Aristides José Alfaro Gálvez investigated the Late Cenozoic magmatism of the Talamanca Cordillera, Southern Central America. Six to five Ma continental-arc shoshonites and other high-K rocks crop out among the summits of that region. Their trace element composition (Sr~1700 ppm at Rb~120 ppm concentrations) suggests a genesis related to subduction processes rather than lower crustal melting. This work integrates Monte Carlo simulations of trace element geochemistry and isotopic evidence in

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... to explain the origin of these highly enriched continental arc igneous rocks. The main conclusion is that the trace element budget of the Talamanca arc rocks requires the input of an incompatible element-enriched component, similar in composition to the Cocos Island Province (Pacific Ocean), as a result of slab melting of subducted seamounts. iii BIOGRAPHICAL SKETCH Aristides J. Alfaro was born on September 25 th , 1990 in San José, Costa Rica. The first son of geologists María Gálvez and Aristides Alfaro, since early years Aristides developed curiosity and passion for science. He decided to follow the tracks of his parents in the career of Geology at the University of Costa Rica (2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016), where he got involved in the exploration of the Talamanca Cordillera (2013)(2014)(2015)(2016). After working in geologic mapping and a new stratigraphic model, Aristides applied to a graduate program at Cornell University in 2017, where he investigated the geochemistry and petrology of the Talamanca Cordillera. xi LIST OF ABBREVIATIONS AOC Altered Oceanic Crust of the subducting slab (used for composition of that layer in ABS, (Kimura, 2017) ABS Arc Basalt Simulator, software developed by Kimura (2017, version 5.0) CI Cocos Island CIP Cocos Island Province CLIP Caribbean Large Igneous Province CCR Cocos/Coiba Ridge C.R. Coiba Ridge DIKE Dike+gabbro complex of the subducting slab (used for composition of that layer in ABS, (Kimura, 2017) DM Depleted Mantle (Composition defined by Salters and Stracke, 2004) DSDP Deep Sea Drilling Project. The composition of the sediment used in this work is from DSDP495 (Patino et al., 2000) For Forearc (referring to forearc complexes) IE Incompatible elements Ma Million years ago N-MORB N-type MORB as defined by Sun and McDonough (1989) MORB Mid-Ocean Ridge Basalt M.R. Malpelo Ridge MwP Mantle wedge peridotite (used for composition of that layer in ABS, (Kimura, 2017) NHRL Northern Hemisphere Reference Line, defined by Hart (1984) OIB Ocean Island Basalt SED Sediment of the subducting slab (used for composition of that layer in ABS, (Kimura, 2017) SlbP Slab Peridotite (used for composition of that layer in ABS, (Kimura, 2017) xii PREFACE The Talamanca Cordillera is a young (<10 Ma) orogenic zone in Southern Central America, with regions that include tropical rainforests at the lower elevations and paramo above 3000 m a.s.l. (~10000 ft). Most of the range is a protected area into the La Amistad International Park (Costa Rica and Panama). Geologic and geochemical data are restricted to the more accessible areas on the Pacific slope of these Costa Rican mountains. The highest peak in the region, Chirripó peak (3820 m a.s.l or 12532 ft a.s.l.) has a well-developed system of trails and facilities for tourists, for which it is frequently visited and is relatively well known from a geologic and geochemical point of view. Other peaks as Dúrika, Utyum, Kámuk, Cuericí, Ena, Echandi, lack previous petrological studies. With help of field assistants and expert local guides, I had the opportunity to climb these mountains, collect some samples from them and run analyses to study their geochemistry. Several samples were sent to other laboratories in the United States as Hamilton Analytical Lab, for trace elements of plutonic rocks, and Stony Brook University, for isotopic results. Then I worked in modeling of these new data, trying to develop an internally consistent model for trace element geochemistry. The main result of this modeling was that ~5 Ma potassiumrich volcanic rocks found near the central part of the Talamanca Cordillera require the input (through partial melting) of subducted seamounts enriched in incompatible elements, similar to some seamounts found nowadays on the subducting Cocos Plate.