Primitive Values Research Articles

Exploring the tectono-magmatic evolution of intraoceanic fore-arc setting during subduction initiation: perspectives from trace and platinum group element systematics of the Jijal ultramafic arc system, NE Pakistan

ABSTRACT The Jijal Complex is considered one of the largest Neo-Tethyan remnants in the intra-oceanic Cretaceous–Palaeogene Kohistan Arc of Pakistan. This complex largely consists of gabbros, peridotites, and chromitites. Previous studies documented the genesis of gabbros and chromitites in detail; however, detailed geochemistry and magma genesis were lacking. In this investigation, we present whole-rock geochemical and platinum group elements (PGEs) data of Jijal peridotites (dunites and harzburgites). The objectives of this study are to elucidate magmatic processes and tectonic regimes involved in the formation of peridotites, factors influencing the concentration and dispersion of PGEs in them, and their tectonic evolution. The investigated peridotite samples are depleted in magmaphile major elements (Al2O3: 0.23–0.57, TiO2: 0.01–0.04, and CaO: 0.08–0.69 wt%), relative to the primitive mantle values, reflecting melt-rock interaction during their magmatic evolution. In addition, rare-earth element (REE) contents in harzburgites are relatively higher compared to the dunites; however, both rock types exhibit depletion with respect to the chondrite-normalized values. The obvious negative anomalies of Nb, Zr, and enriched LREE and large ion lithophiles collectively substantiate their association with depleted arc-type mantle components, metasomatism, and melt/fluid-rock reactions after partial melting episodes. Bulk-rock and geochemical modelling of PGEs data of the peridotites suggest their shallow depth spinel-bearing depleted heterogeneous mantle source and generation from refractory mantle residuum along with boninitic signatures in a supra-subduction zone (SSZ). The PGE’s geochemistry additionally reveals that partial melting, fractionation, metasomatism, and sulphur under-saturation were the key factors that controlled the concentration and distribution of PGEs in the studied rocks. The boninitic features of the Jijal peridotites are equated with intraoceanic fore-arc followed by subduction initiation, and melt-rock reactions in a hydrated forearc mantle, indicating robust evidence of mantle depletion and pervasive refertilisation in an embryonic Neo-Tethyan arc system. Tectonically, the investigated rocks encapsulate vestiges of the Cretaceous Tethyan Ocean and record multifaceted history from boninitic to slab-proximal island arc affinity in compliance with an intraoceanic SSZ fore-arc regime coherent with the subduction inception.

Petrogenesis and tectonic implications of the Bloubergstrand basaltic andesites, Tygerberg Formation, Malmesbury Group, Pan-African Saldania Belt, southwestern Africa

Abstract The Bloubergstrand Member, consisting of mafic to intermediate tuffs and flows within the Tygerberg Formation of the Malmesbury Group, is a crucial but understudied component of the western Saldania Belt in southwestern Africa. With a U-Pb zircon age of 555 ± 5 Ma, these volcanic rocks provide valuable insights into the origins and, more broadly, the tectonic setting of the Saldania Belt during the final stages of Malmesbury Group sedimentation in the context of the construction of southwestern Gondwana at approximately 560 to 540 Ma. The Bloubergstrand Member amygdaloidal volcanic rocks vary from basaltic andesitic to andesitic and have experienced varying degrees of alteration. The volcanic rocks are enriched in the large ion lithophile elements (LILE) relative to the high field strength elements (HFSE). When normalised to primitive mantle values, they show enrichment in Cs, Rb, K and Pb and mild enrichment in Th, U, Zr and Hf, with the light rare earth elements (LREE) enriched relative to the heavy rare earth elements (HREE). They are depleted in Ba, Nb, Ta, Sr, Eu, P and Ti. εNd(t) values are mildly negative ranging from -3.60 to -2.39, and Nd TDM model ages range from 1.4 to 1.7 Ga. Initial 87Sr/86Sr ratios vary from 0.70478 to 0.70620, with one higher value of 0.72270, the latter likely due to extensive alteration. The Bloubergstrand Member volcanic rocks exhibit characteristics suggesting their origin from partial melting of lithospheric to transitional asthenospheric upper mantle, influenced by sediment-derived melts and variable degrees of crustal contamination. With continental arc basalt compositions and similarities to shoshonites, the samples reflect variable degrees of partial melting and source heterogeneities. Fractional crystallisation of pyroxenes, hornblende, and plagioclase contributes to compositional variability. Erupting in a continental arc margin, likely part of the Arachania block of the Kalahari craton, separated during the Tonian break-up of Rodinia, the volcanics were associated with the Marmora basin formed by eastward-directed subduction below the western Kaapvaal Craton margin. Extruded in a distal position relative to the Cuchilla Dionisio Arc in present-day southern Brazil and Uruguay, these volcanic rocks preceded the closure of the southern Marmora basin. The mantle melting, possibly a result of slab roll-back, break-off, ridge subduction, or a combination, served as a precursor to the lower crustal heating that generated the granitic magmas of the Cape Granite Suite.

