Presenter: Jian-cheng Huang
Date: 2016/11/24
Abstract
This study shows the first detailed geomorphological characterization of field-scale geological features associated with hydrothermal systems in the southern Mariana Trough. The study uses the high resolution near-bottom swath mapping data collected by the autonomous underwater vehicle (AUV) Urashima , and also uses the dive observation acquired by the submersible Shinkai6500. The goal of this research is to realize about the relationship between geomorphological characteristics and hydrothermal activity , and to realize about the nature of tectonic and volcanic controls on the hydrothermal system in the study area. Three of the hydrothermal sites in the study area are located on the active backarc spreading axis (the Snail and Yamanaka sites), two is located at the eastern foot of the axial high (the Archean site), and three are located on an off-axis knoll about 5 km from the spreading axis (the Pika and Urashima sites). The on-axis area is divided into tectonically dominant and volcanically dominant zones; volcanically dominant zones are characterized by mounds cut by fissures. The Snail and Yamanaka sites are located adjacent to these fissure. Differently, the off-axis sites show no evidence of faulting. The Archean site at the foot of the axial high is characterized by a single mound, pronounced off-axial lava flows, and the presence of rugged seafloor features; the site is located at the top of the mound. Many ridge lines extend radially from the top of the mound and some chimney-like structures appear on the slopes and top of the mound. The Pika site is located on the western peak of an off-axis knoll, and the newly discovered Urashima site is located at the northern foot of the western peak of the same knoll. The eastern peak has smooth top and slope, and shows no signal of hydrothermal activity. However the western peak has bumpy seabed feature and ridge lines. On the basis of the associated geomorphological features, the three off-axis sites ((Archean, Pika, and Urashima) were identified as localities formed by long-term large-scale hydrothermal activity, as compared with sites in the on-axis area. The three off-axis site are consist of breccia assemblages that probably originated from hydrothermal activity with black smoker venting, and these are characterized by many ridge lines, conical mounds, and bumpy seabed texture. The on- axis sites are characterized by the absence of ridge lines, and the presence of white smoker and shimmering observed on dome-shape pillow mounds. Hence, the distribution of ridge lines , mound morphology and bumpy seabed textures is likely to correlate with hydrothermal activity.
Reference
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