Ph.D., Geophysical Sciences, The University of Chicago, 2007
Dissertation: Crystal and bubble populations in the Bishop pre-eruptive magma: Microscopy, x-ray tomography and microanalysis of pumice clasts

M.Sc., Mineralogy and Petrology, Universidade de São Paulo, 2001
Thesis: Petrographic and mineralogical evolution of the alkaline and aluminous associations of the Graciosa A-type Granites, PR

B.Sc., Geology, Universidade de São Paulo, 1999
Senior Thesis: Chemical variations in mafic minerals and the evolution of agpaitic magmas from the Anel Norte Lujavritic-Khibinitic Body - Poços de Caldas Alkaline Massif (MG-SP)

B.Sc. Secondary Education, Geology, Universidade de São Paulo, 1999

General: Igneous petrology, volcanology, mineralogy, geochemistry

Specific: Quantitative petrography, crystals & bubbles in magmas, mineral zoning, silicic magmatism

Approaches: X-ray tomography, microscopy and microanalysis

Motivation

The existence of molten rock within the Earth is an idea that has fascinated scientists for millennia, and understanding the origins and the evolution of magmas is a subject at the core of the geological sciences. My research is concerned with the detailed evolution of igneous systems. In particular, I have concentrated on the evolution of silicic magmas.

The main challenge in studying the evolution of magma bodies is our inability to witness the relevant magmatic processes occurring at depth and on timescales orders of magnitude longer than our lifetimes. Given these constraints, we rely on the study of rocks to understand the evolution of magmas.

Volcanic rocks may provide snapshots of the evolution of the magma bodies from which they erupted, while plutonic rocks represent a time-integrated record of the magmatic system. A complete understanding of magmatic systems can only emerge from the integrated study of the volcanic and plutonic components. However, each of these facets of the record has its specificities and complexities, and the record is only useful to the extent that we know how to interpret it.

Although the chemical composition and evolution of many magmas are well documented, their physical and textural attributes are poorly quantified or understood. A complete picture of the evolution of magmatic systems would greatly benefit from better understanding of the physical aspect of magmatic systems, integrated with this relatively well-studied chemical evolution. The key to this integration is the study of chemical zoning in minerals. This is the perspective that motivates my research.

I pursue the problem of the evolution of magma bodies by exploring the detailed record of magmatic processes preserved in minerals, such that my research lies at the interface between petrology and mineralogy, in what has been called modern petrography. In simple terms, the goal is to use the detailed textural record preserved in igneous rocks to decipher their crystallization history and the evolution of the magma bodies from which they derive. Texture is understood in its broadest sense, including observations in various length scales – from field to microscopic – and in two independent but related fronts: (i) the physical organization of rocks, and (ii) the compositional evolution of minerals in rocks.

Current Interests

In my ongoing quantitative textural studies of the Bishop Tuff rhyolite, my colleagues and I have been using conventional petrography (Gualda et al. 2004) and x-ray tomography (Gualda & Rivers 2006, Gualda 2006) to quantitatively study the textures of pumice clasts. We have pioneered the use of x-ray tomography to study pumice, and have shown that x-ray tomography provides invaluable information in three dimensions regarding the crystal and bubble populations present.

By focusing on the crystal population of pumice clasts from the Bishop Tuff, we have shown that fragmentation is widespread and at least some of it must have occurred prior to ascent and eruption (Gualda et al. 2004, Gualda & Rivers 2006). By focusing on the vesicle population, we have argued that the few largest vesicles in pumice from the Bishop Tuff may be pre-eruptive in origin (Gualda & Anderson 2004). Finally, we have discovered what may be the first direct evidence for pre-eruptive bubbles in the Bishop magma, which allowed us to constrain the size of bubbles under pre-eruptive conditions (Gualda & Anderson, in press).

What emerges from these studies is an improved view of the pre-eruptive state of the Bishop magma body. Constraining the pre-eruptive state of magma systems is important because it facilitates the understanding of both syn-eruptive and pre-eruptive processes.

