Intraplate seamounts as a window into deep earth processes

Seamounts are windows into the deep Earth that are helping to elucidate various deep Earth processes. For example, thermal and mechanical properties of oceanic lithosphere can be determined from the flexing of oceanic crust caused by the growth of seamounts on top of it. Seamount trails also are excellent recorders of absolute plate tectonic motions and provide key insights into the relationships among plate motion, plume motion, whole-Earth motion, and mantle convection. And, because seamounts are created from the partial melts of deep mantle sources, they offer unique glimpses into the chemical development and heterogeneity of Earth’s deepest regions. Current research efforts focus on resolving the fundamental differences between magmas generated by passive upwelling from upper mantle regions and deep mantle plumes rising from the core-mantle boundary, mapping the different modes of mantle plumes and mantle convection, reconciling fixed and nonfixed mantle plumes, and understanding the prolonged volcanic evolution of seamounts. The role of intraplate seamounts is pivotal to this research, and we must collect vast amounts more geochemical and geophysical data to advance our knowledge. These data needs leave the ocean wide open for future seamount exploration

Seamount subduction and earthquakes

Seamounts are ubiquitous features of the seafloor that form part of the fabric of oceanic crust. When a seamount enters a subduction zone, it has a major affect on forearc morphology, the uplift history of the island arc, and the structure of the downgoing slab. It is not known, however, what controls whether a seamount is accreted to the forearc or carried down into the subduction zone and recycled into the deep mantle. Of societal interest is the role seamounts play in geohazards, in particular, the generation of large earthquakes

Dating Clinopyroxene Phenocrysts in Submarine Basalts Using ^(40)Ar/^(39)Ar Geochronology

Dating submarine basalts using ^(40)Ar/^(39)Ar geochronology is often hindered by a lack of potassium‐bearing phenocrystic phases and severe alteration in the groundmass. Clinopyroxene is a common phenocrystic phase in seafloor basalts and is highly resistive to low‐temperature alteration. Here we show that clinopyroxene phenocrysts separated from marine basalts are a viable phase for ^(40)Ar/^(39)Ar incremental heating age determinations. We provide results from a pilot study comprising 16 age experiments from nine clinopyroxene separates, five of which from samples with dated coeval phases. The clinopyroxene ages range from 11.5 to 112 Ma with relatively high uncertainties (ranging from 0.8% to 7.1%; median of 1.9%) compared to more traditional phases. The clinopyroxene age plateaus form at low to moderate temperature steps and are characterized by relatively elevated K/Ca of 0.002–0.4, suggesting that other K‐bearing phases hosted within the clinopyroxene are likely degassing to yield the ^(40)Ar/^(39)Ar age information. There are three possible origins for the K and corresponding ^(40)Ar* including films of trapped melt/nanomineral inclusions along grain defects, secondary melt inclusion bands, or variations in degassing behaviors between lower and higher crystalline Ca pyroxene phases. Regardless of the source of the K, the age determinations are successful with 75% of the experiments producing long plateaus (>60% ^(39)Ar released) with mean square of the weighted deviations ranging from 0.6 to 1.5 and probability of fit values >0.05. We conclude that clinopyroxene dating by the ^(40)Ar/^(39)Ar method has the potential to provide a wealth of information for previously undated, altered seafloor lithologies and continental equivalents

Scalable models of data sharing in Earth sciences

Many Earth science disciplines are currently experiencing the emergence of new ways of data publication and the establishment of an information technology infrastructure for data archiving and exchange. Building on efforts to standardize data and metadata publication in geochemistry [Staudigel et al., 2002], here we discuss options for data publication, archiving and exchange. All of these options have to be structured to meet some minimum requirements of scholarly publication, in particular reliability of archival, reproducibility and falsifiability. All data publication and archival methods should strive to produce databases that are fully interoperable and this requires an appropriate data and metadata interchange protocol. To accomplish the latter we propose a new Metadata Interchange Format (.mif ) that can be used for more effective sharing of data and metadata across digital libraries, data archives, and research projects. This is not a proposal for a particular set of metadata parameters but rather of a methodology that will enable metadata parameter sets to be easily developed and interchanged between research organizations. Examples are provided for geochemical data as well as map images to illustrate the flexibility of the approach.Keywords: geosciences, metadata, publication, interdisciplinary, data management, data sharingKeywords: geosciences, metadata, publication, interdisciplinary, data management, data sharin

High-resolution ⁴⁰Ar/³⁹Ar dating of the oldest oceanic basement basalts in the western Pacific basin

