Phanerozoic record of mantle-dominated arc magmatic surges in the Zealandia Cordillera

M.F Ringwood,A.J Tulloch,R.E Turnbull,J.J Schwartz

doi:10.1130/g48916.1

Abstract

Abstract We integrated new and existing bedrock and detrital zircon dates from the Zealandia Cordillera to explore the tempo of Phanerozoic arc magmatism along the paleo-Pacific margin of southeast Gondwana. We found that episodic magmatism was dominated by two high-magma-addition-rate (MAR) events spaced ∼250 m.y. apart in the Devonian (370–368 Ma) and the Early Cretaceous (129–105 Ma). The intervening interval between high-MAR events was characterized by prolonged, low-MAR activity in a geographically stable location for more than 100 m.y. We found that the two high-MAR events in Zealandia have distinct chemistries (S-type for the Devonian and I-type for the Cretaceous) and are unlikely to have been related by a repeating, cyclical process. Like other well-studied arc systems worldwide, the Zealandia Cordillera high-MAR events were associated with upper-plate deformation; however, the magmatic events were triggered by enhanced asthenospheric mantle melting in two distinct arc-tectonic settings—a retreating slab and an advancing slab, respectively. Our results demonstrate that dynamic changes in the subducting slab were primary controls in triggering mantle flare-up events in the Phanerozoic Zealandia Cordillera.

Highlights

Phanerozoic continental arcs are factories for the growth and refinement of modern continental crust (e.g., Rudnick, 1995; Hawkesworth and Kemp, 2006)
Others have noted that many arc segments do not display patterns of 30–70 m.y. high-magmatism was dominated by two highmagma-addition-rate (MAR) events (e.g., Kirsch et al, 2016), and in these cases, episodic magmatic surges may be driven instead by enhanced mantle melting rather than upper-plate deformation (e.g., Cecil et al, 2018). These conflicting views on the significance of episodic magmatic surges create an important and unresolved question in arc petrology: what processes drive the initiation of high-MAR events in continental arcs? Are they triggered by upper-plate compression and related phenomena, or are they triggered by mantle processes such as changes in subduction zone dynamics related to lowerplate geometry and/or changes in volatile or melt contributions?. We addressed these questions by integrating >380 new and existing bedrock zircon ages with >2280 detrital zircon ages from 46 samples deposited on the Zealandia Cordillera to investigate the tempo of arc magmatism and the causes of high-MAR events (Figs. 1A and 1B)
Plutonic samples spanned the entire age range of magmatism in the Zealandia Cordillera, and we focused exclusively on arcrelated magmatic rocks and excluded smallvolume dikes and nonsubduction rocks

Summary

Introduction

Phanerozoic continental arcs are factories for the growth and refinement of modern continental crust (e.g., Rudnick, 1995; Hawkesworth and Kemp, 2006). We addressed these questions by integrating >380 new and existing bedrock zircon ages with >2280 detrital zircon ages from 46 samples deposited on the Zealandia Cordillera to investigate the tempo of arc magmatism and the causes of high-MAR events

Results

Conclusion