Hot lherzolite exhumation, UHT migmatite formation, and acid volcanism driven by Miocene rollback of the Banda Arc, eastern Indonesia

The northern Banda Arc, eastern Indonesia, exposes upper mantle/lower crustal complexes comprising lherzolites and granulite facies migmatites of the ‘Kobipoto Complex’. Residual garnet–sillimanite granulites, which contain spinel + quartz inclusions within garnet, experienced ultrahigh-temperature (UHT; > 900 °C) conditions at 16 Ma due to heat supplied by lherzolites exhumed during slab rollback in the Banda Arc. Here, we present U–Pb zircon ages and new whole-rock geochemical analyses that document a protracted history of high-T metamorphism, melting, and acid magmatism of a common sedimentary protolith. Detrital zircons from the Kobipoto Complex migmatites, with ages between 3.4 Ga and 216 Ma, show that their protolith was derived from both West Papua and the Archean of Western Australia, and that metamorphism of these rocks on Seram could not have occurred until the Late Triassic. Zircons within the granulites then experienced three subsequent episodes of growth – at 215–173 Ma, 25–20 Ma, and at c. 16 Ma. The population of zircon rims with ages between 215 and 173 Ma document significant metamorphic (± partial melting) events that we attribute to subduction beneath the Bird's Head peninsula and Sula Spur, which occurred until the Banda and Argo continental blocks were rifted from the NW Australian margin of Gondwana in the Late Jurassic (from c. 160 Ma). Late Oligocene-Early Miocene collision between Australia (the Sula Spur) and SE Asia (northern Sulawesi) was then recorded by crystallisation of several 25–20 Ma zircon rims. Thereafter, a large population of c. 16 Ma zircon rims grew during subsequent and extensive Middle Miocene metamorphism and melting of the Kobipoto complex rocks beneath Seram under high- to ultrahigh-temperature (HT–UHT) conditions. Lherzolites located adjacent to the granulite-facies migmatites in central Seram equilibrated at 1280–1300 °C upon their exhumation to 1 GPa (~ 37 km) depth, whereupon they supplied sufficient heat to have metamorphosed adjacent Kobipoto Complex migmatites under UHT conditions at 16 Ma. Calculations suggesting slight (~ 10 vol%) mantle melting are consistent with observations of minor gabbroic intrusions and scarce harzburgites. Subsequent extension during continued slab rollback exhumed both the lherzolites and adjacent granulite-facies migmatites beneath extensional detachment faults in western Seram at 6.0–5.5 Ma, and on Ambon at 3.5 Ma, as recorded by subsequent zircon growth and 40Ar/39Ar ages in these regions. Ambonites, cordierite- and garnet-bearing dacites sourced predominantly from melts generated in the Kobipoto Complex migmatites, were later erupted on Ambon from 3.0 to 1.9 Ma

Rolling open Earth’s deepest forearc basin

The Weber Deep—a 7.2-km-deep forearc basin within the tightly curved Banda arc of eastern Indonesia—is the deepest point of the Earth’s oceans not within a trench. Several models have been proposed to explain the tectonic evolution of the Banda arc in the context of the ongoing (ca. 23 Ma–present) Australia–Southeast Asia collision, but no model explicitly accounts for how the Weber Deep achieved its anomalous depth. Here we propose that the Weber Deep formed by forearc extension driven by eastward subduction rollback. Substantial lithospheric extension in the upper plate was accommodated by a major, previously unidentified, low-angle normal fault system we name the “Banda detachment.” High-resolution bathymetry data reveal that the Banda detachment is exposed underwater over much of its 120 km down-dip and 450 km lateral extent, having produced the largest bathymetric expression of any fault discernable in the world’s oceans. The Banda arc is a modern analogue for highly extended terranes preserved in the many regions that may similarly have “rolled open” behind migrating subduction zones

Extreme extension across Seram and Ambon, eastern Indonesia: Evidence for Banda slab rollback

The island of Seram, which lies in the northern part of the 180°-curved Banda Arc, has previously been interpreted as a fold-and-thrust belt formed during arc-continent collision, which incorporates ophiolites intruded by granites thought to have been produced by anatexis within a metamorphic sole. However, new geological mapping and a re-examination of the field relations cause us to question this model. We instead propose that there is evidence for recent and rapid N–S extension that has caused the high-temperature exhumation of lherzolites beneath low-angle lithospheric detachment faults that induced high-temperature metamorphism and melting in overlying crustal rocks. These "Kobipoto Complex" migmatites include highly residual Al–Mg-rich garnet + cordierite + sillimanite + spinel + corundum granulites (exposed in the Kobipoto Mountains) which contain coexisting spinel + quartz, indicating that peak metamorphic temperatures likely approached 900 °C. Associated with these residual granulites are voluminous Mio-Pliocene granitic diatexites, or "cordierite granites", which crop out on Ambon, western Seram, and in the Kobipoto Mountains and incorporate abundant schlieren of spinel- and sillimanite-bearing residuum. Quaternary "ambonites" (cordierite + garnet dacites) emplaced on Ambon were also evidently sourced from the Kobipoto Complex migmatites as demonstrated by granulite-inherited xenoliths. Exhumation of the hot peridotites and granulite-facies Kobipoto Complex migmatites to shallower structural levels caused greenschist- to lower-amphibolite facies metapelites and amphibolites of the Tehoru Formation to be overprinted by sillimanite-grade metamorphism, migmatisation, and limited localised anatexis to form the Taunusa Complex. The extreme extension required to have driven Kobipoto Complex exhumation evidently occurred throughout Seram and along much of the northern Banda Arc. The lherzolites must have been juxtaposed against the crust at typical lithospheric mantle temperatures in order to account for such high-temperature metamorphism and therefore could not have been part of a cooled ophiolite. In central Seram, lenses of peridotites are incorporated with a major left-lateral strike-slip shear zone (the "Kawa Shear Zone"), demonstrating that strike-slip motions likely initiated shortly after the mantle had been partly exhumed by detachment faulting and that the main strike-slip faults may themselves be reactivated and steepened low-angle detachments. The geodynamic driver for mantle exhumation along the detachment faults and strike-slip faulting in central Seram is very likely the same; we interpret the extreme extension to be the result of eastward slab rollback into the Banda Embayment as outlined by the latest plate reconstructions for Banda Arc evolution

