Southeastern Papua Research Articles

New species of Gehyra (Squamata: Gekkonidae) from Papua New Guinea

I describe four new species of Gehyra from New Guinea and immediately adjacent islands. Two of these are giant species that have long been misassigned to either G. vorax or G. membranacruralis; the other two were previously referred to G. oceanica. Each of the new species has a very circumscribed geographic distribution, with one being known from only a single island, a second from a small portion of southeastern New Guinea and immediately adjacent islands, a third from a small archipelago, and the fourth from foothill forest along the northern versant of eastern New Guinea. Three of these species are found only in the Milne Bay Region of southeastern Papua New Guinea, a region previously identified as having a globally high density of narrow-range endemic reptile and amphibian species. These species provide further extension of that pattern by increasing the number of known endemic herpetofaunal species from that small region to 165. Variation in subcaudal shape is taxonomically useful in Gehyra, but its character-state coding must rely on original tails because aberrant development of subcaudals in some regenerated tails could lead to mischaracterization of this feature.

Indirect dating of secondary cave burials in the Massim region of Papua New Guinea reveals last millennium reorganisation of social practices

ABSTRACTIn the Massim Island region of southeastern Papua New Guinea secondary interment of skeletal remains was widely practiced historically, but its social context and regional expression in the deeper past remains uncertain. In this paper the chronology of secondary burial on Panaeati Island is established indirectly by reconstructing the cultural and spatiotemporal association of 21 clay pots placed with human skeletal remains at Biniwaga Cave, coincidently establishing the first whole vessel typology of Southern Massim Combed Pottery (SMCP) and Southern Massim Pottery (SMP). Comparison with excavated pottery assemblages on Panaeati and elsewhere in the region demonstrates that the Biniwaga pots are consistent with SMCP and early SMP, dating from 740 to 470 calBP. Secondary burial practices on Panaeati are contemporary with those recorded elsewhere in the region and coincide with changes in pottery production centres. Compared to excavated pottery assemblages from contemporary sites, a relatively narrow range of pots are represented at Biniwaga. It is hypothesised that pots were selected to reflect the cultural affiliation of deceased individuals during a period of increasing inter‐island interaction.

Temporal Variability in Gas Emissions at Bagana Volcano Revealed by Aerial, Ground, and Satellite Observations

AbstractBagana is a remote, highly active volcano, located on Bougainville Island in southeastern Papua New Guinea. The volcano has exhibited sustained and prodigious sulfur dioxide gas emissions in recent decades, accompanied by frequent episodes of lava extrusion. The remote location of Bagana and its persistent activity have made it a valuable case study for satellite observations of active volcanism. This remoteness has also left many features of Bagana relatively unexplored. Here, we present the first measurements of volcanic gas composition, achieved by unoccupied aerial system (UAS) flights through the volcano's summit plume, and a payload comprising a miniaturized MultiGAS. We combine our measurements of the molar CO2/SO2 ratio in the plume with coincident remote sensing measurements (ground‐ and satellite‐based) of SO2 emission rate to compute the first estimate of CO2 flux at Bagana. We report low SO2 and CO2 fluxes at Bagana from our fieldwork in September 2019, ∼320 ± 76 td−1 and ∼320 ± 84 td−1, respectively, which we attribute to the volcano's low level of activity at the time of our visit. We use satellite observations to demonstrate that Bagana's activity and emissions behavior are highly variable and advance the argument that such variability is likely an inherent feature of many volcanoes worldwide and yet is inadequately captured by our extant volcanic gas inventories, which are often biased to sporadic measurements. We argue that there is great value in the use of UAS combined with MultiGAS‐type instruments for remote monitoring of gas emissions from other inaccessible volcanoes.

