Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds

Pearson, D. Graham; Canil, Dante; Shirey, Steven B.

doi:10.1016/b0-08-043751-6/02005-3

Cited by 382 publications

(324 citation statements)

References 391 publications

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“…Second, the constancy and uniformity of d am are well supported. Independent of age of emplacement or location, diamonds from peridotitic xenoliths have dZK5‰ (Pearson et al 2004). The same value is found in carbonatites and mantle-derived basalts (Kyser 1986;Mattey 1987).…”

Section: The Structure Of the Carbon Cyclesupporting

confidence: 50%

Molecular biogeochemistry of modern and ancient marine microbes

Waldbauer¹

2010

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Biological activity has shaped the surface of the earth in numerous ways, but life's most pervasive and persistent global impact has been the secular oxidation of the surface environment. Through primary production -the biochemical reduction of carbon dioxide to synthesize biomass -large amounts of oxidants such as molecular oxygen, sulfate and ferric iron have accumulated in the ocean, atmosphere and crust, fundamentally altering the chemical environment of the earth's surface. This thesis addresses aspects of the role of marine microorganisms in driving this process. In the first section of the thesis, biomarkers (hydrocarbon molecular fossils) are used to investigate the early history of microbial diversity and biogeochemistry. Molecular fossils from the Transvaal Supergroup, South Africa, document the presence in the oceans of a diverse microbiota, including eukaryotes, as well as oxygenic photosynthesis and aerobic biochemistry, by ca. 2.7Ga. Experimental study of the oxygen requirements of steroid biosynthesis suggests that sterane biomarkers in late Archean rocks are consistent with the persistence of microaerobic surface ocean environments long before the initial oxygenation of the atmosphere. In the second part, using Prochlorococcus (a marine cyanobacterium that is the most abundant primary producer on earth today) as a model system, we explored how microbes use the limited nutrient resources available in the marine environment to make the protein catalysts that enable primary production. Quantification of the Prochlorococcus proteome over the diel cell-division cycle reveals that protein abundances are distinct from transcript-level dynamics, and that small temporal shifts in enzyme levels can redirect metabolic fluxes. This thesis illustrates how molecular techniques can contribute to a systems-level understanding of biogeochemical processes, which will aid in reconstructing the past of, and predicting future change in, earth surface environments. ACKNOWLEDGMENTSI have incurred many debts of gratitude and appreciation over the course of this work. None are greater than those to my advisors, Penny Chisholm and Roger Summons, who allowed and enabled me to pursue such a wide range of scientific interests and offered their help and advice every step of the way. I have been very lucky to have had the chance to learn so much during my Ph.D., and none of that would have been possible without their guidance and support.I have also had the great fortune to know and work with all the members of the Chisholm and Summons labs, who have made this an enjoyable and rewarding place to be. I am especially grateful to Laura Sherman for her skill and dedication in analyzing biomarkers in the late Archean cores -it was truly getting blood from a stone. I was lucky to collaborate with Sébastien Rodrigue, whose expertise and collegiality made the diel experiment even more fruitful than I could have hoped. IntroductionThe coevolution of life and earth surface environments is central to the history and functionin...

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Section: The Structure Of the Carbon Cyclesupporting

confidence: 50%

Molecular biogeochemistry of modern and ancient marine microbes

Waldbauer¹

2010

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“…Ideally, a geologic record would exist, but proxies for ( J ad CJ od ) are rare. The low d 13 C values of some diamonds, particularly those of eclogite paragenesis, strongly suggest derivation from crustal organic carbon (Pearson et al 2004), though this has been disputed (Deines et al 2001). Recently, it is been suggested that organic carbon can be subducted beyond 250 km and contribute to sublithospheric diamonds (Tappert et al 2005).…”

