Download or read book Transtensional Strains Tap Magmas from the Middle Crust and Low degree Melts in Crystal liquid Mush Zones written by Amalie Larsen-Van Vleet (Graduate student) and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crustal Deformation During Arc Flare Up Magmatism Field and Microstructural Analysis of a Mid Crustal Melt Enhanced Shear Zone written by John Bennett Gilbert and published by . This book was released on 2017 with total page 446 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study combines structural field data with microstructural observations in an analysis of a mid-crustal shear zone related to the emplacement of the Misty pluton during a high-flux magmatic event in Northern Fiordland, New Zealand. These high-flux magmatic events transport massive amounts of heat and material as they develop along accretionary continental margins, and represent a primary source of continental crust. Fiordland, New Zealand possesses, perhaps, the most extensive middle and lower crustal exposure of these systems on earth. Therefore, this study area provides a significant opportunity to understand processes of continental crust formation in the mid-crust and how these events relate to the broader construction of continents. Herein, I document the four-stage geologic history of the Cozette Burn field area. Pre-existing structures along the Gondwana accretionary margin hosted a regional flare-up magmatic event that produced the Misty pluton and several other large plutons of the West Fiordland Orthogneiss (WFO). This study primarily focuses on the mid-crustal emplacement of the Misty pluton during oblique convergence along the accretionary margin, forming the upper-amphibolite facies Misty Shear Zone (MSZ). The exposures of the MSZ within the Cozette Burn preserve rare structural relationships between host rock and the intrusive Misty pluton. Together, these structures developed during end-stage contractional tectonics that constructed a long-lived (~270+ Ma) composite batholith. Heterogeneous ductile shearing defines the MSZ, with microstructural evidence indicating an interplay of high-temperature crystal plastic deformation along with partial melting of host rock and melt channeling. This resulted in focused, melt-assisted shearing under regional transpressive deformation. These accommodative processes provided an efficient mechanism for moving heat, fluids and magma sourced from the lower crust/mantle boundary into the mid-crust during 15-25 km of crustal thickening related to arc flare-up magmatism. This flare up magmatism and MSZ formation occurred during the final stages of crustal thickening along Gondwana continental margin. High-strain, mylonitic- ultramylonitic shear zones developed in a later phase of deformation, cutting MSZ fabrics near contacts between the Misty pluton and host rock. These more localized shear zones can be attributed to either accommodation of localized melt-pressure buildup or the shift to extensional tectonics. Brittle faulting cut these structures with oblique-thrust in the Tertiary. These mid-crustal structures carry economic relevance: thickened-crust events along accretionary continental margins produce deep-crustal sourced, metal-bearing magmas that are transferred into mid-crust prior to their hydrothermal emplacement as ore deposits in the upper crust. The lasting influence of these processes warrants consideration when assessing continental crust architecture at all scales.
Download or read book Synextensional Magmatism in the Basin and Range Province written by Phillip B. Gans and published by Geological Society of America. This book was released on 1989 with total page 62 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crystal Archives of Magmatic Processes written by Teresa Ubide and published by Frontiers Media SA. This book was released on 2021-10-13 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book On the Kinematic and Dynamic Evolution of a Magma Mush written by Michael Zackery McIntire and published by . This book was released on 2021 with total page 118 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magmas are dynamic hydrogranular systems where the interactions between the melt and the residing crystals influences the eruptive behavior of volcanoes, the concentration of economic metals, and the stratification of the Earth's crust. Despite the importance of the interaction between these phases, little is known about the mechanics of these systems. The purpose of this dissertation is to investigate the interactions of the melt and crystals of magma from the formation of the crystal-rich mush to the expulsion of the melt from its interstitial spaces. I first examine the dilute case where suspended crystals are coupled to the fluid. I employed a combination of discrete element computational fluid dynamic (DEM-CFD) numerical simulations, field observations, and electron backscatter diffraction (EBSD) analyses to explore the mechanics of the interactions between the crystals and the melt of magmas. The formation of crystal clusters was explored using Voronoi tessellations in both a settling only model at a solid volume percent of 9 and an open system models (where a magma like fluid is injected into the accumulating mush) with