scholarly journals The role of lithospheric thickness in the formation of ocean islands and seamounts: contrasts between the Louisville and Emperor-Hawaiian hotspot trails

2021 ◽  
Author(s):  
J Godfrey Fitton ◽  
Rebecca Williams ◽  
Tiffany L Barry ◽  
Andrew D Saunders
Keyword(s):  
Mantle Plume ◽  
Alkali Basalt ◽  
Hawaiian Islands ◽  
Dehydration Melting ◽  
Garnet Lherzolite ◽  
Lithospheric Thickness ◽  
Mantle Sources ◽  
Lithosphere Thickness ◽  
Emperor Seamounts ◽  
Ocean Islands

Abstract The Hawaii-Emperor and Louisville seamounts form the two most prominent time-progressive hotspot trails on Earth. Both formed over a similar time interval on lithosphere with a similar range of ages and thickness. The Hawaii-Emperor seamounts are large and magma productivity appears to be increasing at present. The Louisville seamounts, by contrast, are smaller and the trail appears to be waning. We present new major- and trace element data from five of the older (74–50 Ma) Louisville seamounts drilled during International Ocean Drilling Program (IODP) Expedition 330 and compare these to published data from the Emperor seamounts of the same age. Despite drilling deep into the shield-forming volcanic rocks at three of the Louisville seamounts, our data confirm the results of earlier studies based on dredge samples that the Louisville seamounts are composed of remarkably uniform alkali basalt. The basalt composition can be modelled by ∼1.5–3% partial melting of a dominantly garnet lherzolite mantle with a composition similar to that of the Ontong Java Plateau mantle source. Rock samples recovered by dredging and drilling on the Emperor Seamounts range in composition from tholeiitic to alkali basalt and require larger degrees of melting (2–10%) and spinel- to garnet lherzolite mantle sources. We use a simple decompression melting model to show that melting of mantle with a potential temperature of 1500ºC under lithosphere of varying thickness can account for the composition of the shield-forming tholeiitic basalts from the Emperor seamounts, while post-shield alkali basalt requires a lower temperature (1300–1400ºC). This is consistent with the derivation of Hawaii-Emperor shield-forming magmas from the hotter axis of a mantle plume and the post-shield magmas from the cooler plume sheath as the seamount drifts away from the plume axis. The composition of basalt from the Louisville seamounts shows no significant variation with lithosphere thickness at the time of seamount formation, contrary to the predictions of our decompression melting model. This lack of influence of lithospheric thickness is characteristic of basalt from most ocean islands. The problem can be resolved if the Louisville seamounts were formed by dehydration melting of mantle containing a small amount of water in a cooler plume. Hydrous melting in a relatively cool mantle plume (Tp = 1350–1400 °C) could produce a small amount of melt and then be inhibited by increasing viscosity from reaching the dry mantle solidus and melting further. The failure of the plume to reach the dry mantle solidus or the base of the lithosphere means that the resulting magmas would have the same composition irrespective of lithosphere thickness. A hotter mantle plume (Tp ≈ 1500 °C) beneath the Emperor seamounts and the Hawaiian Islands would have lower viscosity before the onset of melting, melt to a larger extent, and decompress to the base of the lithosphere. Thus our decompression melting model could potentially explain the composition of both the Emperor and Louisville seamounts. The absence of a significant lithospheric control on the composition of basalt from nearly all ocean islands suggests that dehydration melting is the rule and the Hawaiian islands the exception. Alternatively, many ocean islands may not be the product of mantle plumes but instead be formed by decompression melting of heterogeneous mantle sources composed of peridotite containing discrete bodies of carbonated and silica-oversaturated eclogite within the general upper mantle convective flow.

scholarly journals Lithosphere thickness controls continental basalt compositions: An illustration using Cenozoic basalts from eastern China

