pinecone/core-2020-05-10-deduplication huggingface dataset:
Low-volume intraplate volcanism in the Early/Middle Jurassic Pacific basin documented by accreted sequences in Costa Rica

Countless seamounts occur on Earth that can provide important constraints on intraplate volcanism and plate tectonics in the oceans, yet their nature and origin remain poorly known due to difficulties in investigating the deep ocean. We present here new lithostratigraphic, age and geochemical data from Lower/Middle Jurassic and Lower Cretaceous sequences in the Santa Rosa accretionary complex, Costa Rica, which offer a valuable opportunity to study a small-sized seamount from a subducted plate segment of the Pacific basin. The seamount is characterized by very unusual lithostratigraphic sequences with sills of potassic alkaline basalt emplaced within thick beds of radiolarite, basaltic breccia and hyaloclastite. An integration of new geochemical, biochronological and geochronological data with lithostratigraphic observations suggests that the seamount formed ~175 Ma ago on thick oceanic crust away from subduction zones and mid-ocean ridges. This seamount travelled ~65 Ma in the Pacific before accretion. It resembles lithologically and compositionally “petit-spot” volcanoes found off Japan, which form in response to plate flexure near subduction zones. Also, the composition of the sills and lava flows in the accreted seamount closely resembles that of potassic alkaline basalts produced by lithosphere cracking along the Line Islands chain. We hypothesize based on these observations, petrological constraints and formation of the accreted seamount coeval with the early stages of development of the Pacific plate that the seamount formed by extraction of small volumes of melt from the base of the lithosphere in response to propagating fractures at the scale of the Pacific basin
Temporal trends in vent fluid iron and sulfide chemistry following the 2005/2006 eruption at East Pacific Rise, 9°50′N

The chemistry of vent fluids that emanate to the seafloor undergoes dramatic changes after volcanic eruptions. Data on these changes are still limited, but the best studied example is the East Pacific Rise (EPR) at 9°50′N, where the temporal evolution of the vent fluid chemistry after the 1991/1992 eruption was documented. The area underwent another eruption sequence during late 2005/early 2006, and here we show that a similar evolution is recurring in the iron and sulfide contents of the high-temperature fluids sampled in June 2006, January 2007, and June 2008. The vents have had increasing dissolved iron and decreasing acid-volatile sulfide (free sulfide plus FeS) concentrations with 1 order of magnitude variation. In addition, chromium reducible sulfide (mainly pyrite) also had fivefold decreasing concentrations over the 3 years. Our results confirm a pattern that was noted only once before for 9°50′N EPR and emphasize the dramatic yearly variability in the concentrations of iron-sulfur species emanating from vents
In situ redeposition of trace metals mobilized by CO2-charged brines

Mobilization of contaminants by CO2-charged brines is one concern relating to injection of CO2 as part of carbon capture and storage projects. This study monitors the mobility of trace metals in an exhumed CO2-charged aquifer near the town of Green River, Utah (USA), where CO2-charged brines have bleached red sandstones, and concentrated trace metals at the bleaching reaction front. Mass balance calculations on the trace metal enrichments are used to calculate time-integrated fluid fluxes and show that a significant fraction of the metals mobilized by the CO2-rich brines are redeposited locally. A sequential extraction procedure on metal-enriched samples shows that these metals are incorporated into secondary carbonate and oxide phases which have been shown to grow at the CO2-promoted bleaching reaction front. We argue that while CO2-charged brines are capable of mobilizing trace metals, local metal redeposition implies that the potential for contamination of overlying freshwater aquifers is low
Depositional architecture, provenance, and tectonic/eustatic modulation of Miocene submarine fans in the Shikoku Basin: Results from Nankai Trough Seismogenic Zone Experiment

