Mineral fabrics in high-level intrusions recording crustal strain and volcano–tectonic interactions: the Shellenbarger pluton, Sierra Nevada, California

Tomek, Filip; Žák, Jiří; Verner, Kryštof; Holub, František V.; Sláma, Jiří; Paterson, Scott R.; Memeti, Vali

doi:10.1144/jgs2015-151

Cited by 21 publications

(22 citation statements)

References 104 publications

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“…(3) During the waning stages of caldera magmatism, postcaldera intrusions of various shapes and dimensions intrude at shallow levels, concurrently with emplacement of caldera-filling lavas and minor pyroclastic eruptions (e.g., Galetto et al, 2017;Marsh, 1984;Smith & Bailey, 1968). These include ring dikes, intrusive necks, laccoliths, and other resurgent intrusions that can be associated with extensive hydrothermal alteration and mineral deposits (e.g., Beavon, 1980;Bethke et al, 1997;Fridrich et al, 1991;Kennedy et al, 2012;Lexa et al, 1999;Saunders, 2001;Swanson & McDowell, 1985;Tomek et al, 2017).…”

Section: Citationmentioning

confidence: 99%

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

Tomek

Gilmer

Petronis

et al. 2019

Geochem Geophys Geosyst

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Many eroded calderas expose associated postcollapse plutons, but detailed fieldwork‐supported studies have rarely focused on the internal structure that can contribute to understanding of emplacement dynamics. The Alamosa River monzonite pluton is a postcollapse intrusion at the Platoro caldera complex that erupted six large ignimbrites between 30.2 and 28.8 Ma in the Southern Rocky Mountains volcanic field. Magnetic fabrics in this intrusion indicate the pulsed emplacement of a vertically extensive pluton. The magmatic pulses are documented by three concentric domains of magnetic foliations elongated in ~NE‐SW direction, corresponding to structural trends at the Platoro caldera complex and preexisting regional structures. As no evidence for deformation of wall rocks and the adjacent resurgent block has been identified, we interpret the Alamosa River pluton as a postresurgent intrusion. The space‐opening process involved magmatic stoping and small‐scale magma wedging. New SHRIMP‐RG U/Pb zircon dates (28.98 ± 0.18, 27.42 ± 0.35, and 27.32 ± 0.38 Ma) suggest a magmatic lifespan of ~1.7 My for the Alamosa River pluton. Our results indicate that postcaldera magmatism includes pulsed and protracted activity from large intracaldera resurgent plutons to smaller postresurgent stocks and sheeted complexes. As demonstrated by the Alamosa River pluton, some intrusions are emplaced shortly after collapse and resurgence, but postcaldera volcano‐plutonic systems may remain active for several million years or more. We also suggest that subvolcanic magma bodies may be assembled incrementally and that the record of early composite magma lenses preserved as magma wedges are later obliterated by convective flowage and crystallization.

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Section: Citationmentioning

confidence: 99%

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

Tomek

Gilmer

Petronis

et al. 2019

Geochem Geophys Geosyst

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“…An example of syn-magmatic pure shear deformation is documented from Cretaceous batholiths of the Sierra Nevada (Tomek et al, 2017). Pure shear was dominant in Figure 13.…”

Section: Structural Features Of the St Peter Suitementioning

confidence: 99%

“…Data tabulated in is likely enough time to account for emplacement and cooling of earlier plutonic bodies that could then form the cool, host rocks for zones of magma transfer and attendant pure shear. By way of contrast, simple shear and pervasive deformation is the dominant process late in the formation of the Sierra Nevada batholiths when the volume of magma increased such that sheet-like intrusions and associated crystallising plutons become the weakest portion of the crust, thereby becoming wholesale zones of shear to accommodate the syn-magmatic strain (Tomek et al, 2017). This style of deformation is more akin to that described by Symington et al (2014) for the more gneissic, and likely more deeply emplaced portions of the St Peter Suite exposed at the Rocky Point locality.…”

Section: Structural Features Of the St Peter Suitementioning

confidence: 99%

Resolving tectonic settings of ancient magmatic suites using structural, geochemical and isotopic constraints: the example of the St Peter Suite, southern Australia

