Prelude to a Supervolcano: REU Investigations in the Miocene volcanic field of the southern Black Mountains, Arizona

Transcription

1 Prelude to a Supervolcano: REU Investigations in the Miocene volcanic field of the southern Black Mountains, Arizona Lily Claiborne Nick Lang Calvin Miller Susanne McDowell Charles Ferguson Warner Cribb Aaron Covey

2 Peach Spring Tuff and Silver Creek Caldera

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6 Year 1: Prelude to a Supervolcano How are supervolcano-sized magma bodies generated? Pre-eruptive magmatism and genetic relationships (or lack of relationships) with Peach Spring Tuff Thermal input in the form of mafic magmas - Evidence within the PST itself What does a supervolcano look like? Unconformities and coeval sedimentary units

7 Sr (ppm) MgO Creek caldera, Cook showing intracaldera Canyon tuff, Silver Creek Tuff intrusives, and historic Gold Road Mine (newly reopened). (b) Secret Pass area, showing pre-pst trachyte lavas, post PST volcanics (here mostly rhyolite), and 17.6 Ma trachyte plug, unconformity (PST absent). (c) Thick ignimbrite sections exposed at S edge of Warm Springs Wilderness Area: Peach Spring Tuff (100 m), Cook Canyon Tuff (50 m), Bulk major element chemistry similar to older Pre-PST trachyte lavas potential genetic relationship al. in press). Furthermore, isotopic and geochemical studies (Fig 4b) of some of the intrusive rocks within the caldera indicate that sub-caldera magmatic processes persisted for ka after the supereruption, and that the majority of the intrusive rocks are likely not equivalent to the eruptive products, though they may record similar processes such as magmatic heating and Glass compositions enation (McDowell et al. 2012). e recognize that we have only scratched the surface of research opportunities in this area, cially with respect to the Ma volcanics that pre- and post-date 0.6 the PST, the conspicuous but studied 500 unconformities within this volcanic sequence, the numerous compositionally diverse, postdikes (~ Ma) within and outside of the caldera (McDowell et al. 2012), and the connections een this evolving magmatic system and the rich mineral deposits produced 0.5 during this episode (e.g. ome ; DeWitt et al. 1991). There remain a multitude of exciting questions to be addressed and rience to be gained in coordinated, appropriately-scaled projects that can effectively engage rgraduates with various levels of experience. The well-exposed, comprehensive 0.4 record of pre-, synost-supereruptive magmatism (both intrusive and volcanic) in the southern Black Mountains makes n ideal 300 location to study Miocene-age volcanism in the CREC, observe similarities and differences s g diverse eruptive styles and products (super ax well s a normal scale), 0.3he amine tee rl ationships een coeval volcanic and intrusive rocks, and constrain magmatic processes through petrologic, hemical, and remote sensing investigations. The mineral deposits, though not likely to be a major 200 rch focus, are an exciting facet of the geological setting that will enrich 0.2the REU experience. eneral scientific aims and significance: This REU will provide student participants with basic field, enhanced understanding of geoscience concepts, improved written and oral communication skills, n appreciation 100 of field observation as a basis for understanding Earth 0.1 processes and of the value of ing a variety of lab and theoretical techniques for pursuing scientific questions. They will gain an ciation for collaboration 0.75 by working 1.25 with their 1.75 peers, the REU leaders, and Senior Participants who ring additional ideas and expertise (see below). Taking ownership of a research project from its tion through the final products CaO will not wt% only give students the opportunity to develop an Si02

8 Measured trachyte groundmass Pre-PST Trachytes 25-35% phenocrysts Trachytes (avg. 63 wt% SiO 2 ) Fractional Crystallization Model Equilibrium Crystal-Melt Modeled Pre-PST Trachyte melt PST Modeled Pre-PST Trachyte melt PST

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10 (1) Trachyte enclave (2) Trachyte enclave (3) Monzodiorite enclave Host trachyte enclave enclave host trachyte enclave host trachyte

11 Lege nd ( ( ( ( ( Fault Inferred Fa ult Copyright: 2013 National Geographic Society, i-cubed

12 Mafic Input Lavas and Enclaves

13 Model melt temperatures using Rhyolite-MELTS (Gualda et al., 2011) T~1020 C solids T~1080 C solids Mafic Enclaves in the PST = 1020 C T~1070 C solids Pre-PST Mafic lavas = 1080 C Esperanza trachyte temperature = 1070 C