Seismostratigraphy, coring, and logging while drilling during Integrated Ocean Drilling Program Expeditions 319, 322, and 333 (Sites C0011/C0012) show three Miocene submarine fans in the NE Shikoku Basin, with broadly coeval deposits at Ocean Drilling Program Site 1177 and Deep Sea Drilling Project Site 297 (NW Shikoku Basin). The sediment dispersal patterns have major implications for paleogeographies at that time. The oldest, finer-grained (Kyushu) fan has sheet-like geometry; quartz-rich flows were fed mostly from an ancestral landmass in the East China Sea. During prolonged hemipelagic mud deposition at C0011-C0012 (similar to 12.2 to 9.1 Ma), sand supply continued at Sites 1177 and 297. Sand delivery to much of the Shikoku Basin halted during a phase of sinistral strike slip to oblique plate motion, after which the Daiichi Zenisu Fan (similar to 9.1 to 8.0 Ma) was fed by submarine channels. The youngest fan (Daini Zenisu; similar to 8.0 to 7.6 Ma) has sheet-like geometry with thick-bedded, coarse-grained pumiceous sandstones. The pumice fragments were fed from a mixed provenance that included the collision zone of the Izu-Bonin and Honshu Arcs. The shift from channelized to sheet-like flows was favored by renewal of relatively rapid northward subduction, which accentuated the trench as a bathymetric depression. Increased sand supply appears to correlate with long-term eustatic lowstands of sea level. The stratigraphic position and 3-D geometry of the sandbodies have important implications for subduction-related processes, including the potential for focused fluid flow and fluid overpressures above and below the plate boundary fault: In sheet-like sands, pathways for fluid flow have greater horizontal permeability compared with those in channel sands
Lead isotope provinciality of central North Pacific Deep Water over the Cenozoic

Understanding the pre-anthropogenic Pb cycle of central North Pacific deep water has attracted a lot of\ud
attention in recent years, partly because of its unique geographical location in that it is a remote gyre system\ud
characterized by high dust fluxes and sluggish overturning circulation. However, the factors controlling Pb\ud
isotope evolution in this area over the Cenozoic are still controversial and various mechanisms have been\ud
proposed in previous studies. Here we report new Pb and Nd isotope time series of four ferromanganese\ud
crusts (two from the western Pacific near the Mariana arc and the other two from the central Pacific).\ud
Together with previously published records, we discuss for the first time the significance of a persistent\ud
and systematic Pb isotopic provinciality recorded by central North Pacific crusts over the Cenozoic. We\ud
propose that globally well mixed stratosphere volcanic aerosols could contribute Pb but have not been\ud
the major factors controlling the Pb isotope distribution in the central North Pacific over time. Island arc\ud
input (and probably enhanced hydrothermal input between about 45 and 20 Ma) likely controlled the Pb\ud
isotope provinciality and evolution prior to ~20 Ma, when coeval Pb isotope records in different crusts\ud
showed large differences and atmospheric silicate dust flux was extremely low. After the Eocene, in particular\ud
after 20 Ma, Asian dust input has become an isotopically resolvable source, while island arc-derived Pb\ud
has remained important to balance the dust input and to produce the observed Pb isotope distribution in the\ud
central North Pacific during this period
Constraints on core-mantle boundary topography from normal mode splitting

The frequencies of Earth's normal modes are split by rotation, ellipticity, and internal structure of the Earth. Thus, models of mantle heterogeneity and discontinuity topography generate splitting that may be tested against observations. We insert maps of core-mantle boundary (CMB) topography, which are derived via either a purely seismic or a joint tomographic/geodynamic inversion of body waves data, on top of tomographic model S20RTS. We then calculate synthetic splitting functions for normal modes that have been shown to be sensitive to CMB topography and compare these to observed normal mode splitting data. The CMB topography maps obtained via geodynamically-constrained tomography fit normal mode data better than purely seismic maps, in particular when the geodynamic constraint also accounts for the presence of post-perovskite in the D" region. We test the significance of the reduction in misfit using the concept of observability which suggests that normal modes are able to observe the difference between the different CMB topography maps. In addition, we find that the statistical significance, assessed by checking what fraction of 1000 randomly generated CMB models achieve a comparatively good fit as the desired model, is higher than 92 % for degree 2 and 98 % for all degrees. In summary, we have identified a model of CMB topography that fits body wave data and improves, at least to some extent, the fit to normal mode data, and is coherent with the large-scale pattern of deep mantle heterogeneity expected on the basis of convection modelling
Asian dust input in the western Philippine Sea: Evidence from radiogenic Sr and Nd isotopes

