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

Compositional fields for spinels from a wide variety of mafic– a wide range of conditions from mafic and ultramafic ultramafic igneous rock types and tectonic environments have been magmas and, in the case of chromites, are often among determined from a global database of over 26 000 analyses. the first phases to crystallize. They also exhibit a wide These fields are defined using contoured data density plots based range of solid solution, the thermodynamics of which has on the spinel prism, and plots of TiO2 vs ferric iron, for mantle been studied extensively (O’Neill & Wall, 1987; Mattioli xenoliths, ophiolitic rocks, continental layered intrusions, alkalic & Wood, 1988; Wood, 1990; Sack & Ghiorso, 1991; and lamprophyric rocks, tholeiitic basalts, Alaskan ultramafic Poustovetov, 2000). They are relatively refractory and complexes and komatiites. Several trends appear regularly in the resistant to alteration, particularly compared with other various environments: a trend of widely variable Cr/(Cr + Al) high-temperature igneous minerals such as olivine. They at low Fe/(Mg + Fe) (the Cr–Al trend); increasing Fe, occur in a high proportion of terrestrial mafic and ultraFe/(Mg + Fe) and TiO2 at constant Cr/(Cr + Al) mafic rocks, and a very large volume of microprobe data (Fe–Ti trend); a trend found primarily in kimberlites, similar is available on their compositions. to Fe–Ti but at constant Fe/(Mg + Fe); and an unusual Publications on spinels (particularly chromites) have trend of increasing Al found only in layered intrusions. The routinely used compositional fields based on the spinel Cr–Al and Fe–Ti trends are both found to varying degrees in prism to compare populations of analyses. Some of tholeiitic basalts. The Cr–Al trend is prevalent in rocks that these fields have remarkable longevity, particularly those have equilibrated over a range of pressures, whereas the Fe–Ti defined for layered intrusions and Alpine peridotites by trend is dominantly due to low-pressure fractionation. The most Irvine (1967, 1977). Many new data have become availCr-rich chromites found in nature occur in boninites, diamondable in the last 20 years, however, and it has become bearing kimberlites, some komatiites and ophiolitic chromitites. apparent that a new compilation of data is necessary to Exceptionally reduced chromites are found in some komatiites reflect this. The prime purpose of this paper is to analyse and in ophiolitic chromitites. Detrital chromites from the a global database of about 26 000 spinel analyses from Witwatersrand conglomerates are of komatiitic provenance. terrestrial igneous and metamorphosed igneous rocks, and to extract from this database the characteristic compositional fields of spinels from the wide variety of magma types and tectonic environments in which they occur.

https://eps.mcgill.ca/~courses/c186-501/2010/Week10_Readings/Kristal_Leung_Range_Of_Spinel_Compositions_2001.pdf

The Range of Spinel Compositions in Terrestrial Mafic and Ultramafic Rocks

Ultrasonic longitudinal acoustic velocities in oxidized silicate liquids indicate that the pressure derivative of the partial-molar volume of Fe2O3 is the same in iron-rich alkali-, alkaline earth- and natural silicate melt compositions at 1 bar. The dV/dP for multicomponent silicate liquids can be expressed as a linear combination of partial-molar constants plus a positive excess term for Na2O−Al2O3 mixing. Partial-molar properties for FeO and Fe2O3 components allow extension of the empirical expression of Sack et al. (1980) to permit the calculation of Fe-redox equilibrium in a natural silicate liquid as a function of composition, temperature, fo2 and pressure; a more formal thermodynamic expression is presented in the Appendix. The predicted equilibrium fo2 of natural silicate melts, of fixed oxygen content, closely parallels that defined by the metastable assemblage fayalite+magnetite+β-quartz (FMQ), in pressure-temperature space. A silicate melt initially equilibrated at 3 GPa and FMQ, will remain within approximately 0.5 log10 units of FMQ during its closed-system ascent. Thus, for magmas closed to oxygen, iron-redox equilibrium in crystal-poor pristine glassy lavas represents an excellent probe of the relative oxidation state of their source regions.

