All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1769.
San Andreas fault zone velocity structure at SAFOD at core, log, and seismic scales
Journal of Geophysical Research: Solid Earth,
120
(7)
4983-4997
2015
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
acoustic property; elastic modulus; fault zone; laboratory method; P-wave; S-wave; San Andreas Fault; seismic velocity; ultrasonics; velocity structure; wave velocity
Abstract: ▾ The San Andreas Fault (SAF), like other mature brittle faults, exhibits a zone of low seismic velocity hypothesized to result from fluid pressure effects and/or development of a damage zone. To address the relative contributions of these mechanisms in developing low-velocity zones, we measured P and S wave velocities ultrasonically at elevated confining and pore pressures on core samples from the San Andreas Fault Observatory at Depth (SAFOD). We compared those data to wireline and seismic-scale velocities to examine the scale dependence of acoustic properties of the fault core and damage zone. Average laboratory P and S wave velocities of the fault gouge at estimated in situ conditions are 3.1 and 1.5 km/s, respectively, consistent with the sonic log from the same intervals. These data show that fault core has intrinsically low velocity, even if no anomalous pore pressure is assumed, due to alteration and mechanical damage. In contrast, laboratory average P and S wave velocities for the damage zone are 4.7 and 2.5 km/s, up to 41% greater than the sonic log in the damage zone. This scale dependence indicates that stress conditions or macroscale features dominate the damage zone's acoustic properties, although velocity dispersion could play a role. Because no pressure anomaly was detected while drilling the SAFOD borehole, we infer that damage at a scale larger than core samples controls the elastic properties of the broader damage zone. This result bolsters other independent lines of evidence that the SAF does not contain major pore fluid overpressure at SAFOD. ©2015. American Geophysical Union. All Rights Reserved.
1768.
Seawater incursion events in a cretaceous paleo-lake revealed by specific marine biological markers
Scientific Reports,
5
2015
ISSN: 20452322
Publisher: Nature Publishing Group
Keywords:▾
biological marker; carbon; sea water, China; lake, Biomarkers; Carbon; China; Lakes; Seawater
Abstract: ▾ Many large paleo-lakes in North China were formed after the Triassic Era. Seawater incursion events (SWIEs) in these lakes have been extensively discussed in the literature, yet lack reliable methodology and solid evidence, which are essential for reconstructing and confirming SWIEs. The present study employs specific marine biological markers (24-n-propyl and 24-isopropyl cholestanes) to trace SWIEs in a dated core taken from the Songliao Basin (SLB). Two SWIEs were identified. The first SWIE from 91.37 to 89.00 Ma, was continuous and variable but not strong, while the second SWIE from 84.72 to 83.72 Ma was episodic and strong. SWIEs caused high total organic carbon (TOC) and negative δ13Corg values in the sediments, which were interpreted as an indication of high productivity in the lake, due to the enhancement of nutrient supplies as well as high levels of aqueous CO2, due to the mixing of alkaline seawater and acidic lake water. The SWIEs in SLB were controlled by regional tectonic activity and eustatic variation. Movement direction changes of the Izanagi/Kula Plate in 90 Ma and 84 Ma created faults and triggered SWIEs. A high sea level, from 90 to 84 Ma, also facilitated the occurrence of SWIEs in SLB.
1767.
Sedimentary and tectonic evolution of Lake Ohrid (Macedonia/Albania)
Basin Research,
27
(1)
84 – 101
2015
ISSN: 0950091XKeywords:▾
Albania; Lake Ohrid; Macedonia [Southern Europe]; facies analysis; neotectonics; normal fault; sedimentary structure; sedimentation rate; tectonic evolution
Abstract: ▾ Lake Ohrid, located on the Balkan Peninsula within the Dinaride-Albanide-Hellenide mountain belt, is a tectonically active graben within the South Balkan Extensional Regime (SBER). Interpretation of multichannel seismic cross sections and bathymetric data reveals that Lake Ohrid formed during two main phases of deformation: (1) a transtensional phase which opened a pull-apart basin, and (2) an extensional phase which led to the present geometry of Lake Ohrid. After the initial opening, a symmetrical graben formed during the Late Miocene, bounded by major normal faults on each side in a pull-apart type basin. The early-stage geometry of the basin has a typical rhomboidal shape restricted by two sets of major normal faults. Thick undisturbed sediments are present today at the site where the acoustic basement is deepest, illustrating that Lake Ohrid is a potential target for drilling a long and continuous sediment core for studying environmental changes within the Mediterranean region. Neotectonic activity since the Pliocene takes place along the roughly N-S-striking Eastern and Western Major Boundary Normal Faults that are partly exposed at the present lake floor. The tectono-sedimentary structure of the basin is divided into three main seismic units overlying the acoustic basement associated with fluvial deposits and lacustrine sediments. A seismic facies analysis reveals a prominent cyclic pattern of high- and low-amplitude reflectors. We correlate this facies cyclicity with vegetation changes within the surrounding area that are associated with glacial/interglacial cycles. A clear correlation is possible back to ca. 450 kyrs. Extrapolation of average sedimentation rates for the above mentioned period results in age estimate of ca. 2 Myrs for the oldest sediments in Lake Ohrid. © 2014 The Authors.
