Primitive Magmas in the Early Central American Volcanic Arc System Generated by Plume-Induced Subduction Initiation

Scott A Whattam

doi:10.3389/feart.2018.00114

Abstract

Primitive lavas with Mg# ≥60 have been identified in the literature from the Sona-Azuero, Golfito and Chagres-Bayano forearc segments of southern Costa Rica and Panama of the early (75-39 Ma) Central American Volcanic Arc system (CAVAS). Primitive CAVAS basalts are remarkably similar in terms of major and many trace elements to primitive MORB and primitive basalts of the Mariana Arc. Significant differences however, are apparent between primitive lavas of Chagres-Bayano relative to those of Sona-Azuero and Golfito. Primitive Chagres-Bayano lavas record much higher degrees of partial melting and higher amounts of shallow and deep subduction additions (e.g., higher Ba/Th, Th/Nb) than those of the older Sona-Azuero and Golfito arc segments which reflects the early petrologic and tectonic evolution of the CAVAS which is similar to other forearc systems. As shown in previous studies, early CAVAS lavas are exceptionally similar in radiogenic isotopic composition to those of the Caribbean Large Igneous Province (CLIP) oceanic plateau at 90 Ma, the approximate timing of onset of the volumetrically dominant phase of CLIP magmatism. This recognition is consistent with subduction initiation models which require plume-subduction interaction. Such models also dictate that an elevated sub-arc thermal anomaly was present at inception of the CAVAS. It is postulated that in addition to providing an anomalously high temperature regime in the sub-arc mantle at inception of the CAVAS, that extrusion of the CLIP also resulted in lithospheric weakening and extension which allowed for production and rapid ascent of a high percentage of primitive lavas.

Highlights

Subduction zone magmatism results primarily due to slab dehydration and the subsequent transfer of fluids from the dehydrating and metasomatically altered oceanic slab and its sediment cover to the mantle wedge where partial melting occurs (Tatsumi et al, 1983; White and Patchett, 1984; McCulloch and Gamble, 1991; Hawkesworth et al, 1993a,b; Plank and Langmuir, 1993; Ishikawa and Tera, 1999)
In the study of Etrography, Alteration, and Low-T Metamorphism. As this is a study of data in the literature, most samples discussed are not available for petrographic description
In the aforementioned papers there is no mention of olivine apart from it comprising the non-arc related plateau and enriched Type II basalts (Buchs et al, 2010; Whattam et al, under review)

Summary

Introduction

Subduction zone magmatism (see review of Pearce and Peate, 1995) results primarily due to slab dehydration and the subsequent transfer of fluids from the dehydrating and metasomatically altered oceanic slab and its sediment cover to the mantle wedge where partial melting occurs (Tatsumi et al, 1983; White and Patchett, 1984; McCulloch and Gamble, 1991; Hawkesworth et al, 1993a,b; Plank and Langmuir, 1993; Ishikawa and Tera, 1999). The diagnostic chemical signature of subduction zone magmas is enrichment of large ion lithophile elements (LILE) relative to the light rare earth elements (LREE) and high field strength elements (HFSE) (e.g., Arculus, 1994). This signature is a function of a variety of parameters, for example, the mode and extent of partial melting, composition and thermal state of the mantle, and the relative contributions of fluids and sediments to the source. Estimates of the mass proportion of continents formed at subduction zones are of the order of ∼85–95% (Rudnick, 1995; Barth et al, 2000)

Results

Discussion

Conclusion