Demian, Melissa. In memory of times to come: ironies of history in southeastern Papua New Guinea. xii, 228 pp., map, table, figs, illus., bibliogr. Oxford, New York: Berghahn Books, 2021. £99.00 (cloth)

Demian, Melissa. In memory of times to come: ironies of history in southeastern Papua New Guinea. xii, 228 pp., map, table, figs, illus., bibliogr. Oxford, New York: Berghahn Books, 2021. £99.00 (cloth)

Regional‐Scale Low‐Angle Normal Fault Friction and Cohesion Constrained From Mohr‐Coulomb Models of Active and Abandoned Range‐Front Faults in Papua New Guinea

AbstractLow‐angle normal faults (LANFs) are poorly understood, as their slip at <30° dips appears inconsistent with Byerlee friction and Andersonian stresses. Rider blocks are fault slices formed when the uppermost part of a LANF is abandoned in favor of a new, steeper fault. Mohr‐Coulomb modeling of rider blocks can constrain fault frictional and cohesive strength provided known fault geometries. Analytical modeling shows that LANF viability depends on fault geometry and on the frictional and cohesive strength of the fault relative to that of the surrounding crust. Modeling of the Gwoira rider block, located atop the Mai'iu LANF, southeastern Papua New Guinea, indicates that this fault segment is frictionally weak (0.04 ≤ µf ≤ 0.17) in the shallow crust, with neither non‐Andersonian stresses nor supra‐hydrostatic fluid pressures required. Such weakness favors slip localization onto a single fault, enabling rapid slip rates at shallow dips. We show that slip at a second site, which lacks a rider block, does not require a weak fault because of a large fault/crust cohesion contrast and a rapid steepening of dip on the convex‐upward fault from only 21° at the surface to >30° down‐dip. From our results, we characterize four possible styles of faulting on convex‐up normal faults: (a) total fault slip, (b) footwall damage, (c) fault partial abandonment, and (d) total fault abandonment. Our results reveal that LANF faulting style depends on the strength of the fault compared to the surrounding crust, fault geometry, and the distribution of differential stress required for slip as a function of depth.

Continental Break‐Up Under a Convergent Setting: Insights From P Wave Radial Anisotropy Tomography of the Woodlark Rift in Papua New Guinea

AbstractTo explore the dynamic mechanism of continental rifting within a convergent setting, we determine the first P wave radial anisotropic tomography beneath the Woodlark rift in southeastern Papua New Guinea, which develops within the obliquely colliding zone between the Australian and southwest Pacific plates. The rift zone is depicted as localized low‐velocity anomalies with positive radial anisotropy, which rules out a dominant role of active mantle upwelling in promoting the rift development and favors passive rifting with decompression melting as main processes. Downwelling slab relics in the upper mantle bounding the rift zone are revealed based on observed high‐velocity anomalies and negative radial anisotropy, which may contribute to the ultra‐high pressure rock exhumations and rift initiation. Our observations thus indicate that the Woodlark rift follows a passive model and is mainly driven by slab pull from the northward subduction of the Solomon plate.

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

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.

The thermo-tectonic evolution of the actively exhuming Mai'iu Fault footwall – Suckling-Dayman metamorphic core complex – in the Woodlark Rift of Papua New Guinea

The Mai'iu Fault in the Woodlark Rift of southeastern Papua New Guinea is an active north-dipping low-angle normal fault (LANF) that has exhumed the spectacular Suckling-Dayman metamorphic core complex (SDMCC) in its footwall. While its youthful domal geomorphology suggests recent tectonic exhumation of the SDMCC, the cooling and exhumation history of this active metamorphic core complex have not been studied in detail before. Here we provide the first zircon and apatite fission-track (FT) and (U-Th)/He thermochronometric data on the SDMCC based on a suite of samples from slip-parallel footwall transects and syn-extensional alluvial deposits shed from the emerging dome. In addition, we double dated zircon using U–Pb LA-ICP-MS. These chronometric techniques are complemented by temperature and pressure estimates from Raman spectroscopy of carbonaceous material (RSCM) and Al-in-amphibole and Al-in-biotite barometry on footwall phyllites/schists and granitoids, respectively. The data indicate that slip on the Mai'iu Fault had initiated by ~4 Ma. We show that slip on the Mai'iu Fault has persisted at cm/year rates since the onset of extension, making it one of Earth's most rapidly slipping continental LANF. Integrating temperature estimates from FT and (U-Th)/He thermochronometry and RSCM, we calculated a down-dip, fault-parallel paleo-field temperature gradient along the now-exhumed part of the Mai'iu Fault of ~11 °C/km. For a likely range of pre-extensional geothermal gradients in the Woodlark Rift (10–20 °C/km), this paleo-field temperature gradient implies an average initial dip of the Mai'iu Fault of ~46°. Given the present dip of ~21° at the surface, the thermal data reinforce other evidence that the footwall of the Mai'iu Fault has been back-rotated to the south by ≥20° during progressive unroofing since fault inception, consistent with a rolling hinge style evolution of the SDMCC.