1766.
Seismic imaging through the volcanic rocks of the Snake River Plain: Insights from Project Hotspot
Geophysical Prospecting,
63
(4)
919-936
2015
ISSN: 00168025Keywords:▾
Boreholes; Geothermal fields; Geothermal wells; Infill drilling; Lithology; Rivers; Sedimentology; Seismic waves; Seismology; Signal processing; Stratigraphy; Volcanoes, Geothermal; Geothermal drilling; Geothermal systems; High frequency attenuation; High temperature zones; Seismic imaging; Seismic interpretation; Snake river plains, Volcanic rocks, body wave; borehole; data interpretation; geothermal system; imaging method; seismology; signal processing; volcanic rock, Idaho; Snake River Plain; United States
Abstract: ▾ Hotspot: The Snake River Geothermal Drilling Project was undertaken to better understand geothermal systems across the Snake River Plain volcanic province. A series of surface and borehole seismic profiles were obtained to provide insights into volcanic stratigraphy and test the capabilities of engineering-scale seismic imaging in such terranes. The Kimberly site drilled through 1.9 km of mostly rhyolite, with thin sedimentary interbeds in the upper part of the section. The Kimama site drilled through 1.9 km of mostly basalt with sedimentary interbeds at ∼200 m depth and 1700 m depth. The Mountain Home site contained numerous sediment and volcanic rock layers. Downhole and surface vibroseis seismic results suggest sedimentary interbeds at depth correspond with low-velocity, high-temperature zones that relate to reflections on seismic profiles. Our results suggest that eruption flow volumes can be estimated and flow boundaries can be imaged with surface seismic methods using relatively high-fold and wide-angle coverage. High-frequency attenuation is observed at all sites, and this deficit may be countered by acquisition design and a focus on signal processing steps. Separation of surface and body waves was obtained by muting, and the potential for large static effects was identified and addressed in processing. An accurate velocity model and lithology contacts derived from borehole information improved the confidence of our seismic interpretations. © 2015 European Association of Geoscientists & Engineers.
1765.
Seismic tomography reveals a mid-crustal intrusive body, fluid pathways and their relation to the earthquake swarms in West Bohemia/Vogtland
Geophysical Journal International,
203
(2)
1113 – 1127
2015
ISSN: 0956540X
Publisher: Oxford University Press
Keywords:▾
Germany; Vogtland; Flow of fluids; Seismographs; Body waves; Earthquake swarms; Europe; Fault structure; Fluid pathways; Near-surface geology; Seismic tomography; Seismicity and tectonics; body wave; earthquake swarm; seismic tomography; seismic velocity; seismicity; tectonics; Earthquakes
Abstract: ▾ The region of West Bohemia/Vogtland in the Czech-German border area is well known for the repeated occurrence of earthquake swarms, CO2 emanations and mofette fields. We present a local earthquake tomography study undertaken to image the Vp and Vp/Vs structure in the broader area of earthquake swarm activity. In comparison with previous investigations, more details of the near-surface geology, potential fluid pathways and features around and below the swarm focal zone could be revealed. In the uppermost crust, for the first time the Cheb basin and the Bublák/Hartoušov mofette fields were imaged as distinct anomalies of Vp and Vp/Vs. The well-pronounced low-Vp anomaly of the Cheb basin is not continuing into the Eger rift indicating a particular role of the basin within the rift system. A steep channel of increased Vp/Vs is interpreted as the pathway for fluids ascending from the earthquake swarm focal zone up to the Bublák/Hartoušov mofette fields. As a new feature, a mid-crustal body of high Vp and increased Vp/Vs is revealed just below and north of the earthquake swarm focal zone. It may represent a solidified intrusive body which emplaced prior or during the formation of the rift system. We speculate that enhanced fluid flow into the focal zone and triggering of earthquakes could be driven by the presence of the intrusive body if cooling is not fully completed. We consider the assumed intrusive structure as a heterogeneity leading to higher stress particularly at the junction of the rift system with the basin and prominent fault structures. This may additionally contribute to the triggering of earthquakes. © The Authors 2015.
1764.
Shear behavior of DFDP-1 borehole samples from the Alpine Fault, New Zealand, under a wide range of experimental conditions
International Journal of Earth Sciences,
104
(6)
1523-1535
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
borehole; drilling; fault zone; friction; seismic hazard; seismic moment; shear stress; slip rate, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ The Alpine Fault is a major plate-boundary fault zone that poses a major seismic hazard in southern New Zealand. The initial stage of the Deep Fault Drilling Project has provided sample material from the major lithological constituents of the Alpine Fault from two pilot boreholes. We use laboratory shearing experiments to show that the friction coefficient µ of fault-related rocks and their precursors varies between 0.38 and 0.80 depending on the lithology, presence of pore fluid, effective normal stress, and temperature. Under conditions appropriate for several kilometers depth on the Alpine Fault (100 MPa, 160 °C, fluid-saturated), a gouge sample located very near to the principal slip zone exhibits µ = 0.67, which is high compared with other major fault zones targeted by scientific drilling, and suggests the capacity for large shear stresses at depth. A consistent observation is that every major lithological unit tested exhibits positive and negative values of friction velocity dependence. Critical nucleation patch lengths estimated using representative values of the friction velocity-dependent parameter a−b and the critical slip distance Dc, combined with previously documented elastic properties of the wall rock, may be as low as ~3 m. This small value, consistent with a seismic moment Mo = ~4 × 1010 for an Mw = ~1 earthquake, suggests that events of this size or larger are expected to occur as ordinary earthquakes and that slow or transient slip events are unlikely in the approximate depth range of 3–7 km. © 2015, The Author(s).