Iron isotope heterogeneity in magmas of subduction zones and its origin

Iron isotope heterogeneity of subduction-related primitive magmas was traditionally thought to be predominantly attributed to the addition of slab-derived components. However, the specific subducted material responsible for inducing Fe isotope heterogeneity in the subarc-backarc mantle remains poorly constrained. Here we report Fe isotopic compositions of a series of backarc basin basalts (BABBs) from the Woodlark Basin (an intra-arc rift basin), Vate Trough (a nascent rear-rift basin), and Lau Basin (a relatively mature basin) in the southwestern Pacific. Even though these BABBs have various geochemical compositions ranging from mid-ocean ridge basalts (MORB)-like to arc-like, which should be affected by various amounts of the slab-derived fluids and/or sediment melts, their δ56Fe values (0.05–0.18‰) are within the range of global MORB (0.05–0.17‰). After correction for crystal fractionation, the primitive δ56Fe values (δ56Fe-prim) displayed no co-variation with indicators of subduction contributions (e.g., Ce/Pb, Nb/U, Ba/La, and Th/Yb) or source redox conditions caused by slab inputs (e.g., V/Yb, V/Ti), suggesting that the δ56Fe-prim values of these BABBs are rarely affected by subduction metasomatism and the change in oxygen fugacity caused by subducted input. Therefore, we proposed that the MORB-like δ56Fe values of the studied BABBs were primarily caused by mantle melting processes. Furthermore, we presented a compilation of available Fe isotopic data for BABBs and island arc basalts (IABs) and used these data to evaluate Fe isotope heterogeneity in subduction settings. In particular, compared with δ56Fe-prim of MORB, the δ56Fe-prim of BABBs from the Central Lau Spreading Centre in the Lau Basin and the IABs have lower values, whereas BABBs from the Rochambeau Ridges in the Lau Basin have higher δ56Fe-prim values. By comprehensively considering the factors affecting the variation in Fe isotopic compositions in magmatic rocks in subduction zones (e.g., crystal fractionation, partial melting of the mantle, redox conditions, and subduction-related metasomatism), we proposed that the varied Fe isotopic compositions in subduction settings could reflect their heterogeneous sources, which may be related to plate subduction. Specifically, during plate subduction, a melt-depleted refractory forearc mantle peridotite (with low δ56Fe values) could be dragged by subducted slab into subarc or backarc depths, resulting in light Fe isotopic enrichment in island arc magmas or BABBs; additionally, serpentinites (both in the slab and mantle wedge) can generate light Fe isotopic enrichment in island arc magmas. High δ56Fe values in the BABB (e.g., from the Rochambeau Ridges in the Lau Basin) may result from the toroidal influx of nearby upwelling plume components or the assimilation of hydrothermally altered oceanic crust.

Chromium isotope system of intraplate basaltic lavas: Implication for recycling materials into mantle

To explore the mantle source properties and the magmatic evolution process for intraplate basaltic lavas, as well as to investigate the potential of Cr isotopes to trace recycled crustal materials, we present Cr isotope compositions for 72 well-characterized samples of Cenozoic intraplate basaltic lavas from eastern China. These basalts display a resolvable δ53Cr range of −0.24‰ to −0.03‰ (n = 72), comparable to MORB and OIB. With respect to the evolved lavas, their δ53Cr scatter can be interpreted as a result of fractional crystallization of predominant olivine (or/and clinopyroxene) with 1% to 3% spinel from heterogeneous magma sources under different oxygen fugacity conditions. Combined with Sr-Nd-Zn-Fe isotope data, the least evolved basalts with MgO of ∼10% display a large δ53Cr range, indicating the presence of different magma component end-members, including one low-Si and two high-Si components. Two high-Si enriched components have δ53Cr values lower than those of primitive N-MORB and OIB magmas, consistent with their derivations most likely from relatively enriched mantle pyroxenites. Notably, the low-Si nephelinitic component could not be a simple end-member as proposed before. Correlations of δ53Cr with εNd(t)-87Sr/86Sr(i)-Fe/Mn-Ti/Ti*-Hf/Hf*-δ66Zn-δ56Fe [Ti/Ti* = TiN/(NdN-0.055 × SmN0.333 × GdN0.722), Hf/Hf* = HfN/(SmN × NdN)0.5. N represents the primitive mantle-normalized values] for nephelinites from both the North China Block and the South China Block suggest mixing between partial melts of carbonated peridotite and pyroxenite sources. The carbonated peridotite derived melt is characterized by depleted SrNd isotopes, low Fe/Mn, Ti/Ti* and Hf/Hf* ratios, and heavier than BSE's Cr-Fe-Zn isotope compositions. The highly oxidized environment induced by carbonatization effectively reduces Cr isotope fractionation between melts and residues during partial melting of the carbonated peridotite, resulting in the heavy Cr isotope feature of melts being inherited from the carbonated mantle source, consistent with the heavy Cr isotope compositions of carbonated mantle xenoliths obtained previously. Thus, this work highlights that Cr isotopes might act as a potential tracer for subducted sedimentary carbonates.

