Lecture: Diamond Eruptions
Speaker:
Entry Fee
Members: Free
Visitors: £5.00
Date and Time
19:30 -
Location
Bath Royal Literary and Scientific Institution, 16-18 Queen Square, Bath BA1 2HN
Lecture Description
Kimberlite volcanism typically involves the formation of diverging pipes or diatremes (see image below), which are the locus of high-intensity explosive eruptions. The talk will first provide an overview of diatreme formation. I will then focus on a conspicuous and previously enigmatic feature of diatreme fills known as ‘pelletal lapilli’ — well-rounded clasts that consist of an inner ‘seed’ particle with a complex rim, thought to represent quenched juvenile melt. Such clasts are widely documented in a range of pyroclastic successions on Earth, yet are not fully understood. New observations of pelletal lapilli in kimberlites show they coincide with a transition from magmatic to pyroclastic behaviour, thus offering fundamental insights into eruption dynamics and constraints on vent conditions.
We provide strong evidence that pelletal lapilli form by fluidized spray granulation — a coating process used widely in industrial applications, including the chocolate industry. We propose that pelletal lapilli are formed when fluid volatile-rich melts (akin to molten chocolate) intrude into earlier volcaniclastic infill close to the diatreme root zone. Intensive degassing produces a gas jet in which locally-scavenged particles are simultaneously fluidized and coated by a spray of low-viscosity melt. Most fine particles are either agglomerated to pelletal coatings or elutriated by powerful gas flows. The origin of pelletal lapilli is important for understanding how magmatic pyroclasts are transported to the surface during explosive eruptions, where they can be asociated with high diamond grades. A similar origin may apply to pelletal lapilli in a range of alkaline volcanic rocks.
Attending via Zoom
This is a hybrid meeting: you can attend in person or join online via Zoom.
Bath Geological Society Members: Free of charge. Joining instructions and the Zoom link are sent to members by email prior to the lecture.
Visitors & Non-Members: (including members of the Geologists' Association and affiliated societies) Please book via Eventbrite to receive Zoom access (see the Entry Fee details above).
How to join: Click the Zoom link provided in your email or Eventbrite confirmation. You can join using the Zoom desktop or mobile app, or directly via your web browser without installing any software. The virtual waiting room opens approximately 15 minutes before the scheduled start time, and attendees will be admitted before the talk commences.
For any queries about joining online, please contact [email protected].