Petit spot-like volcanoes exposed in Costa Rica

摘要: The study of volcanism in the ocean is fundamental to better understand dynamics Earth mantle and plate tectonics. However, our understanding this is limited by difficulties to access roots volcanoes and floor. Recent results Panama shown that exposed accreted volcanoes can provide another way of understanding oceans [1]. Petit spot found on subducting plate off Japan are considered reflect response plate flexure [2]. petit very small and it remains unclear if they a common feature ocean floor; documenting new occurrences is a key multidisciplinary issue. We recognize here ancient petit spot-like Costa Rica based new geochemical, geological, 40Ar-39Ar, biochronologic data. Petit spot-like acccreted consists of tectonic stacks volcano-sedimentary material that includes vesiculated pillow lavas, volcanic breccias thick radiolarite beds. Igneous sills compositionnally similar the lavas radiolarite Major trace element contents igneous rocks indicate an alkalic, moderately fractionated composition, support low degrees partial melting garnet stability field. Normalized trace element patterns those of petit Japan, distinct from of typical OIB, MORB off-axis seamounts. Step-heating 40Ar-39Ar dating co-magmatic amphiboles gave two ~175 Ma ages formation for spot-like volcanoes Rica. Tectonostratigraphic and biochronologic data clearly document ~110 age of accretion, that did not formed close to subduction zone or mid-ocean ridge. Therefore, we propose may represent a ubiquitous floor, which form far from mid-ocean ridges zones. Possibly, spotlike volcanoes exposed tectonicallyinduced leaking melts pre-existing at base the lithosphere.