Reid

Pawley

Wade

et al. 2019

Australian Journal of Earth Sciences

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Reconstructing ancient tectonic environments is inherently difficult and requires the integration of many datasets. Here we attempt to reconstruct the tectonic setting of a Proterozoic magmatic rock suite from the Archean to Mesoproterozoic Gawler Craton, South Australia. We evaluate previous models of subduction or non-subduction tectonics for the St Peter Suite through field observations coupled with geochemical and isotopic data. Field observations indicate the presence of mafic magma chambers, felsic plutons and zones of mixing represented by multiphase plutons and zones of magma transfer. Syn-magmatic and solid-state deformation fabrics suggest magmatism was associated with a compressional tectonic regime, at least during some stages of magmatism. Zircon U-Pb geochronology suggests magmatism occurred between ca 1633 and ca 1608 Ma, an interval of ca 25 Myr. Mafic rocks are tholeiitic and enrichment in high field strength and light rare earth elements supports a modified mantle source region. Mafic rocks have eNd 1620 Ma values around 0, and zircon eHf (t) values around 4, supporting minor crustal contamination. Felsic plutons have a geochemical signature similar to average continental crust, eNd 1620 Ma between -3.7 and 0.4, and zircon Lu-Hf isotopic compositions that yield to eHf (t) values between -1.8 and 7.7, suggesting they were derived from fractionation of enriched tholeiitic parent magmas. A model for the formation of the St Peter Suite that is most consistent with the available data is one that places the magmatism in a broadly continental magmatic arc setting, albeit one in which little or no Archean crust was involved. Potentially this magmatic arc could have been built on a thinned, or hyper-extended continental margin. The integration of structural, geochemical and isotopic constraints has provided a more holistic view of the St Peter Suite petrogenesis than previously available. HIGHLIGHTSEvaluation of models of subduction vs non-subduction tectonics for formation of Paleoproterozoic magmatic suite Evidence for syn-magmatic compression and mafic-felsic magma mingling Isotopically juvenile (Nd-Sr-Hf) with mantle-like zircon d 18 O values Continental arc setting proposed, possibly on hyper-extended continental margin ARTICLE HISTORY

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“…Magmatic fabrics are commonly used to make inferences about the tectonic regime at the moment of pluton emplacement (e.g., Archanjo et al, 1994;Benn et al, 1997Benn et al, , 2001Bouchez & Gleizes, 1995;Marre, 1986;Paterson et al, 1998;Pignotta & Benn, 1999;Tomek et al, 2017;Žák et al, 2007). In the Huemul pluton, the microstructural observations suggest a lack of solid-state deformation, such that we interpret the magnetic fabrics as being acquired in the magmatic state.…”

Section: Tectonic Shortening Recorded By Huemul Foliationsmentioning

confidence: 99%

Interpreting Granitic Fabrics in Terms of Rhyolitic Melt Segregation, Accumulation, and Escape Via Tectonic Filter Pressing in the Huemul Pluton, Chile

et al. 2018

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The physical process of rhyolite segregation from crystal mushes remains elusive as microstructural evidence of conventional segregation mechanisms is not available. This study provides direct fabric evidence for deformation‐assisted segregation of eruptible rhyolite in the Chilean Andean arc. The shallow (<7 km), 6.4–6.2 Ma Huemul pluton comprises domains of quartz monzonite, granite, and high‐silica granite. Compositional modeling shows that rhyolitic melt (high‐silica granite) was extracted from a granitic parent, leaving behind silicic cumulates (quartz monzonite). To understand mechanisms of rhyolite segregation, we investigate magmatic fabrics in the pluton. Anisotropy of Magnetic Susceptibility analyses reveal oblate magnetic fabrics and NNW‐striking, subvertical magnetic foliations throughout Huemul. Within the high‐silica granite, magnetic lineations are subvertical and parallel to elongate miarolitic cavities. Magnetic lineations in the quartz monzonite plunge moderately to the NNW, away from the high‐silica granite. In the quartz monzonite, the Shape‐Preferred Orientation of early feldspars is parallel to the magnetic lineation and developed while suspended in melt. Estimations of early feldspar clustering and crystallinity yield ~38% of interstitial volume loss in the quartz monzonite and no volume loss in the granite. These fabric data suggest ENE tectonic shortening coeval with rhyolite extraction. We explain these observations with a model of tectonic filter pressing in which shortening is accommodated by interstitial melt flow at slow (10−5 km3/yr) rates, segregating moderate volumes of rhyolite in Myr time scales. These interactions link plutonism, tectonic deformation, and upward mobility of eruptible rhyolite in tectonically active margins.

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Mineral fabrics in high-level intrusions recording crustal strain and volcano–tectonic interactions: the Shellenbarger pluton, Sierra Nevada, California

Cited by 21 publications

References 104 publications

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

Resolving tectonic settings of ancient magmatic suites using structural, geochemical and isotopic constraints: the example of the St Peter Suite, southern Australia

Interpreting Granitic Fabrics in Terms of Rhyolitic Melt Segregation, Accumulation, and Escape Via Tectonic Filter Pressing in the Huemul Pluton, Chile

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