11B Values Research Articles

Boron and boron isotopes in pore waters from ODP Leg 127, Sea of Japan

Interstitial waters that have been recovered from the Sea of Japan down to a depth of 662 m below seafloor were analysed for B and δ 11B. B concentrations cover the range 0.12–3.37 mM (0.3–8 × seawater) and vary isotopically from +11.5 to +51.3‰ (relative to SRM 951 boric acid). Consistent concentration depth profiles demonstrate that the behaviour of this element is non-conservative and much more complicated during early diagenesis than previously thought. Small departures from seawater B concentration and isotopic composition in the core tops from sites in the Yamato Basin result from the desorption of an isotopically light B fraction. In the Japan Basin a large positive δ 11B anomaly seems to be related to the preferential adsorption of 10B in the depth range of more frequent ash layers. A large negative B anomaly seems to result from the alteration of volcaniclastic sands in a recently uplifted area. It seems that the thermal regime, in particular high heat flow, leads to B and Li maxima, δ 11B values lighter than seawater, and rather low Sr 87/Sr 86 ratios. B seems to be removed from pore waters at greater depth. It is finally incorporated into the sediment itself or altered basement rocks. Adsorption/desorption processes and alteration reactions within the sedimentary column and in the basement rocks govern the distribution of B in the pore fluids and should also influence the B content and isotopic composition of the alteration products, mainly clay minerals.

Boron isotopic compositions of brine, sediments, and source water in Da Qaidam Lake, Qinghai, China

The isotopic compositions of boron in Da Qaidam Lake, Quinghai, have been determined by using the technique of thermal ionization mass spectrometry of cesium tetraborate. The brines are enriched in 11B, with an average δ 11B of +5.49 ± 2.34%., compared with those of lake sediments and boron minerals produced by the lake. The apparent isotopic fractionation factors between brine and lake sediments as well as boron minerals are 0.988 ± 0.001 and 0.986 ± 0.001, respectively. Source water δ 11B values range from −11.72 to + 16.69%., depending on their origin.

Secular boron isotope variations in the continental crust: an ion microprobe study

Tourmalines of various chemical compositions, hosted in magmatic rocks with ages ranging from 3.8 Ga to the present were analysed for δ 11B by ion microprobe. A large range of δ 11B values, from − 2‰ to − 30 ± 1.5‰, was observed. The δ 11B values are correlated with the chemical composition of the tourmalines, the Li-rich tourmalines being enriched in 11B compared to Fe and/or Mg-rich tourmalines. This may reflect mixing in the continental crust between a marine reservoir characterized by high Li contents and δ 11B values and a continental reservoir characterized by low Li contents and δ 11B values. No relationship between the age and the δ 11B values is observed for the Fe- or for the Mg-rich tourmalines. In contrast the δ 11B values of the Li-rich tourmalines show a tendency to regularly decrease with increasing age. This pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents. A variation in the mean δ 11B value of the continental crust, from ≈ − 20‰ Ga ago to ≈ − 7‰ at present, is predicted by the model. The largest variation occurred during the first 2.5 Ga.

Boron isotope geochemistry as a tracer for the evolution of brines and associated hot springs from the Dead Sea, Israel

A boron isotope study combined with analyses of elemental boron, lithium, and chlorine is used to suggest that brines from the Dead Sea and on-shore hypersaline thermal springs (Hamme Yesha, Hamme Zohar, and Hamme Mazor) are the products of interaction of evaporated seawater with detrital sediments. The high δ 11B values of the Dead Sea brines (55.7 to 57.4%. versus NBS-951) and the hot springs (52.2 to 55.7%.), and low B Li ratios (2.0 to 2.3 and 2.5 to 2.7, respectively), relative to seawater, indicate preferential removal of 10B from the brines and hence boron adsorption onto clay minerals. The brackish 'En Feshcha springs and the freshwater 'En Dawid and Nahal Arugot springs yield lower B contents and δ 11B values (37.7 to 40.6%. and 33.8 to 36.9%., respectively). The δ 11B values and B contents of diluted Dead Sea brines lie on calculated mixing lines between the composition of the brackish and freshwater springs with the composition of the Dead Sea. The δ 11 B values of the hot springs, however, given their boron content, are significantly lower than those of the mixing lines. Thus, waters from the hot springs cannot be a mixing product of the Dead Sea brine with freshwater. Instead, the Dead Sea brine has evolved from the brines of the hot springs through further isotopic fractionation and boron adsorption onto detrital sediments.

