Iwamori et al., (2015) Isotopic heterogeneity of oceanic, arc and continental basalts and its implications for mantle dynamics
By mining geochemical data of basalts from databases, such as PetDB, Iwamori and Nakamura created a large data set of isotopic values from Mid-ocean Ridge Basalts, Ocean Island Basalts and Continental Basalts. Independent Component Analysis was found to be applicable in capturing the overall structure of the data, including mantle geochemical end-members. They propose top-down hemispherical dynamics involving both the mantle and the core, with focused subduction towards the supercontinents forming a fluid component-rich hemispheric domain anchored to the asthenosphere during continental dispersal in the past several hundred million years. This process may affect the temperature and growth rate of the inner core, resulting in synchronized hemispherical structures in the mantle and the core.
Iwamori and Nakamura, (2015). Isotopic heterogeneity of oceanic, arc and continental basalts and its implications for mantle dynamics. Gondwana Research Vol 27, 1131-1152. DOI: 10.1016/j.gr.2014.09.003
Carbotte et al., (2015) Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observation.
Do ridge axis geometry and geochemical properties reflect source composition variations of the underlying magmatic plumbing system? Carbotte et al. (2015) explore this question by examining the relationship between magmatic and tectonic segmentation at mid-ocean ridges using a synthesis of geophysical and geochemical data from a large number of sources. Combining higher resolution seafloor mapping from the GMRT Synthesis, which can identify tectonic segments including small discontinuities, with more detailed geophysical imaging of below-seafloor melt distribution and comprehensive geochemical data from PetDB, the authors confirm that global mid ocean ridges are composed of a number of magmatic spreading segments, each with its own magma plumbing system extending into the asthenosphere below.
Fig. 13. Sketch showing along-axis section of idealized magmatic spreading segment at fast and slow ridges based onstudies summarized in this article. (a) At fast-spreading ridges, rising mantle melts accumulate at the base of the crust (orange–grey) beneath each principal magmatic segment. The crustal magmatic system is composed of a more or less steady state magma lens or sill (red) that is partitioned into finer-scale segments coincident with the finest-scale seafloor segmentation. This shallow magma lens resides above a lower crustal zone of crystal mush and possible lower crustal sills (red lozenges embedded in red –grey). Red arrows in the dyke section indicate trajectories of magma transport during dyking (primarily vertical with minor lateral transport in places). (b) At slow-spreading ridges, strong focusing of mantle melts leads to thick crust/thin axial lithosphere at centre and thin crust/thick axial lithosphere at ends of each principal magmatic segment. Crustal magma bodies are more localized and ephemeral; both vertical and lateral magma transport during dyking may occur. Normal faulting is highly localized in detachments at segment ends and more distributed between several axial valley faults at segment centres. See text for further discussion.
Carbotte et al., (2015) Tectonic and magmatic segmentation of the Global Ocean Ridge System: a synthesis of observation. Geological Society of London, Special Publications 420. DOI:10.1144/SP420.5.
Multivariate statistical analysis and partitioning of sedimentary geochemical data sets: General principles and specific MATLAB scripts
Multivariate statistical treatments of large datasets in sedimentary geochemistry (e.g., SedDB, PetDB, VentDB, etc.) are rapidly becoming more popular as analytical and computational capabilities expand. Because geochemical datasets present a unique set of conditions (e.g., the closed array), application of generic off-the-shelf applications is not straightforward and can yield misleading results.
This paper presents annotated MATLAB scripts (and specific guidelines for their use) for Q-mode factor analysis, a constrained least squares multiple linear regression technique, and a total inversion protocol, that are based on the well-known approaches taken by Dymond , Leinen and Pisias , Kyte et al. , and their predecessors. Although these techniques have been used by investigators for the past decades, their application has been neither consistent nor transparent, as their code has remained in-house or in formats not commonly used by many of today’s researchers (e.g., Fortran]. In addition to providing the annotated scripts and instructions for use, this paper also discusses general principles to be considered when performing multivariate statistical treatments of large geochemical datasets, provides a brief contextual history of each approach, explains their similarities and differences, and includes a sample data set for the user to test their own manipulation of the scripts.
Figure Caption: Q-mode varimax rotated factor scores from a fifty-five sample dataset of sedimentary chemistry from ODP Site 1149 in the northwest Pacific Ocean. These factor scores show the weight of each element on the discrimination of each factor. The “% explained” values indicate how much of the dataset’s variability is explained by the given factor. Results from this Q-mode analysis was subsequently used to identify potential end members contributing volcanic ash to the bulk marine sediment. These end members were then used in a constrained least squares multiple linear regression to quantify the abundance of each end member in each sample. From Scudder et al. (2009, EPSL, 284, 639-648, doi:10.1016/j.epsl.2009.05.037), and using earlier versions of the scripts presented in Pisias et al. (2013, G3).
Nicklas G. Pisias, Richard W. Murray, Rachel P. Scudder (2013), Multivariate statistical analysis and partitioning of sedimentary geochemical data sets: General principles and specific MATLAB scripts, Geochemistry, Geophysics, Geosystems. DOI: 10.1002/ggge.20247
Access the scripts at the EarthChem Library.
Venti & Billups (2013), Surface water hydrography of the Kuroshio Extension during the Pliocene-Pleistocene climate transition
Despite its vast size and key role in climate, relatively little is known about the Pacific’s paleoceanographic evolution. Since the late Neogene, the Pacific sea floor has lain largely beneath the carbonate compensation depth such that continuous carbonate sections from this interval are rare beyond the equatorial region. This sedimentation pattern stymies many traditional dating approaches; planktic foraminifer and calcareous nannofossil biostratigraphy and benthic foraminifer oxygen isotope stratigraphy all require good carbonate preservation.
