A detailed Rb-Sr geochronological and geochemical study has been carried out on granitoids of the North Patagonian batholith in Aysén. The results for 25 plutonic bodies reveal a complex age pattern. The principal zones defined are, from west to east: Late Cretaceous (a single 76 Ma pluton), Early Cretaceous ( c. 135 Ma), Eocene ( c. 45 Ma), and Early Miocene (25-15 Ma), reverting to mid-Cretaceous (120-90 Ma) in the Main Cordillera. The igneous suite is typically metaluminous and calc-alkaline, with hornblende-biotite granodiorite and tonalite dominant, although small bodies of Late Miocene/Pliocene ( c. 10-5 Ma) peraluminous leucogranite occur sporadically. Tertiary plutonism extends to gabbroic compositions and is concentrated in the vicinity of the dextral strike-slip Liquine-Ofqui fault zone. The highest initial 87 Sr/ 86 Sr ratios ( c. 0.7050) occur in the Early Cretaceous group, with a sharp decrease to 0.7034–0.7045 that persists until a Late Miocene reversal to higher values (0.7040–0.7048). These variations are reflected by Nd isotopes, but trends in the ɛSr, v. ɛNd, diagram show that this is not due to contamination from the accretionary complex into which the batholith was emplaced. An origin by melting of mafic crustal underplate and lower crust is suggested for the main magma suite. The discrete episodes of magmatism correlate with significant changes in subduction kinematics.

The Caleu pluton, in the Coastal Range of central Chile, represents the last magmatic event related to the Early Cretaceous rifting along the western margin of South America. The pluton was emplaced into a c. 10 km thick pile of mainly basalts and basaltic andesites deposited in an Early Cretaceous subsiding basin, and affected by very low-grade metamorphism. The cooling history of the pluton is documented on the basis of U-Pb, 40 Ar/ 39 Ar step-heating and fission-track dating. The U-Pb date suggests an age of emplacement in the interval 94.2-97.3 Ma. Rapid subsolidus cooling between 550-500 8C and 250 8C is documented by 40 Ar/ 39 Ar plateau ages on amphibole, biotite and plagioclase between 94.9 AE 1.8 and 93.2 AE 1.1 Ma. Slower subsolidus cooling to c. 100 8C is identified at the 94-90 Ma interval by the fission-track thermal model. The geochronological data show that the emplacement of the pluton is coeval with the very low-grade metamorphism of the host rocks. Therefore, this metamorphism is probably not the result simply of burial, but also of a regional thermal gradient related to the plutonism. Exhumation of the pluton started coevally with its emplacement and continued to about 90 Ma, being associated with the closure of the Early Cretaceous rifting. The Caleu plutonism represents an asthenospheric-derived event during maximum extension, and marks a turning point between extensional-and compressional-related magmatism.

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This article provides a review of the state of the art of technologies in providing automated feedback toopen-ended student work on complex problems. It includes a description of the nature of complex problems and elements of effective feedback in the context of engineering education. Existing technologies based on traditional machine learning methods and deep learning methods are compared in light of the cognitive skills, transfer skills and student performance expected in a complex problemsolving setting. Areas of interest for future research are identified.