Tracking the exhumation of a Pliocene (U)HP terrane: U-Pb and trace-element constraints from zircon, D'Entrecasteaux Islands, Papua New Guinea

Abstract

Domal structures within the D'Entrecasteaux Islands of eastern Papua New Guinea expose ultrahigh-pressure (UHP) Pliocene (5.6-4.6 Ma) eclogites and evidence for partial melting. To better interpret the (U)HP exhumation history, U-Pb geochronology and trace-element abundances were determined in zircon from variably deformed host gneiss and crystallized melt (leucosomes, sills, dikes, and plutons) from the Goodenough and Normanby Domes by ID-TIMS (isotope-dilution thermal ionization mass spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry), respectively, to constrain the timing of melt crystallization and deformation relative to UHP metamorphism. Zircons extracted from orthogneiss and deformed granodiorite sills of Normanby Dome, located 40 km southeast of the UHP eclogite, record HP metamorphism from 5.66 6 0.02 to 5.04 6 0.07 Ma, and melt crystallization at 4.1 Ma. Strongly deformed, layer-parallel leucosomes from Goodenough Dome, 20 km northwest of the UHP eclogite, began to crystallize by 3.85 6 0.02 Ma. These dates indicate that melt crystallization began in the Goodenough and Normanby Domes within 0.75 m.y. of (U)HP metamorphism. The ID-TIMS dates from the orthogneiss and crystallized melt show that exhumation and cooling of the (U)HP rocks in the PNG terrane began first in the east, within Normanby Dome, then to the west, in the Goodenough Dome 1 m.y. later, and finally the middle dome rocks, exposed within the Mailolo Dome, cooled 2 m.y. after exhumation of Normanby Dome. All domes reveal synchronous crystallization of late, nondeformed melts, and final extension-driven exhumation by 1.82 6 0.03 Ma.

Tectonics of the Papua‐Woodlark Region

“…An erosional unconformity at 8.4 Ma across the Trobriand forearc and Woodlark Rise has been interpreted to mark the onset of rifting ahead of seafloor spreading that began in the eastern Woodlark Basin by 6 Ma (Taylor, 1987;Taylor & Huchon, 2002;Taylor et al, 1999 Metamorphic core complex formation and, in the east, transitional basalt-peralkaline rhyolite Quaternary volcanism near Dawson Strait (comendites, Smith, 1976;Stolz et al, 1993), accompanied the late Miocene-recent rifting of the continental arc ( Figure 1). Gneissic domes developed along the volcanic front (D'Entrecasteaux Islands and Misima) and core complexes formed on the peninsula just behind it (basic Suckling-Dayman massif and Emo Metamorphics) (Baldwin et al, 1993(Baldwin et al, , 2004Daczkco et al, 2009Daczkco et al, , 2011Davies, 1980;Davies & Warren, 1988, 1992DesOrmeau et al, 2014;Gordon et al, 2012;Hill, 1994;Hill et al, 1992Hill et al, , 1995Korchinski et al, 2014;Little et al, 2007Little et al, , 2011Little et al, , 2019Mizera et al, 2019;Osterle et al, 2020;Webber et al, 2018). Syn-extensional granitoids with calc-alkaline (Suckling Granite) and high-K (Mai'iu Monzonite and Bonua Porphyry) compositions that intruded the Suckling-Dayman massif have U-Pb crystallization ages on zircons between 4 and 2 Ma (Osterle et al, 2020).…”

“…The Papuan Peninsula‐Woodlark Basin region (Figure 1) has been the focus of intense geological study given the important association of globally high extensional strain rates (rifting 10–20 mm/yr), seismogenic shallow‐dipping (∼30°), and low‐angle (22°) normal faults, the rapid emplacement (>10–20 mm/yr vertically) of the youngest (7–5 Ma) high‐ and ultra‐high‐pressure rocks in metamorphic core complexes and gneissic domes, the active breakup of a continent and the transition to seafloor spreading (Abers, 1991, 2001; Abers et al., 1997, 2016; Baldwin et al., 2008; DesOrmeau et al., 2014; Goodliffe & Taylor, 2007; Gordon et al., 2012; Little et al., 2011, 2019; B. Taylor & Huchon, 2002; Taylor et al., 1995, 1999; Tregoning et al., 1998; Wallace et al., 2004, 2014; Webber et al., 2018).…”

“…(Abers et al., 2016; Kington & Goodliffe, 2008; B. Taylor, 1987; B. Taylor et al., 1999; Tregoning et al., 1998; Wallace et al., 2004, 2014) Is the rapid emplacement of metamorphic core complexes and gneissic domes exhumed in the continental rift dominantly by horizontal (extension on low‐angle normal faults) or vertical (diapir) tectonics, and related to former northward or recent/current southward subduction and magmatic arc processes? (Abers et al., 2016, 2002; Baldwin et al., 2004, 2008, 1993; Biemiller et al., 2019; Daczko et al., 2011, 2009; DesOrmeau et al., 2014; Ellis et al., 2011; Fitz & Mann, 2013a, 2013b; Gordon et al., 2012; Hill, 1994; Hill & Baldwin, 1993; Hill et al., 1992, 1995; Korchinski et al., 2014; Little et al., 2011, 2013, 2019, 2007; Martinez et al., 2001; Mizera et al., 2019; Webb et al., 2008; Webber et al., 2018)…”

The thermo-tectonic evolution of the Suckling-Dayman metamorphic core complex, southeastern Papua New Guinea

“…The significance of the WVP as a source of volcanoclastic sediments for the protolith of the Kagi Metamorphics before the opening of the Coral Sea (see below) in the Paleocene is evinced by Cretaceous (∼120-80 Ma) detrital zircon U-Pb signatures in metasedimentary rocks of the Wau area (Kopi et al, 2004), basement gneisses on the D'Entrecasteaux Islands and the Calvados Schist on the Louisiade Archipelago (Zirakparvar et al, 2013), and inherited xenocrystic zircon in 8.1-1.8 Ma-old granitoids on the D'Entrecasteaux Islands (DesOrmeau et al, 2014;Gordon et al, 2012) and Misima Island (Adshead and Appleby, 1996) (Figure 2.1). A petrogenetic link between the WVP and the granitoids of the greater D'Entrecasteaux Islands region is also suggested by their overlapping 87 Sr/ 86 Sr i isotopic values of 0.70312-0.70440 (Ewart et al, 1992) and 0.70380-0.70442 (Korchinski et al, 2014), respectively.…”

“…Abbreviations: n a -number of analyses used to calculate the age; nnumber of analyses; n zrn -number of zircons analysed. showing age distributions of (a) inherited (i.e., xenocrystic) zircons from igneous rocks of the Suckling-Dayman metamorphic core complex (Suckling Granite, Mai'iu Monzonite, Bonua Porphyry), (b) detrital zircons from the Kagi Metamorphics in the Wau area (Kopi et al, 2004), (c) detrital zircons from basement gneisses on Goodenough Island and the Louisiade Archipelago (Zirakparvar et al, 2013) and (d) inherited zircons in granitoids from Goodenough and Normanby Islands (DesOrmeau et al, 2014). The grey bar marks the duration of igneous activity associated with the Whitsunday Volcanic Province (Bryan et al, 1997;Ewart et al, 1992;Tulloch et al, 2010).…”