The compressibility of silicate liquids containing Fe 2 O 3 and the effect of composition, temperature, oxygen fugacity and pressure on their redox states

This work focuses on a rigorous analysis of the physical–chemical, compositional and textural relationships of amphibole stability and the development of new thermobarometric formulations for amphibole-bearing calc-alkaline products of subduction-related systems Literature experimental results (550–1,120°C, 021) and are inferred to represent xenocrysts of crustal or mantle materials Most experimental results on calc-alkaline suites have been found to be unsuitable for using in thermobarometric calibrations due to the high Al# (>021) of amphiboles and high Al2O3/SiO2 ratios of the coexisting melts The pre-eruptive crystallization of consistent amphiboles is confined to relatively narrow physical–chemical ranges, next to their dehydration curves The widespread occurrence of amphiboles with dehydration (breakdown) rims made of anhydrous phases and/or glass, related to sub-volcanic processes such as magma mixing and/or slow ascent during extrusion, confirms that crystal destabilization occurs with relatively low T–P shifts At the stability curves, the variance of the system decreases so that amphibole composition and physical–chemical conditions are strictly linked to each other This allowed us to retrieve some empirical thermobarometric formulations which work independently with different compositional components (ie Si*, AlT, Mg*, [6]Al*) of a single phase (amphibole), and are therefore easily applicable to all types of calc-alkaline volcanic products (including hybrid andesites) The Si*-sensitive thermometer and the fO2–Mg* equation account for accuracies of ±22°C (σest) and 04 log units (maximum error), respectively The uncertainties of the AlT-sensitive barometer increase with pressure and decrease with temperature Near the P–T stability curve, the error is 35%) and lower-T magmas, the uncertainty increases up to 24%, consistent with depth uncertainties of 04 km, at 90 MPa (~34 km), and 79 km, at 800 MPa (~30 km), respectively For magnesiohornblendes, the [6]Al*-sensitive hygrometer has an accuracy of 04 wt% (σest) whereas for magnesiohastingsite and tschermakitic pargasite species, H2Omelt uncertainties can be as high as 15% relative The thermobarometric results obtained with the application of these equations to calc-alkaline amphibole-bearing products were finally, and successfully, crosschecked on several subduction-related volcanoes, through complementary methodologies such as pre-eruptive seismicity (volcano-tectonic earthquake locations and frequency), seismic tomography, Fe–Ti oxides, amphibole–plagioclase, plagioclase–liquid equilibria thermobarometry and melt inclusion studies A user-friendly spreadsheet (ie AMP-TBxls) to calculate the physical–chemical conditions of amphibole crystallization is also provided

Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes

Results of chemical analyses of glasses produced in 46 melting experiments in air at 1,350° C and 1,450° C on rocks ranging in composition from nephelinite to rhyolite have been combined with other published data to obtain an empirical equation relating in \((X_{{\text{Fe}}_{\text{2}} {\text{O}}_{\text{3}} }^{{\text{liq}}} /X_{{\text{FeO}}}^{{\text{liq}}} )\) to T, \(\ln f_{{\text{O}}_{\text{2}} } \) and bulk composition. The whole set of experimental data range over 1,200–1,450° C and oxygen fugacities of 10−9.00 to 10−0.69 bars, respectively. The standard errors of temperature and \(\log _{10} f_{{\text{O}}_{\text{2}} } \) predictions from this equation are 52° C and 0.5 units, respectively, for 186 experiments.

The ferric-ferrous ratio of natural silicate liquids equilibrated in air

Data on the variation of temperature with time and in space are essential to a complete understanding of the crystallization history of basaltic magma in Kilauea Iki lava lake Methods used to determine temperatures in the lake have included direct, downhole thermocouple measurements and Fe-Ti oxide geothermometry In addition, the temperature variations of MgO and CaO contents of glasses, as determined in melting experiments on appropriate Kilauean samples, have been calibrated for use as purely empirical geothermometers and are directly applicable to interstitial glasses in olivine-bearing core from Kilauea Iki The uncertainty in inferred quenching temperatures is ±8−10° C Comparison of the three methods shows that (1) oxide and glass geothermometry give results that are consistent with each other and consistent with the petrography and relative position of samples, (2) downhole thermo-couple measurements are low in all but the earliest, shallowest holes because the deeper holes never completely recover to predrilling temperatures, (3) glass geothermometry provides the greatest detail on temperature profiles in the partially molten zone, much of which is otherwise inaccessible, and (4) all three methods are necessary to construct a complete temperature profile for any given drill hole Application of glass-based geothermometry to partially molten drill core recovered in 1975–1981 reveals in great detail the variation of temperature, in both time and space, within the partially molten zone of Kilauea Iki lava lake The geothermometers developed here are also potentially applicable to glassy samples from other Kilauea lava lakes and to rapidly quenched lava samples from eruptions of Kilauea and Mauna Loa