MetaViz – A graphical meta-model instantiator for generating information dashboards and visualizations

ObjectivesThis work presents the application of meta-modeling to the data visualization and dashboards' domain to obtain two main products: a system that allows the instantiation of the meta-model through a graphical interface and a code generator that takes the instantiation of the meta-model as an input to generate visualizations and dashboards. MethodsA domain engineering approach complemented with an example-driven methodology was iteratively employed to develop the dashboard meta-model. This meta-model was subsequently used as an input to implement a code generator of information dashboards. These two artifacts were finally combined to design and develop the architecture of MetaViz. ResultsThrough this process, it was possible to generate visualizations and dashboards using visual elements and basic interactions. MetaViz allows the generation of basic charts (line charts, scatter plots, pie charts, etc.) as well as more complex displays with interactive behavior along different views, layouts, and operations. ConclusionsThe development of MetaViz has served as proof of the viability and benefits of applying these methodologies to a complex domain, but also to set the foundations of a system that allows users to trace every single element from a data visualization to its most primitive values.

An SPH scheme based on targeted essentially nonoscillatory reconstruction and its applications

<p indent="0mm">In this paper, we developed an SPH scheme based on targeted essentially nonoscillatory (TENO) reconstruction. In this scheme, the Riemann-SPH method is applied to solve governing equations. However, the original Riemann-SPH generates excessive numerical dissipations due to the adoption of an approximate Riemann solver, thus exhibiting low numerical accuracy for simulating fluid flows. To solve this problem, we applied a five-point TENO method to reconstruct the left and right states of the Riemann problem. In the original TENO method, five equidistant stencil points are required. However, due to the nature of the Lagrangian-SPH method, the particle distribution is typically random. It is difficult for SPH to find equidistant points. To mitigate this issue, we first consider a particle pair as two stencil points and find the particle closest to the missing point. Through the gradient approximation, we can obtain the primitive values of the missing point. Based on these values, we can implement the TENO reconstruction smoothly. The excessive numerical dissipations are successfully reduced through TENO reconstruction, and the numerical accuracy is further improved. Importantly, the proposed TENO-SPH scheme avoids using the artificial viscosity commonly used in the conventional SPH. Moreover, TENO-SPH has a robust numerical ability, and thus, it can be applied to reproduce typical compressible flows, vortex flows, and free surface flows with superior accuracy.

Exploring Motivational Factors of Indigenous House Form for Value-Based Development: The Tiv People of Central Nigeria in Context

The quest for contextual identity and value-based developments by concerned authorities justifies the necessity to explore the inherent motivating factors that influence housing formation and the built environments of the varied Nigerian ethnic groups. Rapoport's identification of socio-cultural values as the primary influencers of house form has come under scrutiny, stipulating a replication in different contexts. One tends to ask about the motivating factors for the indigenous house form of the different ethnic groups in Nigeria that need to be explored and harnessed for value-based planning, design, and development for future infrastructure. This study explores the motivating factors of the indigenous house form of the Tiv people of central Nigeria, filtered through Maslow's Hierarchy of needs. This qualitative study utilised the Means-End Chain soft laddering technique, where 24 participants were interviewed, analysed, and ranked. According to the findings, Tiv indigenous dwellings are circular-shaped, connecting them to their cultural heritage. The open compounds also permit communal interactions in their natural setting and express their determination to live independent family lives. For housing stakeholders in Nigeria, the primitive values evoked in this study are essential for developing a contemporary, culturally sustainable society.