The radiogenic strontium (Sr) and neodymium (Nd) isotope compositions of the detrital fraction of surface and subsurface sediments have been determined to trace sediment provenance and contributions from Asian dust off the east coast of Luzon Islands in the western Philippine Sea. The Sr and Nd isotope compositions have been very homogenous near the east coast of the Luzon Islands during the latest Quaternary yielding relatively least radiogenic Sr (87Sr/86Sr = 0.70453 to 0.70491) and more radiogenic Nd isotope compositions (εNd(0) = +5.3 to +5.5). These isotope compositions are similar to Luzon rocks and show that these sediments were mainly derived from the Luzon Islands. In contrast, the Sr and Nd isotope compositions of sediments on the Benham Rise and in the Philippine Basin are markedly different in that they are characterized by overall more variable and more radiogenic Sr isotope compositions (87Sr/86Sr = 0.70452 to 0.70723) and less radiogenic Nd isotope compositions (εNd(0) = −5.3 to +2.4). The Sr isotope composition in the Huatung Basin is intermediate between those of the east coast of Luzon and Benham Rise, but shows the least radiogenic Nd isotope compositions. The data are consistent with a two end-member mixing relationship between Luzon volcanic rocks and eolian dust from the Asian continent, which is characterized by highly radiogenic Sr and unradiogenic Nd isotope compositions. The results show that Asian continental dust contributes about 10–50% of the detrital fraction of the sediments on Benham Rise in the western Philippine Sea, which offers the potentials to reconstruct the climatic evolution of eastern Asia from these sediments and compare this information to the records from the central and northern Pacific
New views on old carbon in the Amazon river : insight from the source of organic carbon eroded from the Peruvian Andes.

[1] Mountain rivers play a key role in the delivery of particulate organic carbon (POC) to large river systems and the ocean. Due to the extent of its drainage area and runoff, the Amazon River is one of Earth's most important biogeochemical systems. However, the source of POC eroded from the humid region of the Eastern Andes and the input of fossil POC from sedimentary rocks (POCfossil) remains poorly constrained. Here we collected suspended sediments from the Kosñipata River during flood events to better characterize Andean POC, measuring the nitrogen to organic carbon ratio (N/C), stable carbon isotopes (δ13Corg) and radiocarbon (Δ14Corg). Δ14Corg values ranged from −711‰ to −15‰, and significant linear trends between Δ14Corg, N/C and δ13Corg suggested that this reflects the mixing of POCfossil with very young organic matter (Δ14Corg ~ 50‰) from the terrestrial biosphere (POCnon-fossil). Using N/C and Δ14Corg in an end-member mixing analysis, we quantify the fraction of POCfossil (to within 0.1) and find that it contributes a constant proportion of the suspended sediment mass (0.37 ± 0.03%) and up to 80% of total POC. In contrast, the relative contribution of POCnon-fossil was variable, being most important during the rising limb and peak discharges of flood events. The new data shed light on published measurements of “old” POC (low Δ14Corg) in Andean-fed tributaries of the Amazon River, with their Δ14Corg and δ13Corg values consistent with variable addition of POCfossil. The findings suggest a greater persistence of Andean POC in the lowland Amazon than previously recognized
Sulfide geochronology along the Endeavour Segment of the Juan de Fuca Ridge

