Evolutionary cycles during the Andean orogeny: repeated slab breakoff and flat subduction?

Abstract

Tectonomagmatic similarities between the modern Chilean flat‐slab region and pre‐Neogene magmatic episodes suggest that they represent analogues to flat subduction. Evolutionary patterns in each magmatic suite include (i) increasing La/Yb ratios and Sr‐and Nd‐isotopic enrichment through time, (ii) eastward‐migration of magmatism after periods of transpressional/transtensional intra‐arc deformation, and (iii) subsequent termination and virtual absence of main‐arc activity for 5–10 Myr. These patterns may reflect slab shallowing followed by flat subduction and thickening of the overlying crust. If repeated, they require interchanging episodes of slab steepening. Increasing convergence rates force slab kinking and eventual failure of the oversteepened slab, followed by rebound of the slab tip (owing to lack of further slab pull), flat subduction and termination of subduction‐related magmatism. Rapid subduction leads to shallow overriding of the detached slab fragment. Eclogitization of the gradually steepening slab tip at depth and subsequent slab pull permits asthenospheric corner flow and subduction‐related magmatism.

Continental crust formation at arcs, the arclogite “delamination” cycle, and one origin for fertile melting anomalies in the mantle

“…There is some evidence that magmatism in continental arcs, such as the Sierra Nevada, may be episodic [89]. There is also some tentative evidence for multiple delamination events in the Sierra Nevada [43,90] and the Andes in South America [91]. It is even likely that delamination events in continental arcs are closely coupled with foreland fold-andthrust belts because removal of arc lower crust and lithospheric mantle provides room for continental basement to be underthrust beneath the arc [92].…”

Reappraisal of the Geology and Geochemistry of Volcán Zamorano, Central Mexico: Implications for Discriminating the Sierra Madre Occidental and Mexican Volcanic Belt Provinces

“…Another important quest ion th at r e m ai n s to b e an s w er ed i s h ow subhorizontal subduction could give rise to voluminous subduction-related volcanism. In this regard, subhorizontal subduction of the Nazca plate beneath the Andes is postulated to cause a diminution or even cessation of arc-related volcanism (Kay et al, 1987;Haschke et al, 2002).…”

Initiation of the Wrangell Arc: A Record of Tectonic Changes in an Arc-Transform Junction Revealed by New Geochemistry and Geochronology of the ~29–18 Ma Sonya Creek Volcanic Field, Alaska

“…Additionally, continental crust thickened by underplated basalt metamorphosed to eclogite or amphibolite facies can melt and produce adakite-like magmas (Petford and Atherton, 1996;Arculus et al, 1999;Haschke et al, 2002;Karlsi et al, 2011). All the above scenarios are possible causes of SCVF adakite-like magmas, and resolving the nature of magma genesis will have tectonic implications for the initiation of the WA.…”

“…Melting of some mafic lower crustal garnet-bearing rock (i.e., eclogite or garnetamphibolite) can generate the adakite signature of elevated Sr/Y and La/Yb ratios (Petford and Atherton, 2003;Arculus et al, 1999;Haschke et al, 2002;Karlsi et al, 2011), and characterizing the difference between melting of in situ lower crust and melting of lower crust that has delaminated and sunk into the mantle can be accomplished by examining the MgO, Ni, and Cr contents of the resulting magmas (Xu et al, 2002;Wang et al, 2006;Karlsi et al, 2011 (Chiaradia, 2015). Adakites from China are shown to have been derived via melting of underplated basaltic magmas following delamination and sinking into the mantle (Xu et al, 2002;Wang et al, 2006).…”