However, at Shatsky Rise an extraordinary volume of effusive volcanic material provides a seafloor environment sufficiently broad and shallow for accumulation of thick and continuous carbonate-rich sediment from the Late Neogene onward, thereby allowing excellent age control. Serendipitously, Shatsky Rise underlies the Kuroshio Current Extension (KCE). This is the North Pacific’s primary oceanographic feature, a powerful western boundary current that insulates the warm subtropical gyre from cooler waters in the mid-latitude and subarctic regions. In the modern ocean, transfer of heat from the warm KCE to the cold atmosphere during winter (>100Wm-2) is sufficient to cool the sea surface by 10°C and virtually erases the thermocline. Only ocean-atmosphere heat transport from the Gulf Stream exceeds that in the NW Pacific. Thus Shatsky Rise provides an ideal location to investigate the Neogene evolution of the North Pacific in a climatic context.
Here we examine the KCE’s relationship to the Plio-Pleistocene onset of Northern Hemisphere glaciation (NHG). To reconstruct KCE hydrography (temperature and salinity), we measured δ18O in a planktic foraminifer, Globigerinoides (Gs.) ruber, at high resolution (2500-year time step) at Ocean Drilling Program Site 1208 (36.1°N, 158.5°E; panel b). This is to date the longest Plio-Pleistocene oxygen isotope record from a planktic foraminifer at such high resolution in the open North Pacific. As Gs. ruber requires warm temperatures, i.e., the KCE’s warm mixed layer during summer and fall, this measurement should largely reflect heat transported to the mid latitudes in the subtropical gyre via the powerful current. To more clearly resolve surface hydrography (Δδ18O; panel c), we remove secular δ18O variability of the marine reservoir using an approximation based on our previously published companion benthic δ18O record (panel d). The summer/fall hydrographic reconstruction reveals increased temperatures and thus suggests increased heat availability in the Kuroshio Extension after NHG onset at 2.7 Ma. Though this may seem counterintuitive, these warmer KCE waters would have potentially provided an important moisture source for snow fall in North America. On the orbital timescale, KCE hydrography (likely temperature) varied with overhead insolation during summer/fall via precession (panel a), as is common in subtropical records. In contrast, high-latitude climate, as represented by the benthic δ18O record, followed obliquity, illustrating the insensitivity of the Kuroshio Current system to climate change at higher latitudes.
Comparison of Site 1208 Globigerinoides ruber δ18O measurements (b) to summer (June 21–July 20) insolation at 36°N (a; Laskar et al., 1993), Δδ18O, a measure of sea surface hydrography (c, see text for details), and the Site 1208 benthic δ18O record (d). The gray curve in (d) reflects the 10-kyr running mean (see text for details). Individual Gs. ruber δ18O measurements plot as dots (b); the line connects sample averages. The shaded interval and arrow in (d) indicates the onset of NHG. Gray lines in (c) show hydrographic means before and after NHG onset.
Surface water hydrography of the Kuroshio Extension during the Pliocene-Pleistocene climate transition, Nicholas L. Venti and Katharina Billups, Marine Micropaleontology, 2013; doi:10.1016/j.marmicro.2013.02.004
Journal of Geochemical Exploration, 110 (2), pg. 193-201. doi: dx.doi.org/10.1016/j.gexplo.2011.05.008
Recent efforts to understand Earth's elemental metal cycles have produced estimates for the integrated human-natural system metal mass reservoir stocks and inter-reservoir metal mass flows. These globally comprehensive metal cycles, called anthrobiogeochemical cycles, have been generated for Al, Fe, Cu, Zn, Ni, Pb, Ag, and Cr. While useful in visualizing the totality of Earth's metal cycle system, these global cycles lack the specificity that spatial resolution of these cycles can provide. Spatial resolution both informs global value estimation and provides a deeper understanding of the heterogeneity underlying the global estimate. SedDB was among many geochemical databases utilized to improve the accuracy and usefulness (via spatial disaggregation) of quantifying the natural metal stock reservoirs of Earth's anthrobiogeochemical cycles. This particular publication focuses upon the global maps at 1° × 1° that were produced to estimate the concentrations and masses of Fe, Al, Cu, and Zn contained in Earth's sediments and soils. The global maps were generated by inverse distance weighting (IDW) and cokriging, allowing geospatially weighted mean global concentrations for these metallic micronutrients to be estimated. These geostatical techniques were applied as follows: IDW of sediment samples produced sediment metal concentration maps; cokriging upon an underlying parent rock dataset composed of both surface bedrock and sediment samples produced global soil maps. The resulting information contained in these maps was utilized to produce new, independent estimates for the global mean concentrations in continental sediments (Fe = 3.1 wt.%, Al = 6.1 wt.%, Cu = 45 μg/g, Zn = 86 μg/g) and soils (Fe = 2.5 wt.%, Al = 3.9 wt.%, Cu = 17 μg/g, Zn = 50 μg/g). While Fe, Al, and Cu concentrations in continental sediments confirm previous estimates, Zn concentrations are found to be relatively higher, ~ 20 μg/g above prior estimates. The maps also highlight those areas of the globe for which little to no readily accessible, public data are yet available to help constrain sediment and soil metal concentration estimates.