Geology ◽  
2020 ◽  
Vol 48 (2) ◽  
pp. 128-133 ◽  
Author(s):  
Pengyuan Guo ◽  
Yaoling Niu ◽  
Pu Sun ◽  
Hongmei Gong ◽  
Xiaohong Wang
Keyword(s):  
Eastern China ◽  
Primitive Mantle ◽  
Thickness Variation ◽  
Compositional Variation ◽  
Primary Control ◽  
Mantle Dynamics ◽  
Lithospheric Thickness ◽  
Geochemical Parameters ◽  
Lithosphere Thickness ◽  
Compositional Variability

Abstract Recent studies demonstrate that lithosphere thickness variation exerts the primary control on global seafloor basalt compositions. If the mechanism of such control, i.e., the lid effect, is indeed at work, lithosphere thickness variation must also influence basaltic compositions in continental settings. To test this hypothesis, we chose to study Cenozoic basalts in eastern continental China over a distance of ∼260 km along a southeast-to-northwest traverse with a steep topographic gradient (∼500 to ∼1500 m above sea level) mirrored with a steep lithospheric thickness gradient (∼80 to ∼120 km). The basalts erupted on the thinned lithosphere to the east are characterized by lower pressure (e.g., higher Si72, lower Mg72, Fe72, and [Sm/Yb]N; subscript “72” refers to corresponding oxides corrected for fractionation effect to Mg# = 72; N—primitive mantle normalized) and higher extent (e.g., low Ti72, P72, K72, Rb, Ba, Th, and ratios of more- to less-incompatible elements such as [La/Sm]N, Ba/Zr, and Zr/Yb) of melting than basalts erupted on the thickened lithosphere to the west. Importantly, these geochemical parameters all show significant correlations with both lithosphere thickness and topographic elevation. These first-order observations are a straightforward manifestation of the lid effect. Lithospheric contamination and mantle-source compositional variation can indeed contribute to the compositional variability of these continental basalts, but these latter effects are averaged out and are overshadowed by the lid effect. This finding emphasizes the importance of evaluating the lid effect before interpreting the petrogenesis of continental basalts and mantle dynamics. Our results also indicate that the continental surface elevation is isostatically balanced above a mantle depth that is deeper than the lithosphere-asthenosphere boundary.

scholarly journals Hotspot swells and the lifespan of volcanic ocean islands

2020 ◽  
Vol 6 (1) ◽  
pp. eaaw6906 ◽  
Author(s):  
Kimberly L. Huppert ◽  
J. Taylor Perron ◽  
Leigh H. Royden
Keyword(s):  
Residence Time ◽  
Plate Motion ◽  
Tectonic Plate ◽  
Mantle Sources ◽  
Volcanic Islands ◽  
Ocean Islands

Volcanic ocean islands generally form on swells—seafloor that is shallower than expected for its age over areas hundreds to more than a thousand kilometers wide—and ultimately subside to form atolls and guyots (flat-topped seamounts). The mechanisms of island drowning remain enigmatic, however, and the subaerial lifespan of volcanic islands varies widely. We examine swell bathymetry and island drowning at 14 hotspots and find a correspondence between island lifespan and residence time atop swell bathymetry, implying that islands drown as tectonic plate motion transports them past mantle sources of swell uplift. This correspondence argues strongly for dynamic uplift of the lithosphere at ocean hotspots. Our results also explain global variations in island lifespan, which influence island topography, biodiversity, and climate.

scholarly journals Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion

2020 ◽  
Vol 117 (25) ◽  
pp. 13997-14004 ◽  
Author(s):  
Michael W. Broadley ◽  
Peter H. Barry ◽  
David V. Bekaert ◽  
David J. Byrne ◽  
Antonio Caracausi ◽  
...  
Keyword(s):  
Mantle Plume ◽  
Noble Gases ◽  
Noble Gas ◽  
Mid Ocean Ridge ◽  
Mantle Sources ◽  
Source Mantle ◽  
Morb Source ◽  
Protosolar Nebula ◽  
Ocean Ridge ◽  
Yellowstone Caldera