14 Creek caldera, showing intracaldera tuff, Silver Creek intrusives, and historic Gold Road Mine (newly reopened). Intra-caldera Peach (b) Secret Pass area, showing pre-pst trachyte lavas, post PST volcanics (here mostly rhyolite), and 17.6 Ma trachyte plug, unconformity (PST absent). (c) Thick ignimbrite sections exposed at S edge of Warm Springs Wilderness Area: Peach Spring Tuff (100 m), Cook Canyon Tuff (50 m), Spring Tuff trachyte al. in press). Furthermore, isotopic and geochemical studies (Fig 4b) of some of the intrusive rocks within the caldera indicate that sub-caldera magmatic processes persisted for ka after the supereruption, and that the majority of the intrusive rocks are likely not equivalent to the eruptive products, though they may record similar processes Peach Spring such as Tuff magmatic host heating and enation (McDowell et al. 2012). e recognize that we have only scratched the surface of research opportunities in this area, cially with respect to the Ma volcanics that pre- and post-date the PST, the conspicuous but studied unconformities within this volcanic sequence, the numerous compositionally diverse, postdikes (~ Ma) within and outside of the caldera (McDowell et al. 2012), and the connections een this evolving magmatic system and the rich mineral deposits produced during this episode (e.g. ome 1923; DeWitt et al. 1991). There remain a multitude of exciting questions to be addressed and rience to be gained in coordinated, appropriately-scaled projects that can effectively engage rgraduates with various levels of experience. The well-exposed, comprehensive record of pre-, synost-supereruptive magmatism (both intrusive and volcanic) in the southern Black Mountains makes n ideal location to study Miocene-age volcanism in the CREC, observe similarities and differences s g diverse eruptive styles and products (super ax well s a normal scale), he amine tee rl ationships een coeval volcanic and intrusive rocks, and constrain magmatic processes through petrologic, hemical, and remote sensing investigations. The mineral deposits, though not likely to be a major rch focus, are an exciting facet of the geological setting that will enrich the REU experience. eneral scientific aims and significance: This REU will provide student participants with basic field, enhanced understanding of geoscience concepts, improved written and oral communication skills, n appreciation of field observation as a basis for understanding Earth processes and of the value of ing a variety of lab and theoretical techniques for pursuing scientific questions. They will gain an ciation for collaboration by working with their peers, the REU leaders, and Senior Participants who ring additional ideas and expertise (see below). Taking ownership of a research project from its tion through the final products will not only give students the opportunity to develop an rstanding of the process of science and the fundamental concepts involved in their research tions, it will also help them cultivate confidence in their own abilities to successfully participate with, Peach Spring Tuff fiamme

15 Sr High-Silica Rhyolite Low-Silica Rhyolite Trachyte Pumice WSB-Fo1 and WSB Fo7 (this study) Whole rock compositions from XRF SiO 2 (from Frazier, VU MS thesis, 2012)

16 ock/chondrites 1000 PST Glass Sun+McDon. Trace Element 1989-REEs Compositions 100 Intra-caldera Trachyte (this study) 10 Distal outflow Rhyolite* 1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu *from Colombini et al 2011, Padilla & Gualda in review

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18 PST is not a direct fractionate of earlier homogenous, massive trachyte lavas Significant thermal input leading up to and coeval with the supereruption in the form of more mafic magmas Intra-caldera PST trachyte appears to be reheated MUSH from base of PST magma chamber Relationship between Peach Spring Tuff and cook Canyon Tuff is possible - still under investigation Surface changed from depositional center to erosional regime around time of PST

19 Years 2 & 3 What does a supervolcano look like? What happens after a supereruption? Why the switch from trachytic to rhyolitic magmatism? Continue investigations into generation of and relationship between Peach Spring Tuff and the Cook Canyon Tuff (and other tuffs??)

20 Now Accepting Applications (due Nov. 3) Field season begins Dec. 27!

21 Questions? For more information on the REU Supereruptions program, contact and/or go to supereruptionreu/

22 (Pamukcu et al., 2013)