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Lake Rotorua

16 February 2024
Electromagnetism, Geology

At https://www.livescience.com/planet-earth/bizarre-magnetic-anomaly-discovered-deep-below-new-zealands-lake-rotorua … Lake Rotorua sits in the crater of a dormant volcano and has been mapped, or 68% of it, in detail. This has revealed a hidden hydrothermal system beneath the lake. Clouds of steam drift around the lake shore and sulfur provides a blue-green colouration to the water. It is a tourist must visit site. Magnetic surveys come up with positive anomalies – but in this case it was a negative anomaly. An absence of magnetism. Volcanic rocks typically  contain the magnetic mineral magnetite. However, researchers think hydrothermal fluids have poured through the rocks, transforming magnetite into pyrite – otherwise known as fools gold. This has no magnetic signal – and would explain the mystery.

At https://phys.org/news/2024-02-rio-grande-giant-mineral-rich.html … in this case the Rio Grande Rise, possibly once a continental basalt plateau. Not far away is a chain of submerged sea mounts, suggesting volcanism at some point in the past. The research was undertaken by the University of Sao Paulo – with some input, or equipment, courtesy of the University of Southampton. The Rio Grande Rise lies in the South Atlantic, 1200 km off shore from Brazil. It may once have been a giant tropical island – rich in minerals and covered in vegetation. How does that fit into the concept of Pangaea?

Geologists have dated sediments from the Rise to between 45 and 40 million years ago. Red clay in the sediments was formed after the last episode of volcanic activity around 45 million years ago. The island probably dates between 40 and 30 million years ago as the soil, or red earth, is similar to soils in many parts of Sao Paulo State. The Eocene, on the geochronology column, dates from 56 to 34 million years ago. The current interest in the Rio Grande Rise is economical as it contains cobalt, nickel, and lithium, as well as tellurium and rare earths critical for renewable energy.

At https://www.sciencedaily.com/releases/2024/02/240206144920.htm … we are looking at the origin of the Seattle Fault. It is in fact a network of shallow faults slicing through Paget Sound. It is thought to be a source of seismic activity in what is now a well populated region. In this we are back to the Eocene, again. At that time the coastline was well east of where Seattle sits now and a chain of volcanic islands lay offshore. Apparently, at the beginning of the Eocene, the island chain was pulled towards the continent – and while some of it was swallowed [subducted] a lot of it went up and above the continental crust. This is said to have created a tear zone. This is part and parcel of the Seattle Fault.

It is known the fault ruptured in AD923-924 – based on local indigenous oral tradition as well as geological evidence along the Paget Sound shoreline.

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