Identifying the origin of noble gases in Earth’s mantle can provide crucial constraints on the source and timing of volatile (C, N, H2O, noble gases, etc.) delivery to Earth. It remains unclear whether the early Earth was able to directly capture and retain volatiles throughout accretion or whether it accreted anhydrously and subsequently acquired volatiles through later additions of chondritic material. Here, we report high-precision noble gas isotopic data from volcanic gases emanating from, in and around, the Yellowstone caldera (Wyoming, United States). We show that the He and Ne isotopic and elemental signatures of the Yellowstone gas requires an input from an undegassed mantle plume. Coupled with the distinct ratio of129Xe to primordial Xe isotopes in Yellowstone compared with mid-ocean ridge basalt (MORB) samples, this confirms that the deep plume and shallow MORB mantles have remained distinct from one another for the majority of Earth’s history. Krypton and xenon isotopes in the Yellowstone mantle plume are found to be chondritic in origin, similar to the MORB source mantle. This is in contrast with the origin of neon in the mantle, which exhibits an isotopic dichotomy between solar plume and chondritic MORB mantle sources. The co-occurrence of solar and chondritic noble gases in the deep mantle is thought to reflect the heterogeneous nature of Earth’s volatile accretion during the lifetime of the protosolar nebula. It notably implies that the Earth was able to retain its chondritic volatiles since its earliest stages of accretion, and not only through late additions.

The effects of solid-solid phase equilibria on the oxygen fugacity of the upper mantle

2020 ◽  
Vol 105 (10) ◽  
pp. 1445-1471
Author(s):  
Edward M. Stolper ◽  
Oliver Shorttle ◽  
Paula M. Antoshechkina ◽  
Paul D. Asimow
Keyword(s):  
Phase Equilibria ◽  
Oxygen Fugacity ◽  
Upper Mantle ◽  
Phase Changes ◽  
Primitive Mantle ◽  
Spinel Lherzolite ◽  
Garnet Lherzolite ◽  
Constant Composition ◽  
Al Content ◽  
Mantle Sources

Abstract Decades of study have documented several orders of magnitude variation in the oxygen fugacity (fO2) of terrestrial magmas and of mantle peridotites. This variability has commonly been attributed either to differences in the redox state of multivalent elements (e.g., Fe3+/Fe2+) in mantle sources or to processes acting on melts after segregation from their sources (e.g., crystallization or degassing). We show here that the phase equilibria of plagioclase, spinel, and garnet lherzolites of constant bulk composition (including whole-rock Fe3+/Fe2+) can also lead to systematic variations in fO2 in the shallowest ~100 km of the mantle. Two different thermodynamic models were used to calculate fO2 vs. pressure and temperature for a representative, slightly depleted peridotite of constant composition (including total oxygen). Under subsolidus conditions, increasing pressure in the plagioclase-lherzolite facies from 1 bar up to the disappearance of plagioclase at the lower pressure limit of the spinel-lherzolite facies leads to an fO2 decrease (normalized to a metastable plagioclase-free peridotite of the same composition at the same pressure and temperature) of ~1.25 orders of magnitude. The spinel-lherzolite facies defines a minimum in fO2 and increasing pressure in this facies has little influence on fO2 (normalized to a metastable spinel-free peridotite of the same composition at the same pressure and temperature) up to the appearance of garnet in the stable assemblage. Increasing pressure across the garnet-lherzolite facies leads to increases in fO2 (normalized to a metastable garnet-free peridotite of the same composition at the same pressure and temperature) of ~1 order of magnitude from the low values of the spinel-lherzolite facies. These changes in normalized fO2 reflect primarily the indirect effects of reactions involving aluminous phases in the peridotite that either produce or consume pyroxene with increasing pressure: Reactions that produce pyroxene with increasing pressure (e.g., forsterite + anorthite ⇄ Mg-Tschermak + diopside in plagioclase lherzolite) lead to dilution of Fe3+-bearing components in pyroxene and therefore to decreases in normalized fO2, whereas pyroxene-consuming reactions (e.g., in the garnet stability field) lead initially to enrichment of Fe3+-bearing components in pyroxene and to increases in normalized fO2 (although this is counteracted to some degree by progressive partitioning of Fe3+ from the pyroxene into the garnet with increasing pressure). Thus, the variations in normalized fO2 inferred from thermodynamic modeling of upper mantle peridotite of constant composition are primarily passive consequences of the same phase changes that produce the transitions from plagioclase → spinel → garnet lherzolite and the variations in Al content in pyroxenes within each of these facies. Because these variations are largely driven by phase changes among Al-rich phases, they are predicted to diminish with the decrease in bulk Al content that results from melt extraction from peridotite, and this is consistent with our calculations. Observed variations in FMQ-normalized fO2 of primitive mantle-derived basalts and peridotites within and across different tectonic environments probably mostly reflect variations in the chemical compositions (e.g., Fe3+/Fe2+ or bulk O2 content) of their sources (e.g., produced by subduction of oxidizing fluids, sediments, and altered oceanic crust or of reducing organic material; by equilibration with graphite- or diamond-saturated fluids; or by the effects of partial melting). However, we conclude that in nature the predicted effects of pressure- and temperature-dependent phase equilibria on the fO2 of peridotites of constant composition are likely to be superimposed on variations in fO2 that reflect differences in the whole-rock Fe3+/Fe2+ ratios of peridotites and therefore that the effects of phase equilibria should also be considered in efforts to understand observed variations in the oxygen fugacities of magmas and their mantle sources.

