![]() ![]() More recently, petrogenetic models for the origin of HKCA igneous rocks (predominantly I-type granitoids) have been proposed, including the anatexis of mafic lower crust, due to additional heating by underplated basaltic magma in continental arcs or in collision settings (e.g., Jiang et al. Roberts and Clemens ( 1993) affirmed that HKCA geochemical fingerprint could be derived mainly from the partial melting of hydrous, calc-alkaline to HKCA (mafic or intermediate) metamorphic crustal protoliths. 2021), but also because their petrogenesis and geological settings are still the subject of considerable controversy. Notwithstanding this fact, high-K calc-alkaline (HKCA) type rocks require special attention, not only because they are spatially and temporally widespread (e.g., Liégeois et al. ![]() The rocks grouped under the generic term “granitoids” are the major lithologic component of the Earth's continental crust. We conclude that the parental source of the COIC was derived from partial melting of the lower crust triggered by emplacement of an underplated magma at the base of the crust during the end of an orogenic cycle. Whole-rock isotopic data suggest a magma source mixing juvenile material with older continental crust, as indicated by 87Sr/ 86Sr ( t = 40) ratios between 0.704583 and 0.707783, 143Nd/ 144Nd ( t = 40) ratios varying in the ranges of 0.512478–0.512702 (εNd ( t = 40) = from + 2.18 to − 2.10), and TDM (Nd) ranging from 1.03 to 0.62 Ga. Moreover, the systematic variations in the ratios of highly incompatible elements, such as La/Sm (6.54–3.79) and Rb/Sr (0.32–0.10), and relatively narrow ranges in Zr/Hf (36.25–48.84) and 147Sm/ 144Nd (0.0941–0.1261), suggest fractional crystallization as the main petrogenetic process involved in the formation of the COIC rocks. Ti-in-zircon temperatures and zircon saturation thermometry suggest a magmatic origin from evolved and relatively cold melts (~ 700 ☌). ![]() Whole-rock and zircon geochemistry indicate a post-collisional setting with an inherited magmatic arc fingerprint. In addition, the mantle-normalized spider diagram shows enrichment of LILE, such as Rb and Ba, and depletion of HFSE, such as Nb, Ta, Ti, and P. ![]() The chondrite-normalized REE diagram summarizes enrichment of LREE ( N = 5.94–19.19) and moderate to slightly negative Eu anomalies (Eu/Eu* = 0.63–0.94). The granodiorites exhibit geochemical features typical of I-type, high-K calc-alkaline, Magnesian rocks. U–Pb zircon analyzes of four samples from the largest plutonic center of the COIC yielded ages ranging from 42.6 ± 0.2 Ma to 41.8 ± 0.1 Ma. Petrographic observations reveal mainly fine-to-coarse-grained granodioritic composition for most plutonic masses. In this work, plutonic rocks from the COIC were studied using petrography, U–Pb geochronology, whole rock and zircon geochemistry, and Rb–Sr and Sm–Nd isotopes. The Concepción del Oro Igneous Complex (COIC) represents one of the most internal and isolated magmatic pulses that occurred during this magmatic activity. During the Mexican fold-and-thrust belt tectonics, the inboard migration of long-term cordilleran magmatism typifies the geological setting during the Cretaceous–Paleogene period. ![]()
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