Julian Pearce

• Cardiff University

This preliminary report has been presented at the workshop held on August 30th at Busan during the 37th International Geological Congress, to report the first conclusions of the IUGS Task Group on Igneous Rocks (TGIR). Comments and suggestions are very welcome.

Background Global and trichoscopic photography are fundamental in the clinical assessment of hair loss. Standardised protocols in this respect are lacking. Objectives To create novel, pragmatic and flexible standardised photography protocols for hair loss, which are practical to use for clinicians and medical photographers alike. Methods Publishe...

The petrogenesis of contemporary igneous and metamorphic rocks is commonly explained by plate tectonics, but how far back in time does this relationship hold? Here we investigate whether the distinctive petrological features of recent ocean crust, subduction-related magmatism and regional metamorphism can be unambiguously identified in the Archean...

The composition of the intrusive gabbroic lower oceanic crust remains poorly characterized in comparison to the extrusive portion of the oceanic crust, especially for intermediate‐fast spreading mid‐ocean ridges. This is a consequence of limited exposures of extant lower oceanic crust or ophiolites similar to mid‐ocean ridge crust. One of the best...

LIP printing is a term adapted from forensic science to describe the use of geochemical proxies for tectonic and petrogenetic fingerprinting of Large Igneous Provinces (LIPs). Here, we investigate in detail the LIP printing of basic lavas, sills and dykes using two immobile element proxies: Th/Nb, a crustal input proxy, to monitor subduction-metaso...

Space probes in our solar system have examined all bodies larger than about 400 km in diameter and shown that Earth is the only silicate planet with extant plate tectonics sensu stricto. Venus and Earth are about the same size at 12 000 km diameter, and close in density at 5 200 and 5 500 kg.m-3 respectively. Venus and Mars are stagnant lid planets...

International Ocean Discovery Program Expedition 352 to the Bonin forearc drilled the sequence of volcanic rocks erupted in the immediate aftermath of subduction initiation along the western margin of the Pacific Plate. Pristine volcanic glasses collected during this expedition were analyzed for major and trace elements, halogens, sulfur, and H and...

International Ocean Discovery Program Expedition 352 to the Izu‐Bonin forearc cored over 800 m of basement comprising boninite and boninite‐series lavas. This is the most extensive, well‐constrained suite of boninite series lavas ever obtained from in situ oceanic crust. The boninites are characterized as high‐silica boninite (HSB), low‐silica boni...

Central aims of IODP Expedition 352 were to delineate and characterize the magmatic stratigraphy in the Bonin forearc to define key magmatic processes associated with subduction initiation and their potential links to ophiolites. Expedition 352 penetrated 1.2 km of magmatic basement at four sites and recovered three principal lithologies: tholeiiti...

Boninites are lavas and hypabyssal intrusive rocks with the rare combination of high concentrations of MgO (> 8 wt%) and high concentrations of SiO2 (> 52 wt%), coupled with low concentrations of TiO2 (< 0.5 wt%). They may be divided into high-Si and low-Si, and/or low-Ca and high-Ca, subtypes. They are characterized mineralogically by an abundance...

Boninites are rare, high-Si, high-Mg, low-Ti lavas that have considerable tectonic significance, especially for recognizing and interpreting episodes of subduction initiation in the geologic record. Formal identification and classification of boninites may be carried out using MgO-SiO2 and MgO-TiO2 diagrams to find compositions that satisfy modifie...

Subduction initiation is one of the least understood aspects of plate tectonics. In an effort to obtain the first in situ magmatic record of subduction initiation, the International Ocean Discovery Program Expedition 352 drilled at four sites in the inner trench wall of the Bonin Trench to recover 1.22 km of oceanic upper crust accreted within a fe...

The association of deep-sea trenches—steeply angled, planar zones where earthquakes occur deep into Earth’s interior—and chains, or arcs, of active, explosive volcanoes had been recognized for 90 years prior to the development of plate tectonic theory in the 1960s. Oceanic lithosphere is created at mid-ocean ridge spreading centers and recycled int...

The Izu-Bonin-Mariana (IBM) forearc preserves igneous rock assemblages that formed during subduction initiation circa 52 Ma. International Ocean Discovery Program (IODP) Expedition 352 cored four sites in the forearc near the Ogasawara Plateau in order to document the magmatic response to subduction initiation, and the physical, petrologic, and che...

The Izu–Bonin–Mariana (IBM) forearc contains a record of a widespread and short-lived subduction initiation event in the early Eocene. We present new high-precision ages to determine the rates and length scales of ocean crust production following subduction initiation along the IBM convergent margin. We also explore the implications of these ages f...