Gesturing to the Past: The Case for an Ethnography of Melanesian Poetics

The driving theme of this article is the loss of poetics in the language of the Vula‘a people of southeastern Papua New Guinea, in particular the relationship between language loss and knowledge loss—the type of knowledge that connects people to ancestors and is central to a group’s identity. Drawing on examples from my fieldwork, I argue for the value of an ethnography of poetic language and for rethinking approaches to the study of Indigenous languages beyond instances when endangerment is imminent. My approach is influenced by Martin Heidegger and sits comfortably with recent theoretical perspectives that draw on the work of Edward S Casey (1996) and Tim Ingold (2000). Poetic language is not only prevalent in immediately recognizable genres; it also plays a significant role in many other oral traditions as well as in day-to-day life. Consequently, there is a pressing need to pay attention to disappearing poetic forms if we are to comprehend past and present lifeworlds. To this end, we should not be distracted by models that would reduce language to types of expression or to component parts. After presenting examples from my own research, I explore the work of other Melanesian ethnographers to reveal the relationship between poetic language, place, and Indigenous ways of knowing.

Mechanical Implications of Creep and Partial Coupling on the World's Fastest Slipping Low‐Angle Normal Fault in Southeastern Papua New Guinea

AbstractWe use densely spaced campaign GPS observations and laboratory friction experiments on fault rocks from one of the world's most rapidly slipping low‐angle normal faults, the Mai'iu fault in Papua New Guinea, to investigate the nature of interseismic deformation on active low‐angle normal faults. GPS velocities reveal 8.3 ± 1.2 mm/year of horizontal extension across the Mai'iu fault, and are fit well by dislocation models with shallow fault locking (above 2 km depth), or by deeper locking (from ~5–16 km depth) together with shallower creep. Laboratory friction experiments show that gouges from the shallowest portion of the fault zone are predominantly weak and velocity‐strengthening, while fault rocks deformed at greater depths are stronger and velocity‐weakening. Evaluating the geodetic and friction results together with geophysical and microstructural evidence for mixed‐mode seismic and aseismic slip at depth, we find that the Mai'iu fault is most likely strongly locked at depths of ~5–16 km and creeping updip and downdip of this region. Our results suggest that the Mai'iu fault and other active low‐angle normal faults can slip in large (Mw > 7) earthquakes despite near‐surface interseismic creep on frictionally stable clay‐rich gouges.

The petrology, geochronology and tectono-magmatic setting of igneous rocks in the Suckling-Dayman metamorphic core complex, Papua New Guinea

Southeastern Papua New Guinea has hosted magmatism throughout the Cenozoic, with the latest phase being concurrent with active extension in the Woodlark Rift. There, the Suckling-Dayman metamorphic core complex (SDMCC) has exhumed middle-crustal rocks in the past few million years along a still-active low-angle normal fault, the Mai'iu Fault. Uplift of the SDMCC has exposed metasedimentary and metaigneous rocks of Late Cretaceous-Pleistocene age that record an evolution from oceanic spreading to subduction, to collision, and finally to subduction-inversion and extensional exhumation. We present new petrographic, whole-rock geochemical and geochronologic (zircon U–Pb LA-ICP-MS) data from the SDMCC to reconstruct its long-term evolution. The dominant footwall-lithology of the SDMCC, the Goropu Metabasalt, has a MORB composition. Detrital zircons from metasedimentary beds intercalated with these basalts yield U–Pb-based maximum estimates for deposition of ~103 and ~72 Ma, suggesting a Late Cretaceous spreading age of the oceanic protolith. Bulk compositions of low-grade tholeiitic meta-gabbroic and -tonalitic rocks (Yau Igneous Complex) that intrude the Goropu Metabasalt reveal both enriched and depleted light rare earth element patterns. Zircon U–Pb ages from the Yau Igneous Complex range between ~60 and ~57 Ma, providing a minimum age for the formation of the Goropu Metabasalt. Much younger syn-extensional granitoids in the mafic footwall of the SDMCC have calc-alkaline to high-K compositions and U–Pb ages on zircon between ~3.7 and ~2.0 Ma. Our data indicate that the Mai'iu Fault had re-activated a Paleogene thrust as an extensional detachment fault by 3.7 ± 0.2 Ma. U–Pb ages of detrital zircons in modern streams draining the footwall of the SDMCC essentially reflect the ages revealed by the Paleocene and Plio-Pleistocene intrusions. Xenocrystic zircons in the Plio-Pleistocene granitoids imply that the crust underlying the metabasaltic carapace of the SDMCC consists chiefly of Australian-continent derived sedimentary rocks.

