Effusive eruptions from a large silicic magma chamber: the Bearhead Rhyolite, Jemez volcanic field, NM
40
Citation
51
Reference
10
Related Paper
Citation Trend
Keywords:
Silicic
Caldera
Magma chamber
Fractional crystallization (geology)
Magma chamber
Silicic
Fractional crystallization (geology)
Phenocryst
Igneous differentiation
Layered intrusion
Cite
Citations (93)
Silicic
Cite
Citations (1)
Silicic
Magma chamber
Fractional crystallization (geology)
Caldera
Igneous differentiation
Phenocryst
Cite
Citations (21)
The 1·60Ma Otowi Member of the BandelierTuff is a chemically and isotopically zoned high-silica rhyolite ignimbrite with subchondritic concentrations of Sr. Sanidine phenocrysts and glasses from early erupted to late-erupted tuff exhibit systematic large variations in Sr/Sr (0·70519^0·70947) and small ranges in Pb isotope ratios (Pb/Pb1⁄417·795^17·835). In all but the earliest-erupted tuff, sanidine phenocrysts are zoned with relatively Srand Ba-rich overgrowths on Srand Ba-poor cores.We estimate sodic sanidine/ melt partition coefficients for Rb, Cs, Sr, Ba and Pb to aid in understanding the origins of the elemental and isotopic variations. Isotopic heterogeneity is observed within single pieces of pumice, single quartz^sanidine glomerocrysts and single crystals. At the observed high values of Rb/Sr ( 1000) caused by the extreme Sr depletion, radiogenic ingrowth or contamination of the magma by small amounts of country-rock could both be responsible for elevated Sr/Sr.The Pb isotope variations cannot be due to ingrowth and unequivocally indicate open-system behavior. Among the sanidine phenocrysts, positive correlations of Sr/Sr vs Rb/Sr superficially resemble isochrons but are better modelled as mixing arrays; at least three such arrays, corresponding to three distinct magmatic recharge events, can be identified.The latest event may have played a role in destabilizing the system and triggering eruption. In all cases the recharging magma was another high-silica rhyolite only slightly less depleted in Sr.These relationships are explained by a model that starts with a crystal-poor high-silica rhyolite melt lens overlying a sanidineþ quartz crystal pile. Successive melting events within the crystal pile and mixing of new and old melts (recharge) causes isotopic and chemical zoning in the main melt lens and short length scale disequilibrium in the crystal pile. A late episode of quartz crystallization may have captured inclusions of melt that had been additionally contaminated by Precambrian granitoid country-rock as the magma began the upward journey that culminated in eruption.
Caldera
Magma chamber
Cite
Citations (47)
Caldera
Bonito
Cite
Citations (2)
Silicic
Caldera
Magma chamber
Fractional crystallization (geology)
Cite
Citations (40)
Silicic
Caldera
Magma chamber
Cite
Citations (35)
Voluminous silicic volcanism of the Mahogany Mountain--Three Fingers rhyolite field (MM--TFrf) is spatially and temporally associated with mid-Miocene flood basalts of the Columbia River Basalt province. Early studies of the area advocated for a two-caldera model consisting of the Mahogany Mountain and the slightly younger Three Fingers caldera with pre- and post-caldera effusive rhyolite eruptions. Although close in time, the calderas were thought to be spatially offset producing the tuff of Leslie Gulch and the tuff of Spring Creek. Finding that the tuff of Spring Creek, that is exposed in Leslie Gulch, is an altered product of the tuff of Leslie Gulch, Benson & Mahood (2016) suggested only one large caldera with pre- to post-caldera lavas. With the new data of my study, building on results by Marcy (2013), we can address key outstanding questions regarding the stratigraphic and geochemical evolution of mid-Miocene rhyolite volcanism at the MM--TFrf. Abundant and compositionally variable effusive rhyolites largely postdate the tuff of Leslie Gulch, including the Mahogany Mountain as well as the McIntyre Ridge rhyolite that were considered pre-caldera before. New ages of the Mahogany Mountain rhyolite suite (15.82-15.71 Ma) and stratigraphic, mineral & compositional data, and age relationships along Succor Creek indicate both rhyolites are post-caldera. The only rhyolite underlying the tuff of Leslie Gulch was identified in the Leslie Gulch locality itself, yielding an age of 16.02 Ma. Stratigraphic data reveal that the tuff of Leslie Gulch is a complex, multi-phase deposit with eruptive breaks in between. There are additional discrete explosive events with deposits along Succor Creek and north of Leslie Gulch that are distinguished by age or composition. Similarly, geochronological and compositional data can be used to identify distinct post-caldera rhyolite magmas. In summary, the MM--TFrf represents a prolific rhyolite center that was active from 16.02 to 15.71 Ma thus shifting initiation of rhyolite activity back, to the end of Grande Ronde Basalt volcanism. Rhyolite eruptions recommenced in the SW of the field with the eruption of the 14.94 Ma Birch Creek rhyolite, and 14.42 Ma McCain Creek rhyolite.
