Vestiges of the proto-Caribbean seaway: Origin of the San Souci Volcanic Group, Trinidad

Iain Neill,Alan R Hastie,Kevin R Chamberlain,Ian L Millar,Tiffany L Barry,Axel K Schmitt,James L Pindell,Andrew C Kerr,Franco Urbani

doi:10.1016/j.tecto.2014.04.019

Abstract

Outcrops of volcanic–hypabyssal rocks in Trinidad document the opening of the proto-Caribbean seaway during Jurassic–Cretaceous break-up of the Americas. The San Souci Group on the northern coast of Trinidad comprises the San Souci Volcanic Formation (SSVF) and passive margin sediments of the ~ 130–125 Ma Toco Formation. The Group was trapped at the leading edge of the Pacific-derived Caribbean Plate during the Cretaceous–Palaeogene, colliding with the para-autochthonous margin of Trinidad during the Oligocene–Miocene. In-situ U–Pb ion probe dating of micro-zircons from a mafic volcanic breccia reveal the SSVF crystallised at 135.0 ± 7.3 Ma. The age of the SSVF is within error of the age of the Toco Formation. Assuming a conformable contact, geodynamic models indicate a likely origin for the SSVF on the passive margin close to the northern tip of South America. Immobile element and Nd–Hf radiogenic isotope signatures of the mafic rocks indicate the SSVF was formed by ≪10% partial melting of a heterogeneous spinel peridotite source with no subduction or continental lithospheric mantle component. Felsic breccias within the SSVF are more enriched in incompatible elements, with isotope signatures that are less radiogenic than the mafic rocks of the SSVF. The felsic rocks may be derived from re-melting of mafic crust. Although geochemical comparisons are drawn here with proto-Caribbean igneous outcrops in Venezuela and elsewhere in the Caribbean more work is needed to elucidate the development of the proto-Caribbean seaway and its rifted margins. In particular, ion probe dating of micro-zircons may yield valuable insights into magmatism and metamorphism in the Caribbean, and in altered basaltic terranes more generally.

Highlights

Rifting of the supercontinent Pangaea and the opening of the Central Atlantic during the Mesozoic represents both a classic example of continental break-up and passive margin development, and an enduring enigma in assessing the role of mantle plumes in such a process (e.g., Callegaro et al, 2013; Hill, 1993; McHone, 2000)
We present new ion microprobe U–Pb zircon geochronology along with immobile element and Nd–Hf radiogenic isotope data from the San Souci Volcanic Formation of northeast Trinidad (Fig. 2), the easternmost exposure of igneous rocks on the Caribbean coast of South America
The simplest explanation for the ~108 Ma fission track ages from the Toco Formation is that they are the result of partial thermal resetting during metamorphism, whilst the Toco Formation itself was formed during the Barremian (~ 130–125 Ma) by accumulation of continentderived sediments on the proto-Caribbean passive margin

Summary

Introduction

Rifting of the supercontinent Pangaea and the opening of the Central Atlantic during the Mesozoic represents both a classic example of continental break-up and passive margin development, and an enduring enigma in assessing the role of mantle plumes in such a process (e.g., Callegaro et al, 2013; Hill, 1993; McHone, 2000). One branch of the Pangaea break-up story that has hitherto received little attention is the rifting of North and South America from the latest Triassic onwards (e.g., Bartok, 1993; Ostos et al, 2005). Fragments of proto-Caribbean crust which have been either accreted to the Caribbean Plate or thrust onto South America remain, from which the tectono-magmatic evolution of the proto-Caribbean oceanic crust have to be pieced together Many of these ‘fragments’ in South America have hitherto received little attention

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