Supporting Information S1

The sinking of older and thicker oceanic plate within the deep Earth at subduction zones is one of the key components of plate tectonics on Earth. However, how subduction zones initiate has remained poorly understood. The long-standing view is that the rapid sinking of the nascent subducting plate in intra-oceanic systems generated extension that g...

The Li-O isotopes of olivine and pyroxene from the mantle sequence of the Luobusa ophiolite, a fragment of Neo-Tethyan forearc lithosphere in Tibet, reveal a series of magmatic processes and geochemical evolution in a nascent mantle wedge during subduction initiation. Olivine grains from the ophiolitic mantle sequence display δ¹⁸O values similar to...

We present a new comprehensive isotope and trace element dataset for north and central Tongan lavas including high-precision High Field Strength Element measurements. The emphasis of our study is on lavas from the northernmost volcanic islands of Tafahi and Niuatoputapu that exhibit unique compositions compared with other Tongan volcanoes, in parti...

International Ocean Discovery Program (IODP) Expedition 352 recovered a high-fidelity record of volcanism related to subduction initiation in the Bonin fore-arc. Two sites (U1440 and U1441) located in deep water nearer to the trench recovered basalts and related rocks; two sites (U1439 and U1442) located in shallower water further from the trench r...

Handheld energy dispersive portable X-ray spectrometers (pXRF) are generally designed and used for qualitative survey applications. We developed shipboard quantitative analysis protocols for pXRF and employed the instrument to make over 2000 individual abundance measurements for a selection of major and trace elements on over 1200 m of recovered co...

The Izu-Bonin-Mariana (IBM) forearc is the preeminent location to study subduction initiation and, by inference, the origin of most ophiolites. Subduction in the IBM system began circa 55 Ma on a long-offset fracture zone that juxtaposed crust of significantly different ages. IODP Expedition 352 cored four holes in the forearc near Chichi Jima in o...

The objectives for Expedition 352 were to drill through the entire volcanic sequence of the Bonin fore arc to 1. Obtain a high-fidelity record of magmatic evolution during subduction initiation and early arc development, 2. Test the hypothesis that fore-arc basalt lies beneath boninite and understand chemical gradients within these units and across...

Much of our understanding of ocean ridges has come from the collection and analysis of glasses recovered from ridge axes. However, applying the resulting methodologies to ophiolite complexes is not straightforward because ophiolites typically experience intense alteration during their passage from ridge to subduction zone to mountain belt. Instead,...

In this issue of Geology , [Turner et al. (2014][1], p. 139) take a new look at the geochemistry of amphibolite-facies lavas from Nuvvuagittuq ([O’Neil et al., 2011][2]), possibly the Earth’s oldest volcanic rocks ([O’Neil et al., 2012][3]). Geochemical fingerprinting had already been used to

The central Scotia Sea, located between the South American and Antarctic plates, is an inte- gral part of the marine conduit that permits eastward deep-water flow from the Pacific Ocean to the Atlantic Ocean. The geologic history of the central Scotia Sea is therefore critical for a full understanding of the initiation and subsequent evolution of t...

Methods of identification of volcanic arc lavas may utilize: (1) the selective enrichment of the mantle wedge by 'subduction-mobile' elements; (2) the distinctive preconditioning of mantle along its flow path to the arc front; (3) the distinctive combination of fluid-flux and decompression melting; and (4) the effects of fluids on crystallization o...

The Fonualei Spreading Center affords an excellent opportunity to evaluate geochemical changes with increasing depth to the slab in the Lau back-arc basin. We present H2O and CO2 concentrations and Sr, Nd, Pb, Hf and U-Th-Ra isotope data for selected glasses as well as new Hf isotope data from boninites and seamounts to the north of the Tonga arc....

Subduction-zone metamorphism is considered to be a major chemical filter for both the arc magmatism and mantle compositional heterogeneity. To understand the element transport during this process, we conducted a petrographic and geochemical study of the bulk-rock blueschists and eclogites from the western Tianshan ultrahigh-pressure metamorphic bel...

The earliest subaerially exposed magmatic products of the Fiji–Tonga–Kermadec (FTK) arc are preserved in the Yavuna Group of Viti Levu, Fiji, and cobbles from ‘Eua, Tonga. They are similar in age and magma types to the earliest rocks of the Izu–Bonin–Mariana (IBM) arc. In Fiji they include typical island arc tholeiitic (IAT), boninitic (BON), and M...

In the study of geochemical mass balances at subduction zones, the composition of the mantle wedge prior to additions from the slab is a critically important yet poorly constrained parameter. Deconvolving the influence of ancient versus modern enrichments is particularly difficult, especially when considering elements that are highly mobile. Here w...

