Jaime D. Barnes

Chlorine isotope variations along the Central American volcanic front and back arc

Volcanic outputs (ash, tephra, and lava samples) of 23 volcanic centers from the volcanic front, secondary front, and back arc in Central America were analyzed for their δ37Cl values with the goal of using chlorine isotopes as a tracer of fluids sourced from the subducting Cocos slab. δ37Cl values range from −2.6 to +3.0‰ with systematic variations along the length of the front. Values from the northernmost (Guatemala and El Salvador) and southernmost (Costa Rica) ends of the front have mantle-like signatures. In contrast, δ37Cl values are both positive and negative in the center of the front (Nicaragua), implying a sediment and/or serpentinite-derived component. Geophysical observations are consistent with extensive hydration of the Cocos plate offshore of Nicaragua, in support of a serpentinite-derived fluid source. Fluids from dehydrating serpentinites may also incorporate Cl from overlying sediments, resulting in a multiple-source chlorine signature.

A phonological expression for physical movement monitoring in body sensor networks

Monitoring human activities using wearable wireless sensor nodes has the potential to enable many useful applications for everyday situations. The deployment of a compact and computationally efficient grammatical representation of actions reduces the complexities involved in the detection and recognition of human behaviors in a distributed system. In this paper, we introduce a road map to a linguistic framework for the symbolic representation of inertial information for physical movement monitoring. Our method for creating phonetic descriptions consists of constructing primitives across the network and assigning certain primitives to each movement. Our technique exploits the notion of a decision tree to identify atomic actions corresponding to every given movement. We pose an optimization problem for the fast identification of primitives. We then prove that this problem is NP-Complete and provide a fast greedy algorithm to approximate the solution. Finally, we demonstrate the effectiveness of our phonetic model on data collected from three subjects.

A detailed record of shallow hydrothermal fluid flow in the Sierra Nevada magmatic arc from low-δ18O skarn garnets

Garnet from skarns exposed at Empire Mountain, Sierra Nevada (California, United States) batholith, have variable δ18O values including the lowest known δ18O values of skarn garnet (–4.0‰) in North America. Such values indicate that surface-derived meteoric water was a significant component of the fluid budget of the skarn-forming hydrothermal system, which developed in response to shallow emplacement (∼3.3 km) of the 109 Ma quartz diorite of Empire Mountain. Values of δ18O, measured in situ across single garnet crystals by secondary ion mass spectrometry, vary considerably (up to 7‰) and sometimes abruptly, indicating variable mixing of meteoric, magmatic, and metamorphic water. Brecciation in the skarns and alteration of the Empire Mountain pluton suggests that fracture-enhanced permeability was a critical control on the depth to which surface waters penetrated to form skarns and later alter the pluton. Compared to other Sierran systems, much greater volumes of skarn rock suggest an exceptionally vigorous hydrothermal system that saw unusually high levels of decarbonation reaction progress, likely a consequence of the magma intruding relatively cold wallrocks inboard of the main locus of magmatism in the Sierran arc at that time.

Human identification by gait analysis

Human movement monitoring using wireless sensors has become an important area of research today. The use of wireless sensors in human identification is a relatively new idea with interesting applications in portable device security and user recognition. In this paper, we describe a real-time wireless sensor system based on inexpensive inertial sensors that uses gait analysis to uniquely identify subjects.

Locomotion Monitoring Using Body Sensor Networks

Body sensor networks (BSNs) create an enormous opportunity to revolutionalize the way we learn, work, entertain and live today. A particularly promising application of BSNs is in health monitoring. Research indicates that various disorders in aging ranging from mild cognitive impairment to dementia and Alzheimer’s could be diagnosed early based on the study of locomotion. Sensor platforms integrated into clothing provide the possibility of reliable locomotion monitoring. In this work, we demonstrate a real-time wireless sensor system that quantitatively measures some of the factors involved in locomotion.

Subducted lithosphere controls halogen enrichments in the Iceland mantle plume source

The chlorine isotope composition of Earth’s interior can place strong constraints on deep-Earth cycling of halogens and the origin of mantle chemical heterogeneity. However, all mantle-derived volcanic samples studied for Cl isotopes thus far originate from submarine volcanic systems, where the influence of seawater-derived Cl is pervasive. Here, we present Cl isotope data from subglacial volcanic glasses from Iceland, where the mid-ocean ridge system emerges above sea level and is free of seawater influence. The Iceland data display significant variability in δ 37 Cl values, from −1.8‰ to +1.4‰, and are devoid of regional controls. The absence of correlations between Cl and O isotope ratios and the lack of evidence for seawater-derived enrichments in Cl indicate that the variation in δ 37 Cl values in Icelandic basalts can be solely attributed to mantle heterogeneity. Indeed, positive correlations are evident between δ 37 Cl values and incompatible trace element ratios (e.g., La/Y), and long-lived radiogenic Pb isotope ratios. The data are consistent with the incorporation of altered lithosphere, including the uppermost sedimentary package, subducted into the Iceland mantle plume source, resulting in notable halogen enrichments in Icelandic basalts relative to lavas from adjacent mid-ocean ridges.

