Along-Strike Rapid Structural and Geomorphic Transition From Transpression to Strike-Slip to Transtension Related to Active Microplate Rotation, Papua New Guinea

Lei Sun,Paul Mann

doi:10.3389/feart.2021.652352

Abstract

The area of southeastern Papua New Guinea includes three active microplates – the Trobriand, Woodlark, and Solomon Sea plates – that are being deformed by regional convergence between the much larger Pacific and Australian Plates. The landward extent of the plate boundary between the Trobriand and Australian Plates corresponds to the Owen-Stanley Fault Zone (OSFZ), an onland and continuous 510 km-long left-lateral strike-slip fault that forms a linear, intermontane valley within the elongate Owen-Stanley Range (OSR) and continues as a 250 km-long low-angle normal fault along the margins of Goodenough and Woodlark basins. GPS geodesy reveals that the Trobriand microplate has undergone rapid counter-clockwise rotation since the Late Miocene (8.4 Ma) and that this rotation about a nearby pole of rotation predicts transpressional deformation along the 250 km-long northwestern segment of the OSFZ, strike-slip motion along a 100 km-long central segment, and transtension along the 270 km-long ESE-trending southeastern segment of OSFZ. In order to illustrate the along-strike variations in neotectonic uplift resulting from the changing structure of the OSFZ, we delineated 3903 river segments in the northeastern side of the OSR drainage divide and derived river longitudinal profiles along each river segment. Normalized steepness indices (ksn) and knickpoint clusters are the highest and most concentrated, respectively, for the northwestern transpressional segment of the OSR, moderately high and concentrated along the southeastern segment of the OSR, and the lowest and least concentrated along the central strike-slip segment. These geomorphological indices indicate that most of the plate boundary uplift occurs along the transpressional and transtensional segments that are connected by the central strike-slip zone. Within this overall pattern of structural variation, abrupt changes in the azimuth of the OSFZ create more localized anomalies in the geomorphological indices.

Highlights

The eastern margin of the Papuan Peninsula and the Solomon Sea has been identified using GPS-based geodesy as the landward extent of the 135,000 km2 Trobriand microplate – one of the three microplates in the Woodlark region between the much larger Pacific and Australian Plates (Baldwin et al, 2012; Ott and Mann, 2015)
The plate boundary follows the Owen-Stanley Fault Zone (OSFZ) that is dominated by left-lateral oblique convergence, strike-slip, and extension between the Woodlark region and the Australian Plate (Wallace et al, 2004; Daczko et al, 2011; Baldwin et al, 2012; Wallace et al, 2014; Figure 1)
With the recognition that slow subduction occurs along the 600 km-long Trobriand Trench and that right-lateral strike-slip motion occurs along the Nubara Transform (Lock et al, 1987; Wallace et al, 2014; Benyshek and Taylor, 2021), the Woodlark region is perceived as three discrete and active fault-bounded microplates that include the Trobriand Plate in the west, the Solomon Sea Plate in the northeast, and the Woodlark Plate in the southeast (Kington and Goodliffe, 2008; Benyshek and Taylor, 2021)

Summary

Introduction

The eastern margin of the Papuan Peninsula and the Solomon Sea has been identified using GPS-based geodesy as the landward extent of the 135,000 km Trobriand microplate – one of the three microplates in the Woodlark region between the much larger Pacific and Australian Plates (Baldwin et al, 2012; Ott and Mann, 2015). It has been proposed that this rapid microplate rotation about a nearby pole of rotation is driven by a downward pull from the 600 kmlong Solomon Sea slab that is subducted at the New Britain Trench that is terminated at its western end by the Finisterre collisional zone (Weissel et al, 1982; Wallace et al, 2014) This slab-driven plate rotation leads to the westward propagation and transition of the Woodlark oceanic spreading center into a more diffuse zone of continental rifting along the southeastern segment of the OSFZ (Abers, 2001; Abers et al, 2016). This large-scale rotation of the Solomon Sea and Trobriand plates explains the distinctive V-shape of the Woodlark oceanic crust – a hallmark of rotationally-controlled plate boundaries (Figure 1)

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Discussion

Conclusion