Distribution of Te, As, Bi, Sb, and Se in Mid-Ocean Ridge Basalt and Komatiites and in Picrites and Basalts from Large Igneous Provinces: Implications for the Formation of Magmatic Ni-Cu-Platinum Group Element Deposits

Abstract In magmatic nickel-copper-platinum-group element (PGE) deposits, the PGEs are found both in solid solution in base metal sulfides and as platinum group minerals (PGMs). Apart from S, the most common elements that the PGEs combine with to form PGMs are Te, As, Bi, Sb, and Sn (TABS). Whether the TABS play a role in collecting the PGEs or simply partition into the sulfide liquid along with the PGEs and later combine with PGEs when the sulfide phase becomes saturated with PGMs is not currently clear. This is in part because the concentrations of TABS in the magmas (picrites and basalts from large igneous province and komatiites) that form these types of deposits are not well established, and hence it is not evident whether the magmas contain sufficient TABS to control PGEs. In order to establish the concentrations of Te, As, Bi, Sb, and Se (TABS+) in these rock types and to document the processes affecting these concentrations, we have determined TABS+ concentrations in komatiites, in mid-ocean ridge basalt, and in picrites and basalts from large igneous provinces. Using TABS+ mantle-normalized diagrams, the affects of different mantle sources, crystal fractionation, crustal assimilation, degassing, and alteration are considered. We estimate the concentrations of TABS+ in komatiites to be approximately twice primitive mantle values. In picrites the concentrations vary: approximately 10 times primitive mantle values for As and Sb and decreasing through Bi to Te from 7 to 2 times primitive mantle. Assimilation of S-bearing sedimentary rocks is thought to be important in triggering sulfide saturation leading to the formation of Ni-Cu-PGE deposits. Assimilation of such sediments would enrich the magma in Th over Nb and in As, Sb, and Bi. Evidence of assimilation in the form of TABS and Th enrichment is clear in the PGE reef deposits of the Bushveld and Stillwater Complexes, but the deposits do not contain sufficient TABS to control the PGEs. This is also true in the Norilsk-Talnakh Ni-Cu-PGE deposits. However, at Norilsk degassing of the magma has resulted in the loss of TABS, which results in negative As, Bi, Se, and Te anomalies on primitive mantle-normalized plots.

A targeted essentially non-oscillatory (TENO) SPH method and its applications in hydrodynamics

In this paper, we propose a targeted essentially non-oscillatory (TENO) SPH scheme. In this scheme, a 5-point stencil consisting of 3 candidate sub-stencils is adopted to implement the TENO reconstruction as originally proposed in the mesh-based methods. In the original TENO reconstruction, these five points are fixed and equidistant. However, it is difficult for SPH to determine these five points due to the random particle distribution. To remedy this issue, for two interacting particles, we first consider them as two existing stencil points. Then, for the other three points, we search for the closest particles to their exact positions. Subsequently, considering the gradient of these particles, we can finally obtain the values of these target points. Afterwards, the primitive values of points are reconstructed by TENO reconstruction where the polynomial interpolations are modified. Numerical results show that the proposed TENO-SPH scheme can be applied to reproduce some compressible flows involving shocks and small-scale structures, some incompressible vortex flows and free surface flows with superior accuracy.

A Comparative Study of Chinese Xiangliu and Greek Hydra

Mythology reflects ancient people's primitive understanding of the origin of the world, natural phenomena and social life, so the mythological narration is usually full of imagination and symbolic meanings. In both Chinese and Greek Mythology, there is a similar legend of nine-headed snakes, which reflects those ancient people's exploration of unaccountable great floods. These nine-headed monsters are called Xiangliu and Hydra respectively. According to Guideways Through Mountains and Seas, a classic collection of Chinese ancient stories, Xiangliu is the courtier of Gonggong, a legendary god of Water. Hydra in Greek mythology is a gigantic snake-like monster with nine heads, living near Lake Lerna. Both the two malicious beasts have nine heads, and are trouble-makers through taking advantage of floods, always producing poisonous smell and breath. Xiangliu has nine human faces, and his heads do not have the ability to regenerate, while Hydra has dragon-like heads with teeth and claws, and he has the ability to regenerate. Both stories are symbolic with hero-worshiping and flood-controlling themes, reflecting primitive common values in both cultures. Through comparing Xiangliu and Hydra, discussing their prototypes and their evolutionary forms in later works, we may have a better understanding of Chinese and western mythical stories, and then promote mutual respect to divergences.

