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1.
Mercury vapor (Hg0) emission from plants contributes to the atmospheric Hg cycle. Young barley (Hordeum vulgare L.) plants grown on a hydroponic cultivation medium containing Hg(II) have previously been shown to increase their Hg0 emission significantly by reduction of Hg(II) with endogenous ascorbic acid. Regarding the potential contribution to the Hg cycle from the vast forest-covered areas, it was important to investigate this mechanism in trees. The increase in Hg0 emission from young European beech plants cultivated on a HgCl2 medium exceeded that from controls by ca. tenfold and was proportional to the Hg(II) concentration. From these experiments, a flux of 12.8 μg Hg0/h/m2 was estimated at an exposure of the roots to 20 μM Hg(II). Mercury vapor release from homogenates of Norway spruce needles exceeded that from European beech leaves by a factor of 2.3–4, i.e. in proportion to the reported AA concentrations; the reduction was maximal at alkaline pH which is typical for AA. The 8.4-fold difference in Hg0 release between homogenates from wild-type Arabidopsis thaliana and from its AA-deficient mutant vtc 1-1 also paralleled the reported difference in AA levels of both species. It is concluded that the phytoreduction and vaporization of Hg by AA is an important mechanism as much for Hg detoxification in trees as for Hg emission to the atmosphere. The efficiency of this process seems to result from the optimal coordination of transfer and biochemical transformation of mercuric ions and Hg vapor. There is no evidence for a relevant difference in the mechanisms of biogenic Hg(II) reduction between grass plants and trees. 相似文献
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Whole-rock and sulfide lead-isotope data from the hydrothermal JADE field in the Okinawa back-arc trough 总被引:7,自引:0,他引:7
The mineralization of the active hydrothermal JADE field resembles in many aspects the Kuroko-type mineralization. The JADE
field is located in a back-arc graben and is associated with a bimodal volcanism. Lead isotope data from igneous rocks, sediments,
and ores further emphasize the similarities with the Kuroko ores and suggest that both sediments and volcanic rocks contributed
comparable amounts of lead to the deposit. When compared to the sediments, a much larger volume of volcanic rocks must have
contributed lead to the deposit, because of the considerably lower lead concentration of volcanic rocks. In contrast to the
crustal type lead of the JADE field and the Kuroko-type sulfide deposits the lead isotope signatures of VMS-type deposits
at mid-ocean ridges is distinctly different. In the absence of a sedimentary cover it reflects the composition of the mantle
source, whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even
be completely dominated by the latter.
Received: 5 October 1995 / Accepted: 10 May 1996 相似文献
4.
The technique of linear parametric programming has been applied to derive sets of internally consistent thermodynamic data for 21 condensed phases of the quaternary system CaO-Al2O3-SiO2-H2O (CASH) (Table 4). This was achieved by simultaneously processing:
- calorimetric data for 16 of these phases (Table 1), and
- experimental phase equilibria reversal brackets for 27 reactions (Table 3) involving these phases.
5.
Summary Ten manganese nodules from a manganese nodule field in the northeast Pacific were chemically and mineralogically investigated.Two kinds of growth-zones could be observed within these nodules; according to structure they are called laminated zones and dendritic zones.Some correlations between sediment layers and manganese nodules zones could be observed, as follows:Dendritic zones in manganese nodules are products of diagenetic mobilization of metals from the sediment-they correspond to the sediment layers in which diagenetic processes took place.Laminated zones in manganese nodules are products of precipitation of hyroxides from sea water. They correspond to periods of sedimentation without diagenetic mobilization of metals.Ratios for Mn to Ni, Cu, Zn, and Mg are constant through different growth zones, independent of the form in which manganese occurs.Ratio for Co to Fe changes from laminated zones to dendritic zones.The only component which changes its content with diagenesis seems to be water: older parts of nodules contain less water than younger parts.Due to the described results the growth of manganese nodules can be adjusted in the geological record. The history of existent nodules begins within the sedimentation hiatus between Early Miocene and Late Pliocene. The sedimentation record is reflected in the structure of manganese nodules.