Forty-nine hydrothermal sulfide-sulfate rock samples from the Endeavour Segment of the Juan de Fuca Ridge, northeastern Pacific Ocean, were dated by measuring the decay of 226Ra (half-life of 1600 years) in hydrothermal barite to provide a history of hydrothermal venting at the site over the past 6000 years. This dating method is effective for samples ranging in age from ∼200 to 20,000 years old and effectively bridges an age gap between shorter- and longer-lived U-series dating techniques for hydrothermal deposits. Results show that hydrothermal venting at the active High Rise, Sasquatch, and Main Endeavour fields began at least 850, 1450, and 2300 years ago, respectively. Barite ages of other inactive deposits on the axial valley floor are between ∼1200 and ∼2200 years old, indicating past widespread hydrothermal venting outside of the currently active vent fields. Samples from the half-graben on the eastern slope of the axial valley range in age from ∼1700 to ∼2925 years, and a single sample from outside the axial valley, near the westernmost valley fault scarp is ∼5850 ± 205 years old. The spatial relationship between hydrothermal venting and normal faulting suggests a temporal relationship, with progressive younging of sulfide deposits from the edges of the axial valley toward the center of the rift. These relationships are consistent with the inward migration of normal faulting toward the center of the valley over time and a minimum age of onset of hydrothermal activity in this region of 5850 years
Multistage collapse of eight western Canary Island landslides in the last 1.5 Ma: Sedimentological and geochemical evidence from subunits in submarine flow deposits

Volcaniclastic turbidites in the Madeira Abyssal Plain provide a record of major landslides from the Western Canary Islands in the last 1.5 Ma. These volcaniclastic turbidites are composed of multiple fining-upward turbidite sands, known as subunits. The subunits indicate that the landslides responsible for the sediment gravity flows occurred in multiple stages. The subunits cannot result from flow reflection or splitting because the compositions of volcanic glasses from each individual subunit in an event bed are subtly different. This indicates that each subunit represents a discrete failure as part of a multistage landslide. This has significant implications for geohazard assessments, as multistage failures reduce the magnitude of the associated tsunami. The multistage failure mechanism reduces individual landslide volumes from up to 350 km3 to less than 100 km3. Thus although multistage failure ultimately reduce the potential landslide and tsunami threat, the landslide events may still generate significant tsunamis close to source
Turbidite record of frequency and source of large volume (>100 km3) Canary Island landslides in the last 1.5 Ma: Implications for landslide triggers and geohazards

During the last two decades, numerous studies have focused on resolving the landslide histories of the Canary Islands. Issues surrounding the preservation and dating of onshore and proximal submarine landslide deposits precludes accurate determination of event ages. However, submarine landslides often disaggregate and generate sediment gravity flows. Volcaniclastic turbidites sampled from Madeira Abyssal Plain piston cores represent a record of eight large-volume failures from the Western Canary Islands in the last 1.5 Ma. During this time, there is a mean recurrence rate of 200 ka, while the islands of El Hierro and Tenerife have individual landslide recurrences of 500 ka and 330 ka, respectively. Deposits from the 15 ka El Golfo landslide from El Hierro and 165 ka Icod landslide from Tenerife are examined. This study also identifies potential deposits associated with the Orotava (535 ka), Güímar (850 ka), and Rogues de García landslides (1.2 Ma) from Tenerife, El Julan (540 ka), and El Tiñor (1.05 Ma) landslides from El Hierro, and the Cumbre Nueva landslide (485 ka) from La Palma. Seven of eight landslides occurred during major deglaciations or subsequent interglacial periods, which represent 55% of the time. However, all of the studied landslides occur during or at the end of periods of protracted island volcanism, which generally represent 60% of the island histories. Although climate may precondition failures, it is suggested that volcanism presents a more viable preconditioning and trigger mechanism for Canary Island landslides
The 1874–1876 volcano-tectonic episode at Askja, North Iceland: Lateral flow revisited

[1] The Askja volcanic system, North Iceland, experienced a volcano-tectonic episode between 1874 and 1876, the climax of which was a rhyolitic, phreatoplinian to Plinian eruption at Askja central volcano on 28–29 March 1875. Fissure eruptions also occurred in 1875, producing the Nýjahraun lava, 45–65 km north of Askja. The Nýjahraun basalt is indistinguishable, in terms of whole-rock major elements, from the small-volume basaltic eruptions that took place at Askja in the early 20th century. It has been suggested that all of these basalts originated from a shallow magma chamber beneath Askja, with the Nýjahraun eruptions being fed by northward-propagating lateral dykes. It has also been conjectured that the Holuhraun lava, located at the southern tip of the Askja volcanic system 15–25 km south of Askja, was connected with the 1874–1876 Askja volcano-tectonic episode. We re-examine these interpretations in light of new whole-rock, glass and melt inclusion analyses from samples collected along the length of the Askja volcanic system. Glasses from Nýjahraun and the Askja 20th century eruptions are geochemically distinct. We suggest that the Askja 20th century basalts mixed with evolved melts in the crust, while the Nýjahraun magma evolved without such interactions. The Holuhraun basalt is more similar to lavas erupted on the Bárðarbunga-Veiðivötn volcanic system than to postglacial basalts from Askja, indicating that particular geochemical signatures are not necessarily confined to the tectonic or structural surface expression of single volcanic systems. This has important implications for the identification and delineation of individual volcanic systems beneath the northwest sector of Vatnajökull
The 1874–1876 volcano-tectonic episode at Askja, North Iceland: Lateral flow revisited

