Jurassic magmatism in the Garzón region of the Colombian Andes: insights from whole-rock geochemistry and zircon isotope analysis of granites and subvolcanic rocks

New whole-rock geochemical and zircon U – Pb dating and Lu – Hf isotope data are presented for the Garzón granites and related subvolcanic rocks, which formed during widespread Jurassic arc magmatism in the Colombian Andes. This magmatism resulted from the subduction of a proto-Pacific plate under the NW South American margin. Our data indicate that the granitic and related rocks of the Algeciras, Altamira, and Sombrerillo Plutonic Massifs in the Garzón region have crystallization ages ranging from 179 to 169 Ma. These rocks are characterized as high-K alkali-calcic or calc-alkaline, magnesian, with 0.66 ≤ Fe# ≤ 0.94, and metaluminous to slightly peraluminous, with 0.67 ≤ ASI ≤ 1.01, exhibiting geochemical signatures. The trace element patterns normalized to MORB reveal pronounced negative anomalies for Nb, P, and Ti, alongside positive anomalies for Pb, Rb, Sr, Y, Zr, and Ba. The REE patterns display strong LREE fractionation over HREEs, with moderate to absent negative Eu anomalies in mafic to intermediate rocks (0.5 ≤ Eu/Eu* ≤ 1.0) and greater significance in felsic rocks (Eu/Eu* up to 0.6). Most granitic rocks display negative εHf(t)-in-zircon values (−7.7 to −1.2), indicating substantial contributions from ancient continental crust. In contrast, the subvolcanic rocks have a mix of positive and negative εHf(t) values (from −7.9 to + 11.5), reflecting significant input from both juvenile mantle and ancient crustal sources (221 Ma ≤ TDM ≤1516 Ma). After 167 Ma, the magmatic activity diminished and ceased in the Garzón region, while it continued to the west in the Central Cordillera until ca. 129–110 Ma, with a gradual increase in contributions from the mantle, as indicated by systematic zircon Hf isotopes, arguably due to changes in the subduction regimes.