GEOCHEMISTRY AND MAGMATIC EVOLUTION OF MORNE PATATES VOLCANO AND NEIGHBORING LAVA DOMES, DOMINICA, LESSER ANTILLES

Dominica is located in the center of the Lesser Antilles island arc and has produced the most explosive and most voluminous eruptions in the arc. Whereas all the other islands have only one potentially active volcano, Dominica has eleven, making its inhabitants particularly vulnerable to volcanic hazards.

The Plat Pays volcanic complex (PPVC), situated at the southern end of Dominica, consists of the main Plat Pays stratovolcano, the smaller Morne Patates volcano and 12 lava domes. Together, they comprise the youngest eruptions on Dominica, the most recent of which emanated from Morne Patates 450-685 years BP. Approximately 28 ka ago, the Plat Pays stratovolcano underwent a catastrophic collapse of its southwestern flank. Subsequently, from within the sector collapse scar, Morne Patates volcano and several lava domes emerged. We have initiated a detailed petrographic, geochemical and isotopic investigation of Morne Patates and neighboring post-collapse lava domes to determine if they are petrogenetically related to the main Plat Pays stratovolcano or if they comprise a distinct volcanic center.

We have collected a suite of volcanic rocks from Plat Pays and Morne Patates, as well as nearby lava domes within the sector collapse scar, for major and trace element and Sr, Pb and Nd isotopic analysis to investigate petrogenetic relationships amongst individual eruptions within the PPVC and the Plat Pays stratovolcano. Samples from the lava domes and pumice fall deposits are all dacitic, with ~63 wt% SiO₂. Our preliminary isotopic and trace element data for the PPVC samples display limited variations, with ⁸⁷Sr/⁸⁶Sr ranging from 0.7043 to 0.7045. The limited compositional variations in the PPVC lava and pumice samples suggest that the eruptions within the Plat Pays sector collapse scar may have tapped a common magma source. However, mafic enclaves (48-58 wt% SiO₂) found in abundance within the Morne Patates lavas are isotopically distinct from their hosts (both more and less radiogenic). These data suggest that the Morne Patates magma chamber evolved by complex processes involving recharge and mingling with more mafic magmas originating from sources distinct from those of the PPVC, thereby revealing a more complex evolution of the Morne Patates volcano compared to that of the lava domes in the PPVC.