Tourmaline mineralization in the Barberton greenstone belt, South Africa: early Archean metasomatism by evaporite-derived boron.

Tourmaline-rich rocks are common in the low-grade, interior portions of the Barberton greenstone belt of South Africa, where shallow-marine sediments and underlying altered basaltic and komatiitic lavas contain up to 50% tourmaline. The presence of tourmaline-bearing rip-up clasts, intraformational tourmaline pebbles and tourmaline-coated grains indicate that boron mineralization was a low-temperature, surficial process. The association of these lithologies with stromatolites, evaporites, and shallow-water sedimentary structures and the virtual absence of tourmaline in correlative deep-water facies rocks in the greenstone belt strengthens this model. Five tourmaline-bearing lithologic groups (basalts, komatiites, evaporite-bearing sediments, stromatolitic sediments, and quartz veins) are distinguished based on field, petrographic, and geochemical criteria. Individual tourmaline crystals within these lithologies show internal chemical and textural variations that reflect continued growth through intervals of change in bulk-rock and fluid composition accompanying one or more metasomatic events. Large single-crystal variations exist in Fe/Mg, Al/Fe, and alkali-site vacancies. A wide range in tourmaline composition exists in rocks altered from similar protoliths, but tourmalines in sediments and lavas have similar compositional variations. Boron-isotope analyses of the tourmalines suggest that the boron enrichment in these rocks has a major marine evaporitic component. Sediments with gypsum pseudomorphs and lavas altered at low temperatures by shallow-level brines have the highest delta 11B values (+2.2 to -1.9%); lower delta 11B values of late quartz veins (-3.7 to -5.7%) reflect intermediate temperature, hydrothermal remobilization of evaporitic boron. The delta 11B values of tourmaline-rich stromatolitic sediments (-9.8 and -10.5%) are consistent with two-stage boron enrichment, in which earlier marine evaporitic boron was hydrothermally remobilized and vented in shallow-marine or subaerial sites, mineralizing algal stromatolites. The stromatolite-forming algae preferentially may have lived near the sites of hydrothermal discharge in Archean times.

The boron isotope systematics of the Yellowstone National Park (Wyoming) hydrothermal system: A reconnaissance

Boron concentrations and isotope compositions have been measured in fourteen hot spring waters, two drill hole waters, an unaltered rhyolite flow, and hydrothermally altered rhyolite from the geothermal system in Yellowstone National Park, Wyoming. The samples are representative of the major thermal areas within the park and span the range of fluid types. For the fluids, the B concentrations range from 0.043–2.69 mM/kg, and the δ 11B values range from −9.3 to +4.4%.. There is no relationship between the dissolved B concentrations or isotope compositions with the concentration of any major element (other than Cl) or physical property. Each basin is characterized by a restricted range in B/Cl ratios and δ 11B values. Hot spring waters from the Morris Basin, Upper Geyser Basin, Calcite Springs, and Clearwater have δ 11B values close to that of unaltered rhyolite (−5.2%.) and are interpreted to have derived their B from this source. Waters from Mammoth Hot Springs, Sheepeater, and Rainbow Springs have lower δ 11B values close to −8%.. These lower values may reflect leaching of B from sedimentary rocks outside the Yellowstone caldera, but they are similar to the δ 11B value of hydrothermally altered rhyolite (−9.7%.). Hence, the light boron isotope compositions recorded in these hot spring waters may reflect leaching of previously deposited hydrothermal minerals. Cooler springs along the Yellowstone River just outside the park boundary have lower B concentrations and higher δ 11B values that may reflect mixing with shallow meteoric water.

