the Central Eastern Cordillera and Upper Magdalena valley.

This magmatic record marks the transition to Pangea break-up, subduction resume in the Pacific and the formation of the Proto-Caribbean in the Early Cretaceous.

New and published U-Pb data and whole rock geochemistry from plutonic and volcanic rocks collected in Southern Colombia show the existence of a Middle Jurassic (190 - 170 Ma) plutonic and volcanic sequences characterized by a mix of arc and intra-plate signature. A younger Late Jurassic plutonic belt with ages between 160 – 140 My is represented by predominantly plutonic rocks, locally deformed in middle to high grade mylonitic conditions. Following this magmatic record there seems to be a major magmatic quiescence until the Late Cretaceous.

We suggest that the older Jurassic magmatism is related to the onset of Pacific (Farallon) subduction following the Late Paleozoic to Triassic collision lick to the agglutination of Pangea. Significant slab roll-back link to early subduction will be responsible for the mixed geochemical signatures and its extensive distribution. The Late Jurassic magmatism which seems to be mostly represented by plutonic remnants and the subsequent magmatic shut-off apparently record a transition to extremely oblique plate convergence and subsequent capture of this magmatic province in the early phases of proto-Caribbean formation.

Similar magmatic evolutionary pattern seems to be a major feature along the Andes and reflects the evolving nature of the Mesozoic convergent margin of the Americas.