Geothermometry of Kilauea Iki lava lake, Hawaii

Samples collected from a lava channel active at Kilauea Volcano during May 1997 are used to con- strain rates of lava cooling and crystallization during early stages of flow. Lava erupted at near-liquidus tem- peratures (F1150 7C) cooled and crystallized rapidly in upper parts of the channel. Glass geothermometry indi- cates cooling by 12-14 7C over the first 2 km of trans- port. At flow velocities of 1-2 m/s, this translates to cooling rates of 22-50 7C/h. Cooling rates this high can be explained by radiative cooling of a well-stirred flow, consistent with observations of non-steady flow in proximal regions of the channel. Crystallization of plag- ioclase and pyroxene microlites occurred in response to cooling, with crystallization rates of 20-50% per hour. Crystallization proceeded primarily by nucleation of new crystals, and nucleation rates of F10 4 /cm 3 s are similar to those measured in the 1984 open channel flow from Mauna Loa Volcano. There is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts, possibly a reflection of enhanced nucleation due to stirring of the flow. The transition of the flow surface morphology from pahoehoe to 'a'aoccurred at a distance of 1.9 km from the vent. At this point, the flow was thermally stratified, with an interior temperature of F1137 7C and crystallinity of F15%, and a flow surface tempera- ture of F1100 7C and crystallinity of F45%. 'A'afor- mation initiated along channel margins, where crust was continuously disrupted, and involved tearing and clotting of the flow surface. Both observations suggest that the transition involved crossing of a rheological threshold. We suggest this threshold to be the develop- ment of a lava yield strength sufficient to prevent vis- cous flow of lava at the channel margin. We use this concept to propose that 'a'aformation in open chan- nels requires both sufficiently high strain rates for con- tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress. In Hawai'i, where lava is typically microlite poor on eruption, these combined requirements help to explain two common observations on 'a'aformation: (a) 'a'aflow fields are generated when effusion rates are high (thus promoting crustal disruption); and (b) under most eruption conditions, lava issues from the vent as pahoehoe and changes to 'a'aonly after flowing some distance, thus permitting sufficient crystallization.

/pdf/cooling-and-crystallization-of-lava-in-open-channels-and-the-34zv9wv8n7.pdf

Cooling and crystallization of lava in open channels, and the transition of Pāhoehoe Lava to 'A'ā

From 1986 to 1997, the Pu'u 'O'o-Kupaianaha eruption of Kilauea produced a vast pahoehoe flow field fed by lava tubes that extended 10–12 km from vents on the volcano's east rift zone to the ocean. Within a kilometer of the vent, tubes were as much as 20 m high and 10–25 m wide. On steep slopes (4–10°) a little farther away from the vent, some tubes formed by roofing over of lava channels. Lava streams were typically 1–2 m deep flowing within a tube that here was typically 5 m high and 3 m wide. On the coastal plain (<1°), tubes within inflated sheet flows were completely filled, typically 1–2 m high, and several tens of meters wide. Tubes develop as a flow's crust grows on the top, bottom, and sides of the tubes, restricting the size of the fluid core. The tubes start out with nearly elliptical cross-sectional shapes, many times wider than high. Broad, flat sheet flows evolve into elongate tumuli with an axial crack as the flanks of the original flow were progressively buried by breakouts. Temperature measurements and the presence of stalactites in active tubes confirmed that the tube walls were above the solidus and subject to melting. Sometimes, the tubes began downcutting. Progressive downcutting was frequently observed through skylights; a rate of 10 cm/d was measured at one skylight for nearly 2 months.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/97JB03576

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

The supply of magma to Kīlauea Volcano, Hawai‘i, was thought to have been steady over the past decades. Measurements of deformation, gas emissions, seismicity and lava composition and temperatures show that instead magma supply from the mantle doubled in 2003–2007, implying that hotspots can provide varying amounts of magma over just a few years.

A mantle-driven surge in magma supply to Kīlauea Volcano during 2003–2007

Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering: Chapter 30 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006

Carl R. Thornber

Papers

Geothermometry of Kilauea Iki lava lake, Hawaii

Cooling and crystallization of lava in open channels, and the transition of Pāhoehoe Lava to 'A'ā

Observations on basaltic lava streams in tubes from Kilauea Volcano, island of Hawai'i

A mantle-driven surge in magma supply to Kīlauea Volcano during 2003–2007

Petrology of the 2004-2006 Mount St. Helens lava dome -- implications for magmatic plumbing and eruption triggering: Chapter 30 in A volcano rekindled: the renewed eruption of Mount St. Helens, 2004-2006