Monday, January 27, 2025

VULCANOLOGY

Unveiling Japan's geological history through volcanogenic massive sulfide deposits

Researchers unveil key insights into Japan's geological history through Re–Os dating of volcanogenic massive sulfide deposits

Waseda University

Unlocking Japan's geological history: Insights from volcanogenic massive sulfide deposits — image:
Explore the groundbreaking study that uses Re–Os isotope dating to reveal the timing of key tectonic events beneath Japan. Learn how Besshi-type volcanogenic massive sulfide (VMS) deposits are helping scientists understand ridge subduction, volcanic activity, and the formation of Japan’s unique geological landscape. Discover the role of mineral deposits in shaping Earth’s history and their potential in future mineral exploration.
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Credit: Professor Tatsuo Nozaki from the Waseda University

The Earth’s surface is constantly reshaped by the movement of tectonic plates, which make up the continental crust on which we are living. These tectonic plates are in continuous motion, and when one plate is pushed under another, it is called “subduction.” These processes play a crucial role in shaping the Earth’s landmasses, including the islands of Japan, over several hundred million years. Studying ancient mineral deposits offers a valuable way to uncover the timing of these events. However, determining the precise timing of these tectonic events has long been a challenge due to the destruction of microfossil evidence caused by intense heat.

With the growing interest in understanding Japan's detailed geological history, accurately determining the timing of past tectonic events has become increasingly important. To address this challenge, a research team led by Professor Tatsuo Nozaki (Waseda University, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), The University of Tokyo, and Kobe University) collaborated with Associate Professor Yutaro Takaya (The University of Tokyo, Waseda University, JAMSTEC), Adjunct Assistant Professor Ken Nakayama (Kochi University), and Professor Yasuhiro Kato (The University of Tokyo, Chiba Institute of Technology) to utilize mineral deposits for precisely dating these tectonic processes.

Their study focused on Besshi-type volcanogenic massive sulfide (VMS) deposits distributed in Miyazaki and Hokkaido Prefectures. VMS deposits are rich in sulfide minerals and typically form near the ocean floor where volcanic activity occurs. These deposits, associated with in situ greenstone (a type of metamorphosed volcanic rock (basalt)), provided the researchers with an opportunity to establish the timing of ridge subduction beneath the Japanese Islands. The team used Re–Os (rhenium-osmium) isotope geochronology, a technique that allows scientists to date the age of the mineral deposits with great precision. Their findings were published in the journal of Scientific Reports on 3 December, 2024.

Ridge subduction is an important geological process that triggers volcanic activity, thermal metamorphism (the alteration of rocks by heat), and hydrothermal activity (chemical reactions between hydrothermal fluids and rocks). However, dating ridge subduction has been often difficult because the heat from this process destroys fossil records. To overcome this challenge, the researchers focused on Besshi-type VMS deposits that formed on sediment-covered mid-ocean ridges. The ages of these deposits can serve as precise markers for the timing of subduction.

Using the Re–Os isotope method, the team dated the Makimine VMS deposit in Miyazaki Prefecture to 89.4 ± 1.2 million years ago and the Shimokawa VMS deposit in Hokkaido Prefecture to 48.2 ± 0.9 million years ago. These deposits were formed just before the Izanagi–Pacific Ridge was subducted beneath Japan. Several factors supported this conclusion, such as the deposits' ages matching those of the surrounding sedimentary rocks, their close association with in situ greenstone, and the absence of chert (sedimentary rock originating from pelagic sediment). Evidence from sulfur and lead isotopes, along with high thermal gradients in the Makimine area, further confirmed their formation in a mid-ocean ridge environment before subduction.

“These VMS deposits are essential for understanding ridge subduction timing beneath Japan,” said Nozaki. “Dating them has allowed us to pinpoint when this tectonic event occurred, offering new insights into Japan's geological evolution.”

“This study not only sheds light on the timing of ridge subduction but also opens new possibilities for mineral exploration. Accurate dating could help identify new mineral deposits formed by similar tectonic processes, in Japan and globally,” Nozaki concluded.

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Reference

Authors: Tatsuo Nozaki1,2,3,8, YutaroTakaya1,4,5, Ken Nakayama6, and Yasuhiro Kato4,7

Title of original paper: Re–Os dating of the Makimine and Shimokawa VMS deposits for new age constraints on ridge subduction beneath Japanese Islands

Journal: Scientific Reports

DOI: 10.1038/s41598-024-80799-z

Affiliations

1Submarine Resources Research Center, Research Institute for Marine Resources Utilization, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan

2Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, Japan

3Department of Planetology, Graduate School of Science, Kobe University, Japan

4Department of Systems Innovation, The University of Tokyo, Japan

5Faculty of Science and Engineering, Waseda University, Japan

6Marine Core Research Institute, Kochi University, Japan

7Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, Japan

8Faculty of Science and Engineering, Waseda University, Japan

About Waseda University

Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including nine prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015.

