[SIT32-P02] Origin of the Caroline Plateau/Seamount Chain from a short lived mantle plume
キーワード：alkali basalt, age-date, geochemistry, hotspot, mantle plume, Caroline plateau
The genesis of an oceanic plateau bears important information on the mantle dynamics and mantle compositions. The Caroline Rise (or Caroline ridges) has played an important role in the tectonic frame of the western Pacific, however, the nature and origin of the Caroline Rise has long been unclear. In this study we first confirmed that it represents an oceanic plateau formed as a large igneous province based on seafloor sampling program. The Caroline Plateau is connected to the east with the Caroline Seamount Chain that is considered to have been formed by a deep-rooted hotspot. To investigate the mantle source nature of the Caroline Plateau and its genetic relationship with the Caroline Seamount Chain, we age-dated and analyzed the geochemistry (major and trace elements and Sr-Nd-Pb-Hf isotopes) of the basalt samples from the Caroline Plateau. The basalt samples are classified into two groups, the alkali and the tholeiite groups. The results of age-dating indicate older ages for the tholeiite group than the alkali group. Thus, the tholeiite group basalts are apparently older than the Caroline Islands and are close to the basalts of Ontong Java Plateau in trace element patterns. We suggest that the tholeiite group basalts represent the main stage volcanism and the alkali group basalts represent the late stage volcanism of the Caroline Plateau. The alkali group basalts show trace element and isotope compositions similar to those of the Caroline Islands to the east. The tholeiitie group basalts can be formed by mixing between the alkali group basalts and the depleted Caroline plate basalts based on Sr-Nd-Pb-Hf isotope compositions, suggesting involvement of depleted upper mantle components in the mantle source. The MORB-like depleted geochemical nature of the tholeiite group basalts indicates formation of the Caroline Plateau under the thin Caroline plate lithosphere. The Caroline Plateau/Seamount volcanic chain could be explained by the Caroline hotspot based on their formation ages of and tectonic reconstruction. The Caroline Plateau/Islands volcanic system shows increasing alkalinity and Sm/Yb ratio of basalts with time, which implies for decreasing activities of a short-lived mantle plume. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).