Mineral chemistry and thermobarometry of Jurassic arc granitoids: Implications for petrotectonic and unroofing history of the southern Colombian Andes

The Jurassic magmatic record in the southern Colombian (Northern Andes) includes numerous subduction-related I-type calc-alkaline granitoids with diverse structures and textures, formed in two main episodes at ∼ 195 to 165 Ma and ∼ 165 to 145 Ma. We provide new insights into the mineral chemistry, estimates of intensive parameters and petrogenetic processes of 12 plutonic occurrences in the region, grouped in 4 petrographic associations. Primary mineral assemblages include labradorite-to-oligoclase, alkali feldspars, ferroan enstatite, Mg-rich augite to ferroan-diopside, tschermakite to hastingsite and hornblende and Mg-rich annite; Fe-rich phlogopite and actinolite are post-magmatic phases. Amphibole chemistry indicates that the older (195-165 Ma) Jurassic bodies formed from relatively highly oxidized (f _O2 values buffered at -0.1 ≤ NNO ≤ +1.4) hydrous (∼ 4 to 6 wt % H₂O) magmas and their differentiation involves significant crustal assimilation and/or magma mixing, fractional crystallization and late-magmatic re-equilibration processes. In contrast, the younger (165-145 Ma) Jurassic intrusives, derived from subducted-modified mantle sources, record moderately lower oxidized hydrous conditions (f _O2 values -0.7 to 0.8 ≤ NNO; ∼ 5 wt % H₂O) with magma evolution mainly controlled by fractional crystallization and late-magmatic re-equilibration processes. Clinopyroxene-only, amphibole-only and amphibole-plagioclase thermobarometry estimations suggest that the Jurassic occurrences crystallized over variable temperature (647°C-1087°C) and pressure (0.7-6.3 kbar) conditions, corresponding to emplacement depths ranging from ∼ 15, ∼ 8 to 11, ∼ 5 to 7 and <4 km along the arc crustal column. The obtained data combined with time evolution allow the identification of exhumed and fragmented arc blocks in the Jurassic magmatic system and provide an essential link between the orogenic deformation event poorly constrained in the Northern Andes.