UC Santa Barbara geologist Jim Boles found evidence of helium leakage from the Earth’s mantle along a 30-mile stretch of the Newport-Inglewood Fault Zone in the Los Angeles Basin.
He claims the results show that the Newport-Inglewood fault is deeper than scientists previously thought.
Using samples of casing gas from two dozen oil wells ranging from LA’s Westside to Newport Beach in Orange County, Boles discovered that more than one-third of the sites show evidence of high levels of helium-3 (3He).
‘The results are unexpected for the area, because the LA Basin is different from where most mantle helium anomalies occur,’ said Boles, professor emeritus in UCSB’s Department of Earth Science.
‘The Newport-Inglewood fault appears to sit on a 30-million-year-old subduction zone, so it is surprising that it maintains a significant pathway through the crust.’
Considered primordial, 3He is a vestige of the Big Bang, and its only terrestrial source is the mantle.
Boles’s findings appear in Geochemistry, Geophysics, Geosystems (G-Cubed), an electronic journal of the American Geophysical Union and the Geochemical Society.
When Boles and his co-authors analyzed the 24 gas samples, they found that high levels of 3He inversely correlate with carbon dioxide (CO2), which Boles noted acts as a carrier gas for 3He.
An analysis showed that the CO2 was also from the mantle, confirming leakage from deep inside the Earth.
Blueschist found at the bottom of nearby deep wells indicates that the Newport-Inglewood fault is an ancient subduction zone – where two tectonic plates collide – even though its location is more than 40 miles west of the current plate boundary of the San Andreas Fault System.
Found 20 miles down, blueschist is a metamorphic rock only revealed when regurgitated to the surface via geologic upheaval.