Tectonic Evolution of the Mariana Trough

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Abstract
The Mariana Trough is an active back‐arc basin formed by subduction of the Pacific Plate beneath the Philippine Sea Plate and provides an ideal setting for investigating the evolution of back‐arc basins. In this study, we compile bathymetric, magnetic, and gravity data to reconstruct the formation history of the entire basin. Based on bathymetry and backscatter intensity, the spreading axis is divided into 18 second‐order segments. Thirteen oceanic core complex–like structures are also identified both near axis and in off‐axis regions using topography and gravity anomaly data. Magnetic anomaly data indicate that seafloor spreading initiated at approximately 6.3 Ma in the central part of the basin near 17°30′N. During the initial stage (6.3–4 Ma), the oceanic crust was anomalously thick (∼8 km), likely reflecting enhanced melt production associated with slab‐derived fluids when the spreading axis was located close to the arc. Abyssal hill patterns and magnetic anomalies suggest that spreading was oriented NE–SW during this stage and began to change toward a trench‐normal direction between 4 and 3 Ma in each region. After 3 Ma, the basin evolved into its present crescent‐shaped geometry, with full spreading rates ranging from 25 to 45 km/Myr, which are higher in the southern region than in the north. Half‐spreading rates are generally higher on the western side of the spreading axis than on the eastern side, indicating persistent asymmetric spreading. Estimates of the Euler pole for the Mariana Plate suggest arc‐parallel extension, implying non‐rigid plate behavior during back‐arc basin opening.

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