https://doi.org/10.1130/G46708.1 Manuscript received 12 December 2018 Revised manuscript received 1 July 2019 Manuscript accepted 4 July 2019 © 2019 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Published online 12 August 2019 The role of arc migration in the development of the Lesser Antilles: A new tectonic model for the Cenozoic evolution of the eastern Caribbean R.W. Allen1, J.S. Collier1, A.G. Stewart2, T. Henstock3, S. Goes1, A. Rietbrock4, and the VoiLA Team* 1Department of Earth Sciences and Engineering, Imperial College London, London SW7 2BP, UK 2School of Earth Sciences, University of Bristol, Bristol BS8 1RL, UK 3Ocean and Earth Science, National Oceanography Centre, Southampton SO14 3ZH, UK 4Geophysical Institute, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany ABSTRACT tion-related rocks tracking migration eastward Continental arc systems often show evidence of large-scale migration both toward and through the Greater Antilles toward the Virgin away from the incoming plate. In oceanic arc systems, however, while slab roll-back and the Islands (Cox et al., 1977; Jolly et al., 1998), associated processes of backarc spreading and arc migration toward the incoming plate are convincing evidence for backarc spreading in commonplace, arc migration away from the incoming plate is rarely observed. We present the Grenada Basin (GB) to accompany this arc a new compilation of marine magnetic anomaly and seismic data in order to propose a new migration has yet to be found. Scarce regional tectonic model for the eastern Caribbean region that includes arc migration in both direc- seismic and well data mean that the geometry tions. We synthesized new evidence to show two phases of backarc spreading and eastward of any spreading, and the nature of the crust arc migration toward the incoming Atlantic. A third and final phase of arc migration to the underlying the basin are highly debated (Bird west subdivided the earlier backarc basin on either side of the present-day Lesser Antilles et al., 1999). It has even been suggested that arc. This is the first example of regional multidirectional arc migration in an intra-oceanic the GB is an extended forearc, leaving its role setting, and it has implications for along-arc structural and geochemical variations. The back in arc migration in the Paleogene highly uncer- and forth arc migrations were probably due to the constraints imposed by the neighboring tain (Aitken et al., 2011). A further unknown American plates on this isolated subduction system, rather than variations in subducting is the location of the southern arc during this slab buoyancy. time. Speed et al. (1993) recognized the need for a source of volcanic sediment here during INTRODUCTION down (e.g., Gerya et al., 2009). Such events the Eocene and Oligocene, yet they found no Arc migration is a common feature of oce- are commonly attributed to the subduction of magmatic evidence for an arc at the site of the anic subduction systems. When upper-plate large buoyant features, such as extinct mid- southern modern Lesser Antilles. extension results in backarc spreading, gen- ocean ridges or plateaus, which results in The final arc migration occurred in the ear- erally due to slab roll-back, arcs often split a flattening of the slab (Gerya et al., 2009; ly Miocene, when the Limestone Caribbees into extinct and active arc segments (Karig, Martinod et al., 2013). became extinct and the 750-km-long modern 1974). This results in the movement of both The eastern Caribbean is a complex region Lesser Antilles Arc (LAA) was established to the trench and active magmatic front toward with a history of island-arc migration (Fig. 1). the west. It has been proposed that this event the incoming plate. Arc migration in the op- Three separate subduction systems have been was triggered by the subduction of an oceanic posite direction, however, is very unusual and active at different times, although the mecha- ridge, causing the migration of the northern rarely impacts the whole arc front (e.g., Yang nisms that relate them are disputed. The oldest arc segment (McCann and Sykes, 1984). The et al., 1996). In contrast, in continent-ocean volcanic system is known as the Great Arc of southern portion of the LAA is assumed to have systems, arc migration in both directions is the Caribbean (GAC). This Cretaceous–Pa- formed in its current location with no interme- common. Migration away from the incom- leocene arc, of which the Aves Ridge is the diate phase of arc magmatism between extinc- ing plate of many hundreds of kilometers is clearest remaining expression, is identified tion of the GAC (ca. 59 Ma) and the initiation often accompanied by (temporary) arc shut- from remnants throughout the Dutch, Venezu- of LAA volcanism at ca. 25 Ma (Aitken et al., elan, and Greater Antilles and became extinct 