Two-stage garnet growth in coesite eclogite from the southeastern Papua New Guinea (U)HP terrane and its geodynamic significance

Mineral compositions and textures of Late Miocene coesite eclogite from Tomagabuna Island were investigated to constrain P–T conditions during UHP metamorphism and subsequent exhumation. Two stages of garnet growth (core and rim), at eclogite-facies conditions, were documented. In addition to core garnet (I), peak assemblages include omphacite, coesite, phengite, and rutile. Rim garnet (II), amphibole, paragonite, plagioclase, quartz, and accessory biotite and spinel were formed after peak pressure conditions. Although a compositional gradient is present at the core–rim garnet interface, the garnet core has a relatively flat compositional profile, suggesting its crystallization in the coesite stability field. Together with minerals formed subsequent to peak pressure (UHP) conditions, the composition of the garnet rim indicates heating of the eclogite during its decompression into the amphibolite facies mineral stability field. Based on compositional zoning in garnet and application of diffusion modelling, we propose that eclogite-facies metamorphism of the mafic protolith and its host lithologies occurred at, or near, UHP conditions. The core garnet (I) formed at 650 °C at 8 Myr in the coesite stability field and was partially resorbed during the onset of exhumation. We infer that garnet rim growth at < 7.1 Ma occurred at P–T conditions corresponding to the boundary between the eclogite and amphibolite facies fields. Diffusion modelling for the garnet core–rim boundary compositions suggests a transient heating event (0.3 Myr) occurred at 1.5 GPa that we infer resulted from heat transport within the Australian—Woodlark plate boundary zone as the coesite eclogite was exhumed. Results caution that apparent P–T paths documented for many UHP terranes may not result from isothermal decompression corresponding to peak temperatures. Instead, paths may link P–T points’ set during transient mineral growth events when the UHP rocks form within the subduction channel, and during subsequent heating events, when UHP rocks are exhumed from mantle depths.

A New Insular Species ofOreophryne(Anura, Microhylidae) from Papua New Guinea

Abstract.— I describe a new species of Oreophryne from Woodlark Island, the most isolated large island in southeastern Papua New Guinea. The new species is a member of the O. equus species group, characterized by having a “whinny” call consisting of a rapid series of high-pitched peeps. It differs from other members of that group in a combination of features, including having a cartilaginous connection between the scapula and procoracoid, well-webbed digits on the feet, fifth toe longer than the third, a largely unicolor brown dorsum, and red flash markings on the hidden surfaces of the thighs. All members of this species group inhabit the southeasternmost portion of Papua New Guinea, with most species endemic to single offshore islands. The species is common in secondary rain forests on Woodlark, but continued commercial interest in developing large-scale extractive industries on the island could potentially threaten this and other endemic species on Woodlark if developments were to occur across a large-...

A New Species ofOreophryne(Anura: Microhylidae) from the Mountains of Southeastern Papua New Guinea

Abstract: I describe a new frog of the microhylid genus Oreophryne from the mountains of southeastern Papua New Guinea that is unique in its combination of having a ligamentous connection between the procoracoid and scapula, webbing that reaches to the middle or distal to the penultimate tubercle of the fifth toe, fifth and third toes subequal in length, largely unpatterned dark-brown dorsum, and an advertisement call consisting of rapidly delivered unpulsed notes that sounds to the human ear like a rattle. The new species is known from the uplands of Cape Nelson and from the nearby Mt. Dayman/Mt. Suckling massif. Although its total range is relatively small, it inhabits remote high-quality rainforests that are largely undisturbed by humans at this time, although rapid climate change could pose a future threat to the species. Sixteen endemic Oreophryne species are now reported from Milne Bay Province.