1763.
Quantifying closed-basin lake temperature and hydrology by inversion of oxygen isotope and trace element paleoclimate records
American Journal of Science,
315
(9)
781-808
2015
ISSN: 00029599
Publisher: Yale University
Keywords:▾
lacustrine deposit; lake water; oxygen isotope; paleoclimate; paleohydrology; trace element; water chemistry; water quality; water temperature, Gastropoda; Mollusca; Ostracoda
Abstract: ▾ Lake systems are important paleoclimate archives that preserve ecosystem and hydrologic responses to critical periods in Earth history, such as carbon cycle perturbations and glacial-interglacial cycles. Geochemical measurements of biogenic carbonate (for example, δ18O, δ13C, 87Sr/86Sr, [Li], [U], [Sr], and [Mg]) are indicators of hydrologic variability in lake systems throughout the geologic record. In this study, we present a new closed-basin lake modeling approach, HyBIM (the Hydrologic Balance Inverse Model) that employs a system of total differential equations and uses the measured δ18O, Sr/Ca, and Mg/Ca of biogenic carbonate to determine changes in temperature, runoff, and lake evaporation. Using equally-spaced time steps, these equations are simultaneously solved to constrain the hydrologic parameters of the lake as recorded in biogenic carbonate. We use a Monte Carlo approach to account for uncertainty in the input parameters, such as δ18O temperature relationships, partition coefficient uncertainty, and watershed solute chemistry. For illustrative purposes, we apply the model to two ostracod valve datasets covering different timescales: (1) the Cretaceous Songliao Basin, northeast China, and (2) Holocene Lake Miragoane, Haiti. Modern water measurements of water isotopes and cation concentrations from each location are required as model inputs. We compare our modeling results with author interpretations and geologic observations. The modeling approach presented in this study can be applied to other closed-basin lake records, can be modified for other calcifying species (for example, gastropods or mollusks) or with calibration to inorganic lacustrine carbonate. In addition, this approach holds promise for extension with additional proxy measurements (that is, δD, U/Ca or Li/Ca) and changing source area on tectonic timescales using proxies that reflect changing source lithology (that is, Sr and Pb isotopes). Future incorporation of age model uncertainty in the Monte Carlo approach will also provide utility by quantifying temporal uncertainty on the hydrologic response recorded by lake sediments.
1762.
Petrography and composition of Martian regolith breccia meteorite Northwest Africa 7475
Meteoritics and Planetary Science,
50
(2)
326-352
2015
Abstract: ▾ The Northwest Africa (NWA) 7475 meteorite is one of the several stones of paired regolith breccias from Mars based on petrography, oxygen isotope, mineral compositions, and bulk rock compositions. Its inventory of lithic clasts is dominated by vitrophyre impact melts that were emplaced while they were still molten. Other clast types include crystallized impact melt rocks, evolved plutonic rocks, possible basalts, contact metamorphosed rocks, and siltstones. Impact spherules and vitrophyre shards record airborne transport, and accreted dust rims were sintered on most clasts, presumably during residence in an ejecta plume. The clast assemblage records at least three impact events, one that formed an impact melt sheet on Mars ≤4.4 Ga ago, a second that assembled NWA 7475 from impactites associated with the impact melt sheet at 1.7-1.4 Ga, and a third that launched NWA 7475 from Mars ~5 Ma ago. Mildly shocked pyroxene and plagioclase constrain shock metamorphic conditions during launch to >5 and <15 GPa. The mild postshock-heating that resulted from these shock pressures would have been insufficient to sterilize this water-bearing lithology during launch. Magnetite, maghemite, and pyrite are likely products of secondary alteration on Mars. Textural relationships suggest that calcium-carbonate and goethite are probably of terrestrial origin, yet trace element chemistry indicates relatively low terrestrial alteration. Comparison of Mars Odyssey gamma-ray spectrometer data with the Fe and Th abundances of NWA 7475 points to a provenance in the ancient southern highlands of Mars. Gratteri crater, with an age of ~5 Ma and an apparent diameter of 6.9 km, marks one possible launch site of NWA 7475. © The Meteoritical Society, 2015.
1761.
Progress of reactive iron burial in the marine and terrestrial sediments with its implications to the genesis of source rock in Songliao Basin (in Chinese with English abstract);[海陆相活性铁埋藏研究进展及其对松辽盆地烃源岩成因的启示]
Chinese Journal of Nature,
37
(02)
79-85
2015
1760.
