Tectonic Mode Switches Recorded at the Northern Edge of the Australian Plate During the Pliocene and Pleistocene

Abstract

We report new data from medium-high grade metamorphic rocks found at the northern margin of the Lengguru Fold Belt in West Papua. The study involved a systematic analysis of cross-cutting structures to establish the relative timing of deformation, together with isotopic dating to define when these tectono-thermal events occurred. These data show that the region underwent multiple episodes of deformation within the last six million years. Metamorphic mineral growth was associated with the development of ductile shear zones. This episode occurred during a phase of crustal stretching associated with the formation of a metamorphic core complex. Metamorphic zircon growth at 4.9 to 5.3 Ma was documented in two of the dated samples. These data are interpreted to postdate the peak pressure and temperature conditions of the phase of regional crustal stretching. The shear fabrics associated with the metamorphic core complex were later overprinted by at least two generations of folds. The change in mode from crustal extension to shortening reflects a tectonic mode switch. A subsequent mode switch is documented by numerous brittle extensional faults that cross-cut the earlier formed ductile fabrics. We interpret ca. 0.75-1.51 Ma (U-Th)/He age data to reflect cooling associated with the later stages of crustal shortening (marked by folds) or the later extensional unroofing of the peninsula. This work demonstrates that an orogen can record multiple tectonic mode switches within several million years. These outcomes should be considered in studies of ancient orogens where analytical uncertainties associated with isotopic dating may mask short-lived mode switches.Plain Language Summary How much time is required for a mountain belt to develop? Our knowledge of mountain building is somewhat limited because many of the best-studied mountain belts are quite old and our ability to date tectonic events is less precise the farther back we look through time. The work presented here investigates a mountainous peninsula that developed at the northern margin of the Australian Plate within the last six million years. This region records multiple episodes of deformation-we show that the relatively young rocks have been stretched, then pushed together and then stretched again (much like an accordion). These cycles must occur over a period of one to two million years, which is very fast compared to numerous studies of ancient mountain belts that consider the same processes occur over tens of millions of years.

New Guinean orogenic dynamics and biota evolution revealed using a custom geospatial analysis pipeline

“…While the inference of areas above sea-level and regions of poor data coverage remains tentative, their evidence suggests a strongly varying configuration of land and sea in the region since the Carboniferous, with possible submergence of the entire region from the middle Miocene until a period of rapid uplift in the late Pliocene–Pleistocene. This work, together with other geological studies, indicates that the uplift and formation of the present-day, rugged, west New Guinea landscape is due to recent tectonism associated with the interaction between the Australian and Pacific plates, primarily during the past 5 Ma (e.g., [ 4 , 13 , 16 – 20 ]). These paleogeographic models have found an unexpected echo in recent empirical evolutionary studies.…”

“…The Central Range was uplifted within the last 5 Ma, with uplift propagating from the north towards the south [ 4 , 18 ]. There is some evidence that indicates this uplift may have propagated westward from Papua New Guinea, into Papua at ~ 2–3 Ma [ 5 , 13 ], as well as eastward (e.g., [ 75 ]), including rapid rates of uplift after 3 Ma in the Papuan Peninsula (e.g., the Dayman Dome: [ 80 ] [ 81 ]).…”

“…The Central Range continued to grow as the fold-and-thrust belt rapidly developed from 5 Ma to present. This period of time also saw the formation of mountains associated with crustal stretching and metamorphic core complex development (e.g., the Wandamen Peninsula in West Papua [ 13 ] and the Dayman Dome of the Papuan Peninsula, e.g., [ 80 , 81 ]). New Guinea’s emergence from the sea was progressive as there were multiple phases of uplift and submergence in western New Guinea over the past 5 Ma [ 7 ].…”

“…While we provide an outline of the elevational evolution of New Guinea in the introduction, note that it is currently not possible to suggest a reliable paleoaltimetric model for the island. Uplift was comparably fast with a rate of up to 10 mm/year −1 for some areas (e.g., the Wandamen Peninsula: [ 13 ] and up to 51 mm/year −1 for others (e.g., 17–51 mm/year −1 D’Entrecasteaux Island; [ 101 ]), at least from 3 Ma to the present. This might also apply for (parts of the) Central Range, which has seen rapid uplift in the past 5 Ma.…”

“…A series of recent papers on different groups of animals (e.g., [ 13 , 21 – 40 ]; summaries in [ 33 ] and [ 41 ]) and plants (see e.g., [ 42 ] and references therein) identifies three major processes fueling biological diversification in New Guinea: (1) ancient diversification events on smaller proto Papuan islands including a proto Papuan Peninsula, or on the northern part of the Australian craton (see [ 27 , 33 , 43 – 45 ]), (2) more recent but substantial lineage diversification connected to the New Guinea orogeny (e.g., [ 41 , 46 ]), or (3) formation of land in the north and south of the central highlands by various processes (volcanism, accretion/uplift of island arcs and ophiolites). The latter includes complex phylogeographic processes across the New Guinea lowland rainforest belts that led to the formation of allopatric species pairs (e.g., crowned pigeons: [ 47 ]) and orogeny related vicariance [ 48 ] (see Table 4 ).…”