9 research outputs found
Introduction to geochemistry : principles and applications
This book is intended to serve as a text for an introductory course in geochemistry for undergraduate/graduate students with at least an elementary�level background in earth sciences, chemistry, and mathematics. The text, containing 83 tables and 181 figures, covers a wide variety of topics � ranging from atomic structure to chemical and isotopic equilibria to modern biogeochemical cycles � which are divided into four interrelated parts: Crystal Chemistry; Chemical Reactions (and biochemical reactions involving bacteria); Isotope Geochemistry (radiogenic and stable isotopes); and The Earth Supersystem, which includes discussions pertinent to the evolution of the solid Earth, the atmosphere, and the hydrosphere. In keeping with the modern trend in the field of geochemistry, the book emphasizes computational techniques by developing appropriate mathematical relations, solving a variety of problems to illustrate application of the mathematical relations, and leaving a set of questions at the end of each chapter to be solved by students. However, so as not to interrupt the flow of the text, involved chemical concepts and mathematical derivations are separated in the form of boxes. Supplementary materials are packaged into ten appendixes that include a standard�state (298.15 K, 1 bar) thermodynamic data table and a listing of answers to selected chapter�end questions
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Multi-stage metasomatism of diamondiferous eclogite xenoliths from the Udachnaya kimberlite pipe, Yakutia, Siberia
The primary garnet (pyrope-almandine)-omphacite
(Cpx 1, 6.5–7 wt% Na2O)-sulfide (Fe-Ni-Co
mss) assemblage of the two diamondiferous eclogite
xenoliths studied (U33/1 and UX/1) experienced two
mantle metasomatic events. The metasomatic event I
is recorded by the formation of platy phlogopite ( 10 wt% K2O), prior to incorporation of the xenoliths
in the kimberlite. The bulk of the metasomatic alteration,
consisting of spongy-textured clinopyroxene
(Cpx 2A, 1–3 wt% Na2O), coarser-grained clinopyroxene
(Cpx 2B, 2–5 wt% Na2O), pargasitic amphibole
( 0.8 wt% K2O; 3–3.5 wt% Na2O), kelyphite
(Cpx 3, mostly <1 wt% Na2O; and zoned Mg-Fe-Al
spinel), sodalite, calcite, K-feldspar, djerfisherite
(K5.95Na0.02Fe18.72Ni2.36Co0.01Cu4.08S26Cl ) and a small
amount of K-Ca-Fe-Mg glass, is ascribed to the
metasomatic event II that occurred also in the upper
mantle, but after the xenoliths were incorporated in
the kimberlite. A pervasive chloritic alteration (mainly
clinochlore + magnetite) that overprints earlier
assemblages probably took place in the upper crustal
environment. The diamonds are invariably associated
with secondary clinopyroxene and chlorite, but the
diamonds formed before the entrainment of the
xenoliths in the Udachnaya kimberlite
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KREEPy lunar meteorite Dhofar 287A: A new lunar mare basalt
Dhofar 287 (Dho 287) is a new lunar meteorite, found in Oman on January 14, 2001. The
main portion of this meteorite (Dho 287A) consists of a mare basalt, while a smaller portion of breccia
(Dho 287B) is attached on the side. Dho 287A is only the fourth crystalline mare basalt meteorite
found on Earth to date and is the subject of the present study. The basalt consists mainly of
phenocrysts of olivine and pyroxene set in a finer-grained matrix, which is composed of elongated
pyroxene and plagioclase crystals radiating from a common nucleii. The majority of olivine and
pyroxene grains are zoned, from core to rim, in terms of Fe and Mg. Accessory minerals include
ilmenite, chromite, ulvöspinel, troilite, and FeNi metal. Chromite is invariably mantled by ulvöspinel.
This rock is unusually rich in late-stage mesostasis, composed largely of fayalite, Si-K-Ba-rich glass,
fluorapatite, and whitlockite. In texture and mineralogy, Dho 287A is a low-Ti mare basalt, with
similarities to Apollo 12 (A-12) and Apollo 15 (A-15) basalts. However, all plagioclase is now
present as maskelynite, and its composition is atypical for known low-Ti mare basalts. The Fe to Mn
ratios of olivine and pyroxene, the presence of FeNi metal, and the bulk-rock oxygen isotopic ratios,
along with several other petrological features, are evidence for the lunar origin for this meteorite.
Whole-rock composition further confirms the similarity of Dho 287A with A-12 and A-15 samples
but requires possible KREEP assimilation to account for its rare-earth-element (REE) contents.
Cooling-rate estimates, based on Fo zonation in olivine, yield values of 0.2–0.8°C/hr for the lava,
typical for the center of a 10–20 m thick flow. The recalculated major-element concentrations, after
removing 10–15% modal olivine, are comparable to typical A-15 mare basalts. Crystallization modeling
of the recalculated Dho 287A bulk-composition yields a reasonable fit between predicted and
observed mineral abundances and compositions
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Nature of diamonds in Yakutian eclogites: views from eclogite tomography and mineral inclusions in diamonds
We have performed dissections of two diamondiferous eclogites (UX-1 and U33/1) from the Udachnaya kimberlite, Yakutia in order to understand the nature of diamond formation and the relationship between the diamonds, their mineral inclusions, and host eclogite minerals. Diamonds were carefully recovered from each xenolith, based upon high-resolution X-ray tomography images and three-dimensional models. The nature and physical properties of minerals, in direct contact with diamonds, were investigated at the time of diamond extraction. Polished sections of the eclogites were made, containing the mould areas of the diamonds, to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds. Major- and minor-element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other, and from those in the host eclogites. Oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another Udachnaya eclogite (U51) span the entire range recorded for eclogite xenoliths from Udachnaya. In addition, the reported compositions of almost all clinopyroxene inclusions in U51 diamonds exhibit positive Eu anomaly. This feature, together with the oxygen isotopic characteristics, is consistent with the well-established hypothesis of subduction origin for Udachnaya eclogite xenoliths. It is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage, at least with respect to their included diamonds. However, the variation in the composition of
multiple inclusions within diamonds, and among diamonds, from the same eclogite indicates the involvement of complex
processes in diamond genesis, at least in the eclogite xenoliths from Yakutia that we have studied
Discussion of “Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands” by D.C. Bradley and D.L. Leach
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46045/1/126_2004_Article_422.pd
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Discussion of "Tectonic Controls of Mississippi Valley-type Lead-Zinc Mineralization in Orogenic Forelands"
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Discussion of "Tectonic Controls of Mississippi Valley-type Lead-Zinc Mineralization in Orogenic Forelands"
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