A critical evaluation of the available measurements for the stable isotopes of boron

The reported measurements for the stable isotopes of B ( 11B and 10B) in natural materials are compiled, critically reviewed and evaluated. The selected values along with a discussion of the error, indicate the potential exists for using B isotopes in interpreting geochemical environments. The isotopic values for δ 11B range from -31% 0 for terrestrial rocks to +40% 0 for sea water, relative to NBS SRM-951 which has a reported 11B/ 10B ratio of 4.04362 ± 0.00137 (2σ). Furtherm the isotope ratios generally form a narrow cluster of values for specific rock types. In some instances the reported δ 11B may be shifted substantially from the mean of “unaltered” rock as a result of weathering or reaction such as the progressive enrichment of δ 11B in marine sediments over time due to reaction with sea water. An application of widespread interest is the use of B isotopes in environmental studies. Boron is a contaminant derived from numerous sources such as municipal and industrial waste. The δ 11B in these wastes or processed waters is often significantly different from the δ 11B of the local ground-water, which will likely reflect the δ 11B values of the nearby rocks. This modification by contaminated water can be >20% 0 different from the δ 11B of the unaffected water, providing a useful tool in delineating the source of contamination and the direction of migration.

Synthesen mit 1-phenylbora-2,5-cyclohexadien. Komplexe von eisen, cobalt und nickel mit teilweise hydrierten borabenzol-liganden

Phenylbora-2,5-cyclohexadiene (LH) is a versatile ligand precursor in reactions with Fe(CO) 5, Co 2(CO) 8, Ni(CO) 4, and Ni(η 4-1,5-COD) 2. Photochemical reaction with Fe(CO) 5 gives (η 5-LH)Fe(CO) 3 which under irradiation slowly converts to the known borabenzene derivative [(η 6-L)Fe(CO) 2] 2( Fe Fe). LH reacts with Co 2(CO) 8 to give the known complex (η 6-L)Co(CO) 2 and two isomers (η 4-LH 2)Co(CO) 3 with the novel bora-5-cyclohexen-2-yl and bora-3-cyclohexen-2-yl ligands, respectively. Ni(CO) 4 similarly yields two isomers Ni(η 6-L)(η 4-LH 2), whereas Ni(η 4-1,5-COD) 2 gives Ni(η 6-L)(1,4,5-η 3-C 8H 13). Complexes with ligands of the type of η 4-2-bora-3-buten-1-yl show strong metalboron interactions as evidenced by a NiB distance of 217 pm in the corresponding isomer Ni(η 6-L)(η 4-LH 2) and by δ( 11B) values ranging from 19.6 to 24.4 ppm. In contrast to this, complexes with ligands of the type η 4-1-bora-3-buten-2-yl show weak metalboron interactions as revealed by a comparatively long CoB distance of 248.1(7) pm in the corresponding isomer Co(CO) 2(PMe 3)(η 4-LH 2) and by δ( 11B) values at significantly lower field, ranging from 41.5 to 30.8 ppm.

NMR coupling, hybrid orbital character, and bond distances in boron hydrides

Boron-boron coupling constants for B(1)-B(3) of B 4H 10, B(1)-B(4) of CB 5H 9, and a number of other compounds have been determined. From both J( 11B-H) and J( 11B- 11B) values for B,.H6, 11,11,0, and B 5H 9 a set of s B -orbital populations have been derived, and found to compare favorably to those obtained from PRDDO wavefunctions. Also, J( 11B-H) is shown to be a function of bond distance and from this a more reasonable bond length of 1.30 Å is suggested for the unique bridge hydrogen, bonded to the apex boron of B 5H 11 ; and predictions of J = 14 (±10%) Hz for B(2)-H μ2,3 and J = 41 (±10%) Hz for B(3)-H μ2,3 of B 5H 11, as well as 24 (±10%) Hz for B(5)-H μ of 2,3-C 2B 4H 8, are made.