Present and future of subsurface biosphere studies in lacustrine sediments through scientific drilling
International Journal of Earth Sciences,
104
(6)
1655 – 1665
2015
1759.
Present and future of subsurface biosphere studies in lacustrine sediments through scientific drilling
International Journal of Earth Sciences,
104
(6)
1655-1665
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
biosphere; deep-sea sediment; diagenesis; drilling; environmental change; genomics; geological record; geomicrobiology; lacustrine deposit; microbial activity; paleoclimate; sedimentary basin, Argentina; Dead Sea; Laguna Potrok Aike; Lake Ohrid; Lake Van; Levantine Sea; Mediterranean Sea; Patagonia; Santa Cruz [Argentina]; Turkey
Abstract: ▾ Recently, the discovery of active microbial life in deep-sea sediments has triggered a rapid development of the field known as the “deep biosphere.” Geomicrobiological investigations in lacustrine basins have also shown a substantial microbial impact on lake sediments similar to that described for the marine record. Although only 30 % of the lake sites drilled by the International Continental Drilling Program (ICDP) have included microbial investigations, these lakes cover a relatively wide range of salinities (from 0.15 to 33.8 %), pH (from 6.0 to 9.8) and environmental conditions (from very arid to humid subtropical conditions). Here, we analyze results of very recent ICDP lake sites including subsurface biosphere research from southern Patagonia (Laguna Potrok Aike) to the Levantine area (Dead Sea) as well as the East Anatolian high plateau (Lake Van) and Macedonia (Lake Ohrid). These various settings allow the examination of the impact of contrasting environments on microbial activity and their subsequent role during early diagenesis. Furthermore, they permit the identification of biosignatures of former microbial activity recorded in the sediments as well as investigating the impact of microbes in biogeochemical cycles. One of the general outcomes of these preliminary investigations is data to support the hypothesis that microbes react to climatically driven environmental changes that have a direct impact on their subsurface distribution and diversity. This is clear at conspicuous levels associated with well-known climatic periods such as the Medieval Climatic Anomaly or the Little Ice Age. Although more research is needed, this relationship between prevailing microbial assemblages and different climatic settings appears to dominate the lacustrine sites studied until to date. © 2015, The Author(s).
1758.
Present and future of subsurface biosphere studies in lacustrine sediments through scientific drilling
International Journal of Earth Sciences,
104
(6)
1655 – 1665
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
Argentina; Dead Sea; Laguna Potrok Aike; Lake Ohrid; Lake Van; Levantine Sea; Mediterranean Sea; Patagonia; Santa Cruz [Argentina]; Turkey; biosphere; deep-sea sediment; diagenesis; drilling; environmental change; genomics; geological record; geomicrobiology; lacustrine deposit; microbial activity; paleoclimate; sedimentary basin
Abstract: ▾ Recently, the discovery of active microbial life in deep-sea sediments has triggered a rapid development of the field known as the “deep biosphere.” Geomicrobiological investigations in lacustrine basins have also shown a substantial microbial impact on lake sediments similar to that described for the marine record. Although only 30 % of the lake sites drilled by the International Continental Drilling Program (ICDP) have included microbial investigations, these lakes cover a relatively wide range of salinities (from 0.15 to 33.8 %), pH (from 6.0 to 9.8) and environmental conditions (from very arid to humid subtropical conditions). Here, we analyze results of very recent ICDP lake sites including subsurface biosphere research from southern Patagonia (Laguna Potrok Aike) to the Levantine area (Dead Sea) as well as the East Anatolian high plateau (Lake Van) and Macedonia (Lake Ohrid). These various settings allow the examination of the impact of contrasting environments on microbial activity and their subsequent role during early diagenesis. Furthermore, they permit the identification of biosignatures of former microbial activity recorded in the sediments as well as investigating the impact of microbes in biogeochemical cycles. One of the general outcomes of these preliminary investigations is data to support the hypothesis that microbes react to climatically driven environmental changes that have a direct impact on their subsurface distribution and diversity. This is clear at conspicuous levels associated with well-known climatic periods such as the Medieval Climatic Anomaly or the Little Ice Age. Although more research is needed, this relationship between prevailing microbial assemblages and different climatic settings appears to dominate the lacustrine sites studied until to date. © 2015, The Author(s).
1757.