Continental breakup and UHP rock exhumation in action: GPS results from the Woodlark Rift, Papua New Guinea

AbstractWe show results from a network of campaign Global Positioning System (GPS) sites in the Woodlark Rift, southeastern Papua New Guinea, in a transition from seafloor spreading to continental rifting. GPS velocities indicate anticlockwise rotation (at 2–2.7°/Myr, relative to Australia) of crustal blocks north of the rift, producing 10–15 mm/yr of extension in the continental rift, increasing to 20–40 mm/yr of seafloor spreading at the Woodlark Spreading Center. Extension in the continental rift is distributed among multiple structures. These data demonstrate that low‐angle normal faults in the continents, such as the Mai'iu Fault, can slip at high rates nearing 10 mm/yr. Extensional deformation observed in the D'Entrecasteaux Islands, the site of the world's only actively exhuming Ultra‐High Pressure (UHP) rock terrane, supports the idea that extensional processes play a critical role in UHP rock exhumation. GPS data do not require significant interseismic coupling on faults in the region, suggesting that much of the deformation may be aseismic. Westward transfer of deformation from the Woodlark Spreading Center to the main plate boundary fault in the continental rift (the Mai'iu fault) is accommodated by clockwise rotation of a tectonic block beneath Goodenough Bay, and by dextral strike slip on transfer faults within (and surrounding) Normanby Island. Contemporary extension rates in the Woodlark Spreading Center are 30–50% slower than those from seafloor spreading‐derived magnetic anomalies. The 0.5 Ma to present seafloor spreading estimates for the Woodlark Basin may be overestimated, and a reevaluation of these data in the context of the GPS rates is warranted.

Timing of UHP exhumation and rock fabric development in gneiss domes containing the world's youngest eclogite Facies rocks, southeastern Papua New Guinea

AbstractThe youngest known ultrahigh‐pressure (UHP) rocks in the world occur in the Woodlark Rift of southeastern Papua New Guinea. Since their crystallization in the Late Miocene to Early Pliocene, these eclogite facies rocks have been rapidly exhumed from mantle depths to the surface and today they remain in the still‐active geodynamic setting that caused this exhumation. For this reason, the rocks provide an excellent opportunity to study rates and processes of (U)HP exhumation. We present New Rb–Sr results from 12 rock samples from eclogite‐bearing gneiss domes in the D'Entrecasteaux Islands, and use those results to examine the time lag between (U)HP metamorphism and later ductile thinning, penetrative fabric development and accompanying metamorphic retrogression at amphibolite facies conditions during their exhumation. A Rb–Sr age for a sample of mafic eclogite (with no preserved coesite) from the core zone of the Mailolo gneiss dome (Fergusson Island) provides a new estimate of the timing of HP metamorphism (5.6 ± 1.6 Ma). The strongly deformed quartzofeldspathic and granitic gneisses (90–95% by volume) that enclose variably retrogressed relict blocks of mafic eclogite (5–10% by volume) yield Rb–Sr isochron ages from 4.4 to 2.4 Ma. For the UHP‐bearing gneisses of Mailolo dome, previously published U–Pb ages on zircon and our Rb–Sr isochron ages are consistent with a mean time lag of 2.2 ± 1.5 Ma (~95% c.i.) for passage of the rock between eclogite and amphibolite facies conditions. New thermobarometric data indicate that the main syn‐exhumational foliation developed at amphibolite facies conditions of 630–665 °C and 12.1–14.4 kbar. These pressure estimates indicate that the lower crust of the Woodlark Rift was unusually thick (&gt;40 km) at the time of the amphibolite facies overprint, possibly as a result of accumulation and underplating of UHP‐derived material from below. Our data imply a minimum unroofing rate of 10 ± 7 mm year−1 (~95% c.i.) for the (U)HP body from minimum HP depths (73 ± 7 km) to lower crustal depths. This minimum unroofing rate reinforces previous inferences that the exhumation from the mantle to the surface of the gneiss domes in the D'Entrecasteaux Islands took place at plate tectonic rates. On the basis of previous structural studies and the new thermobarometry, we attribute the high (cm year−1) exhumation to diapiric ascent of the partially molten terrane from mantle depths, with a secondary contribution from pure shear thinning of the terrane after its arrival in the crust.