Mantle control on magmatic flare-ups in the southern Coast Mountains batholith, British Columbia

AbstractThe southern Coast Mountain batholith was episodically active from Jurassic to Eocene time and experienced four distinct high magmatic flux events during that period. Similar episodicity has been recognized in arcs worldwide, yet the mechanism(s) driving such punctuated magmatic behavior are debated. This study uses zircon Hf and O isotopes, with whole-rock and mineral geochemistry, to track spatiotemporal changes in southern Coast Mountains batholith melt sources and to evaluate models of flare-up behavior and crust formation in Cordilleran arc systems. Zircon Hf isotope analysis yielded consistently primitive values, with all zircon grains recording initial εHf between +6 and +16. The majority (97%) of zircons analyzed yielded δ18O values between 4.2‰ and 6.5‰, and only five grains recorded values of up to 8.3‰. These isotopic results are interpreted to reflect magmatism dominated by mantle melting during all time periods and across all areas of the southern batholith, which argues against the periodic input of more melt-fertile crustal materials as the driver of episodic arc magmatism. They also indicate that limited crustal recycling is needed to produce the large volumes of continental crust generated in the batholith. Although the isotopic character of intrusions is relatively invariant through time, magmas emplaced during flare-ups record higher Sr/Y and La/Yb(N) and lower zircon Ti and Yb concentrations, which is consistent with melting in thickened crust with garnet present as a fractionating phase. Flare-ups are also temporally associated with periods when the southern Coast Mountains batholith both widens and advances inboard. We suggest that the landward shift of the arc into more fertile lithospheric mantle domains triggers voluminous magmatism and is accompanied by magmatic and/or tectonic thickening. Overall, these results demonstrate that the magmatic growth of Cordilleran arcs can be spatially and temporally complex without requiring variability in the contributions of crust and/or mantle to the batholith.

New SIMS zircon U-Pb ages and oxygen isotope data for ophiolite nappes in the Eastern Desert of Egypt: Implications for Gondwana assembly

Ophiolite nappes, encompassing dismembered oceanic lithosphere sections, in the Eastern Desert of Egypt are mainly confined to Tonian-Cryogenian inter-terrane sutures. A cohesive geodynamic model of these ophiolites remains elusive in light of the variably obliterated field relationships and lack of ample geochronological information. Available geochemical data of the well-studied ophiolites lead to different interpretations of mid-ocean ridge, back-arc and/or fore-arc affinities. Relevant geochronological data are likewise heterogeneous in terms of methods and the dated lithologic units. Here, we attempt to constrain the timing and genesis of some Eastern Desert ophiolites by using new SIMS zircon U-Pb and oxygen isotope data of gabbros from four different ophiolites.The new zircon U-Pb ages and oxygen isotope values integrated with available geochemical data constrain ages of 737 ± 6 Ma and 720 ± 6 Ma and fore-arc origin of the Wadi El-Sid and Gabal Abu Dahr-Abu Siayil ophiolites, respectively. The δ18O(Zrn) values of these fore-arc ophiolites (+2.5 to +8.5‰) deviate significantly from primitive mantle values, suggestive of substantial degrees of subduction-induced metasomatism. The Gabal El-Rubshi and Wadi Ghadir back-arc ophiolites returned younger and mutually similar ages (702 ± 5 Ma and 698 ± 4 Ma, respectively) and less heterogeneous δ18O(Zrn) values (+3.1 to +6.1‰). Excluding outliers, most measured δ18O(Zrn) values are indistinguishable from the unaltered MORB values and the restricted mantle-like δ18O range.Results of the present study suggest multiple arc-fore-arc accretion events and an extensive late Tonian back-arc basin opening event in the evolution of the Eastern Desert accretionary belt. Subduction tectonics continued to stabilize the immature arc crust ∼750–720 Ma and a tapered back-arc spreading ridge engendered at ∼700 Ma. The final terrane accretion and suturing could have been associated with subduction-related melts that circulated and locally metasomatized back-arc ophiolites. This model is in broad agreement with the recently advocated ∼720 Ma plate reorganization in the closure of the Mozambique Ocean during the course of Gondwana assembly.

Multistage melt impregnation in Tethyan oceanic mantle: Petrochemical constraints from channelized melt flow in the Naga Hills Ophiolite

