In November 2021, I had the great pleasure of going to the amazing British Virgin Islands with my French friends Leny Montheil (PhD student at the University of Montpellier, under my co-supervision), Mélody Philippon (University of the Antilles, Guadeloupe) and Jean-Jacques Cornée (University of Montpellier). The aim was to collect paleomagnetic data from Eo-Oligocene granites that are widely exposed on the islands, in context of Leny’s reasearch on the tectonic contributions to the paleogeographic evolution of the NE Cairbbean region since the Eocene. We also hunted for future research opportunities and projects, and ran into some interesting geology! The Virgin Islands have a strong metamorphic and tectonic history that remains poorly resolved and that has intrigued me, so I can’t wait to return! Below, a picture impression of one of my favorite fieldworks so far.
The participants: Leny Montheil, PhD student at the University of Montpellier, France, and the lucky bastard who gets to do a PhD on Caribbean islands!
Mélody Philippon, Associate Professor at the University of the Antilles at Guadeloupe
Jean-Jacques Cornée, professor at the University of Montpellier, France
…an me!
En route from St. Maarten to the BVI!
…ready for landing on Beef Island
The aim of the trip was to collect paleomagnetic data from granites. These granites are coarse-grained, which is bad for paleomagnetism (such rocks are often ‘multi-domain’, which means that each magnetic mineral contains multiple magnetic domains that cancel each other out). So we collected samples from finer-grained, and more magnetic mafic enclaves, dark ‘droplets’ of basaltic or andesitic melts in the granites.
Here, we’re sampling such mafic enclaves, next to the house we rented on Virgin Gorda.
The granites are part of a ~40-30 million year old volcanic arc – they’re essentially old magmachambers that formed some 10 km or so below volcanoes. At the bottom of such chambers, you find the dark, mafic stuff that crystallizes first, cut by felsic dykes (the white bands)
The dark and white magmas co-existed: sometimes the dykes of dark, mafic magma also cuts the white granites, like here.
…and the magmas intruded into an older part of the magmatic arc, that became sheared and metamorphosed in the amphibolite facies – never really studied before, but we’re excited to get going on it!
Leny, measuring on the rocks
Leny, walking down from the copper mine on Virgin Gorda to the granites we sampled.
The copper is not native to the granite, but formed in secondary cracks and crystallized as the mineral malachite, with its characteristic green color.
Me, enjoying some granite
The most famous spot on Virgin Gorda is the Baths, big rounded boulders of granite (they weather that way) on the west coast. Not a bad place indeed…
To visit the other islands with granites – Norman, Peter, Cooper, Salt, and Fallen Jerusalem – we hired a boat wiith captain Dave. And that was a real pleasure!
A great place to think and enjoy the phenomenal view of the Caribbean Sea between the hardrock peaks of the BVI . With an occasional megalomaniac yaught in the distance.
View from Peter IslandThe beaches and amphibolite exposures of Salt Island … someday we have to camp here and map the whole thing!
The most beautiful of the islands: Fallen Jerusalem, which is called that way because it looks like a ruined city due to the large, rounded blocks of granite.
When you see these cliffs, you can suddenly imagine why there are so many shipwrecks in the Caribbean. Imagine hitting these cliffs in a storm at high seas…
Mélo and I, on our way to the next island
Mélo and Leny, cooling down after a hot site
On our way back to Virgin Gorda, after a coctail on Cooper Island
This welcoming sign on Peter Island didn’t stop us from collecting a good set of samples.
Typical view on the BVI
The last island we visited was Necker Island, in the east. This is a private island of Richard Branson (his mansion is located at the top of the hill in the tropical park), but we were welcome to sample the tuffs there. Can’t wait to work out what their relationship with the granites are…we expect some serious faults.
The redeposited tuffs and volcanic breccias of the Necker Formation
Branson’s lemurs
…and tortoise
Hermite crab!
Lizards
More lizards!
Caterpillars
…more caterpillars
The beaches are littered with large shells
The British Virgin Islands is certainly one of the most beautiful and inspirational places I have been. We have developed advanced plans for proposals, and we certainly intend to let this not be the last time we’ve done fieldwork here!