To learn more about Waseda University, visit https://www.waseda.jp/top/en

About Professor Tatsuo Nozaki

Dr. Tatsuo Nozaki is a Professor at Waseda University and a visiting researcher at The University of Tokyo, Japan. His research focuses on the metallogenic study of seafloor mineral resources including seafloor hydrothermal deposit and their natural analogs on land such as volcanogenic massive sulfide (VMS) deposits, together with Re–Os isotope dating and paleo-environmental studies using sedimentary rocks. He has authored numerous publications, including work on the genesis of mineral deposits and their relationship with global environmental changes. He is a member of academic societies such as the Society of Resource Geology, Society of Economic Geologists, Geological Society of Japan, Geochemical Society of Japan, and Japan Geoscience Union.

Journal

Scientific Reports

DOI

10.1038/s41598-024-80799-z

Method of Research

Observational study

Subject of Research

Not applicable

Article Title

Re–Os dating of the Makimine and Shimokawa VMS deposits for new age constraints on ridge subduction beneath Japanese Islands

Underwater mud volcanos are a haven for marine organisms

UiT The Arctic University of Norway

The underwater volcano Borealis Mud Volcano is located in the Barents Sea and was first discovered by researchers at UiT The Arctic University of Norway in 2023. The discovery received a lot of attention, and images of the volcano circulated around the world. Now researchers from UiT, in collaboration with REV Ocean, have finally published the results from an interdisciplinary investigation showing that Borealis mud volcano has a unique ecological role as a natural sanctuary for several marine species in the Barents Sea.

While some parts of the crater floor of Borealis appear inhospitable to a variety of organisms, the carbonate crusts – a type of mineral formed thousands of years ago – that characterized Borealis provide a suitably hard substrate for species of anemones, serpulids, demosponges, and sparse octocoral colonies.

"Important for maintaining biodiversity"

In addition, the carbonates offer both shelter and feeding opportunities, playing an important role in sustaining the local fish populations. The researchers observed large schools of commercially valuable species like saithe and various demersal species such as spotted wolffish, cod, four-bearded rockling, and redfish (Sebastes spp.) clustering around the jagged carbonate formations.

“The redfish, for instance, is red listed, and we don’t know the consequences if it would disappear. Borealis is an oasis where different species can thrive and flourish. Thus, preserving ecosystems such as the Borealis Mud Volcano is essential for maintaining biodiversity and understanding the interactions between geology, geochemistry and biology in marine environments. We need that understanding, among other things, considering that the Arctic seabed plays an important role in oil and gas extraction activities and the emerging deep-sea mining industry”, says Professor Giuliana Panieri, lead author of the study recently published in Nature Communications.

Methan has leaked out, probably for thousands of years

Onboard the research vessel Kronprins Haakon in May 2024, researchers confirmed the previous discoveries. Using the remotely operated vehicle, ROV Aurora, the research team was able to make a series of observations of the underwater volcano. Among other things, they saw that it warms the surroundings to 11.5 degrees Celsius, while the seabed usually has a temperature of around 4 degrees Celsius.

The researchers also found sediments containing extinct, microscopic marine organisms from up to 2.5 million years ago and that small "mud cones" in the volcanic system are emitting vigorous methane-rich liquids. The fact that the seabed around the volcano is also characterized by extensive carbonate deposits indicates that methane has leaked out, probably for thousands of years.

“The Borealis Mud Volcano is a unique geological and ecological phenomenon that provides a rare insight into the complex interactions between geological processes and marine ecosystems. It is important to preserve these unique habitats, which play a crucial role in maintaining marine biodiversity”, says Panieri.

She reminds that, in the longer term, Norway has committed to the 30x30 target (protecting 30 % of land and sea by 2030) for spatial conservation measures of representative marine ecosystems, including in the deep sea. Protecting large areas of the deep-sea floor along the Norwegian margin may result in seep refugia acting as source populations for wider recolonization and restoration of benthic biological communities.

“The new findings show the power of international cooperation and how such cooperation can contribute to increasing our understanding of the world's oceans”, says Panieri.

Ischnochiton variegatus from the seabed.

Carbonate rock taken from the seabed.

Scott Wieman installs equipment on REV Ocean's ROV Aurora on FF Crown Prince Haakon.

Credit

Jørn Berger-Nyvoll/ UiT