Ophiolitic sequences obducted onto continental margins allow field based observations coupled with petrochemical interrogations of upper mantle lithologies thereby aiding evaluation of compositional heterogeneity of oceanic mantle, depletion-enrichment events and geodynamic conditions governing oceanic lithosphere formation. The Naga Hills Ophiolite (NHO) suite preserves a segment of the Neotethyan oceanic lithosphere encompassing a package of mantle and crustal lithologies. This paper for the first time reports the occurrence of melt flow channels traversing the mantle section near Molen of the NHO and presents a comprehensive study involving chromite-spinel chemistry, bulk rock major, trace and PGE geochemistry to understand the petrogenesis and evolution in a geodynamic transition from mid oceanic ridge (MOR) to suprasubduction zone (SSZ). The spinel chemistry of peridotitic melt channels depicts both MOR-type and SSZ signatures underlining a transitional tectonic frame. Chromite chemistry and high Al2O3/TiO2 ranging from 15.98–35.70 in concurrence with low CaO/Al2O3 ranging from 0.03–0.53; and chondrite normalised LREE > MREE < HREE patterns confirm the influx of boninitic melts into the refractory mantle. The boninitic signature shared by melt channels and host rock invokes a geochemical and geodynamic transition from anhydrous melting of depleted mantle to hydrated fluid flux melting resulting in boninitic melts, that subsequently impregnate and refertilise the fore arc mantle wedge in a SSZ regime at the nascent stage of subduction. The high Ba/Nb, Ba/Th, and Ba/La for the studied peridotites highlight the influx of subduction derived fluids in the supra subduction mantle. Further higher Zr/Hf and Nd/Hf with respect to primitive mantle values in concurrence with lower Nb/Ta suggest progressive refertilisation due to fluid- and melt-driven metasomatism of the refractory fore arc mantle wedge. The chondrite normalised PGE patterns suggest positive Ir and Ru anomalies stipulating the source to be refractory while enriched Pt and Pd underpins the mobilisation of these elements by subduction derived fluids and melts. The elevated abundances of PPGEs than IPGEs as cited by PPGE/IPGE > 1; and Pd/Pt avg. 0.85 for melt channels and 0.84 for host peridotites indicate fluid-fluxed metasomatism of fore arc mantle wedge with a S-undersaturated trend coupled with boninitic affinity. The mineral, trace, REE and PGE chemistry collectively emphasizes that the mantle peridotites of the NHO formed in a transitional geodynamic tectonic setting caused by fore arc extension during subduction initiation followed by rejuvenation by subduction derived fluids and boninitic melts, which typically are of the SSZ tectonic regime. The harzburgitic melt channels and host rock are refractory in nature, reflecting multiple episodes of melt extraction of about 5–15% and ~10–20% respectively from a spinel peridotite mantle source. The occurrences of these melt channels indicate segregation and percolation of melt through porous and channelized network in upper mantle peridotites.

The komatiite-mantle platinum-group element paradox

The platinum-group element (PGE) contents of komatiites have been used to estimate the PGE contents of their mantle sources and investigate temporal variations in the PGE systematics of the mantle throughout Earth history. However, the use of mantle melts to investigate source characteristics is critically dependent on understanding the fractionation of the elements in question between mantle sources and their derived magmas. We present new PGE and Re abundance data, together with Re-Os isotope data for the pristine 1.9 Ga Winnipegosis komatiites, Canada. Whole rock Re-Os isotope data define a 1865 ± 40 Ma isochron, consistent with previous age estimates, with initial γOs of +0.9 ± 1.4. The PGE and Re variations in these komatiites were controlled by fractionation of olivine, chromite, Os-Ir alloys, a Ru-Os rich phase (possibly laurite) from the komatiite melt. The calculated parental melt composition at 23.6 ± 1.6 wt% MgO has 1.1 ± 0.1 ppb Os, 0.91 ± 0.08 ppb Ir, 4.0 ± 0.5 ppb Ru, 7.0 ± 0.8 ppb Pt, 7.2 ± 0.7 ppb Pd, and 0.53 ± 0.06 ppb Re. The calculated PGE contents are low relative to many komatiites; using existing methods for calculating the PGE contents of mantle sources suggests the Winnipegosis source had PGE contents from 25 ± 19 wt% to 57 ± 7 wt% of primitive mantle values. This surprising finding substantiates a growing ‘PGE paradox’, where almost all komatiites appear to have formed from PGE-depleted mantle sources. We suggest the simplest resolution to this paradox is that current methods systematically underestimate mantle source PGE contents. We test the assumptions implicit in these methods by comparing detailed models of PGE behaviour during mantle melting to a large database of parental melt compositions of high degree melts. Ruthenium behaviour in high degree melts can be adequately modelled using our current understanding of Ru partitioning. However, the Ru contents of high degree mantle melts are strongly dependent on the degree of melting, as Ru-rich melts formed after sulphide exhaustion are increasingly mixed into early-formed Ru-poor melts. Platinum and Pd behaviour during mantle melting cannot be successfully modelled under the widespread assumption that they are strongly incompatible following sulphide exhaustion, suggesting that these elements cannot be used to estimate PGE contents of the mantle sources of high degree melts. Parental melt Pt and Pd in many high degree lavas are correlated with Al2O3/TiO2, suggesting a pressure control on their partitioning. We attribute the relatively low PGE contents of the Winnipegosis komatiites to their moderate degrees and depth of melting compared to other komatiites, rather than invoking a PGE-depleted mantle source. More broadly, the complex controls (T, P, fO2, S content, prior depletion) on the PGE contents of komatiites mean that most komatiites can be reconciled with being derived from sources with primitive mantle-like PGE contents, and few komatiites can be confidently asserted to come from PGE-depleted mantle sources. Pending a better understanding of PGE behaviour during mantle melting, we recommend caution when using komatiite PGE systematics to infer the highly siderophile element evolution and accretionary history of Earth’s mantle.