Methodologies for fingerprinting metabasalts have been applied to eclogites with mixed success. Some, including Alpine examples famously studied by Gary Ernst >30 years ago, have been successfully assigned to tectonic settings and the results used to understand the now-disappeared ocean and its margins. Others, however, present two particular, well...

Rhyodacite lavas (Newcastle Volcanic Formation) from the Wagwater Basin in eastern Jamaica dated at 52.74 ± 0.34 Ma (2σ) have adakitic-like major element compositions, low Y and heavy rare Earth element (REE) concentrations and negative Nb and Ta anomalies on a normal mid-ocean ridge basalt normalised multi-element diagram. They also have lower Sr...

New 40Ar–39Ar ages of 5.6 to 1.3 Ma for lavas from the fossil Phoenix Ridge in the Drake Passage show that magmatism continued for at least 2 Ma after the cessation of spreading at 3.3 ± 0.2 Ma. The Phoenix Ridge lavas are incompatible element-enriched relative to average MORB and show an increasing enrichment with decreasing age, corresponding to...

Miyashiro (1973) famously initiated a debate on the tectonic setting of ophiolite complexes by proposing that ‘the Troodos ophiolitic complex was probably formed in an island arc’. This paper evaluates and updates Miyashiro's work by: (a) using the Mehegan–Robinson set of 137 fresh volcanic glass analyses to sidestep the controversy over the effect...

Archean continental crust largely comprises the trondhjemite, tonalite, and granodiorite/dacite (TTG/D) suite of igneous rocks. Formation of the earliest Archean (>3.5 Ga) TTG/Ds is controversial, being attributed to either subduction zone processes with active plate tectonics or thermochemical mantle convection with no plate tectonic processes. A...

Forearcs have long been recognised as important potential protoliths for ophiolites, given that they are the first lithologies to be obducted when a continent `collides' with a trench in an intraoceanic setting. It is therefore perhaps surprising that oceanic forearcs and supra-subduction zone (SSZ) ophiolites are not more similar. One possible rea...

The accessory mineral chrome–spinel, [(Mg,Fe) (Cr,Al,Fe)2O4], is well-established as a useful, alteration-resistant petrogenetic and tectonic setting indicator for mafic–ultramafic rocks. This study of unaltered spinels from 58 peridotites from oceanic and ophiolitic settings further develops the tectonic discrimination of peridotites from mid-ocea...

A wide variety of rock types were produced by the latest Cretaceous magmatism in the Central Anatolian Crystalline Complex. These rocks can be divided into three distinct units: (i) calc-alkaline, (ii) subalkaline/transitional, and (iii) alkaline. The calc-alkaline rocks are mainly metaluminous (I-type) ranging from monzodiorite to granite. The sub...

Geochemically, the asthenosphere can be viewed (at least beneath oceanic lithosphere) as divisible into isotopically distinct domains, with a systematic variability within these domains. Both between-domain and within-domain variations provide evidence for asthenosphere flow fields. Between mantle domains, tracing the domain boundary through time i...

Post-collision magmatic rocks are common in the southern portion of the Marmara region (Kapıdağ, Karabiga, Gönen, Yenice, Çan areas) and also on the small islands (Marmara, Avşa, Paşalimanı) in the Sea of Marmara. They are represented mainly by granitic plutons, stocks and sills within Triassic basement rocks. The granitoids have ages between Late...

Two geochemical proxies are particularly important for the identification and classification of oceanic basalts: the Th–Nb proxy for crustal input and hence for demonstrating an oceanic, non-subduction setting; and the Ti–Yb proxy for melting depth and hence for indicating mantle temperature and thickness of the conductive lithosphere. For the Th–N...

Viti Levu, Fiji and \textquoteleftEua, Tonga have the oldest subaerial exposures of the remnant Vitiaz Arc which formed when subduction initiated (>=45Ma) as the result of a Pacific Plate motion change. We present new high-precision ICP-MS trace element and MC-ICP-MS isotope data for newly collected Fiji rocks and previously analyzed (XRF,TIMS) Vit...

Pb isotope systematics have already been used successfully to demonstrate that the lavas of the arc-basin terrains of the SW Pacific are derived from two mantle domains, one of Pacific-like character and the other of Indian-like character. However, the mobility of Pb during subduction and alteration has mainly restricted the fingerprinting of domai...

Located in the northwestern part of the Aegean region, Dikili-Çandarli volcanic suite contains products representative for the western Anatolian Miocene volcanism. They can be divided into two main groups: the Dikili and the Çandarli groups. The Dikili group is Early-Middle Miocene in age and consists mainly of pyroclastic rocks, andesitic-dacitic...