Anisotropy beneath a highly extended continental rift

AbstractWe have employed shear wave splitting techniques to image anisotropy beneath the D'Entrecasteaux Islands, in southeastern Papua New Guinea. Our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid‐ocean ridge tip; we image the transition from continental to oceanic extension. A dense shear wave splitting data set from a 2010 to 2011 passive‐source seismic deployment is analyzed using single and multichannel methods. Splitting delay times of 1–1.5 s are observed and fast axes of anisotropy trending N‐S, parallel to rifting direction, predominate the results. This trend is linked to lattice‐preferred orientation of olivine, primarily in the shallow convecting mantle, driven by up to 200 km of N‐S continental extension ahead of the westward‐propagating Woodlark Rift. This pattern differs from several other continental rifts that evince rift‐strike‐parallel fast axes and is evident despite the complex recent tectonic history. We contend that across most of this rift, the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid‐ocean‐ridge‐like mantle fabric. Stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region.

Three new species of Oreophryne (Anura, Microhylidae) from Papua New Guinea.

I describe three new species of the diverse microhylid frog genus Oreophryne from Papua New Guinea. Two of these occur in two isolated mountain ranges along the northern coast of Papua New Guinea; the third is from Rossel Island in the very southeasternmost part of the country. All three are the first Oreophryne known from these areas to have a cartilaginous connection between the procoracoid and scapula, a feature usually seen in species far to the west or from the central cordillera of New Guinea. Each of the new species also differs from the many other Papuan Oreophryne in a variety of other morphological, color-pattern, and call features. Advertisement-call data for Oreophryne species from the north-coast region suggest that they represent only two of the several call types seen in regions further south, consistent with the relatively recent derivation of these northern regions as accreted island-arc systems. The distinctively different, whinnying, call type of the new species from Rossel Island occurs among other Oreophryne from southeastern Papua New Guinea but has been unreported elsewhere, raising the possibility that it may characterize a clade endemic to that region.

High-magnesium andesites: the example of the Papuan Volcanic Arc

Abstract The late Cenozoic arc-type volcanic arc in southeastern Papua New Guinea developed in an environment of complex tectonic processes including obduction, subduction, rifting and sea floor spreading. The volcanic arc extends from the Papuan Peninsula south-eastward through the D'Entrecasteaux Islands into the Louisiade Archipelago. Lithologies are predominantly basaltic andesite and andesite, but include basalt, dacite and rhyolite. The rocks have typical arc-type geochemical features but include a group ranging from basalt to dacite which, although comparable in most other aspects of their compositions, are higher in MgO, Cr and Ni. These high-Mg rocks are less porphyritic and have simple olivine- or clinopyroxene- dominated phenocryst assemblages compared with the associated low-Mg rocks. The low-Mg rocks are plagioclase-phyric and contain augite and hypersthene with or without olivine, hornblende and biotite phenocrysts. Boninites are spatially associated with, but genetically unrelated to the arc-type rocks in Papua. The high-Mg rocks represent magmas derived by partial melting of subduction-modified mantle which rose rapidly from their source. In contrast, the low-Mg lavas represent magmas which were modified by shallow processes. The unusual abundance of high-Mg lavas in southeastern Papua is related to extensional tectonics which allowed deep sourced magmas to rise without significant modification. Supplementary material: Major and trace element analyses of lavas from the Papuan volcanic arc are available at http://www.geolsoc.org.uk/SUP18644

A new treefrog of theLitoria gracilentagroup (Hylidae) from Papua New Guinea

I describe a new treefrog of the Litoria gracilenta group from the lowlands along an outlying volcanic peak in southeastern Papua New Guinea. The new species is distinctive among members of that group in a combination of details of color pattern and morphometric characters, and it is further unique within that group in being the only species known to have a call consisting of several notes. It is also unusual for the group in having been found breeding in a stream. This species complex has an extensive but disjunct range spanning the entire extent of New Guinea, outlying islands to the west and the east, and eastern Australia. The new species fills in a range gap of 830 km between its nearest relatives to the northwest and southeast.