Origin of Qinxi Silver Polymetallic Deposit in Southeast Coast, China: Evidences from H–O–S–Pb Isotopes and Mineral Rb–Sr Geochronology

The Qinxi silver deposit is located in eastern Fujian Province, South China. It is hosted in the late Jurassic Nanyuan volcanic unit and controlled spatially by structural alteration zone. The origins of the deposit are understood poorly. In this study, systematic field geology, precise sulfide geochronology, and H–O–S–Pb isotope analyses were carried out. The symbiotic minerals and ore assemblages are interpreted as evidence that Qinxi ore is a typical middle to low temperature hydrothermal deposit. Galena and sphalerite from the ore yield a Rb–Sr isochronal age of 130 ± 2.0 Ma (MSWD = 1.7), and single galena samples yield a Rb–Sr isochronal age of 130 ± 7.1 Ma (MSWD = 2) and are evidence that the ore was formed in the early Cretaceous period. The silver-bearing quartz vein has O:H and 18O:16O ratios intermediately between magmatic and meteoric water (δ18 Owater-smow from −2.50‰ to −0.1‰ and δDv-smow from −73.6‰ to −60.7‰). The δ34 S values of metal sulfide are close to the primitive mantle sulfur values (δ34S = −1.7 to 7.1‰, avg. = 0.92‰). The Pb isotopic compositions from the ore are similar to those of the hosted volcanic unit, with a value between the upper crust and mantle isotope composition (206Pb/204Pb = 18.421~18.605, 207Pb/204Pb = 15.580~15.772, 208Pb/204Pb = 38.591~39.183). Lead–zinc sulfides have mature crustal-derived Sr isotopic features ((87Sr/86Sr)i = 0.7103). Thus, the metallogenic source materials mainly came from the crust. Moreover, regional geological studies suggest that the Qinxi ore deposit was likely formed in an extensional terrane.

Platform-Independent Dynamic Taint Analysis for JavaScript

Previous approaches to dynamic taint analysis for JavaScript are implemented directly in a browser or JavaScript engine, limiting their applicability to a single platform and requiring ongoing maintenance as platforms evolve, or they require nontrivial program transformations. We present an approach that relies on instrumentation to encode taint propagation as instructions for an abstract machine. Our approach has two key advantages: it is platform-independent and can be used with any existing JavaScript engine, and it can track taint on primitive values without requiring the introduction of wrapper objects. Furthermore, our technique enables multiple deployment scenarios by varying when and where the generated instructions are executed and it supports indirect taint sources, i.e., situations where taint enters an application via arguments passed to dynamically registered event-listener functions. We implemented the technique for the ECMAScript 5 language in a tool called Ichnaea, and evaluated it on 22 NPM modules containing several types of injection vulnerabilities, including 4 modules containing vulnerabilities that were not previously discovered and reported. On these modules, run-time overheads range from 3.17x to 38.42x, which is significantly better than a previous transformation-based technique. We also report on a case study that shows how Ichnaea can be used to detect privacy leaks in a Tizen web application for the Samsung Gear S2 smart watch.

Primitive values of rational functions at primitive elements of a finite field

Given a prime power q and an integer n≥2, we establish a sufficient condition for the existence of a primitive pair (α,f(α)) where α∈Fq and f(x)∈Fq(x) is a rational function of degree sum n. (Here f=f1/f2, where f1,f2 are coprime polynomials of degree n1,n2, respectively, and the sum of their degrees n1+n2=n.) For any n, such a pair is guaranteed to exist for sufficiently large q. Indeed, when n=2, such a pair definitely does not exist only for 28 values of q and possibly (but unlikely) only for at most 3911 other values of q.

