Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 10(5) to 10(7) years, rhythmic or periodic cycles driven by orbital processes with 10(4)- to 10(6)-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 10(3) to 10(5) years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.

/pdf/trends-rhythms-and-aberrations-in-global-climate-65-ma-to-cflhxkixnq.pdf

Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present

Data from experimental runs, coexisting phases in ultramafic rocks and phenocryst-matrix pairs in volcanic rocks have been used to compile a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions. These values have then been used to interpret variations of these elements, first in basalts and second, during fractional crystallization from basic to acid magmas. For basalts, petrogenetic modelling of Zr/Y, Zr/Ti, and Zr/Nb ratios, when used in conjunction with REE, Cr and isotopic variations, suggests that: (1) the increase in Zr/Y ratio from mid-ocean ridge to within plate basalts and the low Zr/Nb ratios of alkalic basalts are due to (fluid controlled) source heterogeneities; (2) the low Zr and Zr/Y ratio of volcanic arc basalts results from high degree of partial melting of a depleted source; and (3) the high Zr and similar Zr/Y ratio of basalts from fast spreading relative to slow spreading ridges results from open-system fractional crystallization. Modelling of fractionation trends in more evolved rocks using Y-Zr, Ti-Zr and Nb-Zr diagrams highlights in particular the change in crystallizing mafic phases from island arcs (clinopyroxene-dominated) to Andean-type arcs (amphibole±biotite-dominated). These methods can be applied to altered lavas of unknown affinities to provide additional information on their genesis and eruptive environment.

Petrogenetic implications of Ti, Zr, Y, and Nb variations in volcanic rocks

Amphibole thermodynamics are approximated with the symmetric formalism (regular solution model for within-site non-ideality and a reciprocal solution model for cross-site-terms) in order to formulate improved thermometers for amphibole-plagioclase assemblages. This approximation provides a convenient framework with which to account for composition-dependence of the ideal (mixing-on-sites) equilibrium constants for the equilibria:
 For A and B all possible within-site and cross-site interactions among the species □−K−Na−Ca−Mg−Fe2+−Fe3+−Al−Si on the A, M4, M1, M3, M2 and T1 amphibole crystallographic sites were examined. Of the 36 possible interaction energy terms, application of the symmetric formalism results in a dramatic simplification to eight independent parameters. Plagioclase nonideality is modelled using Darken's quadratic formalism. We have supplemented an experimental data set of 92 amphibole-plagioclase pairs with 215 natural pairs from igneous and metamorphic rocks in which the pressure and temperature of equilibration are well constrained. Regression of the combined dataset yields values for the eight interaction parameters as well as for apparent enthalpy, entropy and volume changes for each reaction. These parameters are used to formulate two new thermometers, which perform well (±40°C) in the range 400–1000°C and 1–15 kbar over a broad range of bulk compositions, including tschermakitic amphiboles from garnet amphibolites which caused problems for the simple thermometer of Blundy and Holland (1990). For silica-saturated rocks both thermometers may be applied: in silica-undersaturated rocks or magmas thermometer B alone can be applied. An improved procedure for estimation of ferric iron in calcic amphiboles is presented in the appendix.

Non-ideal interactions in calcic amphiboles and their bearing on amphibole-plagioclase thermometry

The composition of chromian spinel in alpine-type peridotites has a large reciprocal range of Cr and Al, with increasing Cr# (Cr/(Cr+Al)) reflecting increasing degrees of partial melting in the mantle. Using spinel compositions, alpine-type peridotites can be divided into three groups. Type I peridotites and associated volcanic rocks contain spinels with Cr# 0.60, and Type II peridotites and volcanics are a transitional group and contain spinels spanning the full range of spinel compositions in Type I and Type II peridotites. Spinels in abyssal peridotites lie entirely within the Type I spinel field, making ophiolites with Type I alpine-type peridotites the most likely candidates for sections of ocean lithosphere formed at a midocean ridge. The only modern analogs for Type III peridotites and associated volcanic rocks are found in arc-related volcanic and intrusive rocks, continental intrusive assemblages, and oceanic plateau basalts. We infer a sub-volcanic arc petrogenesis for most Type III alpine-type peridotites. Type II alpine-type peridotites apparently reflect composite origins, such as the formation of an island-arc on ocean crust, resulting in large variations in the degree and provenance of melting over relatively short distances. The essential difference between Type I and Type III peridotites appears to be the presence or absence of diopside in the residue at the end of melting.

Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas

[1] We present a new common stratigraphic timescale for the North Greenland Ice Core Project (NGRIP) and GRIP ice cores. The timescale covers the period 7.9–14.8 kyr before present and includes the Bolling, Allerod, Younger Dryas, and early Holocene periods. We use a combination of new and previously published data, the most prominent being new high-resolution Continuous Flow Analysis (CFA) impurity records from the NGRIP ice core. Several investigators have identified and counted annual layers using a multiparameter approach, and the maximum counting error is estimated to be up to 2% in the Holocene part and about 3% for the older parts. These counting error estimates reflect the number of annual layers that were hard to interpret, but not a possible bias in the set of rules used for annual layer identification. As the GRIP and NGRIP ice cores are not optimal for annual layer counting in the middle and late Holocene, the timescale is tied to a prominent volcanic event inside the 8.2 kyr cold event, recently dated in the DYE-3 ice core to 8236 years before A. D. 2000 (b2k) with a maximum counting error of 47 years. The new timescale dates the Younger Dryas-Preboreal transition to 11,703 b2k, which is 100–150 years older than according to the present GRIP and NGRIP timescales. The age of the transition matches the GISP2 timescale within a few years, but viewed over the entire 7.9–14.8 kyr section, there are significant differences between the new timescale and the GISP2 timescale. The transition from the glacial into the Bolling interstadial is dated to 14,692 b2k. The presented timescale is a part of a new Greenland ice core chronology common to the DYE-3, GRIP, and NGRIP ice cores, named the Greenland Ice Core Chronology 2005 (GICC05). The annual layer thicknesses are observed to be log-normally distributed with good approximation, and compared to the early Holocene, the mean accumulation rates in the Younger Dryas and Bolling periods are found to be 47 ± 2% and 88 ± 2%, respectively.

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A new Greenland ice core chronology for the last glacial termination

Volcanoes are unquestionably one of the most spectacular and awe-inspiring features of the physical world. Our paradoxical fascination with them stems from their majestic beauty and powerful, sometimes deadly, destructiveness. Notwithstanding the tremendous advances in volcanology since ancient times, some of the mystery surrounding volcanic eruptions remains today. The Encyclopedia of Volcanoes summarizes our present knowledge of volcanoes; it provides a comprehensive source of information on the causes of volcanic eruptions and both the destructive and beneficial effects. The early chapters focus on the science of volcanism (melting of source rocks, ascent of magma, eruption processes, extraterrestrial volcanism, etc.). Later chapters discuss human interface with volcanoes, including the history of volcanology, geothermal energy resources, interaction with the oceans and atmosphere, health aspects of volcanism, mitigation of volcanic disasters, post-eruption ecology, and the impact of eruptions on organismal biodiversity. * Provides the only comprehensive reference work to cover all aspects of volcanology * Written by nearly 100 world experts in volcanology * Explores an integrated transition from the physical process of eruptions through hazards and risk, to the social face of volcanism, with an emphasis on how volcanoes have influenced and shaped society * Presents hundreds of color photographs, maps, charts and illustrations making this an aesthetically appealing reference * On-line supplement includes additional multimedia * Glossary of 3,000 key terms with definitions of all key vocabulary items in the field is included