Present and future of subsurface biosphere studies in lacustrine sediments through scientific drilling
International Journal of Earth Sciences,
104
(6)
1655-1665
2015
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
biosphere; deep-sea sediment; diagenesis; drilling; environmental change; genomics; geological record; geomicrobiology; lacustrine deposit; microbial activity; paleoclimate; sedimentary basin, Argentina; Dead Sea; Laguna Potrok Aike; Lake Ohrid; Lake Van; Levantine Sea; Mediterranean Sea; Patagonia; Santa Cruz [Argentina]; Turkey
Abstract: ▾ Recently, the discovery of active microbial life in deep-sea sediments has triggered a rapid development of the field known as the “deep biosphere.” Geomicrobiological investigations in lacustrine basins have also shown a substantial microbial impact on lake sediments similar to that described for the marine record. Although only 30 % of the lake sites drilled by the International Continental Drilling Program (ICDP) have included microbial investigations, these lakes cover a relatively wide range of salinities (from 0.15 to 33.8 %), pH (from 6.0 to 9.8) and environmental conditions (from very arid to humid subtropical conditions). Here, we analyze results of very recent ICDP lake sites including subsurface biosphere research from southern Patagonia (Laguna Potrok Aike) to the Levantine area (Dead Sea) as well as the East Anatolian high plateau (Lake Van) and Macedonia (Lake Ohrid). These various settings allow the examination of the impact of contrasting environments on microbial activity and their subsequent role during early diagenesis. Furthermore, they permit the identification of biosignatures of former microbial activity recorded in the sediments as well as investigating the impact of microbes in biogeochemical cycles. One of the general outcomes of these preliminary investigations is data to support the hypothesis that microbes react to climatically driven environmental changes that have a direct impact on their subsurface distribution and diversity. This is clear at conspicuous levels associated with well-known climatic periods such as the Medieval Climatic Anomaly or the Little Ice Age. Although more research is needed, this relationship between prevailing microbial assemblages and different climatic settings appears to dominate the lacustrine sites studied until to date. © 2015, The Author(s).
1756.
Platinum group elements in proximal impactites of the bukit bunuh impact structure, Malaysia
Current Science,
109
(12)
2303-2308
2015
Abstract: ▾ The Bukit Bunuh in Malaysia has recently been identified as an impact structure after the discovery of possible impact-melt-like rocks and impact breccias from this area. The impact event is believed to have occurred around 1.34-1.84 Ma. Twelve impact-related rocks from this suspected impact structure were analysed in the present study for platinum group of element (PGE) content. The sample population includes proximal impactites (two impact-melt rocks and three impact breccias) and possible impact-related rocks (four mylonites) and basement granite (three in number). The results showed no observable clear distinction between the impactites and basement granite. Compared to other asteroid impact sites in the world, the impactites and impact-related rocks in the Bukit Bunuh structure clearly contain a lower concentration of PGEs. Even though previous studies reported possible evidences of shock metamorphism in the Bukit Bunuh structure and electrical resistivity survey favoured the presence of asteroid impact structure in this area as well, the absence of a clear projectile signature in our study on PGE hinders further discussion on the existence and nature of the impact. We suggest that the absence of any PGE signature in the Bukit Bunuh impactites could be indicative either of (1) an achondrite projectile, or (2) an oblique impact or (3) the presence of a volatile-rich layer.
1755.
Peralkaline felsic magmatism at the Nemrut volcano, Turkey: impact of volcanism on the evolution of Lake Van (Anatolia) IV
Contributions to Mineralogy and Petrology,
169
(4)
1-22
2015
ISSN: 00107999
Publisher: Springer Verlag
Keywords:▾
felsic rock; geothermometry; glass; magmatism; peralkaline rock; phenocryst; rhyolite; tephra; trachyte, Bitlis; Lake Van; Nemrut; Turkey, Trachytes
Abstract: ▾ Nemrut volcano, adjacent to Lake Van (Turkey), is one of the most important peralkaline silicic centres in the world, where magmatism for ~570,000 years has been dominated by peralkaline trachytes and rhyolites. Using onshore and Lake Van drill site tephra samples, we document the phenocryst and glass matrix compositions, confirming a complete spectrum from very rare mafic to dominantly silicic magmas. Magma mixing has been common and, along with the multi-lineage nature of the magmas, indicates that Nemrut has been a very open system where, nevertheless, compositionally zoned caps developed during periods of relative eruptive quiescence. Geothermometry suggests that the intermediate-silicic magmas evolved in an upper crustal magma reservoir at temperatures between 1100 and 750 °C, at fO2 close to the FMQ buffer. The silicic magmas either were halogen poor or exsolved a halogen-rich phase prior to or during eruption. An unusual Pb-rich phase, with up to 98.78 wt% PbO, is interpreted as having exsolved from the intermediate-rhyolitic magmas. © 2015, The Author(s).
1754.