We report new ⁴⁰Ar/³⁹Ar ages for the oldest Pacific oceanic floor at Ocean Drilling Program Site 801C in the Pigafetta basin and Site 1149D close to the Izu-Bonin subduction zone in the Nadezhda basin. These ages were determined by applying high-resolution incremental heating experiments (including 15–30 heating steps) to better resolve the primary argon signal from interfering alteration signatures in these low-potassium ocean crust basalts. Combined with previous results from Pringle [1992] for Site 801B and 801C, we arrive at a multistage history for the formation of the Pigafetta ocean crust. The oldest part of the Pacific plate was formed at the spreading ridges at 167.4 ± 1.4/3.4 Ma (n = 2, 2σ internal/absolute error), offering an important calibration point on the Geological Reversal Timescale (GRTS) since it represents the old end of the Mesozoic magnetic anomalies. This mid-ocean ridge basalt sequence, however, is overlain by more tholeiites and alkali basalts that were formed 7.3 ± 1.5 Myr later around 160.1 ± 0.6 Ma (n = 7, 2σ internal error). The older age group is confirmed independently by radiolarian ages ranging from Late Bajocian to Middle Bathonian (167–173 Ma [Bartolini and Larson, 2001]) and by profound differences in the structural characteristics of this basement section [Pockalny and Larson, 2003]. Thin layers comprising hydrothermal deposits separate these sequences, which in addition to the difference in isotopic age show distinct major and trace element compositions. This indicates that key volcanic and hydrothermal activity took place 400–600 km away from the spreading ridges, on the basis of a Jurassic ~66 km/Myr half spreading rate in the Pacific. It remains unclear if these processes were active continuously after the initial formation of the Pacific oceanic crust, but all our observations seem to point to an episodic history. Site 1149D gives another important calibration point on the GRTS of 127.0 ± 1.5/3.6 Ma (n = 1, 2σ internal/absolute error) for anomaly M12 that is slightly younger when compared to current timescale compilations (134.2 ± 2.1 Ma [Gradstein et al., 1995]). This might suggest that the dated basalt from Site 1149D does not represent the age of the ocean crust formed at its ridge axis; it may also be part of the Early Cretaceous intraplate events that have produced dolerite sills in the Pacific crust at Sites 800 and 802 around 114–126 Ma

Seamount Catalong: Seamount Morphology, Maps, and Data Files

Seamount research, more often than not, is carried out by highly specialized science teams with narrowly focused science objectives. As a result, different seamount science disciplines often do not collaborate or are not even aware of each other. However, it is obvious that interdisciplinary collaboration is the most successful approach to help understand the integrated chemical, physical, and biological systems at seamounts. The Seamount Biogeoscience Network (SBN) was founded to promote the necessary cooperation through workshops, publications, and the development of a database that allows all seamount sciences to share data. Among such data, bathymetric maps are the most fundamental to all disciplines

Implications of a nonlinear ⁴⁰Ar/³⁹Ar age progression along the Louisville seamount trail for models of fixed and moving hot spots

The Louisville seamount trail has been recognized as one of the key examples of hot spot volcanism, comparable to the classic volcanic Hawaiian-Emperor lineaments. The published total fusion ⁴⁰Ar/³⁹Ar data of Watts et al. [1988] showed an astonishing linear age progression, firmly establishing Louisville as a fixed hot spot in the South Pacific mantle. We report new 40Ar/39Ar ages based on high-resolution incremental heating 40Ar/39Ar dating for the same group of samples, showing a marked increase in both precision and accuracy. One of the key findings in our reexamination is that the age progression is not linear after all. The new data show a significantly decreased ‘‘apparent’’ plate velocity for the Louisville seamount trail older than 62 Ma but confirm the linear trend between 47 Ma and the present day (although based on only three samples over 2150 km). The most recent volcanic activity in the Louisville seamount trail has now been dated at 1.11 ± 0.04 Ma for the most southeastern seamount located at 50°26’S and 139°09’W. These results indicate that the Louisville age progression should be interpreted on the basis of both plate and hot spot motion. In this paper we examine our new results in conjunction with the numerical mantle flow models of Steinberger et al. [2004] that also predict marked deviations from simple linear age progressions. With these models we can achieve a good fit to the geometry of both the Hawaiian and Louisville seamount trails and their age progressions as well as the ~15° paleolatitudinal shift observed by Tarduno et al. [2003] for the Hawaiian hot spot between 80 and 47 Ma. If the model is restricted to Pacific hot spots only, we can improve the fit to the nonlinear age trend for the Louisville seamount trail by allowing an additional rotation change of the Pacific plate around 62 Ma and by decreasing the initiation age of the Louisville plume from 120 to 90 Ma. This improved model features a significant eastward hot spot motion of ~5° between 80 and 30 Ma for the Louisville hot spot, which is quite dissimilar to the southward motion of the Hawaiian hot spot during the same time interval, followed by a minor ~2° latitudinal shift over the last 30 Myr. If hot spot tracks are considered globally, the age trend observed for the oldest part of the Louisville seamount trail does not entirely follow the numerical model predictions. This may indicate some remaining inaccuracies in the global plate circuit, but it may also indicate that the Louisville hot spot experienced a motion somewhat different than in the numerical model: faster in the interval between 62 and 47 Ma but slower before that.Copyrighted by American Geophysical Union.Keywords: hot spots, seamounts, ⁴⁰Ar/³⁹Ar geochronology, submarine alteration, guyots, Pacific plat

Defining the word “seamount”

Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, 1 (2010): 20-21.The term seamount has been defined many times (e.g., Menard, 1964; Wessel, 2001; Schmidt and Schmincke, 2000; Pitcher et al., 2007; International Hydrographic Organization, 2008; Wessel et al., 2010) but there is no “generally accepted” definition. Instead, most definitions serve the particular needs of a discipline or a specific paper

Vailulu’u Seamount

Author Posting. © Oceanography Society, 2010. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 23, 1 (2010): 164-165.Vailulu’u seamount is an active underwater volcano that marks the end of the Samoan hotspot trail