Basin-Scale Spatial Distribution and Plumbing Systems of Magmatism in the Taiwan Strait

The Taiwan Strait features rifted basins connected to the South China Sea rifted margin, followed by foreland basins that thicken toward the orogenic belt. Extensive Late Miocene basaltic rocks, dated between 16 and 8 million years ago using K-Ar methods, are widespread across the Taiwan Strait. Despite this, the offshore distribution of these basalts and the basin-scale magmatic plumbing system remain poorly understood. To comprehend offshore igneous formation in the Taiwan Strait, we conducted approximately 4,000 kilometers of multichannel seismic (MCS) profiles to identify strong-amplitude reflectors referring to basaltic layers. The geophysical characteristics of these reflectors, exceeding an order of magnitude in amplitude, were correlated with offshore drillings to confirm their lithology and age.

Our findings reveal that basalt distribution within the Taiwan Strait forms a northeast-southwest oriented zone, with basalts concentrated into northern and southern groups that align with the regional basement highs, specifically the Peikang and Kuanyin Basement Highs. The basaltic layers demonstrate tabular and continuous, with a single reflector suggesting a thickness of approximately a few meters to decimeters. These sequences are divided vertically into four to five distinct layers and erosional surfaces atop magmatic additions, suggesting episodic intrusion and extrusion events over time. 

Additionally, we identified large-scale doming structures with diameters of approximately 70 kilometers in the south, and the estimated vertical uplift reaches 1 to 2 seconds of two-way travel time, corresponding to several hundred meters. The evolving plumbing system has influenced the deformation of preexisting sedimentary sequences and earlier igneous rocks in the vicinity of the Penghu Islands. Onshore drilling and outcrop data also indicate the coeval stratigraphic hiatus within the Late Miocene Nanchuang Formation in southwestern Taiwan. These extensive basaltic sequences provide feasible insights into magma-related crustal or mantle emplacement into the evolving magma pathways within the rifted basins.

The mapping delineates the spatial distribution of basalt in the Taiwan Strait, enhancing the understanding of its offshore plumbing system in shallow depth. Extensive magmatism in this region modified the sedimentary succession and probably crustal structure prior to orogeny, influencing the subsequent development of the fold-thrust belt and overall surface structural evolution.