The encyclopedia of volcanoes

R.D. Ballard, Foreword. Origin and Transport of Magma: H. Sigurdsson, B. Houghton, H. Rymer, J. Stix, and S. McNutt, Introduction. H. Sigurdsson, The History of Volcanology. R. Jeanloz, Mantle of the Earth. P. Asimov, Melting the Mantle. M. Daines, Migration of Melt. M. Perfit and J. Davidson, Tectonics and Volcanism. N.W. Rogers and C.J. Hawkesworth, Composition of Magmas. T.L. Grove, Origin of Magmas. P.J. Wallace and A.T. Anderson, Volatiles in Magmas. F.J. Spera, Physical and Thermodynamic Properties of Magmas. B.D. Marsh, Reservoirs of Magma and Magma Chambers. M.J. Rutherford and J. Gardner, Rates of Magma Ascent. C. Carrigan, Plumbing Systems. C. Jaupart, Magma at Shallow Levels. Eruption: T. Simkin and L. Siebert, Active Volcanoes on the Earth. D.M. Pyle, Sizes of Volcanic Eruptions. H. Sigurdsson, Episodes of Volcanism. Effusive Volcanism: G.P.L. Walker, Basaltic Volcanoes and Volcanic Systems. C. Kilburn, Lava Flows. J. Fink and S. Anderson, Domes and Coulees. J. Wolff and J. Sumner, Spatter-Fed Lavas and Fire-Fountaining. C. Conner and M. Conway, Basaltic Volcanic Fields. P. Hooper, Flood Basalt Provinces. R. Batiza and J. White, Submarine Lavas and Hyaloclastite. R. Schmidt and H.-U. Schmincke, Seamounts, Submarine Volcanoes, and Volcanic Islands. J. Smellie, Sub-Glacial Eruptions. Explosive Volcanism: Cashman, B. Sturtevant, P. Papale, and O. Navon, Magmatic Fragmentation. M.M. Morrisey, B. Zimoriski, K. Wohletz, and R. Buettner, Phreatomagmatic Fragmentation. S. Vergniolle and M. Mangan, Strombolian and Hawaiian Eruptions. M.M. Morrissey and L.G. Mastin, Vulcanian Eruptions. Cioni, P. Marianelli, R. Santecroce, and A. Sbrana, Plinian Eruptions. J.D.L. White and B. Houghton, Pyroclastic Eruptions. B.F. Houghton, C.J.N. Wilson, R.T. Smith, and J.S. Gilbert, Phreatoplinian Eruptions. S. Carey and M.I. Bursik, Volcanic Plumes. C.J.N. Wilson and B.F. Houghton, Pyroclastic Transport and Deposition. B.F. Houghton, C.J.N. Wilson, and D.M. Pyle, Fall Deposits. G. Valentine and R.V. Fisher, Deposits of Surges and Directed Blasts. A. Freundt, S.N. Carey, and C.J.N. Wilson, Ignimbrites and Deposits of Block-and-Ash Flows. J.W. Vallance, Lahar Deposits. T. Ui and M. Yoshimoto, Debris Avalanche Deposits. S. Carey, Volcaniclastic Sedimentation Around Island Arces. P.W. Lipman, Calderas. J.P. Davidson and S. Da Silva, Composite Cones. D. Vespermann and H.U. Schmincke, Scoria Cones and Tuff Rings. Extraterrestrial Volcanism: P.D. Spudis, Volcanism on the Moon. R. Lopes-Gautier, Volcanism on IO. L. Crumpler, Volcanism on Venus.J.R. Zimbelman, Volcanism on Mars.P. Geissler, Cryovolcanism in the Outer Solar System. Volcano Interactions: P. delMelle and J. Stix, Volcanic Gases. F. Goff and C. Janik, Geothermal Systems. P. Browne and M. Hochstein, Surface Manifestations. D. Butterfield, Submarine Hydrothermal Vents. P. delMelle and A. Bernard, Volcanic Lakes. N.C. White and R.J. Harrington, Mineral Deposits Associated with Volcanism. Volcanic Hazards: T.P. Miller and T.J. Casadevall, Volcanic Ash Hazards to Aviation. M.J. Mills and O.B. Toon, Volcanic Aerosol and Global Atmospheric Effect. S. Nekada, Hazards from Pyroclastic Flows and Surges. D. Peterson and R.I. Tilling, Lava Flow Hazards. K. Rodolfo, Lahars and Jokulhlaup Hazards. H. Rymer and G. Williams-Jones, Volcanic Gas Hazards. J.E. Beget, Volcanic Tsunamis. S.R. McNutt, Volcanic Seismicity. P. Baxter, Impacts of Eruptions on Human Health. M. Arthur, The Volcanic Contribution to the Sulfur and Carbon Geochemical Cycle. I. Thornton, The Ecology of Volcanoes-Biological Recovery and Colonization. M. Rampino and S. Self, Volcanism and Biotic Extinction. Eruption Response and Mitigation: S.R. McNutt, Seismic Monitoring. J.B. Murray, C.A. Locke, and H.Rymer, Ground Deformation, Gravity, and Magnetics. J. Stix and H. Gaonach, Gas, Plume, and Thermal Monitoring. S. McNutt, J. Stix, and H. Rymer, Synthesis of Volcano Monitoring. C. Newhall, Volcano Warnings. S. de la Cruz, R. Quaas, and R. Meli, Volcanic Crisis Management. R. Blong, Volcanic Hazards and Risk Management. D. Johnson and K. Ronan, Risk Education and Intervention. Economic Benefits and Cultural Aspects of Volcanism: S. Arnorsson, Exploitation of Geothermal Resources. C-l. Ping, Volcanic Soils. J. Dehn and S.R. McNutt, Volcanic Materials for Commerce and Industry. H. Sigurdsson and R. Lopes-Gautier, Volcanoes and Tourism. S. Harris, Archaeology and Volcanism. H. Sigurdsson, Volcanoes in Art. H. Sigurdsson and R. Lopes, Volcanoes in Literature and Film. Appendices: Units and Physical Properties of the Earth Volcanoes of the Earth.

https://physicstoday.scitation.org/doi/pdf/10.1063/1.1325206

Encyclopedia of Volcanoes

Injection of basic magma into acid magma causes superheating of the acid magma and vigorous convection. Vesiculation induced by convection and increased magma pressure fractures the volcanic edifice triggering an explosive acid eruption. The 1875 plinian eruption of Askja, Iceland is an example of an explosive eruption triggered by magma mixing.

