Goss Adam R.

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Goss
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Adam R.
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  • Article
    Geochemistry of lavas from the 2005–2006 eruption at the East Pacific Rise, 9°46′N–9°56′N : implications for ridge crest plumbing and decadal changes in magma chamber compositions
    (American Geophysical Union, 2010-05-12) Goss, Adam R. ; Perfit, Michael R. ; Ridley, W. Ian ; Rubin, Kenneth H. ; Kamenov, George D. ; Soule, Samuel A. ; Fundis, A. ; Fornari, Daniel J.
    Detailed mapping, sampling, and geochemical analyses of lava flows erupted from an ∼18 km long section of the northern East Pacific Rise (EPR) from 9°46′N to 9°56′N during 2005–2006 provide unique data pertaining to the short-term thermochemical changes in a mid-ocean ridge magmatic system. The 2005–2006 lavas are typical normal mid-oceanic ridge basalt with strongly depleted incompatible trace element patterns with marked negative Sr and Eu/Eu* anomalies and are slightly more evolved than lavas erupted in 1991–1992 at the same location on the EPR. Spatial geochemical differences show that lavas from the northern and southern limits of the 2005–2006 eruption are more evolved than those erupted in the central portion of the fissure system. Similar spatial patterns observed in 1991–1992 lavas suggest geochemical gradients are preserved over decadal time scales. Products of northern axial and off-axis fissure eruptions are consistent with the eruption of cooler, more fractionated lavas that also record a parental melt component not observed in the main suite of 2005–2006 lavas. Radiogenic isotopic ratios for 2005–2006 lavas fall within larger isotopic fields defined for young axial lavas from 9°N to 10°N EPR, including those from the 1991–1992 eruption. Geochemical data from the 2005–2006 eruption are consistent with an invariable mantle source over the spatial extent of the eruption and petrogenetic processes (e.g., fractional crystallization and magma mixing) operating within the crystal mush zone and axial magma chamber (AMC) before and during the 13 year repose period. Geochemical modeling suggests that the 2005–2006 lavas represent differentiated residual liquids from the 1991–1992 eruption that were modified by melts added from deeper within the crust and that the eruption was not initiated by the injection of hotter, more primitive basalt directly into the AMC. Rather, the eruption was driven by AMC pressurization from persistent or episodic addition of more evolved magma from the crystal mush zone into the overlying subridge AMC during the period between the two eruptions. Heat balance calculations of a hydrothermally cooled AMC support this model and show that continual addition of melt from the mush zone was required to maintain a sizable AMC over this time interval.
  • Article
    Lava geochemistry as a probe into crustal formation at the East Pacific Rise
    (The Oceanography Society, 2012-03) Perfit, Michael R. ; Wanless, V. Dorsey ; Ridley, W. Ian ; Klein, Emily M. ; Smith, Matthew C. ; Goss, Adam R. ; Hinds, Jillian S. ; Kutza, Scott W. ; Fornari, Daniel J.
    Basalt lavas comprise the greatest volume of volcanic rocks on Earth, and most of them erupt along the world's mid-ocean ridges (MORs). These MOR basalts (MORBs) are generally thought to be relatively homogeneous in composition over large segments of the global ridge system (e.g., Klein, 2005). However, detailed sampling of two different regions on the northern East Pacific Rise (EPR) and extensive analysis of the samples show that fine-scale mapping and sampling of the ridge axis can reveal significant variations in lava chemistry on both small spatial and short temporal scales. The two most intensely sampled sites within the EPR Integrated Study Site (ISS) lie on and off axis between 9°17'N and 10°N, and from a wide region centered around 9°N where two segments of the EPR overlap (see Fornari et al., 2012, Figure 3, in this issue). The chemical composition of erupted lavas, similar to the genotype of an organism, can be used by igneous petrologists to trace the evolution of magmas from the mantle to the seafloor. The extensive and detailed geochemical studies at the EPR highlight how a thorough understanding of the variability in lava compositions on small spatial scales (i.e., between lava flows) and large spatial scales (i.e., from segment center to segment end and including discontinuities in the ridge crest) can be used in combination with seafloor photography, lava morphology, and bathymetry to provide insights into the magmatic system that drives volcanism and influences hydrothermal chemistry and biology at a fast-spreading MOR.