EAST TENNESSEE GEOLOGICAL SOCIETY

October 2026 Virtual Meeting

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Monday, October 12, 2026
6:00 - 7:30 pm

Note: ETGS members will receive an email with info for logging into the meeting.
 

October Presentation

Suggested Origin Of Middle Paleozoic Hypogene Karst From Magmatism From Pacific Floor Subducted Slabs

By

Gareth Davies, TDEC (Retired)

Investigation of karst typically involves geomorphology and shallow hydrology and exploration of caves. Caves are known to form in almost all lithologies, only requiring enough geological time and variable, sometimes extreme conditions. Lowe (1991) uses inception horizons: faults, unconformities, and shale beds, as cave/conduit pathway initiators, with inferred timing is as far back as post lithification and diagenesis. Some caves have known hydrothermal association and ore deposits often replace carbonates and are often found in paleokarst.

Hypogene karst needs hydrothermal fluid sources, typically from the mantle. Recent interpretation of modeled seismic data and 3D tomographic imaging of subducted Pacific Floor slabs from ~180 Ma shows no flat slab subduction, but, in most cases, steep slab failure and treacle-like pile up in the mantle (Sigloch and Mihalynuk, 2017). In addition, offshore Pacific terrane acretions and arc/trench volcanism are known from tracked plate motions, mapping and advanced paleomagnetic data.

Imaging shows broken off subducted Pacific Floor slabs did not assimilate and piled up on the outer core. Beneath the westward drifting North American Plate this caused intraplate magmatic activity, hot spots and rifting zones across the North America. Current images show the older subducted Farallon Plate debris presently under the Eastern U.S. Modeled seismic data produce images to - 1,800 km depth (Sigloch, 2013).

This suggests correlation of magmatic activity and rising mantle fluids with hypogene karst formation in Mid Paleozoic (Early Mississippian/ Carboniferous) rocks in the U.S. (from west to east). Radiometric dates of secondary deposits from hypogene caves in the US west and mid continent correlate with this based upon slab sinking rates and the NA plate drift rate. They are Late Mesozoic and Cenozoic ages.

An anomaly. An intense maze cave in south central Tennessee is formed in both clastic and carbonate rocks through the complicated and incomplete Silurian-Devonian-Mississippian stratigraphic interval. The cave has hydrothermal features as well as more recent fluvial features. The cave stream has normal temperature but extremely low dissolved solutes, appears to be old water but appears meteoric. This is similar to Fort Payne Formation water (that formation contains part of the cave). Less likely it is from the Precambrian Granite-Rhyolite province continental basement, - 1,520 m deep. However, a nearby well has penetrated fresh water near this depth (~1,500 m) in the Upper Cambrian (Knox Group) Copper Ridge Dolomite, that has similar chemistry and thus also possibly a source. But, recent mantle fluid sources are missing. So, what else might have influenced the formation of this cave?.
 

Biography

Gareth grew up in South Wales in a coal-mining community, next to a major karst area, and thus was interested in caves from the age of 15. He spent many years traveling in Asia, Europe, North America and Mexico exploring caves before marrying and moving to the US. He was awarded a BS degree from Millsaps College and an MS degree from the University of Southern Mississippi. His thesis dated speleothems from Tennessee cave using the uranium-thorium method. He moved to Oak Ridge and spent a couple of decades running his own company doing multiple tracer work from Puerto Rico to the US Rocky Mountains. After being a contractor, he later joined TDEC (now retired). He is a Fellow of the Geological Society of America.

 

 

Greetings, and welcome to the October 12, 2026 ETGS virtual meeting.
 

This meeting will be attended via Zoom and as a courtesy please mute your cell phone or the microphone in your laptop/tablet to minimize background noise and feedback echos. We will also make an effort to mute all participants - at least until the presentation is finished. Please use the chat feature to type any comments or questions you may have. We recommend that you send questions for the speaker to "everyone" so all participants can see the question. In the interest of time, we may hold the Q&A at the end of the presentation.

We will create a virtual attendance list. It is not always possible to tell who is participating on-line, especially for those joining by phone, so please email etgs@etgs.us to be listed on the attendance sheet. Let us know exactly how your name should appear on the list. We will add a note explaining the lack of signatures due to remote participation and have an ETGS officer sign as usual.

Thank you for your patience and understanding as we continue with this online format. As always, we welcome and appreciate your feedback and suggestions for improvement.

 

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President
Tony McClain

Vice President
David Carlone

Secretary
J. Brad Stephenson

Treasurer
Seaira Stephenson

Webmaster/Social Media Coordinator
Bob Gelinas

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Page updated October 06, 2026