Lateral variation in crustal structure along the Lesser Antilles arc from petrology of crustal xenoliths and seismic receiver functions

Abstract

13We reconstruct crustal structure along the Lesser Antilles island arc using an inversion 14 approach combining constraints from petrology of magmatic crustal xenoliths and seismic 15 receiver functions. Xenoliths show considerable island-to-island variation in xenolith 16 petrology from plagioclase-free ultramafic lithologies to gabbros and gabbronorites with 17 variable proportions of amphibole, indicative of changing magma differentiation depths. 18Xenoliths represent predominantly cumulate compositions with equilibration depths in the 19 range 5 to 40 km. We use xenolith mineral modes and compositions to calculate seismic 20 velocities (v P , v S ) and density at the estimated equilibration depths. We create a five-layer 21 model of crustal structure for testing against receiver functions (RF) from island seismic 22 stations along the arc. Lowermost layer (5) comprises peridotite with physical characteristics 23 *Manuscript Click here to view linked References Highlights 44  Arc crustal structure modelled by integrating petrology of 230 igneous xenoliths with 45 seismic data from 23 islands 46  Crust comprises four layers defined on basis of xenolith composition, calculated 47 seismic properties and receiver functions 48 3  Steep lateral velocity gradients and irregular along-arc variations in depth to Moho 49 and mid-crustal discontinuity 50  Lateral variation consistent with island-to-island variation in xenolith petrology 51  Velocity structure reflects heterogeneous upwelling within the mantle wedge, driven 52 by variation in slab-derived H 2 O fluxes 53 54

Petrological and experimental constraints on magma storage for large pumiceous eruptions in Dominica island (Lesser Antilles)

“…These results are confirmed and extended to the whole active arc by a recent reconstruction of the crustal structure using an inversion approach combining petrology of magmatic crustal xenoliths and seismic receiver functions ( Fig. 9a; Melekhova et al 2019). Both studies agree that the mid-crustal discontinuity beneath Dominica is located at~13-16 km, i.e.…”

“…At the Antilles arc, one explanation for the voluminous storage region in Dominica being deeper than the ones on the neighbouring volcanic islands could be an along-arc fluctuation of the crustal structure. Indeed, previous seismic refraction studies suggested significant differences in the crust thickness, with the thickest one being under Dominica (up to 37 km; Melekhova et al 2019) and in the depth of the middlelower crust interface, with variations from 2 to 20 km (Boynton et al 1979;Macdonald et al 2000;Melekhova et al 2019). However, this mid-crustal discontinuity could be at similar depth below Martinique, Montserrat and Dominica ( Fig.…”

“…9 Schematic section of the crust below Dominica. a P wave velocity (Vp) structure beneath the Lesser Antilles arc, modified from Melekhova et al (2019). The Vp of 6.0 km/s outline the upper crust, 6.8 km/s delimit the middle crust and 7.8 km/s outline the lower crust, the basis of which marks the Moho discontinuity with the upper mantle.…”

Evidence for an Active, Transcrustal Magma System in the Last 60 ka and Eruptive Degassing Budget (H2O, CO2, S, F, Cl, Br): The Case of Dominica

“…Balcone‐Boissard et al (2018) and Solaro et al (2019) determined that the magma(s) feeding the ignimbrite eruptions were stored at a depth of approximately 16 km beneath Dominica. Using crustal density models of Kopp et al (2011) and Melekhova et al (2019) to the North of Dominica, Solaro et al (2019) deduced that these depths correspond to the boundary between the lower and middle crusts. According to the same crustal models, our results suggest storage of the magmas that fueled the plinian eruptions at the limit between the middle and upper crusts, or within the upper crust.…”

“…A number of studies thus suggest that a magma ponding zone is commonly developed at a depth of approximately 5 to 8 km beneath the islands of the Lesser Antilles arc, corresponding to the limit between upper and middle crusts, according to the crust model proposed by Melekhova et al (2019). The wide range of storage depths beneath Dominica (Balcone‐Boissard et al, 2018; Solaro et al, 2019; this study), Martinique (Annen et al, 2008; Martel et al, 1998; Pichavant et al, 2002), Guadeloupe (Pichavant et al, 2018), and Montserrat (Devine et al, 2003; Edmonds et al, 2016) is in good agreement with a transcrustal magma system (Cashman et al, 2017) and allows to suspect such plumbing systems also beneath other, less‐studied islands of the Lesser Antilles arc.…”