Caldera
Silicic
Cite
Citations (0)
Gravity data from two silicic volcanic complexes, the Valles Caldera, New Mexico and the Breiddalur central volcano, Iceland, have been modelled and interpreted.
The Rubio Volcano (4 Ma to 1.5 Ma) in the area of the Toledo Embayment in the Jemez Mountains formed the centre of a depression which grew southwestwards and then collapsed to form the Toledo Caldera (1.45 Ma) and then the Valles Caldera (1.12 Ma). Published gravity data covering the Valles Caldera are used to generate three profiles across the caldera. Models in 2½D show a combination of chaotic collapse and a trapdoor caldera up to 3,600 m deep, hinged to the west with some faulted basement blocks. The maximum depth of tuffs filling the caldera are up to 1,000 m less than in previously published models, although in other places the tuffs are found to be over 1,000 m thicker.
Gravity data from Breiddalur in southeastern Iceland indicate that the partly silicic, andesitic volcano was about 2,000 m thick, with a 500 m thick silicic core and that at least two other buried silicic centres may have developed during the volcano's history.
The generation and storage of silicic magmas in these contrasting volcanic provinces is considered. Much more basic material is required at Valles than at Breiddalur to produce the inferred volumes of silicic material. The consequences of this difference are discussed.
Caldera
Silicic
Basement
Magma chamber
Cite
Citations (1)
Despite extensive study, the origin of large-volume silicic magma systems remains poorly constrained. We review the source regions and processes involved in the generation, differentiation, and eruption of caldera-related silicic magma with particular reference to the Bishop Tuff erupted from Long Valley Caldera, California. Nd-isotopic compositions of the earliest-erupted rhyolites (between 2,1 and 1.2 Ma) at Glass Mountain, which may be associated with the Bishop Tuff magma chamber, are consistent with extensive fractional crystallization of basaltic magmas derived from an enriched lithospheric mantle source. In contrast, Nd-isotopic compositions of late Glass Mountain lavas (1.2 to 0.8 Ma) and the Bishop Tuff (0.76 Ma) suggest significant incorporation of continental crust. Shallow-crustal residence histories inferred from Sr-isotopic studies at Long Valley suggest that large-volume silicic magmas reflect either: (1) continuous growth with episodic eruption from a single, large, long-lived magma chamber; or (2) rapid generation and eruption of separate, short-lived magma batches. Residence histories that require several rapid differentiation events (≤104 yr) followed by extended periods (≥105 yr) over which magmas are maintained without significant cooling and crystallization are difficult to reconcile with numerical models of the thermal evolution of shallow-crustal magma reservoirs. Sr-isotopic compositions of the Bishop Tuff and precursor Glass Mountain lavas alternatively may reflect assimilation of wall-rock melts undergoing high-87Sr/86Sr, low-Sr concentration dehydration during convective sidewall fractional crystallization of parental rhyolites. If so, the reported apparent Sr-isochronal relationships may have little or no age significance. Sr-isotopic systematics of the Bishop Tuff also provide insights into the influence of eruption dynamics on compositional gradients recorded in pyroclastic deposits. Sr-isotopic compositions of individual fall and flow pumice are consistent with recent field studies that suggest that the Bishop ignimbrite is intraplinian, and that fall and flow deposits previously interpreted to be sequential are largely coeval. Moreover, the distribution of Sr-isotopic compositions of pumice as a function of stratigraphic height suggests that magmas from different depths with different 87Sr/86Sr ratios were intimately mixed before exiting the vent and can be qualitatively predicted from numerical models of magma withdrawal from zoned crustal reservoirs.
Silicic
Caldera
Magma chamber
Fractional crystallization (geology)
Igneous differentiation
Cite
Citations (37)