Paleoarchean sulfur cycling: Multiple sulfur isotope constraints from the Barberton Greenstone Belt, South Africa
Precambrian Research,
267311 – 322
2015
ISSN: 03019268
Publisher: Elsevier
Keywords:▾
Barberton Greenstone Belt; Bacteria (microorganisms); Archean; black shale; hydrochemistry; isotopic fractionation; komatiite; oceanic crust; paleoceanography; reduction; seawater; sulfate; sulfur isotope
Abstract: ▾ Mass-dependent and mass-independent sulfur isotope fractionation archived in volcanic and sedimentary rocks from the Barberton Greenstone Belt (3550-3215. Ma), South Africa, provide constraints for sulfur cycling on the early Earth. Four different sample suites were studied: komatiites and tholeiites, barite, massive and disseminated sulfide ores, and non-mineralized black shales.Variable but generally slightly positive δ34S values between -0.7 and +5.2‰, negative δ33S values between -0.50 and -0.09‰, and a negative correlation between δ34S and δ33S as well as between δ33S and δ36S for komatiites and tholeiites from the Komati Formation and from the Weltevreden Formation are outside the expected range of unfractionated juvenile sulfur. Instead, results suggest alteration of oceanic crustal rock sulfur through interactions with fluids that most likely derived their sulfur from seawater.Barite from the Mapepe Formation displays positive δ34S values between +3.1 and +8.1‰ and negative δ33S values between -0.77 and -0.34‰. The mass-independent sulfur isotope fractionation indicates an atmospheric sulfur source, notably photolytic sulfate, whereas the positive δ34S values suggest bacterial sulfate reduction of the marine sulfate reservoir.Non-mineralized black shale samples from the presumed stratigraphic equivalent of the Mapepe Formation show positive δ34S values between 0.0 and +1.3‰ and positive δ33S values between +0.59 and +2.45‰. These results are interpreted to result from the reduction of photolytic elemental sulfur, carrying a positive δ33S signature.Positive δ34S values ranging from +0.7 to +3.5‰ and slightly negative δ33S values between -0.17 and -0.12‰ characterize massive and disseminated sulfides from the Bien Venue Prospect. Results suggest unfractionated juvenile magmatic sulfur source as the primary sulfur source, but a contribution from recycled seawater sulfate, which would be indicative of submarine hydrothermal activity, cannot be ruled out.Massive and disseminated sulfides from the M'hlati prospect are distinctly different from massive and disseminated sulfide from the Bien Venue Prospect. They show negative δ34S values between -1.2 and -0.1‰ and positive δ33S values between +2.66 and +3.17‰, thus, displaying a sizeable mass-independent sulfur isotopic fractionation. Again, these samples clearly exhibit the incorporation of an atmospheric MIF-S signal. The source of sulfur for these samples has positive δ33S values, suggesting a connection with photolytic elemental sulfur.In conclusion, the sulfur isotope signatures in Paleoarchean rocks from the Barberton Greenstone Belt are diverse and indicate the incorporation of different sources of sulfur. For komatiites and tholeiites, barite and massive and possibly also disseminated sulfides from Bien Venue, multiple sulfur isotopes are related to ambient seawater sulfate and its photolytic origin, while massive and disseminated sulfides from M'hlati and non-mineralized black shales are related to a second (photolytic elemental sulfur) end member. © 2015 Elsevier B.V.
1753.
Otolith microchemistry of modern versus well-dated ancient naked carp Gymnocypris przewalskii: Implication for water evolution of Lake Qinghai
Journal of Asian Earth Sciences,
105399 – 407
2015
ISSN: 13679120
Publisher: Elsevier Ltd
Abstract: ▾ There is ongoing debate over how the water level and composition of the water in Lake Qinghai changed in the past and might change in future. This study of the microchemistry of otoliths from ancient naked carp explores the chemistry of a relict lake isolated from Lake Qinghai during the Little Ice Age (LIA). A close correlation between the ages measured on fish bone and otoliths by AMS-14C, and by optically stimulated luminescence on overlying sediments, confirms a high water level in Lake Qinghai before 680-300years ago. The contrasting compositions of the ancient otoliths relative to modern otoliths and waters indicate that the relict lake became enriched in 18O, Mg, Li, B and to a lesser extent Ba, but depleted in 13C, owing to strong evaporation, authigenic carbonates precipitation, (micro-)organism activity, and less fresh water input after it was isolated. If there were long-term fresh water input, however, a reverse trend might occur. The most important observation is that, because the waters have been supersaturated with respect to carbonates, authigenic carbonate precipitation would result in low but consistent Sr/Ca ratios in the lakes, as recorded by both the ancient and modern otoliths. The geochemical records of ancient versus modern biogenic carbonates provide insights into the long-term hydroclimatic evolution processes of an inland water body. © 2015 Elsevier Ltd.
1752.
Operational report about phase 1 of the Collisional Orogeny in the Scandinavian Caledonides scientific drilling project (COSC-1)
55
2015
1751.
Nucleation process of an M2 earthquake in a deep gold mine in South Africa inferred from on-fault foreshock activity
Journal of Geophysical Research: Solid Earth,
120
(8)
5574-5594
2015
ISSN: 21699313
Publisher: Blackwell Publishing Ltd
Keywords:▾
acoustic emission; earthquake magnitude; earthquake rupture; fault; foreshock; gold mine; hydrothermal alteration; mining-induced seismicity; nucleation, South Africa
Abstract: ▾ Using a network of sensitive high-frequency acoustic emission sensors, we observed foreshock activity of an Mw 2.2 earthquake (main shock) in a deep gold mine in South Africa. Foreshock activity, which selectively occurred on a part of the rupture plane of the forthcoming main shock, lasted for at least 6 months until the main shock. Rock samples recovered from the main shock source region showed evidence of ancient hydrothermal alteration on the main shock rupture plane, suggesting that the foreshock activity occurred on a preexisting weakness. The foreshocks during 3 months before the main shock were concentrated in three clusters (F1-F3), which we interpret as representing localized preslip at multiple sites. While the location of mining area, the source of stress perturbations, changed with time, the locations of foreshock clusters did not change, suggesting that the preslip patches were controlled by strength heterogeneity rather than stress distribution. Activity over the entire foreshock area was generally constant, but the largest cluster (F2) showed accelerated activity starting at least 7 days before the main shock, while mining stress did not increase in this period. The main shock initiated at a point close to F1, away from F2. All the six foreshocks during the final 41 h occurred in F1 and F2 and in-between. These suggest that in the last stage of the preparation process of the main shock, preslip patches interacted with each other through the stress concentration ahead of the expanding preslip patch (F2), which should be the only driving force of the preparation process under the constant external load. ©2015. American Geophysical Union. All Rights Reserved.