Modelling Antarctica’s lithospheric structure and testing the West Antarctic mantle plume hypothesis

2020 ◽  
Author(s):  
Folker Pappa ◽  
Eva Bredow ◽  
Jörg Ebbing ◽  
Fausto Ferraccioli
Keyword(s):  
Mantle Plume ◽  
Seismic Velocity ◽  
Geophysical Methods ◽  
Moho Depth ◽  
Gravity Gradient ◽  
West Antarctica ◽  
Field Methods ◽  
Amundsen Sea ◽  
Lithospheric Thickness ◽  
The Impact

<p>Numerous unresolved issues exist regarding the lithosphere of Antarctica, especially in terms of its fundamental density, temperature, and compositional structure. Estimates of total lithospheric thickness typically involve assumptions on the depth of the Moho discontinuity, which remains ill-constrained in several parts of Antarctica. Recent estimates of the Moho depth from different geophysical methods show significant discrepancies of 10-20 km in large sectors of the continent. While seismological methods suffer from a limited station coverage and ice reverberation, potential field methods, such as gravity studies, are inherently non-unique. By modelling multiple geophysical parameters in a consistent way and accounting for thermodynamically stable mineral phases of rocks as a function of pressure and temperature conditions, we were able to mitigate the detrimental effects of data sparseness while also reducing geophysical inconsistencies and ambiguities. Gravity gradient data from ESA’s satellite mission ‘GOCE’ are used here to constrain the density distribution within the lithosphere in an integrated 3D model of the Antarctic continent. Independent seismic estimates serve as a benchmark for the robustness of our results. Our model derives new estimates of the crustal and the total lithospheric thickness of Antarctica.<br>Based on our new 3D lithospheric model, we investigate the feasibility of a mantle plume beneath parts of West Antarctica, which has been inferred from previous geochemistry, seismology, and glacial isostatic adjustment studies. The impact of thermal anomalies, simulating ponded plume material, on different geophysical parameters, such as geothermal heat flux, seismic velocities, mineral phase transition changes, gravity, and topographic elevation are modelled for both Marie Byrd Land and Ross Island, two key candidate sites for putative plumes. Combined interpretation of the results is performed together with current understanding of geodynamic processes, such as locations of the LLVPs at the core-mantle boundary, representing potential ‘cradles’ for plumes.<br>Our results suggest that a deep-rooted mantle plume is unlikely beneath West Antarctica. However, the observed low seismic velocity zones could still correspond to proposed hot upper mantle zones characterised by lower viscosity. Alternative/additional explanations, such compositional effects and water content as causes for the seismic anomalies must also be further evaluated to better assess their effects on mantle viscosities. This is particularly important beneath regions of recent ice mass loss and recently observed remarkably high rates of GIA-induced bedrock uplift, such as the Amundsen Sea Embayment.</p>

scholarly journals Layered Lithospheric Mantle Beneath the Ontong Java Plateau: Implications from Xenoliths in Alnöite, Malaita, Solomon Islands

