Geological history and potential hazards of the late-Pleistocene to Recent Plat Pays volcanic complex, Dominica, Lesser Antilles

Abstract

During 1998During -2000, the island of Dominica in the Lesser Antilles experienced a major volcanic earthquake swarm spatially associated with volcanic centres in the south of the island. This swarm provided the motivation for a major re-assessment of geologic history and volcanic hazards in this region. This has led to a reinterpretation of the south-western-most corner of the island as a large volcanic complex, termed the Plat Pays volcanic complex, which has exhibited a wide range of past eruptive activity and which, in the Quaternary, experienced a major caldera collapse triggered by a voluminous pyroclastic eruption. Stratigraphy and new 14 C age determinations reveal a complicated history of development. The earliest activity is represented by the formation of the Plat Pays stratovolcano and associated parasitic domes. A major explosive eruptioñ 39,000 years b.p. produced the Grand Bay ignimbrite and triggered a major caldera collapse of the summit and south-western flank of the Plat Pays stratovolcano. Following the major eruption, re-injection of Plat Pays magma resulted in the extrusion of approximately 12 lava domes both within and outside the resulting depression. Caldera collapse was followed by at least one catastrophic flank collapse, but it is unclear whether or not this was triggered by caldera formation. The only on-shore evidence of flank collapse is the breach of the caldera rim and truncation of post-caldera deposits emplaced on or near the caldera rim; we find no evidence of on-shore large-magnitude rock avalanche deposits within the stratigraphic framework of the Plat Pays volcanic com-plex. Frequent seismic swarms of volcanic earthquakes and vigorous geothermal activity indicate that south Dominica is still underlain by an active magma reservoir system. Our new geological observations, combined with an interpretation of recent seismic swarm activity, suggest that an eruption (probably dome-forming) from the Plat Pays volcanic complex is probable within the next 100 years.

Stream geochemistry, chemical weathering and CO2 consumption potential of andesitic terrains, Dominica, Lesser Antilles

“…These low Ca:Mg ratios for Dominica rivers indicate the importance of the weathering of Mg-rich minerals in these watersheds. Previous studies on Dominica have shown that easily weathered Mgrich minerals such as pyroxenes (ortho-and clino-) and hornblende compose significant portions of both the phenocrysts and groundmass in the volcanic rock (Wills, 1974;Lindsay et al, 2003Lindsay et al, , 2005 and tephra/ignimbrite (Sigurdsson, 1972;Wills, 1974;Carey and Sigurdsson, 1980). These results are consistent with the mineralogy of the rock samples determined as part of this study (Section 4.3).…”

“…However, the relatively low Ca:Mg ratios of Dominica rivers are more consistent with those previously determined for basaltic terrains (0.9-3) by Dessert et al (2003) than with the higher Ca:Mg values characteristic of carbonates. Furthermore, a literature review did not identify the presence of calcite in any previous soil (Rouse et al, 1986;Walsh and Howells, 1988;Reading, 1991), bedrock (Wills, 1974;Sigurdsson and Carey, 1991;Lindsay et al, 2003Lindsay et al, , 2005Smith et al, 2003), or tephra/ignimbrite (Sigurdsson, 1972;Wills, 1974;Carey and Sigurdsson, 1980;Sparks et al, 1980) geochemical/mineralogical studies of the island. While the contribution of Ca 2+ from disseminated calcite cannot be ruled out in these systems, there are currently no data to support its occurrence.…”

“…In fact, the eruption was so voluminous it resulted in submarine pyroclastic flow deposition over 250 km into the Grenada backarc basin to the west and ash fall deposits throughout the North Atlantic to the east of the arc . Other notable Quaternary pyroclastic deposits include the >22 Ka to >40 Ka Grand Savanne Ignimbrite from Morne Diablotins (Sparks et al, 1980) and the 39 Ka Grand Bay Ignimbrite from the Trois Pitons-Micotrin volcanic center (Lindsay et al, 2003). Deposits of the Grand Savanne Ignimbrite extend outward in five radial tongues from Diablotin (Sparks et al, 1980) while outcrops of the Grand Bay ignimbrite can be found in the Geneva river valley (Lindsay et al, 2003).…”

“…Other notable Quaternary pyroclastic deposits include the >22 Ka to >40 Ka Grand Savanne Ignimbrite from Morne Diablotins (Sparks et al, 1980) and the 39 Ka Grand Bay Ignimbrite from the Trois Pitons-Micotrin volcanic center (Lindsay et al, 2003). Deposits of the Grand Savanne Ignimbrite extend outward in five radial tongues from Diablotin (Sparks et al, 1980) while outcrops of the Grand Bay ignimbrite can be found in the Geneva river valley (Lindsay et al, 2003). At present, there are seven active centers located on the southern end of the island, and nearly all of these areas have been active in the last 10 Ka (Lindsay et al, 2005).…”

Evolution of young andesitic–dacitic magmatic systems beneath Dominica, Lesser Antilles

“…Despite these studies, there is limited knowledge on the upper crustal magmatic conditions of the late Quaternary magmas as recorded in rock and mineral chemistry. Lindsay et al (2003) and Smith et al (2013). (C) Simplified geology map of the Plat Pays Volcanic Complex indicating major features.…”