JpGU-AGU Joint Meeting 2017

Presentation information

[EE] Oral

S (Solid Earth Sciences) » S-MP Mineralogy & Petrology

[S-MP41] [EE] Oceanic and Continental Subduction Processes

Mon. May 22, 2017 3:30 PM - 5:00 PM 102 (International Conference Hall 1F)

convener:REHMAN Ur Hafiz(Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University), Tatsuki Tsujimori(Tohoku University), Chin Ho Tsai(National Dong Hwa University), Chairperson:Hafiz REHMAN(Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University), Chairperson:Tatsuki Tsujimori(Tohoku University)

4:00 PM - 4:15 PM

[SMP41-09] Origin of ophiolite pulse and thermal state of the upper mantle in the Ordovician time constrained from the Hayachine-Miyamori Ophiolite

*Takafumi Kimura1, Kazuhito Ozawa1, Tsuyoshi Iizuka1, Takeshi Kuritani2 (1.Graduate School of Science, The University of Tokyo, 2.Graduate School of Science, Hokkaido University)

Keywords:thermal state of the mantle, mantle potential temperature, ophiolite pulse, arc ophiolite

It is critical to know the thermal history of the mantle in order to better understand the evolution of the earth because the mantle under thermal convection occupies 80vol% of the earth.
The mantle potential temperature (MPT) is a temperature of mantle material adiabatically brought to the surface. The thermal history of the mantle has been examined by revealing secular change of MPT estimated from non-arc basalts and modeled with a parametarized convection model. The so far obtained MPT change and the model, however, cannot resolve episodicity, the critical feature of the earth’s thermal history, which can only be tackled by accumulation of data with higher resolution.
Ophiolite pulses, in which a large number of ophiolites formed in a confined period, are thought to reflect thermal episodes. However, the relationship between the Ordovician ophiolite pulses and the proposed plume model are not clear because of the predominance of arc ophiolites and scarcity of LIPS for the Ordovician pulse. This must be resolved by MPT estimation for the Ordovician mantle, for which two difficulties relevant to arc magma genesis must be overcome: the involvement of H2O and complex thermal state.
In this study, we develop a novel method for MPT estimation for arc environment by using ultramafic dikes from Hayachine-Miyamori Ophiolite, northern Japan. The estimated MPT, melting depth and water content in source mantle are ~1360°C, ~170km and ~0.15wt% respectively. The geochemical data of the dike indicate passive upwelling of NMORB source-like garnet peridotite from sub-slub mantle without strong influence of slab-derived fluids. The estimated MPT may reflect the global value if operation of small-scale convection is considered. We conclude that the Ordovician upper mantle has a thermal state similar to the current upper mantle. Surface tectonics, such as assembly and breakup of supercontinents and a peculiar water delivery, might be responsible for the Ordovician ophiolite pulse.