Associated with the textural or physical state we describe, there exists a corresponding chemical state. For instance, in the case of the Bishop, it has been long argued that a chemical stratification or zonation exists within the magma body. In order to understand how the textural variations relate to the chemical zonation, it is necessary to integrate the two approaches, and the most appropriate way of doing so is by studying mineral zonings.

We are currently detailing trace-element and cathodoluminescence zoning of quartz and sanidine from the Bishop with this intent. Our data show that crystal populations are heterogeneous (Gualda & Anderson 2006a), and that quartz and sanidine crystals record significant changes in the nucleation and growth dynamics in the years to decades preceding eruption. These changes led to the growth of Ti and/or Ba-rich rims in large (>100 μm) crystals (Gualda & Anderson 2006b), as well as to the nucleation and growth of a new population of small (< 50 μm) crystals (Pamukçu et al. 2006a, 2006b). The timescales revealed by the zoning patterns and by the small crystal populations (i.e. < 100 years) are compatible with them being a result of the onset of decompression, which led to biotite breakdown and increased undercooling.

What is most significant about these changes is that they can be used as fingerprints of eruptions, which are likely to be preserved in diverse magmatic systems, both volcanic and plutonic. The prospect of being able to use plutonic rocks to study eruptions is a remarkable one and may open an important window into the understanding of the long term dynamics of eruptions, in timescales possibly inaccessible by the study of volcanic systems alone.

Under this perspective, systems in which co-magmatic volcanic and plutonic rocks are preserved are of particular interest. The volcanic-plutonic systems preserved in the Eldorado Mountains in southern Nevada and Arizona are notable examples, and we have just begun exploring the relationships and the record of eruptions in co-magmatic volcanic and plutonic systems in collaboration with Alfred Anderson (University of Chicago), Calvin Miller (Vanderbilt University), Jonathan Miller (San Jose State University), and James Faulds (University of Nevada, Reno).

Opportunities for Students

Opportunities for students are immediately available under this latter project. I expect to continue to develop textural studies in large-volume rhyolitic systems, and opportunities for students are probable. Projects outside the lines outlined above are also possible, and I would be happy to discuss potential projects with prospective students.

Articles

Gualda GAR & Ghiorso MS (2007) Magnetite scavenging and the buoyancy of bubbles in magmas. Part 2: Energetics of crystal-bubble attachment in magmas. Contributions to Mineralogy and Petrology, 154: 479-490 [DOI:10.1007/s00410-007-0206-8]

Gualda GAR & Anderson AT Jr. (2007) Magnetite scavenging and the buoyancy of bubbles in magmas. Part 1: Discovery of a pre-eruptive bubble in early-erupted Bishop rhyolite using x-ray tomography. Contributions to Mineralogy and Petrology, 153: 733-742 [DOI:10.1007/s00410-006-0173-5]

Vlach SRF & Gualda GAR (2007) Allanite and chevkinite in A-type granites and syenites of the Graciosa Province, southern Brazil. Lithos, 97: 98-121 [DOI:10.1016/j.lithos.2006.12.003]

Gualda GAR & Vlach SRF (2007) The Serra da Graciosa A-type Granites & Syenites, southern Brazil. Part 3: Magmatic evolution and post-magmatic breakdown of amphiboles of the alkaline association. Lithos, 93: 328-339 [DOI:10.1016/j.lithos.2006.03.070]

Gualda GAR & Vlach SRF (2007) The Serra da Graciosa A-type Granites & Syenites, southern Brazil. Part 2: Petrographic and mineralogical evolution of the alkaline and aluminous associations. Lithos, 93: 310-327 [DOI:10.1016/j.lithos.2006.06.002]

Gualda GAR & Vlach SRF (2007) The Serra da Graciosa A-type Granites & Syenites, southern Brazil. Part 1: Regional setting and geological characterization. Anais da Academia Brasileira de Ciências, 79: 405-430 [http://www.scielo.br/pdf/aabc/v79n3/a06v79n3.pdf]

Gualda GAR (2006) Crystal size distributions derived from 3D datasets: Sample size versus uncertainties. Journal of Petrology, 47: 1245-1254 [DOI:10.1093/petrology/egl010]

