Plume overriding triggers shallow subduction and orogeny in the southern Central Andes

Highlights

• Tectonic reconstructions indicate Neogene plume-subduction interaction in the Andes.

• Plume overriding correlates with slab shallowing and regional contraction.

• This event is interpreted as a plume-modified orogenesis stage.

Abstract

Plate tectonic theory implies that mantle plumes may be eventually overridden by lithosphere during continental drift. These events have particular tectonomagmatic consequences for active margins and hence related orogenic processes. Since the first documentation of plume overriding and the definition of the plume-modified orogeny concept, only few examples have been recognized in the geologic record. In this study, we analyze the Neogene tectonic evolution of the Southern Central Andes between 35° and 38°S and its potential relation to the subduction of the Payenia plume as a recent analogue of this process. Through a series of tectonic reconstructions we show that progressive Payenia plume overriding correlates with Neogene arc-front migrations linked to slab shallowing, fold belt reactivation in the Main Cordillera and intraplate contraction in the San Rafael block. Additionally, Nazca slab tear determined from tomographic analyses and subsequent diachronous steepening of the subducted plate may also be an aftermath of plume subduction as often described in the final stages of plume-modified orogeny. Finally, we propose a modern analogue for processes previously described, dating back to the Mesoproterozoic, which provides further insights into these complex settings.

Introduction

Plume-subduction zone interaction is nowadays recognized as a relatively common geodynamic phenomenon and a direct consequence of plate tectonics (Murphy et al., 1998, Fletcher and Wyman, 2015, Mériaux et al., 2016, Chang et al., 2016). During this process weak mantle plumes may be suppressed and eventually destroyed if subduction-related mantle flow distorts the plume structure (Druken et al., 2014, Kincaid et al., 2013, Steinberger and O'Connell, 1998). Nevertheless, some plumes may evade subduction leaving particular tectonomagmatic imprints on the upper plate and associated non-collisional orogenic belts. To date, only few examples of this process have been identified in the geologic record (Murphy et al., 1998, Murphy et al., 1999, Dalziel et al., 2000, Betts et al., 2009). In these cases introduction of a plume-related buoyant swell into a convergent margin may trigger changes in the slab angle leading to flat or shallow subduction (Murphy et al., 1998, Murphy and Keppie, 2005, Betts et al., 2009, Betts et al., 2015) (Fig. 1). Such subduction style produces upper plate contraction, a time-transgressive migration of orogenic and magmatic activity into the continental interior, and the eventual cessation of arc magmatism. Additionally, trench advance produced by plume-margin interaction may also contribute to crustal shortening in the overriding plate (Betts et al., 2012) (Fig. 1). Noteworthy, characteristic magmatic responses of mantle plumes, such as flood basalts and dyke swarms, may be inhibited during subduction because the plume is less likely to undergo adiabatic melting (Druken et al., 2014, Murphy, 2016) (Fig.1). Transient upper plate contraction produced by plume-slab contact at a convergent setting has been defined as “plume-modified orogeny” by Murphy et al. (1998). This peculiar process usually ends when the subducting oceanic lithosphere founders due to the buoyancy contrast between the plume and the overlying slab (Murphy et al., 1998, Murphy et al., 1999, Dalziel et al., 2000) or breaks-off, which could be facilitated by the presence of weaknesses in the slab (Macera et al., 2008, Obrebski et al., 2010) (Fig. 1). The final stages of plume-modified orogenesis are usually followed by slab steepening, rollback, renewal of slab-pull and plume impact below the upper plate (Betts et al., 2009, Dalziel et al., 2000, Murphy et al., 1998, Oppliger et al., 1997) (Fig. 1). Among the few documented examples of plume-modified orogeny are the Laramide Orogeny potentially linked to the latest Cretaceous-Paleogene subduction of the ancestral Yellowstone plume (Murphy et al., 1998, Murphy, 2016), Middle to late Paleozoic Acadian orogeny in the northern Appalachians (Murphy et al., 1999, Murphy and Keppie, 2005), Neopaleozoic Gondwanic orogeny triggered by overriding of the Karroo plume (Dalziel et al., 2000) and regional contraction throughout eastern and central Mesoproterozoic Australia (Betts et al., 2009). Similarly to these examples, we suggest based on tectonic reconstructions, that recent tectonic activity associated with the Neogene reactivation of the Southern Central Andes could have been modified when the South American margin overrode an ancient expression of the Payenia plume, a recently identified mantle anomaly beneath the Andean retroarc (Burd et al., 2014) (Fig. 2).

Neogene overriding of this plume by the South American plate explains a number of apparently unconnected tectonic events in the Andes between 35°S and 38°S that are not accounted by current tectonic models.