The geology of the U.S. Virgin Islands includes mafic volcanic rocks, with complex mineralogy that first began to erupt in the Mesozoic overlain and interspersed with carbonate and conglomerate units.
Radiolarian chert deposited along with the submarine volcanic activity, accompanied by dikes and small plutons in the Careen Hill Intrusive Suite.
Pyroclastic flows are preserved on Saint Thomas, together with limited fossil-bearing limestone deposits and calcite cement in upper rock units.
On Saint John, the Tutu Formation is the youngest stratified unit, although volcanism continued on the neighboring British Virgin Islands until the Eocene.
The Narrows pluton and Virgin Gorda batholith, which are dominated by tonalite followed the episode of compression, forming around 39 million years ago in the Eocene.
The formation of the Cayman Trough produced the last significant tectonic feature on the islands after 39 million years ago, with sinistral strike-slip faults.