With 20 Figures 相似文献
Innerer Aufbau von Manganknollen im Vergleich zu den Änderungen der Sedimentationsbedingungen
Zusammenfassung Zehn Manganknollen aus einem Manganknollenfeld im Nordost-Pazifik wurden chemisch und mineralogisch untersucht.Zwei Arten von Wachstumszonen konnten innerhalb dieser Knollen beobachtet werden; sie wurden nach ihren jeweiligen Strukturen laminierte und dendritische Zonen genannt. Zwischen den Zonen in den Manganknollen und den Schichten im Sediment konnten Zusammenhänge beobachtet werden: Dendritische Zonen in den Manganknollen sind Produkte der diagenetischen Mobilisation der Metalle aus dem Sediment-sie entsprechen jeweils einer Sedimentschicht, in der sich frühdiagenetische Vorgänge abgespielt haben.-Laminierte Zonen in den Manganknollen sind Produkte der Ausfällung der Hydroxide aus dem Meereswasser. Sie entsprechen im Sediment den Perioden ohne frühdiagenetische Mobilisierung der Metalle.Die Verhältnisse von Mangan zu Nickel, Kupfer, Zink und Magnesium sind durch alle Wachstumszonen in den Knollen konstant, unabhängig davon, in welcher Form Mangan vorliegt. Das Verhältnis von Kobalt zu Eisen ändert sich von den laminierten zu den dendritischen Zonen.Die einzige Komponente in den Knollen, die ihren Anteil bei diagenetischen Prozessen ändert, ist Wasser: die älteren Zonen enthalten weniger Wasser als die jüngeren.Mit diesen Ereignissen läßt sich das Wachstum der Manganknollen in den geologischen Ablauf einordnen. Die Geschichte der heute vorhandenen Knollen beginnt während des aus der Geologie bekannten Sedimentations-Hiatus zwischen dem frühen Miozän und dem späten Pliozän. Die Sedimentationsgeschichte von diesem Zeitpunkt bis heute spiegelt sich im Aufbau der Knollen wider.
With 20 Figures 相似文献
6.
Cosmas Kongnyuy Shang Muharrem Satir Emmanuel Nkonguin Nsifa Jean-Paul Liégeois Wolfgang Siebel Heiner Taubald 《International Journal of Earth Sciences》2007,96(5):817-841
We present a geochemical and isotopic study that, consistent with observed field relations, suggest Sangmelima late Archaean
high-K granite was derived by partial melting of older Archaean TTG. The TTG formations are sodic-trondhjemitic, showing calcic
and calc-alkalic trends and are metaluminous to peraluminous. High-K granites in contrast show a potassic calc-alkaline affinity
that spans the calcic, calc-alkalic, alkali-calcic and alkalic compositions. The two rock groups (TTG and high-K granites)
on the other hand are both ferroan and magnesian. They have a similar degree of fractionation for LREE but a different one
for HREE. Nd model ages and Sr/Y ratios define Mesoarchaean and slab-mantle derived magma compositions respectively, with
Nb and Ti anomalies indicating a subduction setting for the TTG. Major and trace element in addition to Sr and Nd isotopic
compositions support field observations that indicate the derivation of the high-K granitic group from the partial melting
of the older TTG equivalent at depth. Geochemical characteristics of the high-K granitic group are therefore inherited features
from the TTG protolith and cannot be used for determining their tectonic setting. The heat budget required for TTG partial
melting is ascribed to the upwelling of the mantle marked by a doleritic event of identical age as the generated high-K granite
melts. The cause of this upwelling is related to linear delamination along mega-shear zones in an intracontinental setting. 相似文献
7.
8.
P. Halbach H.-J. Gursky M. M. Gursky R. Schmidt-Effing W. V. Maresch 《Mineralium Deposita》1992,27(2):153-160
Horizons of several types of Upper Jurassic to Lower Cretaceous manganese nodules occur locally in sequences of radiolarian cherts within the Nicoya Ophiolite Complex (NW Costa Rica). Field studies, X-ray diffraction analysis, petrographic, chemical and experimental studies give evidence of a sedimentary, early diagenetic origin of the nodules, in contrast to earlier suggestions. Smooth, discoidal, compact and very dense nodules with diameters of some mm to 9 cm dominate. They are characterized by braunite, hollandite, pyrolusite and quartz as well as 39–61% Mn, 0.9–1.6% Fe, 5–26% SiO2, 1.3–1.9% A12O3, 1.5–3.0% Ba, 460–5400 ppm Cu, 85–340 ppm Ni and 40–130 ppm Co, among others. It is suggested that the original mineralogy (todorokite?) was altered during thermometamorphic (braunite) and hydrothermal (hollandite, pyrolusite) events. Petrographic similarities between the fossil nodules and modern deep-sea nodules are striking. Using standard hydrothermal techniques in an experimental study it is shown that under special conditions, braunite can be produced from modern nodule material. 相似文献
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