Magma mixing: a mechanism for triggering acid explosive eruptions

We report analytical methods based on electron microprobe analysis of volcanic tephra which allow estimation of minimum masses of sulfur and chlorine released to the atmosphere by volcanic eruptions. Differences between sulfur and chlorine contents of glassy melt inclusions (trapped by tephra phenocrysts) and matrix glasses, respectively, scaled to estimated eruption volumes, provide estimates of minimum sulfur and chlorine yield to the atmosphere. Declines in mean northern hemisphere surface temperatures associated with several Recent eruptions (Laki 1783, Tambora 1815, Krakatau 1883, Agung 1963, Mount St. Helens 1980) are positively correlated with our estimates of the rnimimum mass of sulfur released to the atmosphere, reinforcing the idea that sulfate aerosols have a greater climatic impact than volcanic “dust.” Injection of volcanic emissions into the stratosphere increases the optical thickness of the atmosphere which may result in cooling of the earth's surface. Our results indicate that decreases in mean surface temperatures associated with the eruptions listed above appear to vary linearly with the cube root of the estimated minimum mass of sulfur released by the eruptions. This apparent geometric relationship suggests that increases in optical thickness may be completely related to increases in the mass of particulates in the stratospheric aerosol layer-Correlations between observed mean surface temperature decreases and other eruption-related parameters (estimated chlorine yield, estimated total sulfur and chlorine yield, estimated tephra volume dense rock equivalent) are poor compared to the correlation with our estimates of sulfur yield. Application of our methods to the 1982 eruption of El Chichon volcano results in underestimation of the minimum mass of sulfur released to the atmosphere, judging from independent estimates based on airborne sampling and satellite observations of the eruption plume. The presence of anhydrite phenocrysts in El Chichon tephra suggests that decomposition of anhydrite may have contributed to the sulfur yield of this eruption. Potential contributions of volatile species to the atmosphere from eruptions of basaltic magma are generally about an order of magnitude higher in sulfur than eruptions of equal volumes of silicic magma, in spite of the fact that silicic magmas inject more fine ash and total volatiles (H2O, CO2) into the upper atmosphere. In view of the significant climatic impact of the Laki 1783 fissure eruption of basaltic magma, we suggest that flood or fissure basalt eruptions should be taken into account along with explosive silicic volcanism in paleoclimatic reconstructions.

Estimates of sulfur and chlorine yield to the atmosphere from volcanic eruptions and potential climatic effects

The Mount St. Helens, May 18 pumice is a dacite containing 60% glass by weight and phenocrysts of plagioclase, orthopyroxene, amphibole, titaniferous magnetite, and ilmenite. The glass is uniform in composition, a rhyodacite with 73 wt % SiO2; the phenocrysts are also uniform in composition except for the plagioclase, which has cores averaging An57 and rims averaging An49. Analyses of seven pairs of coexisting Fe-Ti oxides in a representative sample of the light pumice were recast using various mineral calculation procedures; they yielded temperatures ranging from 920° to 940°C and a -log ƒO2 of 10.3–10.1. Electron microprobe analyses of 57 glass inclusions trapped in plagioclase phenocrysts in the light pumice showed little deviation from an average rhyodacitic composition (69.90±0.87 wt % SiO2) when special care was taken to account for Na loss during the analysis. The difference between the average total of these glass inclusion analyses and 100% is 4.6±1 wt %, which is interpreted to be volatiles dissolved in the glass. On an anhydrous basis the average glass inclusion composition is identical to the matrix glass, indicating that neither underwent significant fractionation after melt was trapped by the plagioclase. Experimentally determined phase relations for the representative dacite sample place limits on conditions in the May 18 Mount St. Helens magma chamber, assuming that the dissolved volatiles were 4.6±1 wt % and the temperature was 920°–940°C. Hydrothermal experiments over a range of P, T, and ƒO2 indicate that at no pressure is the observed phase assemblage and residual melt chemistry produced when PH2O = PTotal. Experiments using CO2-H2O fluids to achieve PH2's less than PFluid did reproduce the observed residual melt chemistry and an An50 plagioclase at a specific set of conditions, i.e., atƒO2's between the NNO and MNO buffers, at a PFluid of 220 MPa (2.2 kb), and at a PH2 = 110 MPa (all at 920°–940°C). Amphibole was not stable under these conditions but possibly would be if the PH2 / PFluid ratio was raised to 0.7 or if fluorine were added to the experimental system. It is concluded that just prior to eruption, the upper part of the Mount St. Helens magma chamber was at a pressure of 220±30 MPa corresponding to a depth of 7.2±1 km, PH2 was 0.5 to 0.7 PTotal, and the temperature was 930°±10°C.

Haraldur Sigurdsson

Papers

The encyclopedia of volcanoes

Encyclopedia of Volcanoes

Magma mixing: a mechanism for triggering acid explosive eruptions

Estimates of sulfur and chlorine yield to the atmosphere from volcanic eruptions and potential climatic effects

The May 18, 1980, eruption of Mount St. Helens: 1. Melt composition and experimental phase equilibria