The Vila de Cruces ophiolite is one of the ophiolitic units involved in the Variscan suture of the northwest Iberian Massif. This ophiolite consists of a tectonically repeated succession of greenschist facies volcanic rocks, common alternations of metasediments of pelitic or siliceous character, and scarce orthogneisses, metagabbros, and serpen-tin...

Many diagrams conventionally used to classify igneous rocks utilize mobile elements, which commonly renders them unreliable for classifying rocks from the geological record. The K2O–SiO2 diagram, used to subdivide volcanic arc rocks into rock type (basalts, basaltic andesites, andesites, dacites and rhyolites) and volcanic series (tholeiitic, calc-...

The Careón ophiolite (Galicia, NW Iberian Massif) shows lithological and geochemical features suggestive of an origin in a suprasubduction zone setting. As with other Devonian ophiolites in the European Variscan belt, it was generated within a contracting Rheic Ocean. This setting and the general absence of large Silurian-Devonian volcanic arcs on...

Two Paleozoic ophiolites of different age mark the Variscan suture in the Cabo Ortegal Complex (northwestern Iberian Massif). The Moeche and Purrido alloch-thonous ophiolites are structurally located between an exotic terrane of continen-tal affi nity (basal units), below, and another terrane with arc affi nity (upper units), above. The mafi c rock...

176Hf/177Hf isotopes provide information about the behaviour of so-called immobile elements in subduction environments. Early studies of Hf isotopes in subduction zones reached different conclusions regarding the mobility of high-field-strength elements during subduction-related processes. To test the behaviour of Hf during subduction, we have exam...

Lithogeochemical fingerprinting of productive calc-alkaline intrusions (those associated with mineralization) is important in both economic and research geology, yet diagnostic criteria for geochemical prospecting and predicting mineralization are scarce. Previous efforts of finding discriminants for productive host rocks included halogens, water c...

In Northeastern Anatolia, the Erzurum-Kars plateau comprises the northernmost part of a volcanic province related to the collision between the Eurasian and Arabian continents. It contains an almost complete record of the volcanism from 11 Ma to 1.5 Ma. Volcanic units on the plateau are calc-alkaline in character and contain a distinct subduction si...

The compositions of back-arc basin basalts (BABB) can usefully be viewed as products of four factors: (1) the composition of inflowing mantle and its preconditioning during flow to the site of melting; (2) the influx of a subduction component into the arc—basin system; (3) the nature of the interaction between the mantle and subduction components;...

Ophiolites were divided some 20 years ago into two major types: SSZ (Supra-Subduction Zone) Ophiolites, which have a subduction signature; and MOR (Mid-Ocean Ridge) Ophiolites which have no subduction signature. Since then, the term `ophiolite' has become used more generally to include fragments of oceanic lithosphere other than those formed at mid...

Geochemical fingerprinting of past tectonic environments using ancient volcanic rocks is now a well-established method and a large number of empirically-derived geochemical discriminant diagrams have been published for this purpose. The best of these have potential advantages over quantitative discriminant methods because petrogenetic modelling ena...

The Central Anatolian Crystalline Complex (CACC) contains Paleozoic-Mesozoic, medium-high grade metamorphic rocks overthrust by Upper Cretaceous ophiolitic units and intruded by a number of plutons (around 79.5 to 66.6 Ma). Central Anatolia exhibits good examples of calc-alkaline and alkaline magmatism of similar age in a collision-related tectonic...

A new ICP-MS database for glasses from the Mariana Trough, together with published and new ICP-MS data from the Mariana arc, provides the basis for geochemical mapping of the Mariana arc-basin system. The geochemical maps presented here are based on the graphic representation of spatial variations in geochemical proxies for the principal mantle and...

Element release from subducted materials can be investigated using thermodynamics, experiment and observation. Thermodynamic calculations quantify free energy changes for reactions in which an element is converted from a chosen solid state to a chosen dissolved state. Such calculations illustrate the dependency of element mobility on, in particular...

Volcanic arc magmas are characterised, as is well known, by geochemical patterns which feature the selective enrichment of some elements (the subduction-mobile or non-conservative elements) relative to others (the subduction-immobile or conservative elements). More detailed evaluation of these patterns highlights three groups of subduction-mobile e...

Mantle preconditioning may be defined as the extraction of small melt fractions from mantle asthenosphere during its flow to the site of magma generation. Equations may be written for mantle precondi- tioning, assuming that the mantle comprises enriched ‘plums’ in a depleted matrix. The equations take into account variations in mass fraction of plu...