Gualda GAR & Rivers M (2006) Quantitative 3D petrography using x-ray tomography: Application to Bishop Tuff pumice clasts. Journal of Volcanology and Geothermal Research, 154: 48–62 [DOI:10.1016/j.jvolgeores.2005.09.019]

Gualda GAR & Vlach SRF (2005) Stoichiometry-based estimates of ferric iron in calcic, sodic-calcic and sodic amphiboles: A comparison of various methods. Anais da Academia Brasileira de Ciências, 77: 521-534 [http://www.scielo.br/pdf/aabc/v77n3/a12v77n3.pdf]

Gualda GAR, Cook DL, Chopra R, Qin L, Anderson AT Jr., Rivers M (2004) Fragmentation, Nucleation and Migration of Crystals and Bubbles in the Bishop Tuff Rhyolitic Magma. Transactions of the Royal Society of Edinburgh: Earth Sciences, 95: 375-390 [http://www.ingentaconnect.com/content/rse/tes/2005/00000095/F0020001/art00029]

Vlach SRF & Gualda GAR (2000) Microprobe monazite dating and the ages of some granitic and metamorphic rocks from Southeastern Brazil. Revista Brasileira de Geociências, 30: 214-218 [http://www.sbgeo.org.br/rgb/vol30_down/3001/3001214.pdf]  

Abstracts

Gualda GAR, Anderson AT Jr., Sutton SR (2007) Rapid crystallization of the Bishop magma. Eos Transactions AGU, 87(52), Fall Meeting Supplement, Abstract V24C-04 Link

Gualda GAR, Pamukçu A, Anderson AT Jr., Sutton SR (2007) The onset of decompression recorded in phenocrysts of the Bishop Tuff. 24^th IUGG General Assembly, Perugia, 2007 Link

Gualda GAR & Anderson AT Jr. (2006) The pre-eruptive texture of the Bishop magma. Eos Transactions AGU, 87(52), Fall Meeting Supplement, Abstract V24C-04 Link

Pamukçu A, Anderson AT Jr., Gualda GAR (2006) Crystal sinking and bubble rising in late-erupted Bishop Tuff: A study of pumice clasts by x-ray tomography and physical separation. Eos Transactions AGU, 87(52), Fall Meeting Supplement, Abstract V33C-0684 Link

Pamukçu A, Gualda GAR, Anderson AT Jr. (2006) Phenocryst size distributions of late-erupted Bishop Tuff. GSA Abstracts with Programs, 38(7): 446 Link

Vlach SRF & Gualda GAR (2006) Allanite and chevkinite in A-type granites and syenites of the Graciosa Province, Southern Brazil. GSA Abstracts with Programs, 38(7): 558 Link

Gualda GAR & Anderson AT Jr. (2006) Zoning in sanidine and quartz from the Bishop Tuff: Insights into the evolution of the magma body. Eos Transactions AGU, 87(36), Joint Assembly Supplement, Abstract V53A-06 Link

Gualda GAR & Ghiorso MS (2005) Magnetite scavenging and the buoyancy of bubbles in magmas. Eos Transactions AGU, 86(52), Fall Meeting Supplement, Abstract V53A-1531 Link

Gualda GAR, Miller CF, Anderson AT Jr., Rivers M (2005) Bubble accumulation and the origin of a vesicular microgranite. GSA Abstracts with Programs, 37(7): 309 Link

Gualda GAR & Anderson AT Jr. (2005) Magnetite clusters on vesicle walls: Evidence for pre-eruptive bubbles in the early-erupted Bishop Tuff, CA. Geochimica et Cosmochimica Acta, 69(10, Supplement 1): A235 Link

Bleick HA, Miller CF, Furbish DJ, Koteas C, Ericksen SM, Miller JS, Gualda GAR, Walker BA (2005) Production and distribution of hybridized magma in a replenished, open-system magma chamber; Aztec Wash Pluton, Eldorado Mountains, Nevada. GSA Abstracts with Programs, 37(4): 66 Link

Gualda GAR & Anderson AT Jr. (2004) Pre-eruptive bubbles in the Bishop magma? An x-ray tomography study of vesicle size distributions. Eos Transactions AGU, 85(47), Fall Meeting Supplement, Abstract V43D-1448 Link

