MBVRC research grant report. Ricardo Escobar, WWU- Origin of Mount Baker andesite

Ricardo Escobar. All photos courtesy R. Escobar. Click to enlarge any image.

Here is the final report from Mount Baker Volcano Research Center’s 2013 research grantees. Ricardo Escobar is a geology graduate student at Western Washington University under the supervision of Dr. Susan DeBari; he hails from Los Angeles. Ricardo’s tale of his adventures in the field follow, a classic account of field work in the Baker area, and his description of his project. Like May Sas and Ian Delaney, he received $667 towards his thesis study of the origin of andesite lava in the Mount Baker volcanic field (MBVF). Scroll down here to read Ricardo’s research proposal.

Ricardo’s project may seem superficially similar to May’s. But, while May is studying the enigmatic origin of high-magnesium andesites, which have some geochemical signature indicating at least some mantle influence, Ricardo is focusing on the far more voluminous and typical MBVF andesites that have a ‘normal’ Mg composition and are generally believed to differentiate in the crust.

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Petrogenesis of intermediate magmas at Mount Baker volcano, northern Cascade arc. Ricardo Escobar, WWU Geology

Ricardo will sample the circled lava units. Map from Hildreth, 2003.

Several studies have been conducted to better understand the petrologic processes occurring beneath the Mount Baker volcanic field, but none have been aimed at discerning the origin of true intermediate (54-62 wt. % SiO₂) magmas (andesites). Considering andesitic lavas are the most voluminous component of flows in the Mount Baker volcanic field, it is important to gain insight on how these magmas originated. Previously, Moore and DeBari (2012) conducted a study on the primitive magmas (basalts) of the Mount Baker volcanic field, in which they identified three primitive magma types: calc-alkaline basalt, high-Mg andesite and MORB-like low K tholeiite. Most recently, Gross (2012) studied the most differentiated magmas (dacites) of the Mount Baker volcanic field and was unable to constrain the Nooksack Falls dacite with a primitive magma identified by Moore and DeBari (2012). Set up as an ideal framework, I propose to evaluate the relationship(s) intermediate magmas have with the most primitive and differentiated magmas found in the Mount Baker volcanic field. Specifically, the goal is to understand what roles magma mixing and crystal fractionation play in generating the intermediate magmas and possibly constrain the parent-less Nooksack falls dacite.

In order to ensure the collection of true intermediate magmas of the Mount Baker volcanic field, I used Hildreth et al.’s (2003) foundational study, which is the most comprehensive study of Mount Baker volcanic field lava flows, as a starting point. The major element dataset of Hildreth et al. (2003) allowed me to construct geochemical variation diagrams for selecting true intermediate magmas. Four lava flows were selected: andesite of Dobbs Cleaver, andesite of Dobbs Creek, andesite of Coleman Pinnacle and andesite of Swift Creek.

D. Tuckers assists with sampling at the none-too-prominent Dobbs Cleaver andesite.

During the months of August and September, I made several trips to the Mount Baker area to collect rock samples from four flows: Dobbs Cleaver, Dobbs Creek, Swift Creek and Coleman Pinnacle (see the map above). Following field work, I cut billets (blocks of rock about the size of a microscope slide) of each sample for professional thin section preparation by Vancouver Petrographics. I then powdered splits from the remaining rock samples for XRF and ICP-MS analyses, which have now been completed- results will appear in my thesis following comparison and interpretation. Funds received from MBVRC have been used to cover the cost of thin sections ($625) and a portion of the XRF chemical analyses carried out at Washington State University ($42).

Jungle-covered andesite of Dobbs Creek is a thick flow guarded by steep slopes and brush.

Accessibility to the target lava flows is impossible throughout most of the year as they are under snow cover. My field work took place in August and September 2013. The unpaved Wells Creek Road, off the Mount Baker Highway, accesses Dobbs Cleaver and Dobbs Creek on Cougar Divide. Despite dense vegetation and complete absence of trails, I collected seven samples of the andesite of Dobbs Cleaver on August 13, 2013 with the assistance of Dave Tucker and about 30 gazillion mosquitos. I intended to collect samples of the remaining flows over the course of a few days. Taking Wells Creek Road once more on August 25, 2013, I ventured on a steep cross-country hike to gain access to the andesite of Dobbs Creek. Again, due to the difficulties of hiking and spotting outcrops in dense vegetation, only 5 samples were collected on that day.

A large clot of crystals in Coleman Pinnacle andesite.

After camping off a forest road, early the next morning I took the Ptarmigan Ridge trail, at Artist Point, toward the andesite of Coleman Pinnacle. Due to intense fog, rain and dropping temperatures throughout the day I only managed to collect 4 samples. Earlier that week, the forecast had predicted clear skies for the days I planned to be out in the field so as one can imagine I was ill-prepared. Having been completely soaked and experiencing quivers throughout my body I decided to retreat and head home. My next attempt to collect samples from andesite of Swift Creek on August 31, 2013. Two trailheads give access to these remote outcrops on the floor of Swift Creek. On this day I, along with a field assistant, started on the Lake Ann trailhead near Artist Point. To our dismay, the lower channel of Swift Creek below Fourth of July Creek was inaccessible from the trail. Steep cliff drops over 20m high confronted us at every turn. Fortunately, one creek that feeds into Swift Creek contained an exposure that appeared identical to Swift Creek andesites sampled by Hildreth et al. (2003) and so two samples were collected. Two weeks later, on September 13, 2013, I decided to enter Swift Creek from the south side and was much more successful. To access the flows I had to hike and wade upstream, which results in less mileage and more time. I managed to collect three samples, totaling five samples from the andesite of Swift Creek flow. Discontented with my andesite of Coleman Pinnacle collection, I ventured out once more on September 26, 2013 to collect a couple more samples. Fortunately, the weather was promising and my assistant and I successfully collected two more samples from andesite of Coleman Pinnacle, totaling at 6 samples. Though several complications arose throughout my sample collecting, I managed to collect a total of 23 samples.

Beautiful thin columns on the bank of deepest darkest Swift Creek. Now these are worth the effort!

Over the past few months I prepared my rock samples for XRF and ICP-MS analyses, which requires a lengthy and tedious process. The process includes breaking down rock to chips and finally to a powder. Once the powders have been made, they are mixed with a flux, allowing the powder to melt at a much lower temperature, and made into a glass bead. The beads are then analyzed at the GeoAnalytical Lab at Washington State University (WSU). While preparing my samples for XRF and ICP-MS analyses, I sent billets of each sample to Vancouver Petrographics for professional thin sections. I am now conducting microscopic analyses with the thin sections as I await for my XRF and ICP-MS data from WSU. From petrographic analyses I will select minerals for further investigation with an electron microprobe to understand physical properties of the magma chamber(s) beneath the Mount Baker volcanic field. Once I receive the data from the XRF and ICP-MS analyses I can begin to construct diagrams and models for explaining the petrogenesis of intermediate magmas at the Mount Baker volcanic field.

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