Throughout the biological world, a 30 A hydrophobic film typically delimits the environments that serve as the margin between life and death for individual cells. Biochemical and biophysical findings have provided a detailed model of the composition and structure of membranes, which includes levels of dynamic organization both across the lipid bilayer (lipid asymmetry) and in the lateral dimension (lipid domains) of membranes. How do cells apply anabolic and catabolic enzymes, translocases and transporters, plus the intrinsic physical phase behaviour of lipids and their interactions with membrane proteins, to create the unique compositions and multiple functionalities of their individual membranes?

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Membrane lipids: where they are and how they behave.

A revised regular solution-type thermodynamic model for twelve-component silicate liquids in the system SiO2-TiO2-Al2O3-Fe2O3-Cr2O3-FeO-MgO-CaO-Na2O-K2O-P2O5-H2O is calibrated. The model is referenced to previously published standard state thermodynamic properties and is derived from a set of internally consistent thermodynamic models for solid solutions of the igneous rock forming minerals, including: (Mg,Fe2+,Ca)-olivines, (Na,Mg,Fe2+,Ca)M2 (Mg,Fe2+, Ti, Fe3+, Al)M1 (Fe3+, Al,Si)2TETO6-pyroxenes, (Na,Ca,K)-feldspars, (Mg,Fe2+) (Fe3+, Al, Cr)2O4-(Mg,Fe2+)2 TiO4 spinels and (Fe2+, Mg, Mn2+)TiO3-Fe2O3 rhombohedral oxides. The calibration utilizes over 2,500 experimentally determined compositions of silicate liquids coexisting at known temperatures, pressures and oxygen fugacities with apatite ±feldspar ±leucite ±olivine ±pyroxene ±quartz ±rhombohedral oxides ±spinel ±whitlockite ±water. The model is applicable to natural magmatic compositions (both hydrous and anhydrous), ranging from potash ankaratrites to rhyolites, over the temperature (T) range 900°–1700°C and pressures (P) up to 4 GPa. The model is implemented as a software package (MELTS) which may be used to simulate igneous processes such as (1) equilibrium or fractional crystallization, (2) isothermal, isenthalpic or isochoric assimilation, and (3) degassing of volatiles. Phase equilibria are predicted using the MELTS package by specifying bulk composition of the system and either (1) T and P, (2) enthalpy (H) and P, (3) entropy (S) and P, or (4) T and volume (V). Phase relations in systems open to oxygen are determined by directly specifying the fo2 or the T-P-fo2 (or equivalently H-P-fo2, S-P-fo2, T-V-fo2) evolution path. Calculations are performed by constrained minimization of the appropriate thermodynamic potential. Compositions and proportions of solids and liquids in the equilibrium assemblage are computed.

Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures

Knowledge of temperature and pressure, however qualitative, has been central to our views of geology since at least the early 19th century. In 1822, for example, Charles Daubeny presented what may be the very first “Geological Thermometer,” comparing temperatures of various geologic processes (Torrens 2006). Daubeny (1835) may even have been the first to measure the temperature of a lava flow, by laying a thermometer on the top of a flow at Vesuvius—albeit several months following the eruption, after intervening rain (his estimate was 390°F). In any case, pressure ( P ) and temperature ( T ) estimation lie at the heart of fundamental questions: How hot is Earth, and at what rate has the planet cooled. Are volcanoes the products of thermally driven mantle plumes? Where are magmas stored, and how are they transported to the surface—and how do storage and transport relate to plate tectonics? Well-calibrated thermometers and barometers are essential tools if we are to fully appreciate the driving forces and inner workings of volcanic systems.

This chapter presents methods to estimate the P-T conditions of volcanic and other igneous processes. The coverage includes a review of existing geothermometers and geobarometers, and a presentation of approximately 30 new models, including a new plagioclase-liquid hygrometer. Our emphasis is on experimentally calibrated “thermobarometers,” based on analytic expressions using P or T as dependent variables. For numerical reasons (touched on below) such expressions will always provide the most accurate means of P-T estimation, and are also most easily employed. Analytical expressions also allow error to be ascertained; in the absence of estimates of error, P-T estimates are nearly meaningless. This chapter is intended to complement the chapters by Anderson et al. (2008), who cover granitic systems, and by Blundy and Cashman (2008) and Hansteen and Klugel (2008), who consider additional methods …