Hot lherzolite exhumation, UHT migmatite formation, and acid volcanism driven by Miocene rollback of the Banda Arc, eastern Indonesia

Peer reviewe

Geological aspects of Banda Sea ecosystems and how they shape the oceanographical profile

The Banda Sea is a collage of young oceanic basins and fragmented Australian continental crust located at the heart of the Australia–SE Asia collision zone where Australian and Asian biogeographic regions converge. The formation of the sea was governed by the southeastward rollback of the Banda Slab since c. 16 Ma, which in its wake opened new oceanic basins and extended and fragmented Australian crust. These Australian crustal fragments are today either stranded within the Banda Sea where they form the prominent submarine 'Banda Ridges', or now reside as thrust-sheets on the NW Australian shelf after being transported all the way to the southern Banda Arc. The deepest part of the Banda Sea, the 7.2 km Weber Deep, was formed by extreme lithospheric extension that occured in the latter stages of Banda Slab rollback. This extension was accommodated by the vast low-angle 'Banda Detachment', which operated above the subducted fringes of the Australian continental margin

A Delphi study to strengthen research methods training in undergraduate psychology programmes

Psychology programmes often emphasise inferential statistical tests over a solid understanding of data and research design. This imbalance may leave graduates under-equipped to effectively interpret research and employ data to answer questions. We conducted a two-round modified-Delphi to identify the research methods skills that the UK psychology community deems essential for undergraduates to learn. Participants included 103 research methods instructors, academics, students, and non-academic psychologists. Of 78 items included in the consensus process, 34 reached consensus. We coupled these results with a qualitative analysis of 707 open-ended text responses to develop nine recommendations for organisations that accredit undergraduate psychology programmes—such as the British Psychological Society (BPS). We recommend that accreditation standards emphasise (1) dataskills, (2) research design, (3) descriptive statistics, (4) critical analysis, (5) qualitative methods, and (6) both parameter estimation and significance testing; as well as (7) give precedence to foundational skills, (8) promote transferable skills, and (9) create space in curricula to enable these recommendations. Our data and findings can inform modernised accreditation standards to include clearly-defined, assessable, and widely-encouraged skills that foster a competent graduate body for the contemporary world

"If your institution refuses to provide what you need, create it yourself”: Feminist praxis on #AcademicTwitter

Previous research has demonstrated the impact that Twitter can have for promoting and discussing a feminist agenda. Given the gendered neoliberalism that exists within academia, tweets under the hashtag ‘#AcademicTwitter’ may also be an important space for feminist praxis. Yet, to our knowledge, there is no empirical work analysing the function of ‘Academic Twitter’ from a distinctly feminist perspective. Thus, we asked “How is Academic Twitter used for feminist praxis?”. We conducted a reflexive thematic analysis of 596 tweets containing the hashtag #AcademicTwitter. This generated four themes showing how Academic Twitter can be a valuable site for feminist praxis, by enabling academics to 'give testimony to academia', 'access the hidden curriculum’, and engage in both 'academic kindness' and 'resistance and advocacy'. Despite these benefits, we also observed a tension between Academic Twitter as a site for feminist practice, yet 2 also as potentially complicit in promoting the competitiveness and overwork that pervades academia. We recommend that future feminist research interrogates the ways in which more diverse forms of feminist praxis, including more negative experiences, are negotiated on Academic Twitter

Blame it on her ‘baby brain’? Investigating the contents of social stereotypes about pregnant women's warmth and competence

The Stereotype Content Model proposes that social stereotypes broadly exist along two dimensions: warmth and competence. This framework has been used to investigate the contents of stereotypes of gendered groups in a range of contexts. However, it has not been extensively applied to perceptions of pregnant women. This is important, given how pregnant women are typically framed by society to have ‘baby brain’ or reduced competence. Therefore, we investigated the contents of social stereotypes of pregnant women. In Study 1, participants (N = 590) rated a target group (pregnant women) and thirteen other comparison groups on perceptions of warmth (compassion, empathy and comfort) and competence (mathematics ability, logic and memory). Pregnant women were generally stereotyped to have low competence and high warmth, relative to other groups. Study 2 (N = 54) then descriptively investigated the wider contents of stereotypes related to pregnant women, new mothers, men and women using a trait generation task. Generated traits were coded within the dimensions of warmth and competence. This showed, again, that pregnant women were assigned traits related to warmth and poor competence. Taken together, these studies confirmed that perceptions of low competence and ‘baby brain’ in pregnancy is broadly held by a non-pregnant sample

Miocene UHT granulites from Seram, eastern Indonesia: a geochronological-REE study of zircon, monazite and garnet

Peer reviewe