2011; Bird et al., 1999). at ca. 59 Ma (Neill et al., 2011). Arc magma- In this study, we combined new magnetic *Volatile Recycling in the Lesser Antilles: Colin tism from 40 Ma is found on the islands of the (Fig. 2) and seismic (Fig. 3) data sets acquired Macpherson, Jon Blundy, Jon Davidson, Nick Har- Limestone Caribbees along the northeastern in the GB in C.E. 2016–2017 with existing geo- mon, Mike Kendall, Julie Prytulak, Catherine Rychert, Jeroen Van Hunen, Jamie Wilkinson, and Marjorie Caribbean plate boundary. Despite a record physical, geological, and geochronological data Wilson. of various early Paleocene to Eocene subduc- to test current models for the development of the CITATION: Allen, R.W., et al., 2019, The role of arc migration in the development of the Lesser Antilles: A new tectonic model for the Cenozoic evolution of the eastern Caribbean: Geology, v. 47, p. 891–895, https://doi.org/10.1130/G46708.1 Geological Society of America | GEOLOGY | Volume 47 | Number 9 | www.gsapubs.org 891 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/47/9/891/4819520/891.pdf by guest on 02 October 2021 A Figure 1. (A) Map of our understanding of both the structural varia- the Lesser Antilles tions along the LAA and the geochemistry of region highlighting its magmatic products. We consider it a unique the major tectonic fea- tures. Abbreviations: example of a retreating and advancing magmatic LAA—Lesser Antilles front in an oceanic arc setting. arc (red dashed line), LC—Limestone Carib- NEW MODEL FOR THE EVOLUTION bees (blue dashed line), AR—Aves Ridge (yellow OF THE LESSER ANTILLES dashed line), VI—Virgin Figure 2A shows our new reduced-to-pole Islands, BAP—Barba- magnetic anomaly chart for the study area. It dos accretionary prism, is a levelled compilation of over 320 scientific TBR—Tobago-Barbados cruises from 1950 to 2017 (full processing de- Ridge. Individual islands: 1 Gu—Guadeloupe, Ma— tails are provided in the GSA Data Repository ) Martinique, Gr—Grenada, and is a significant improvement on existing Bb—Barbados, Tb— B charts for the region (Ghosh et al., 1984). Two Tobago, May—Mayreau, of these cruises, JC133 and JC149 on the RRS Car—Carriacou; Ld—La Désirade; Do—Dominica. James Cook, conducted as part of the VoiLA (B) Temporal framework (Volatile Recycling in the Lesser Antilles; http:// of arc magmatism in the www.voila.ac.uk) project, also acquired north- eastern Caribbean. A full south–oriented multichannel seismic reflection breakdown of tectono- and wide-angle refraction profiles in the GB magmatic affinities and geochronology is provided in the Data Repository (section 3 and Fig. DR8 [see footnote 1]). (Fig. 3). Wide-angle profiles (see full process- GAC—Great Arc of the Caribbean; LC—Limestone Caribbees; CMQZ—Cretaceous magnetic ing details in the Data Repository) were modeled quiet zone. The geomagnetic polarity time scale is shown for reference (Cande and Kent, using the software RAYINVR (Zelt and Smith, 1995). Q—Quaternary; Pal—Paleocene; Ol—Oligocene; Plio—Pliocene. 1GSA Data Repository item 2019326, extended LAA. We propose a new model for the tectonic entire arc front, then divided the previous back- discussion regarding the processing methodology of evolution of the region in which the Eocene arc into the GB and Tobago Basin (TB). The magnetic and seismic data discussed in the paper, and magmatism (of which the Limestone Caribbees model explains several of the disputed aspects of a detailed breakdown of geochemical data and stud- are the only clear expression) was present to the region’s development and is more consistent ies used to define the three stages of arc volcanism shown in Figure 1, is available online at http://www. the east of the entire length of the current arc. with current geodynamical models of subduc- geosociety.org/datarepository/2019/, or on request A Miocene westward migration, again along the tion behavior. It has significant implications for from [email protected]. ABC D Figure 2. Magnetic and gravity data for the Caribbean region. (A) New regional magnetic anomaly grid. CLIP—Caribbean large igneous prov- ince; BAP—Barbados accretionary prism; CMQZ—Cretaceous magnetic quiet zone. (B) Detail of new magnetic anomaly grid over the Aves Ridge (outlined in yellow), Lesser Antilles arc (LAA, red line), and Outer arc (blue line marked with LC [Limestone Caribbees]). Black dashed line denotes potential extent of backarc spreading. Bb—Barbados. (C) Cartoon of key features in the anomaly grid over the LAA. Regions of normal magnetic anomaly polarity are shown in orange, with reverse in blue. (D) Cross section through magnetic grid along the profile shown in A. Magnetic highs are associated with Aves Ridge, LAA, and outer arc magmatism. Note symmetrical spreading anomalies in the Aves Ridge backarc and Grenada Basin (labeled 1–1′, etc.).