Thermometers and Barometers for Volcanic Systems

The petrogenesis of trondhjemite-tonalite-dacite (TTD) involves all major petrologic models in various tectonic settings. A specific subtype of TTD, high-Al type, is the one most commonly associated with Archean gneiss terranes. During the Archean, continental crust formation was operating at an elevated rate relative to the Phanerozoic, and the generation of high-Al TTD played an integral role in its nucleation and growth. High heat flow, rapid convection, and subduction of hotter, smaller plates were unique tectonic elements to the Archean which optimized conditions required for transformation of subducted oceanic crust into sial via partial melting. Anatexis of Archean mid-ocean ridge basalt (MORB) under eclogitic to garnet amphibolitic conditions produced weakly peraluminous to metaluminous high-Al TTD with low heavy rare earth elements (HREE), Y, Nb, K/Rb, and Rb/Sr and high La/Yb and Sr/Y. This study demonstrates that Archean TTD crustal generation processes are also present in selected high-Al Phanerozoic TTD terranes. The Cenozpic high-Al TTD suites are commonly found in tectonic settings which are thought to recreate the elevated Archean thermal gradients, i.e., at sites of young, hot oceanic plate subduction. These relationships imply a petrologic continuity of TTD generation through time. A fertile zone of melting is envisioned at 23–26 kbar (75–85 km) and 700–775°C, where wet partial melting of the subducting slab occurs concurrently with dehydration reactions. At this depth, the converting mantle wedge continuously feeds hot mantle material to the wedge-slab interface, creating strong temperature gradients, intraslab fluid migration, and slab melting. In summary, in modern arc terranes where young ( 30 Ma) oceanic crust is subducted, mantle-derived magmas are dominant, giving rise to basaltandesite-dacite-rhyolite (BADR) fractionation suites. This study introduces the importance of subducted oceanic crustal age on arc petrogenesis.

A model for Trondhjemite-Tonalite-Dacite Genesis and crustal growth via slab melting: Archean to modern comparisons

However, it can be a residue of komatiite melt extraction at >7 Melting experiments on fertile peridotite KR4003, a ‘pyrolitic’ GPa from a mantle enriched in SiO2 relative to pyrolite. composition, were made from 3 to 7 GPa in piston-cylinder and multi-anvil apparatus. Temperature gradients across the sample were minimized (<25°C), and the compositions of all phases were determined. Modal abundances of coexisting phases were calculated by mass balance, and the results were used to determine phase

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Melting of Garnet Peridotite and the Origin of Komatiite and Depleted Lithosphere

Basalts and Phase Diagrams

Magmatic processes: Physicochemical principles: Edited by B. O. Mysen. The Geochemical Society, spec. pub. no. 1, 1987, 500p., $45.00 (Geochemical Society Members), $65.00 (other). (ISBN 0-941809-005)

Most anorthosites of the massif type crystallized in the episode 1.7-1.2 Gyr, with a pronounced peak of the age distribution near 1.4 Gyr. They were emplaced anorogenically at depths as shallow as 7 km, where the ambient temperature of country rocks was probably less than 250'C. Depths of emplacement may have been as great as 25 km or more in rare cases; the greater depths of equilibration estimated from granulite facies metamorphism may be incorrectly interpreted as emplacement depths, but in any case they are demonstrably not required or characteristic of anorthosite emplacement. Penetrative deformation and metamorphism of anorthosites are post-emplacement accidents of the local geologic history, and are not directly caused by the presence of anorthosites. Granitic rocks (mangerite-charnockite suite) associated with anorthosite are in general later or contemporaneous products of crustal anatexis, with chemical and isotopic signatures distinct from the anorthosites and their residua. Such granitic rocks should not, therefore, be summed with the anorthositic rocks to obtain bulk compositions. The magmas that produced most anorthosites were dry, as shown by high-temperature mineralogy and anhydrous mineral assemblages in contact aureoles. Residua from their crystallization are ferrodiorites to ferrosyenites typical of closed-system fractionation. These residua were locally and frequently ejected into contemporaneously molten granite, where they formed pillows and cooled rapidly. The overall chemistry of anorthosites and residua is broadly tholeiitic and consistent with derivation from the mantle. Olivine-bearing magmas locally ranged from leucotroctolite (anorthosite) to later but coexisting picrite or melatroctolite in the same pluton, confirming a wide spectrum of magma types. A signal feature of troctolitic and noritic magmas is their low augite content, implying high content of spinel component. Large anorthosite complexes such as Nain and Harp Lake consist of many plutons representing repeated injections of separate magma batches with varying chemistry. The abundant true anorthosites, richer in plagioclase than magmas cosaturated with a mafic phase, must represent plagioclase enrichment by either mechanical or chemical processes or both. The role of kinetics in nucleation and solidification of such rocks may be centrally important. It is proposed that hyperfeldspathic (plagioclase-supersaturated) liquids were generated by quasi-isothermal extraction of mafic minerals from tholeiitic magma enroute to and at the site of emplacement, and that such a kinetic process was uniquely permitted in an environment of aborted continental rifting. Anorthositic rocks may have much to say about the episodic versus continuous geochemical evolution of the earth's mantle.

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Stearns A. Morse

Papers

Basalts and Phase Diagrams

Magmatic processes: Physicochemical principles: Edited by B. O. Mysen. The Geochemical Society, spec. pub. no. 1, 1987, 500p., $45.00 (Geochemical Society Members), $65.00 (other). (ISBN 0-941809-005)

A partisan review of Proterozoic anorthosites

The Kiglapait layered intrusion, Labrador

Kiglapait Geochemistry I: Systematics, Sampling, and Density