Section: Cycling Of Carbon and Its Redox Partners Over Timementioning

confidence: 99%

The carbon cycle and associated redox processes through time

Hayes

Waldbauer

2006

Phil. Trans. R. Soc. B

428

308

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Earth's biogeochemical cycle of carbon delivers both limestones and organic materials to the crust. In numerous, biologically catalysed redox reactions, hydrogen, sulphur, iron, and oxygen serve prominently as electron donors and acceptors. The progress of these reactions can be reconstructed from records of variations in the abundance of 13 C in sedimentary carbonate minerals and organic materials. Because the crust is always receiving new CO 2 from the mantle and a portion of it is being reduced by photoautotrophs, the carbon cycle has continuously released oxidizing power. Most of it is represented by Fe 3C that has accumulated in the crust or been returned to the mantle via subduction. Less than 3% of the estimated, integrated production of oxidizing power since 3.8 Gyr ago is represented by O 2 in the atmosphere and dissolved in seawater. The balance is represented by sulphate. The accumulation of oxidizing power can be estimated from budgets summarizing inputs of mantle carbon and rates of organic-carbon burial, but levels of O 2 are only weakly and indirectly coupled to those phenomena and thus to carbon-isotopic records. Elevated abundances of 13 C in carbonate minerals ca 2.3 Gyr old, in particular, are here interpreted as indicating the importance of methanogenic bacteria in sediments rather than increased burial of organic carbon.

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“…Occurrences of mantle rock almost always include minor amounts of pyroxenite, indicating that mafic lithologies represent important heterogeneities in the otherwise peridotitic mantle (for recent reviews, see Pearson et al 2003;Bodinier and Godard 2003;Downes 2007). Most tectonically exhumed ultramafic massifs and ophiolite complexes, which allow for large-scale structural studies, exhibit mm-dm-sized websterite and/or clinopyroxenite bands or layers, typically aligned parallel to the main foliation of the tectonised peridotite (Bodinier and Godard 2003).…”

Section: Introductionmentioning

confidence: 99%

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

Kaeser

Olker

Kalt

et al. 2008

Contrib Mineral Petrol

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Garnet-bearing and garnet-free pyroxenite xenoliths from Quaternary basanites of Marsabit, northern Kenya, were analysed for microstructures and mineral compositions (major and trace elements) to constrain the thermal and compositional evolution of the lithospheric mantle in this region. Garnet-bearing rocks are amphibolebearing websterite with *5-10 vol% orthopyroxene. Clinopyroxene is LREE-depleted and garnet has high HREE contents, in agreement with an origin as cumulates from basaltic mantle melts. Primary orthopyroxene inclusions in garnet suggest that the parental melts were orthopyroxene-saturated. Rock fabrics vary from weakly to strongly deformed. Thermobarometry indicates extensive decompression and cooling (*970-1,100°C at *2.3-2.6 GPa to *700-800°C at *0.5-1.0 GPa) during deformation, best interpreted as pyroxenite intrusion into thick Paleozoic continental lithosphere subsequently followed by continental rifting (i.e., formation of the Mesozoic Anza Graben). During continental rifting, garnet websterites were decompressed (garnet-to-spinel transition) and experienced the same P-T evolution as their host peridotites. Strongly deformed samples show compositional overlaps with cpx-rich, initially garnet-bearing lherzolite, best explained by partial re-equilibration of peridotite and pyroxenite during deformation and mechanical mingling. In contrast, garnet-free pyroxenites include undeformed, cumulate-like samples, indicating that they are younger than the garnet websterites. Major and trace element compositions of clinopyroxene and calculated equilibrium melts suggest crystallisation from alkaline basaltic melt similar to the host basanite, which suggests formation in the context of alkaline magmatism during the development of the Kenya rift.

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Mantle Samples Included in Volcanic Rocks: Xenoliths and Diamonds

Cited by 382 publications

References 391 publications

Molecular biogeochemistry of modern and ancient marine microbes

Molecular biogeochemistry of modern and ancient marine microbes

The carbon cycle and associated redox processes through time

Pyroxenite xenoliths from Marsabit (Northern Kenya): evidence for different magmatic events in the lithospheric mantle and interaction between peridotite and pyroxenite

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