THE BIRTH AND GROWTH OF MARIANA ISLAND ARC SYSTEM: A PERSPECTIVE FROM TECTONIC GEOMORPHOLOGY

The Mariana island arc system is an important component of the typical trench-arc-basin system in the western Pacific. Due to its unique geographical location, the influx of terrigenous materials is small, and individual structural units have not been complicated. It is an ideal place for tectonic geomorphology research. In the Mariana region, a high-resolution DBM (Digital Bathymetric Model, DBM) was constructed based on the multi-source bathymetric data fusion technology. Based on this, the typical tectonic geomorphology of the Mariana region was quantitatively analyzed: seamounts, ridges and submarine canyons. In the Mariana Trough, a large number of linear seamounts, ridges, and deep sea hills parallel to the island arc have been identified. There are steep fault cliffs on the side of the Mariana island arc near the Mariana trough. It is inferred that the interaction between Pacific Plate and Philippine Sea Plate is exactly the reason why the island arc is ruptured and the linear structure is formed, and the location of the ancient Mariana island arc is between the double arcs. At the same time, our study summarizes previous studies in the Mariana Island arc system on sediment coverage, crustal velocity structure and GPS movement monitoring, which explain and support the point that the formation of Mariana double arc is attributed to asymmetric back-arc spreading. Based on topography, earthquake, drilling, GPS, magnetic anomaly strips and other data, the position and time of ruptured of the ancient Mariana arc, and the half spreading rate of the Mariana trough were quantitatively estimated. And then we discussed the formation and evolution of Mariana double island arc systematically. Various data indicate that the Mariana double arc can be traced back to the ancient Izu-Ogasawara-Mariana island arc formed in the Eocene. Under the action of the back-arc expansion, the island arc split twice and the trench gradually retreated. At the same time, it was bent by the collision of the Miocene aseismic ridge. Under the continuous westward subduction of the Pacific Plate, a double-island arc with an eastward convex shape was finally formed. At present, the Mariana arc is still moving slowly to the east.