Volcanic-plutonic connections in a tilted nested caldera complex in Hong Kong

Abstract

Exceptional exposures of four, precisely-dated, Middle Jurassic to Early Cretaceous,silicic volcanic centers and their plutonic equivalents in Hong Kong have provided an excellent opportunity to examine close connections in time and space between magma chambers and their overlying calderas. Here, we describe a ~14 km crustal section through a collapsed caldera in southeastern Hong Kong where the intracaldera fill suggests that the magmatic discharge was of supereruption scale. The main subvolcanic components that link a magma chamber with surface are revealed by well-established field relationships, supplemented by high precision geochronology, whole-rock geochemistry, and geophysical data. Exposures and outcrop reveal kilometer-scale caldera subsidence and evidence of the simultaneous evacuation of hundreds of cubic kilometers of high-silica rhyolite magma through dike-like conduits from a shallow subcrustal reservoir. The resultant volcanotectonic depression, within which is preserved a single cooling unit of massively columnar-jointed densely welded tuff (High Island tuff), is interpreted to form part of a larger tilted Early Cretaceous nested caldera complex. The High Island eruption signaled the end of a 24 Myr-Early Cretaceous silicic magmatism in the Hong Kong region characterized by four discrete ignimbrite ‘flare-ups’