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Why the Challenger Deep, the deepest point on Earth’s solid surface, is so deep is unclear, but part of the reason must be the age and density of the downgoing plate. Northwest Pacific oceanic crust subducting in the Izu-Bonin-Mariana Trench is Cretaceous and Jurassic, but the age and nature of Pacific oceanic crust subducting in the southernmost Mariana Trench remains unknown. Here we present the first study of seafloor basalts recovered by the full-ocean-depth crewed submersible Fendouzhe from the deepest seafloor around the Challenger Deep, from both the overriding and downgoing plates. 40Ar/39Ar ages indicate that downgo¬ing basalts are Early Cretaceous (ca. 125 Ma), indicating they are part of the Pacific plate rather than the nearby Oligocene Caroline microplate. Downgoing-plate basalts are slightly enriched in incompatible elements but have similar trace element and Hf isotope compositions to other northwest Pacific mid-ocean ridge basalts (MORBs). They also have slightly enriched Sr-Nd-Pb isotope compositions like those of the Indian mantle domain. These features may have formed with contributions from plume-derived components via plume-ridge interac¬tions. One sample from the overriding plate gives an 40Ar/39Ar age of ca. 55 Ma, about the same age as subduction initiation, to form the Izu-Bonin-Mariana convergent margin. Our results suggest that 50%–90% of the Pb budget of Mariana arc magmas is derived from the subducted MORBs with Indian-type isotope affinity.
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Geochemical and geochronological constraints on the tectonic and magmatic evolution of the southwestern Mariana subduction zone
Interaction of a subduction zone with an oceanic plateau has implications for plate tectonics. However, the geodynamic processes and petrological responses to oceanic plateau–arc interactions remain enigmatic. The southwestern Mariana and Yap arcs have experienced interactions with the Caroline Plateau, which have affected the regional tectonism. In this study, tholeiitic basalts and metamorphosed volcanic rocks (i.e., greenstones) were recovered from the southwestern Mariana forearc. The protoliths of the metamorphosed volcanic rocks have geochemical affinities to low-silica boninites. These boninitic rocks have similar K–Ar and apatite U–Pb ages of ca. 24 Ma, which record the timing of collision between the southwestern Mariana arc and the Caroline Plateau. 40Ar/39Ar dating of plagioclase in the tholeiitic basalts dates post-collisional magmatism to ca. 18 Ma. The tholeiites have geochemical signatures of fore-arc basalts (e.g., low Ti/V ratios and light rare earth element-depleted patterns) and high Th/Yb ratios, which reflect a depleted mantle source with a subduction component inherited from a pre-collisional subduction event. We suggest that the southwestern Mariana arc is an intra-oceanic arc that underwent plateau–arc collisions. These plateau–arc interactions affected the tectonic and magmatic evolution of the southwestern Mariana arc and nearby western Pacific basins.
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- PAR ID:
- 10505121
- Editor(s):
- Sun, Weeding
- Publisher / Repository:
- Deep-Sea Research Part I
- Date Published:
- Journal Name:
- Deep Sea Research Part I: Oceanographic Research Papers
- Volume:
- 197
- Issue:
- C
- ISSN:
- 0967-0637
- Page Range / eLocation ID:
- 104039
- Subject(s) / Keyword(s):
- Boninitic greenstones Post-collisional magmatism Yap–Mariana junction Plateau–arc interaction
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.dsr.2023.104039