solid volume percents of 1, 9, and 20. I find that there is statistically no difference in the distribution of clustering between the two systems and that clusters are just as likely as a random distribution. Indicating that abundant crystal clusters found in sampled magmatic systems are likely from a disaggregated magma mush. Next, I examined the crystal-rich state where the formation of granular flows transfer momentum to the resident fluid. I employed a DEM-CFD numerical dam break model of a polydisperse particle column to explore the kinematics of the collapse and runout of the particle column. The column develops two collapse regimes a toppling collapse, and a sliding collapse, which transition into three kinematic runout regimes, gravity current, heap flow, and a quasi-static region. Both a force and contact fabric develop in the heap flow where the particles have enduring contacts. The difference in anisotropy between the normal force and contact fabrics illustrates the non-affine nature of granular material and the issue with applying the concepts of continuum modelling to hydrogranular systems. The first two chapters were based on numerical models analyses to create an idealized framework of knowledge on hydrogranular systems. The final chapter builds on geological observations and fieldwork with a goal of determining the mechanisms of pore space reduction in a crystal-rich magma mush. I collected 12 samples from the mafic complex of Sierra Valle Fértil from which I conducted EBSD analyses to quantify the crystallographic preferred orientation (CPO) and the internal lattice distortions. I considered the evidence for tectonic filter pressing, mechanical compaction, and viscous compaction. The internal lattice distortions have a similar distribution across plagioclase, hornblende, and quartz. This suggests the crystal deformation happened subsolidus and was not caused by either viscous compaction or tectonic filter pressing, and that a mechanical compaction process was responsible for pore space reduction. Future work should focus on the physics of hydrogranular systems with non-spherical particles employing analogue and numerical models to better capture natural systems.
Download or read book Magma Genesis written by Henry J. B. Dick and published by . This book was released on 1977 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Magma Migration written by Judson Lewis Ahern and published by . This book was released on 1980 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Evolution of the Quaternary Magmatic System Mineral Mountains Utah written by William P. Nash and published by . This book was released on 1982 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Through the Magma Mush written by Christopher Svoboda and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crystal Records of the Origin Evolution and Thermal Histories of Magmas written by Richard W. Bradshaw and published by . This book was released on 2017 with total page 333 pages. Available in PDF, EPUB and Kindle. Book excerpt: In volcanic systems, magma is generally stored in the shallow crust prior to eruption. The conditions of this storage directly impact whether the magma eventually erupts, or crystallizes within the crust to form a pluton. In this dissertation I present four studies that investigate the storage conditions of a number of volcanic systems and their timescales. A widespread method to quantify the timescales of magmatic processes is diffusion modeling of compositional variations in zoned crystals. Obtaining timescale information from diffusion modeling relies on fitting modeled diffusion profiles to measured compositional gradients. Therefore, the spatial resolution of the geochemical analysis technique used to characterize these gradients has the potential to limit the accuracy and precision of calculated diffusion timescales, especially when the resolution of the individual analyses approaches the width of the observed diffusion gradient. A probabilistic modeling approach is presented to assess the accuracy of short diffusion timescale estimates with respect to the spatial resolution of the geochemical measurement of compositional zoning. We develop a generalized method to quantify these shortest timescales that can be accurately calculated for given spatial resolutions and diffusivity. This provides a simple method to assess the accuracy of short diffusion timescales. Olivine-rich picrites are a relatively common eruptive product of ocean island and flood basalt volcanism. This rock type has a primitive bulk-rock composition similar to mantle-derived melts; however, picrites are olivine-rich. The common interpretation for the formation of picrites is the accumulation of olivine in more evolved, basaltic liquids. Many picrites contain two textural populations of olivine, one with deformation features (kink bands, subgrains or undulose extinction), and one without deformation. Deformation textures in olivine is traditionally thought to form by plastic deformation during storage in a deforming cumulate zone. However, recently it has been proposed that deformation textures could be the result of growth phenomena. We use textural (crystal sizes, deformation textures and minor element zoning patterns) and