Two Massive Hydraulic Tests Completed in Deep KTB Pilot Hole

[No abstract available

Boron isotope composition of geothermal fluids and borate minerals from salar deposits (central Andes/NW Argentina)

We have measured the boron concentration and isotope composition of regionally expansive borate deposits and geothermal fluids from the Cenozoic geothermal system of the Argentine Puna Plateau in the central Andes. The borate minerals borax, colemanite, hydroboracite, inderite, inyoite, kernite, teruggite, tincalconite, and ulexite span a wide range of d 11B values from 229.5 to 20.3‰, whereas fluids cover a range from 218.3 to 0.7‰. The data from recent coexisting borate minerals and fluids allow for the calculation of the isotope composition of the ancient mineralizing fluids and thus for the constraint of the isotope composition of the source rocks sampled by the fluids. The boron isotope composition of ancient mineralizing fluids appears uniform throughout the section of precipitates at a given locality and similar to values obtained from recent thermal fluids. These findings support models that suggest uniform and stable climatic, magmatic, and tectonicconditions during the past 8 million years in this part of the central Andes. Boron in fluids is derived from different sources, depending on the drainage system and local country rocks. One significant boron source is the Paleozoic basement, which has a whole-rock isotopic composition of d 11B ¼ 28.9 ^ 2.2‰ (1 SD); another important boron contribution comes from Neogene-Pleistocene ignimbrites (d 11B ¼ 23.8 ^ 2.8‰, 1 SD). Cenozoic andesites and Mesozoic limestones (d 11B # þ 8‰) provide a potential third boron source.Fil: Kasemann, Simone A.. German Research Centre for Geosciences; AlemaniaFil: Meixner, Anette. German Research Centre for Geosciences; AlemaniaFil: Erzinger, Jörg. German Research Centre for Geosciences; AlemaniaFil: Viramonte, Jose German. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alonso, Ricardo Narciso. Universidad Nacional de Salta; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Franz, Gerhard. Technishe Universitat Berlin; Alemani

Carbonate veins trace seawater circulation during exhumation and uplift of mantle rock : results from ODP Leg 209

Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 311 (2011): 242–252, doi:10.1016/j.epsl.2011.09.021.Carbonate veins hosted in ultramafic basement drilled at two sites in the Mid Atlantic Ridge 15°N area record two different stages of fluid-basement interaction. A first generation of carbonate veins consists of calcite and dolomite that formed syn- to postkinematically in tremolite–chlorite schists and serpentine schists that represent gently dipping large-offset faults. These veins formed at temperatures between 90 and 170 °C (oxygen isotope thermometry) and from fluids that show intense exchange of Sr and Li with the basement (87Sr/86Sr = 0.70387 to 0.70641, δ7LiL-SVEC = + 3.3 to + 8.6‰). Carbon isotopic compositions range to high δ13CPDB values (+ 8.7‰), indicating that methanogenesis took place at depth. The Sr–Li–C isotopic composition suggests temperatures of fluid-rock interaction that are much higher (T > 350–400 °C) than the temperatures of vein mineral precipitation inferred from oxygen isotopes. A possible explanation for this discrepancy is that fluids cooled conductively during upflow within the presumed detachment fault. Aragonite veins were formed during the last 130 kyrs at low-temperatures within the uplifted serpentinized peridotites. Chemical and isotopic data suggest that the aragonites precipitated from cold seawater, which underwent overall little exchange with the basement. Oxygen isotope compositions indicate an increase in formation temperature of the veins by 8–12 °C within the uppermost ~ 80 m of the subseafloor. This increase corresponds to a high regional geothermal gradient of 100–150 °C/km, characteristic of young lithosphere undergoing rapid uplift.WB, MR, and NJ thank the Deutsche Forschungsgemeinschaft (grant no. BA1605/2) for funding. NJ acknowledges support from the DFG-Research Center/Excellence Cluster, The Ocean in the Earth Syste

Chemical composition of basalt at DSDP Sections 92-697C-8-2 and 92-697C-4-5

Two basalts recovered from Hole 597C were selected to be part of an interlaboratory comparison of geochemical analyses being performed by laboratories contributing analytical data to this volume

Major oxide, trace element and rare earth element composition at DSDP Leg 92 holes

The chemical composition of the basement in DSDP Holes 597C, 599B and 601B is examined in this chapter. These holes were drilled during Leg 92 west of the East Pacific Rise (EPR) crest along 19°S. Hole 597C reached a depth of 91 m into the basement with a recovery of about 55%, so it is the most successful hole drilled in fast-spreading crust. On the other hand, only drilling breccia and some basaltic cobbles were recovered from Holes 599B and 601B. In total, 60 samples of the least altered basalts from Hole 597C were analyzed. All these basalts were altered to some extent, as is evident from alteration-sensitive parameters. Oxidative seawater alteration influences the upper portion of basement, with considerable uptake of K, Rb, and H2O, loss of sulfur, and increased iron oxidation. The lowermost basement was affected by a non-oxidative alteration process, showing only enrichment in H2O; the other parameters have values typical of fresh basalts. Despite the alteration, the primary basaltic composition and variations can be established. According to their major and trace element data, the magmas appear to have undergone different degrees of high-level crystal fractionation. Several eruption episodes may have caused the observed downhole variations in Hole 597C. Four basalt samples from Hole 599B show the same features as the basalts recovered from Hole 597C. The three basalt samples from Hole 601B, on the other hand, are more evolved and can be defined as Fe-Ti basalts, which are commonly described from young EPR crust