Gualda GAR & Rivers M (2004) Quantitative 3D petrography using x-ray tomography: application to Bishop Tuff pumice clasts. GSA Abstracts with Programs, 36(5): 245 Link

Miller CF, Miller JS, Furbish DJ, Bleick HA, Walker BA, Koteas GC, Gualda GAR, Faulds JE, Wiebe RA, Metcalf RD, Steinwinder TR, Ericksen SM (2004) Miocene intrusions, Colorado River Rift, Nevada-Arizona: Crystal- to crustal-scale dynamics in an open magmatic system. In: 32^nd International Geological Congress, Florence, 2004. Abstracts Volume, A194-10 Link

Gualda GAR & Vlach SRF (2004) Petrographic and mineralogical evolution of the alkaline and aluminous associations of the Graciosa A-type granites, Brazil. Geochimica et Cosmochimica Acta, 68(11, Supplement 1): A675 Link

Gualda GAR, Cook DL, Chopra R, Qin L, Anderson AT Jr., Rivers M (2003) Crystal Sinking and Bubble Rising in the Bishop Tuff Rhyolitic Magma. Eos Transactions AGU, 84(46), Fall Meeting Supplement, Abstract V12A-0557 Link

Gualda GAR, Cook DL, Chopra R, Qin L, Anderson AT Jr., Rivers M (2003) Fragmentation, Nucleation and Migration of Crystals and Bubbles in the Bishop Tuff Magma: Evidence from Crystal Size Distributions. 5^th Hutton Symposium on the Origin of Granites and Related Rocks. Abstracts with Program. Geological Survey of Japan, Interim-Report 29, pg. 37

Gualda GAR & Vlach SRF (2002) Stoichiometry-based estimates of ferric iron in calcic, sodic-calcic and sodic amphiboles: A comparison of various methods. In: IMA 2002, General Meeting of the International Mineralogical Association, Edinburgh, 2002

Gualda GAR, Ferreira FJF, Portela CV Filho, Vlach SRF (2001) Integration of geological and airborne gamma-ray spectrometric data for the individualization of granitic massifs in the Serra da Graciosa Area (PR). In: 7^th International Congress of the Brazilian Geophysical Society, Salvador, 2001 [in Portuguese] Link

Gualda GAR & Vlach SRF (2000) Chemical and textural evolution of mafic minerals from agpaitic nepheline syenites from the Poços de Caldas Alkaline Massif - Southeastern Brazil. 31^st International Geological Congress, Rio de Janeiro, 2000 Link

Gualda GAR & Vlach SRF (1999) Compositional variations and crystallization history of some pyroxenes from the Poços de Caldas Alkaline Massif (MG-SP). Acta Microscopica 8: 143-144 Link

Gualda GAR & Vlach SRF (1998) Controls on the accessory mineralogy of intermediate to agpaitic rocks from Taquari – Poços de Caldas Alkaline Massif (MG-SP). In: 40^th Congresso Brasileiro de Geologia, Belo Horizonte, 1998. Anais…, p. 460 [in Portuguese] Link

Gualda GAR & Vlach SRF (1998) Lamprophyllite and normandite (titaniferous låvenite) in agpaitic nepheline syenites from the Poços de Caldas Alkaline Massif (MG-SP): mineralogical and petrological characterization. In: 40^th Congresso Brasileiro de Geologia, Belo Horizonte, 1998. Anais…, p. 284 [in Portuguese] Link

Vlach SRF & Gualda GAR (1998) Chemistry of mafic minerals from the Graciosa Granitic Massif, PR: preliminary results and petrogenetic inferences. In: 40^th Congresso Brasileiro de Geologia, Belo Horizonte, 1998. Anais…, p. 518 [in Portuguese] Link

Gualda GAR & Vlach SRF (1996) Eudialyte-eucolite from the Poços de Caldas Alkaline Massif, MG-SP: chemistry and correlation with optic behavior. In: 39^th Congresso Brasileiro de Geologia, Salvador, 1996. Anais…, 3: 34-36 [in Portuguese] Link

Last update: February 11^th, 2008