Sedimentary Xenoliths of the Mesozoic Nicoya Complex, Costa Rica – Data Record from the Playa Arbolito Forearc Basement Assemblage, Nicoya Peninsula

The dataset consists of ten individual research data files over the Cretaceous sedimentary xenolith field of Playa Arbolito, exposed on the western Nicoya Peninsula of Costa Rica (Fig. S1). The data record a unique assemblage of radiolarite, radiolarian chert, chert, siliceous tuffaceous mudstone, and glassy pyroclastic xenoliths hosted in basalt of the Mesozoic forearc basement succession (Fig. S2-S3), called the Nicoya Complex after Dengo (1962). The data were gathered during two different field research campaigns in February 2012 and March 2017. While the 2012 research centered on xenoliths and their host rocks found at Playa Arbolito (Fig. S1), the 2017 campaign dealt in addition with potential xenolith source-rock strata contained in Cretaceous sedimentary sections of the interior Peninsula and NE Gulf of Nicoya coast (e.g., Sardinal, Manzanillo sections) (Table S1). Further key data come from detailed micropaleontological, sedimentological, and volcanological rock examinations in outcrop and laboratory. The dataset includes furthermore a newly detailed examination of Schmidt-Effing’s (1979) and Gursky’s (1984) xenolith rock collections from this locality. They are described and illustrated with full color images in dataset DS1. Despite marine erosion of rock exposures, xenolith samplings in different years still show similar lithologies at Playa Arbolito. As Figure S8 records, boring activity of pholadid bivalves in the intertidal zone actually contributes to active bioerosion of basement exposures, including pyroclastic xenoliths. The micropaleontological data show the notable first record of a Turonian planktic foraminiferal assemblage in marine pyroclastic rock from Nicoya Complex led by the index species Helvetoglobotruncana helvetica (Bolli) (Fig. S5). This find dates Cretaceous highly differentiated explosive arc volcanism in Costa Rica, similarly to that recorded by pyroclastic layers of the nearby Albian to Campanian Loma Chumico Formation, a sedimentary forearc basin succession (Calvo and Bolz, 1994; Calvo, 1998). The unique basalt-hosted xenolith assemblage including sedimentary tuffaceous lithologies, particularly highly differentiated biotite- and hornblende-bearing pyroclastic rocks, evidence bimodal volcanic activity linked to Cretaceous island arc volcanism on the western Caribbean Plate boundary. The variety of sedimentary xenolith lithologies also found in Mesozoic strata sections of Nicoya Peninsula and NE Gulf of Nicoya points out to xenolith formation caused by widespread and long-term (~140 to 70 Ma) intrusion of basalt throughout the Cretaceous deep-sea forearc basin succession. They also show that 90 Ma aged Tortugal komatiite lavas erupted coevally with explosive arc volcanism. These data contribute to understand the nature of igneous forearc basement rock exposed along the Pacific coast of southern Central America, and also provide a useful reference for future research in active forearc and arc settings.