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Earth of fire

Actualité volcanique, Articles de fond sur étude de volcan, tectonique, récits et photos de voyage

Publié le par Bernard Duyck
Publié dans : #volcanic activity

In October 2019, a team of geophysicists published a description of a large igneous province (LIPs) located in the Philippine Sea east of Luzon Island.

A multi-beam bathymetry with a coverage of almost 100% reveals the morphology of Benham Rise: it consists of a main body, 310 km on 330 km / 0,11Mkm², and three spurs, named Narra, Moro and Molave , extending 100 to 200 km on its east side.

Bathymetry revealing the different underwater structures of the western Philippine Basin - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin (Version 18.1, Geodesy Satellite, 2014, Smith and Sandwell, 1997).

Bathymetry revealing the different underwater structures of the western Philippine Basin - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin (Version 18.1, Geodesy Satellite, 2014, Smith and Sandwell, 1997).

Bathymetric map of the Benham Rise region - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin

Bathymetric map of the Benham Rise region - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin

On this basis, the study suggests that the peaks of the plateau have the morphology corresponding to a huge caldera about 150 km in diameter ... it was named caldera Apolaki, (in Filipino : "Giant Lord") qualifying the mythical god sun and war ... for comparison, the biggest calderas known are the Yellowstone (60 km), La Garita (35 x 75 km), Lake Toba (30 x 80 km).

Morphostructural characteristics of the Caldeira Apolaki (red dots). BB = Bank Benham. - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin

Morphostructural characteristics of the Caldeira Apolaki (red dots). BB = Bank Benham. - Doc. Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin

Bathymetry and geological and geophysical data define three main stages in Benham Rise's tectonic history: shield building, caldera formation, and post-caldera / late volcanism.

The base of the platform is thought to have formed on a hot spot under the central basin spreading center during the shield construction phase, between about 47.9 and 42.5 million years ago.

It is believed that the arrow-shaped Molave ​​spur formed late in this stage along a ridge that has spread far away from the hot spot.

The formation of the caldera followed and is presumed to have occurred before ~ ​​41.3-41.5Ma, when Benham Rise was still united to the Urdaneta Plateau.

The Narra spur was formed by late volcanism related to hot spots, the separation of Benham Rise and the Urdaneta Plateau, and ended with the eruptions of Mount Vinogradov at about 26Ma.

 

Further studies on Benham raise are needed not only to understand the processes that formed it, but also to study the possible impact of this LIP on its local and regional environments. Apolaki Caldera could be the biggest caldera in the world. The short but immense magmatic impulses, associated with its formation, had to modify the chemistry and the physics of the waters and the atmosphere in this part of the Pacific.

Full text: see sources.

 

Sources:
- Benham Rise unveiled: Morphology and structure of an Eocene broad igneous province in the West Philippine Basin - By Jenny Baretto, Ray Wood and John Milsom - link
- Scientists discover what might be the world's best known caldera - 08/11/2019 / GNS Science - link

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