1750.
Multiple Palaeoproterozoic carbon burial episodes and excursions
Earth and Planetary Science Letters,
424226--236
2015
1749.
Some observations facing the interpretation of Waqf as Suwwan structure, SE desert of Jordan, as an impact crater
Arabian Journal of Geosciences,
8
(6)
4025-4037
2015
Abstract: ▾ Twenty-seven samples from Waqf as Suwwan structure in the southeastern desert of Jordan were analyzed for their petrography, mineralogy, and geochemistry. All three types of analysis failed to show any evidence supporting the structure as an impact crater, but they cannot be used as an evidence discrediting the structure as an impact crater. This is because of the presence of shatter cones and rare shock metamorphic features. Shatter cones are well established in the Waqf as Suwwan structures and are accepted internationally as a criterion for impact craters. Shock metamorphic features reported in previous works are extremely rare and atypical. Planar features (PFs) were reported in one single quartz grain taken from a 30-m-thick Kurnub sandstone horizon. They are also reported from one single loose chert nodule, despite the extremely abundant bedded and loose chert within the structure. The PFs in the chert nodule are questioned because they are possibly due to diagenesis. More important is the complete absence of any type of breccias, lithic, melt, or suevitic and ejecta within and around the structure. The "deep erosion of the crater" used by advocates cannot stand for rigorous discussion on the amount of erosion in the desert environment in southeastern Jordan. Given the exact age of the cratering event is not yet known, and an approximate long-term rate of erosion of 1 m/Ma breccias and ejecta should be present in and/or around the structure. © 2014, Saudi Society for Geosciences.
1748.
Morphologic and structural mapping of the central uplift of Betiocrater, Thaumasia Planum, Mars
Special Paper of the Geological Society of America,
51865-83
2015
Abstract: ▾ The ~31.7-km-diameter Betio crater (23.15°S, 281.38°E), located within the Hesperian-aged Ridged Plains material in Thaumasia Planum, Mars, contains a wellpreserved asymmetrical central floor pit (~10.8 km NW-SE and ~8.8 km NE-SW in diameter) covering an area of ~67 km2 that exposes discrete megablocks of layered bedrock and preserves a variety of impact-generated deposits. High-resolution images taken by the Mars Reconnaissance Orbiter (MRO) are combined with other data sets to study and map the morphology and structure of the central floor pit. The excellent bedrock exposure of the floor pit enables the comparison of mapped structures with observations from terrestrial craters. Our mapping of the central uplift has revealed a variety of faults, folds (likely radial transpression ridges), and many breccia dikes, in addition to different types of impactites (e.g., breccias, impact melt deposits, and uplifted bedrock [i.e., parautochthonous bedrock]). Through structural mapping, we show that the central portion of the central uplift is characterized by smaller (~60- 300 m in diameter) blocks with high dips of ~45°-85°, and the outer sections of the floor pit have larger (>800 m in diameter) blocks with shallow dip angles of ~5°-15°. Our work shows that extensive brittle deformation and brecciation increase toward the center of the crater and particularly in the SW sector of the central pit. There is also an overall decrease in block size toward the center of the crater. © 2015 The Geological Society of America. All rights reserved.
1747.
Snake river plain play fairway analysis - Phase 1 report
Transactions - Geothermal Resources Council,
39761-769
2015
ISSN: 01935933
Publisher: Geothermal Resources Council
ISBN:
9781510817241
Abstract: ▾ The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America. Our goals for this Phase 1 study are to: (1) adapt the methodology of Play Fairway Analysis for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble relevant data for the SRP from publicly available and private sources, and (3) build a geothermal play fairway model for the SRP and identify the most promising plays, using software tools that are standard in the petroleum industry. The success of play fairway analysis in geothermal exploration depends critically on defining a systematic methodology that is grounded in theory (as developed within the petroleum industry over the last two decades) and within the geologic and hydrologic framework of real geothermal systems. Our preliminary assessment of the data suggests that important undiscovered geothermal resources may be located in several areas of the SRP, including the western SRP (associated with buried lineaments defined by gravity or magnetic anomalies, and capped by extensive deposits of lacustrine sediment), at lineament intersections in the central SRP (along the Banbury-Hagerman trend N W of Twin Falls, and along the northern margin of the Mt Bennett Hills-Camas Prairie area), and along the margins of the eastern SRP. Additional high temperature resources are likely associated with rhyolite domes and crypto-domes in the eastern SRP, but are masked by shallow groundwater flow leading to low upper crustal heat flow values. These blind resources may be exploitable with existing deep drilling technology. Groundwater modeling planned for later phases of the PFA project will address whether temperatures at viable producing depths are sufficient to support electricity production. © Copyright (2015) by Geothermal Resources Council All rights reserved.