Locomotion monitoring using body sensor networks

Body sensor networks (BSNs) create an enormous opportunity to revolutionalize the way we learn, work, entertain and live today. A particularly promising application of BSNs is in health monitoring. Research indicates that various disorders in aging ranging from mild cognitive impairment to dementia and Alzheimers could be diagnosed early based on the study of locomotion. Sensor platforms integrated into clothing provide the possibility of reliable locomotion monitoring. In this work, we demonstrate a real-time wireless sensor system that quantitatively measures some of the factors involved in locomotion.

Mantle melt production during the 1.4 Ga Laurentian magmatic event: Isotopic constraints from Colorado Plateau mantle xenoliths

Plutons associated with a 1.4 Ga magmatic event intrude across southwestern Laurentia. The tectonic setting of this major magmatic province is poorly understood. Proposed melting models include anorogenic heating from the mantle, continental arc or transpressive orogeny, and anatexis from radiogenic heat buildup in thickened crust. Re-Os analyses of refractory mantle xenoliths from the Navajo volcanic field (NVF; central Colorado Plateau) yield Re depletion ages of 2.1–1.7 Ga, consistent with the age of the overlying Yavapai and Mazatzal crust. However, new Sm-Nd isotope data from clinopyroxene in peridotite xenoliths from NVF diatremes show a subset of xenoliths that plot on a ca. 1.4 Ga isochron, which likely reflects mantle melt production and isotopic resetting at 1.4 Ga. This suggests that Paleoproterozoic subcontinental lithospheric mantle was involved in the 1.4 Ga magmatic event. Our constraints support a subduction model for the generation of the 1.4 Ga granites but are inconsistent with rifting and anorogenic anatexis models, both of which would require removal of ancient lithosphere.

The Behavior of Halogens During Subduction-Zone Processes

Halogens (Cl, F, I, Br) are enriched in surface reservoirs compared to the mantle. The subduction of these reservoirs in the form of sedimentary pore fluids, sediments, altered oceanic crust, and serpentinized mantle lithosphere returns halogens to the mantle and to regions of arc magma genesis. Pore fluids are particularly enriched in I, yet shallow pore fluid loss in subduction zones due to compaction, as indicated by 129I/I ratios, makes pore fluids a negligible halogen source at depths >~5 km. Sediments can host large quantities of halogens, particularly I. However, serpentinites ± altered oceanic crust subduct the largest amount of halogens to depths of magma genesis. Due to their hydrophilic nature, halogens are lost to aqueous slab-derived fluids during prograde metamorphic reactions. The addition of halogens, particularly Cl, increases the ability of subduction-zone fluids to transport metals and trace elements. The amount of Cl in solution is a function of the P-T conditions of the subduction zone, such that higher temperatures at a given depth and lower pressures at a given temperature favor ion pair formation (NaClaq, KClaq). Therefore, ion pairing will be more important in subduction zones with warmer geotherms, such as Cascadia, compared to those with cooler geotherms, such as Alaska. High halogen concentrations in melt inclusions and volcanic gas emissions from the arc front support the efficiency of fluid loss and transport from the slab to the region of magma genesis. Despite this high efficiency, mass balance calculations and halogen concentrations in back-arc basalts and ocean island basalts show that more halogens are subducted than returned to the Earth’s surface through volcanic arc fronts, implying transport of halogens into the upper mantle. Chlorine is the halogen most efficiently recycled to the surface, and F the least. Shallow loss of I and Br, through fore-arc fluids that are not accounted for in the mass balance calculation, likely explain the imbalance in these cycles.

Sulphur and carbon cycling in the subduction zone mélange

Subduction zones impose an important control on the geochemical cycling between the surficial and internal reservoirs of the Earth. Sulphur and carbon are transferred into Earth’s mantle by subduction of pelagic sediments and altered oceanic lithosphere. Release of oxidizing sulphate- and carbonate-bearing fluids modifies the redox state of the mantle and the chemical budget of subduction zones. Yet, the mechanisms of sulphur and carbon cycling within subduction zones are still unclear, in part because data are typically derived from arc volcanoes where fluid compositions are modified during transport through the mantle wedge. We determined the bulk rock elemental, and sulphur and carbon isotope compositions of exhumed ultramafic and metabasic rocks from Syros, Greece. Comparison of isotopic data with major and trace element compositions indicates seawater alteration and chemical exchange with sediment-derived fluids within the subduction zone channel. We show that small bodies of detached slab material are subject to metasomatic processes during exhumation, in contrast to large sequences of obducted ophiolitic sections that retain their seafloor alteration signatures. In particular, fluids circulating along the plate interface can cause sulphur mobilization during several stages of exhumation within high-pressure rocks. This takes place more pervasively in serpentinites compared to mafic rocks.