2004 ◽  
Vol 45 (10) ◽  
pp. 2011-2044 ◽  
Author(s):  
AKIRA ISHIKAWA ◽  
SHIGENORI MARUYAMA ◽  
TSUYOSHI KOMIYA
Keyword(s):  
Mantle Plume ◽  
Solomon Islands ◽  
Oceanic Lithosphere ◽  
Mantle Xenoliths ◽  
Garnet Lherzolite ◽  
Ontong Java Plateau ◽  
Basaltic Melt ◽  
Normative Quartz ◽  
Intermediate Part ◽  
Compositional Diversity

Abstract A varied suite of mantle xenoliths from Malaita, Solomon Islands, was investigated to constrain the evolution of the mantle beneath the Ontong Java Plateau. Comprehensive petrological and thermobarometric studies make it possible to identify the dominant processes that produced the compositional diversity and to reconstruct the lithospheric stratigraphy in the context of a paleogeotherm. P–T estimates show that both peridotites and pyroxenites can be assigned to a shallower or deeper origin, separated by a garnet-poor zone of 10 km between 90 and 100 km. This zone is dominated by refractory spinel harzburgites (Fo91–92), indicating the occurrence of an intra-lithospheric depleted zone. Shallower mantle (∼Moho to 95 km) is composed of variably metasomatized peridotite with subordinate pyroxenite derived from metacumulates. Deeper mantle (∼95–120 km) is represented by pyroxenite and variably depleted peridotites that are unevenly distributed; the least-depleted garnet lherzolite (Fo90–91) lies just below the garnet-poor depleted zone (∼100–110 km), whereas the presence of pyroxenite is restricted to the deepest region (∼110–120 km), together with relatively Fe-enriched garnet lherzolite (Fo87–88). This depth-related variation (including the depleted zone) can be explained by assuming that the degree of melting for a basalt–peridotite hybrid source was systematically different at each level of arrival depth within a single adiabatically ascending mantle plume: (1) the depleted zone at the top of the mantle plume, where garnet was totally consumed in the residual solid; (2) an intermediate part of the plume dominated by the least-depleted garnet lherzolite just above the depth of the peridotite solidus; (3) the deepest pyroxenite-rich zone, whose petrochemical variation is best explained by the interaction between peridotite and normative quartz-rich basaltic melt, below the solidus of peridotite and liquidus of basalt. We explain the obvious lack of pyroxenites at shallower depths as the effective extraction of hybrid melt from completely molten basalt through the partially molten ambient peridotite, which caused the voluminous eruption of the Ontong Java Plateau basalts. From these interpretations, we conclude that the lithosphere forms a genetically unrelated two-layered structure, comprising shallower oceanic lithosphere and deeper impinged plume material, which involved a recycled basaltic component, now present as a pyroxenitic heterogeneity. This interpretation for the present lithospheric structure may explain the seismically anomalous root beneath the Ontong Java Plateau.

Volatiles in basaltic magmas of ocean islands and their mantle sources: I. Melt compositions deduced from melt inclusions and glasses in the rocks

2007 ◽  
Vol 45 (2) ◽  
pp. 105-122 ◽  
Author(s):  
V. I. Kovalenko ◽  
V. B. Naumov ◽  
A. V. Girnis ◽  
V. A. Dorofeeva ◽  
V. V. Yarmolyuk
Keyword(s):  
Melt Inclusions ◽  
Mantle Sources ◽  
Basaltic Magmas ◽  
Ocean Islands

scholarly journals Mantle sources of Cenozoic volcanic activities around the South China Sea revealed by geochemical and isotopic data using the principal component analysis (PCA)

2021 ◽  
Author(s):  
Shuangshuang Chen ◽  
Zewei Wang ◽  
Rui Gao
Keyword(s):  
Principal Component Analysis ◽  
South China Sea ◽  
Mantle Plume ◽  
South China ◽  
Principal Component ◽  
Component Analysis ◽  
Isotopic Data ◽  
Mantle Sources ◽  
Basalt Type ◽  
Volcanic Activities