Large iron isotope variation in the eastern Pacific mantle as a consequence of ancient low-degree melt metasomatism

Studies of mid-ocean ridge basalts (MORB) have revealed a heterogeneous asthenospheric mantle in chemical elements and radiogenic isotopes. Here we report that MORB mantle is also heterogeneous in Fe isotopes through studying the glass samples from seamounts flanking the northern East Pacific Rise between 5° and 15°N. These samples show large Fe isotope variation with δ56Fe values (+0.03‰ to +0.36‰) exceeding the known range of MORB (+0.05‰ to +0.17‰). Such highly varied δ56Fe values cannot be well explained by seafloor alteration, fractional crystallization or partial melting processes, but instead require a source mantle significantly heterogeneous in Fe isotope compositions. Importantly, the δ56Fe values of these basalts correlate significantly with major and trace elements and Sr-Nd-Pb-Hf radiogenic isotopes, reflecting melting-induced mixing of a two-component mantle with the enriched component having heavy Fe isotope compositions dispersed as physically distinct domains in the depleted mantle matrix. The major and trace element characteristics of the enriched mantle component, as inferred from these basalts, are consistent with a low-degree melting origin. Such low-degree melts with heavy Fe isotope compositions most likely formed at sites such as the lithosphere-asthenosphere boundary beneath ocean basins, which can metasomatize the overlying oceanic lithosphere by crystallizing dikes/veins of garnet pyroxenite lithologies. Recycling of these dikes/veins with isotopically heavier Fe can readily contribute to the Fe isotope heterogeneity in the MORB mantle. However, the extremely high primitive δ56Fe values of the two alkali basalts (up to 0.34‰) require an enriched source component with unusually high δ56Fe values. We suggest that partial melts from the recycled dikes/veins of garnet pyroxenite lithologies can react with the ambient peridotitic mantle and generate a secondary garnet pyroxenite with heavier Fe isotope compositions than, but similar radiogenic isotope compositions as its precursor. Melting-induced mixing between these garnet pyroxenites (recycled and newly formed) and depleted mantle matrix can readily explain the compositional variations in elements, radiogenic isotopes and Fe isotopes observed in these seamount lavas. These new data and correlated variations offer a new dimension for understanding the origin of mantle chemical and isotopic heterogeneity in the context of chemical differentiation of the Earth.

‘Should Latinas go blond?’ Media representation and the regulation of Latina bodies and Latinas’ social and cultural practices in a beauty magazine

In the United States, ‘Latinas’ is an ethnic category that includes a very diverse population. Since second- and third-generation Latinxs tend to be Englishdominant speakers, it is common to see publications in English that target this group. This study analyses how one of these publications, a beauty magazine for Latinas, uses different linguistic devices in their interviews and beauty advice columns to create a racially/ethnically homogeneous image of this community. My analysis focuses on this publication’s articles about hair, with particular attention to metaphors, the use of Spanish, and the indexicality of the term Latina itself. It shows that while characteristics of, and stereotypes about, Latinas are praised and celebrated, the advice offered contains instructions to regulate the Latina body to conform to beauty norms that are more valued in the United States, those associated with White women. Also, my analysis shows how this publication establishes different levels of Latinidad (Latinity) in which being too Latina represents traditional and primitive values that seem to be part of these Latinas’ imagined community’s heritage but not their own. I argue that these advice articles are intended to discursively create a Latina body acceptable to mainstream America; that while attempting to create a homogeneous image of Latinas, the publication paints a picture of tolerance toward Latinas that many of them do not experience; and that the articles do not take into account racial, social, ethnic and sexual differences among Latinas. I show how instead this publication seeks to regulate the Latina body and establish which Latinas’ social and cultural practices are acceptable for White America, so that they do not disrupt the predominant social order.

A Vector Field Texture Generation Method without Convolution Calculation

In the LIC algorithm process, symmetrical streamline tracing is used to symmetrically convolve the original values of all the primitive values that pass by to obtain the resulting texture. In this process, streamline tracking and convolution consume a lot of computing resources. To generate more expressive textures for vector fields with less time consumption, a novel method named random increment streamline (RIS) is put forward, which can generate streamline textures without convolution calculations. First, the mesh unit filling preprocessing (MUFP) method is presented to transform an undressed irregular grid into a special kind of regular grid named a “texture pixel”, and the point location and interpolation processes of all sampling points in the texture pixels are calculated before streamline tracking. Second, the random increment streamline method is used to generate line integral convolution style textures without any convolution calculations, thus greatly reducing the algorithm’s time consumption. Third, the vector directions at each point in the static vector field are clearly expressed using the periodic cyclic animation method. Finally, several simplifications of the RIS algorithm are discussed, which help to achieve a better visual effect with faster speed. The programming results show that the method is faster and more applicable than the traditional LIC method and provides clearer expression of the vector field.