The Askja volcanic system, North Iceland, experienced a volcano-tectonic episode between 1874 and 1876, the climax of which was a rhyolitic, phreatoplinian to Plinian eruption at Askja central volcano on 28–29 March 1875. Fissure eruptions also occurred in 1875, producing the Nýjahraun lava, 45–65 km north of Askja. The Nýjahraun basalt is indistinguishable, in terms of whole-rock major elements, from the small-volume basaltic eruptions that took place at Askja in the early 20th century. It has been suggested that all of these basalts originated from a shallow magma chamber beneath Askja, with the Nýjahraun eruptions being fed by northward-propagating lateral dykes. It has also been conjectured that the Holuhraun lava, located at the southern tip of the Askja volcanic system 15–25 km south of Askja, was connected with the 1874–1876 Askja volcano-tectonic episode. We re-examine these interpretations in light of new whole-rock, glass and melt inclusion analyses from samples collected along the length of the Askja volcanic system. Glasses from Nýjahraun and the Askja 20th century eruptions are geochemically distinct. We suggest that the Askja 20th century basalts mixed with evolved melts in the crust, while the Nýjahraun magma evolved without such interactions. The Holuhraun basalt is more similar to lavas erupted on the Bárðarbunga-Veiðivötn volcanic system than to postglacial basalts from Askja, indicating that particular geochemical signatures are not necessarily confined to the tectonic or structural surface expression of single volcanic systems. This has important implications for the identification and delineation of individual volcanic systems beneath the northwest sector of Vatnajökull.Access to the Edinburgh Ion Microprobe Facility was funded by NERC grant IMF386/1109. MEH was supported by NERC studentship NE/F008929/1.This is the published version of an article originally published in Geochemistry, Geophysics, Geosystems and is also available at http://onlinelibrary.wiley.com/doi/10.1002/ggge.20151/abstract. Copyright 2013 American Geophysical Union
A low-relief shield volcano origin for the South Kauaʻi Swell

The South Kauaʻi Swell (SKS) is a 110 km x 80 km ovoid bathymetric feature that stands >2 km high and abuts the southern flank of the island of Kauaʻi. The origin of the SKS was investigated using multibeam bathymetry and acoustic backscatter, gravity data, radiometric ages, and geochemistry of rock samples. Most of the SKS rock samples are tholeiitic in composition with ages of 3.9–5.4 Ma indicating they were derived from shield volcanism. The ages and compositions of the SKS rocks partially overlap with those of the nearby Niʻihau, Kauaʻi and West Kaʻena volcano complexes. The SKS was originally described as a landslide; however, this interpretation is problematic given the ovoid shape of SKS, its relatively smooth, flat-to-convex surface, and the lack of an obvious source region that could accommodate what would be one of Earth’s most voluminous (6 x 10^3 km^3) landslides. The morphology, size, and the surrounding gravity anomaly are more consistent with the SKS being a low-relief shield volcano, which was partially covered with a small volume of landside debris from south Kauaʻi and later with some secondary volcanic seamounts. A shield origin would imply that Hawaiian and possibly other hotspot shield volcanoes can take on a wider variety of forms than is commonly thought, ranging from tall island-building shields, to smaller edifices such as Kaʻena Ridge and Mahukona, to even lower-relief volcanoes represented by the SKS and possibly the South West Oʻahu Volcanic Field