Abstract Principal component analysis (PCA) was conducted to analyze geochemical and isotopic data and interpret the characteristics and types of mantle sources of Cenozoic volcanic activities around the South China Sea (SCS). Fifteen trace element indicators and five isotopic indicators were surveyed from 623 volcanic rock samples obtained from the SCS, Hainan Island, Fujian–Zhejiang, Taiwan, Vietnam, and Thailand to characterize the geochemical properties of the volcanic rocks, determine the types of mantle sources, and assess the influence degree of each mantle source. Two principal components (PCs) were extracted by PCA based on trace elements and Sr–Nd–Pb isotopic ratios, which are an enriched oceanic island basalt-type mantle plume and a depleted mid-ocean ridge basalt-type spreading ridge. In the Southeast Asian region, the influence of Hainan mantle plume on younger volcanic activities (< 13 Ma) was greater than that on older ones (> 13 Ma) in the same location. PCA was used to verify the mantle plume–ridge interaction model of volcanic activities beneath the expansion center of the SCS and refute the hypothesis that the tension in the SCS is triggered by the Hainan plume. The results of this study demonstrate the efficiency and applicability of PCA to the discussion of mantle sources of volcanic activities and provide a new method with which to analyze geochemical data.

Linking Lithospheric Structure, Mantle Flow and Intra-Plate Volcanism

2021 ◽  
Author(s):  
Thomas Duvernay ◽  
Rhodri Davies ◽  
Christopher Mathews ◽  
Angus Gibson ◽  
Stephan Kramer
Keyword(s):  
Numerical Investigation ◽  
Mantle Plume ◽  
Temporal Distribution ◽  
Mantle Flow ◽  
Mantle Plumes ◽  
Heterogeneous Distribution ◽  
Passive Margins ◽  
Lithospheric Thickness ◽  
Isolated Points ◽  
Spatio Temporal

&lt;p&gt;Several of Earth's intra-plate volcanic provinces cannot be explained solely through the classical mantle plume hypothesis. Instead, they are believed to be generated by shallower processes that involve the interplay between uppermost mantle flow and the base of Earth's heterogeneous lithosphere. The mechanisms most commonly invoked are edge-driven convection (EDC) and shear-driven upwelling (SDU), both of which act to focus upwelling flow, and the associated decompression melting, adjacent to steps in lithospheric thickness.&lt;/p&gt;&lt;p&gt;In this study, we first undertake a systematic numerical investigation, in both 2-D and 3-D, to quantify the sensitivity of EDC, SDU and their associated melting to several key controlling parameters, in the absence of mantle plumes. Our simulations demonstrate that the spatial and temporal characteristics of EDC are sensitive to the geometry and material properties of the lithospheric step, in addition to the depth-dependence of upper mantle viscosity. These simulations also indicate that asthenospheric shear can either enhance or reduce upwelling velocities and predicted melt volumes, depending upon the magnitude and orientation of flow relative to the lithospheric step. When combined, such sensitivities explain why step changes in lithospheric thickness, which are common along cratonic edges and passive margins, only produce volcanism at isolated points in space and time. Our predicted trends of melt production suggest that, in the absence of potential interactions with mantle plumes, EDC and SDU are viable mechanisms only for Earth's shorter-lived, low-volume intra-plate volcanic provinces.&lt;/p&gt;&lt;p&gt;To complement the results from our first numerical investigation, we subsequently explore how the upwelling of a mantle plume within our 3-D domain modifies the occurrence of melting, both in terms of spatio-temporal distribution and intensity. Preliminary results indicate that edges close to the location of plume impingement have their melting shut off as a result of the intense flow generated through sub-lithospheric spreading. Additionally, the heterogeneous distribution of continental lithosphere thickness constrains plume material spreading and results in melting patterns that do not directly reflect the path of the plume relative to the lithosphere, as described by classical mantle plume theory.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document