1746.
Tourmaline B-isotopes as tracers of fluid sources in silicified Palaeoarchaean oceanic crust of the Mendon Formation, Barberton greenstone belt, South Africa
Chemical Geology,
417134 – 147
2015
ISSN: 00092541
Publisher: Elsevier
Keywords:▾
Barberton Greenstone Belt; Chemical analysis; Clay alteration; Electron probe microanalysis; Isotopes; Magnesium; Mica; Microanalysis; Seawater; Secondary ion mass spectrometry; Sedimentology; Silicate minerals; Zoning; Boron isotopes; Greenstone belts; Hydrothermal alterations; Hydrothermal system; Marine evaporites; Mendon Formation; Tourmaline; Volcano-sedimentary sequences; Archean; boron isotope; concentration (composition); evaporite; hydrothermal alteration; igneous geochemistry; isotopic composition; isotopic fractionation; komatiite; oceanic crust; tourmaline; tracer; Boron
Abstract: ▾ Pervasive silicification is a common phenomenon in Early Archaean volcano-sedimentary sequences, reflecting the interaction between Si-rich fluids and the Archaean oceanic crust. In the Palaeoarchaean Barberton greenstone belt, South Africa, the silicified zones locally contain abundant tourmaline. In order to constrain the source of fluids responsible for the alteration, six tourmaline-bearing samples from the 3.3. Ga Mendon Formation were investigated by in-situ analyses of mineral chemistry and boron isotopes. The samples comprise a silicified, finely laminated sedimentary chert and five highly altered and silicified komatiites. Electron microprobe analysis (EMPA) indicates that tourmaline is mostly dravitic, with one sample between dravite and Mg-foitite. Tourmaline has a weakly-developed patchy colour- and chemical zonation, with variations in Al, Fe and Mg composition. Some samples show strong zoning in Cr-concentration with Cr enrichment in the core, and locally the high-Cr domains are at contacts with other Cr-rich phases such as magnesiochromite and chromian muscovite ("fuchsite").Overall, the boron isotope composition (δ11B) ranges from -20.7 to +10.2‰. Two groups of tourmaline are distinguished based on the variation in δ11B ratios within single samples: 1) those with small (<4‰) range in δ11B values (spinifex-textured komatiites and silicified sediment), and 2) those with a large range in δ11B values of up to 18‰ (brecciated and foliated samples). Positive boron isotope values (+6 to +10‰) are found in one spinifex-textured komatiite and are interpreted as being derived from seawater interacting with Archaean oceanic crust in shallow hydrothermal systems. The intermediate boron isotope values (-5 to -8‰) found in all other samples are similar to MORB and may represent boron derived from the Archaean oceanic crust. The rare and exceptionally light boron isotope values (-10 to -21‰) were found in rims of group 2 tourmaline. These values cannot be produced by fractionation alone, and point to the presence of another fluid source. The source of the light boron has yet to be identified, but possible candidates are remobilized boron either derived from granitic crust or from marine evaporites that precipitated from seawater enriched in 10B. In any case, the isotopically light boron appears to have been present during seafloor hydrothermal alteration and deposition of the Mendon Formation at ca. 3.3Ga. © 2015 Elsevier B.V.
1745.
Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai and their controlling factors
Limnology,
16
(2)
113 – 125
2015
ISSN: 14398621
Publisher: Springer-Verlag Tokyo
Abstract: ▾ To advance the understanding of the spatial variability of sediment composition and its controlling factors in a large hydrologically closed lake, the spatial distributions in the mineralogy and geochemistry of 18 surface sediment samples along three transects across the deepest part of Lake Qinghai on the northeastern Tibetan Plateau were investigated. The data show (1) that the surface lake sediments are almost the same in the XRD patterns, (2) that the sediments do not have considerable changes in geochemical compositions along three transects and (3) that the standard deviations of the lake sediments are low in grain size, elemental abundances, δ13C and δ18O values of carbonates, and total organic carbon and nitrogen, with the exception of one sample (QH-11) from the westernmost part of the northern sub-basin. These characteristics indicate that the spatial variability of the surface sediment across Lake Qinghai is very low in geochemical and silicate mineralogical compositions, with limited differences in the chemical composition of carbonates associated with river water dilution. Sample QH-11 has anomalously high levels of MgO, a high carbonate content, and positive δ13C and δ18O values in bulk and fine-grained carbonates, probably because of the effect of calcareous tufa. Spatial uniformity in the mineralogical and geochemical compositions of surface sediments in Lake Qinghai can be attributed to the flat topography of the lakebed and stable sediment provenances, the latter dominated by dust deposition and authigenic carbonates. The spatial uniformity and dominance of dust and authigenic aragonite of surface sediments across Lake Qinghai provide a potential record of the hydroclimate in the past, which is associated with changes in the Westerlies and the summer monsoons. © 2015, The Japanese Society of Limnology.