geochemical analysis (trace element compositions and minor element diffusion) of olivine from the 1959 eruption of Kīlauea Iki to show that these two olivine populations are derived from different sources and that the deformed population experienced longer residence times than the undeformed population. Our results are consistent with the interpretation that olivine is deformed in cumulate zones, and later entrained in unrelated magmas. The conditions of upper crustal magma storage in arc settings are fundamentally important to the evolution and ultimate fate of arc magmas. Current thermal models suggest that accumulation of significant bodies of eruptible magma require either high magma influx and storage at elevated temperatures, or lower flux and storage as low temperature crystal mushes that are later thermally rejuvenated. We use textural (crystal sizes) and geochemical (plagioclase trace elements and trace element diffusion in plagioclase, quartz and sanidine) analyses of samples from several arc systems ranging in eruptive volume from 1 km3 to 5,000 km3 to obtain observational evidence for the thermal conditions of arc magma storage. In particular we quantify the maximum amount of time a given crystal could have resided in a mobile magma ( 50% crystals, i.e., below the rheological lockup). This study is split into two parts, the first is focused on the large, caldera-forming eruptions (≥ 10 km3) and the second on the smaller, more typical arc eruptions (≤ 13 km3). Diffusion timescales from 11 caldera-forming eruption reveal three types of magmatic systems: 1) relatively small volume systems (
Download or read book The Post caldera Magmatic System at Yellowstone Plateau written by Mark Evan Stelten and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Yellowstone Plateau Volcanic Fields hosts a long-lived magmatic system that has produced three rhyolitic caldera-forming eruptions over the past 2.1 Ma, as well as numerous intracaldera rhyolitic eruptions between caldera-forming events. Whereas caldera-forming eruptions evacuate a large volume of magma near instantaneously, the eruption of intracaldera rhyolite flows intermittently over ≥ 100 kyr can be viewed as snapshots into an evolving magmatic system and allow the assessment of how large, multi-cyclical silicic magma systems evolve through time. I integrate age, trace-element, and isotopic data for minerals and volcanic glasses from the youngest post-caldera eruptive episode at Yellowstone, which generated the Central Plateau Member (CPM) of the Plateau Rhyolite from ca. 170 ka to 70 ka, to constrain [1] the physical nature of the Yellowstone magmatic system, [2] the processes controlling its compositional evolution, [3] the processes that produce compositional diversity within the eruptive sequence, and [4] the mechanisms/timescales of generating eruptible rhyolitic magmas. Linking 238U-230Th crystallization ages of zircon and sanidine hosted in the CPM rhyolites with their trace-element and isotopic compositions demonstrates that the magma reservoir that sourced the CPM rhyolites is characterized by a long-lived (150 - 250 kyr) and compositionally heterogeneous crystal mush, that is evolving over time to more fractionated trace-element compositions via cooling induced crystallization. While most of the CPM rhyolites show a coherent compositional evolution though time, compositionally anomalous rhyolites can be produced by the mixing of extracaldera magmas with the margin of the main Yellowstone magma reservoir. This highlights the dynamic nature of magmatic interactions that occur at the margins of large magma reservoirs, and represents a process by which compositional diversity within a magmatic suite can be produced. Although the crystal mush that sourced the CPM rhyolites is uneruptible due to its high degree of crystallinity, eruptible magmas are generated by extracting melt and antecrystic zircons (i.e., related to older stages of Yellowstone magmatism) from the crystal mush while the major phases (e.g., sanidine) remain trapped in the locked crystal network. The extracted liquids (plus zircon) are then amalgamated into a liquid dominated (i.e., eruptible) magma body from which autocrystic (i.e., akin to their host melt) sanidines and zircon rims crystallize. These liquid-dominated magma bodies reside in the crust for [less than/equal to] 2 kyr (conservatively
Download or read book Storage Fractionation and Melt crust Interaction of Basaltic Magmas at Oceanic and Continental Settings written by Ruohan Gao and published by . This book was released on 2016 with total page 356 pages. Available in PDF, EPUB and Kindle. Book excerpt: This study uses phenocrysts and xenoliths to examine storage, fractionation and melt-crust interaction of basaltic magmas. Gabbroic xenoliths from Hualalai Volcano, Hawaii include fragments of lower oceanic crust (LOC) cumulates. Oxygen and Sr isotope compositions of these gabbros indicate minimal hydrothermal alteration. Magmas from fast ridges fractionate on average at shallower and less variable depths and undergo more homogenization than those from fast ridges. These features suggest a long-lived shallow magma lens exists at fast ridges, which limits the penetration of hydrothermal circulation into the LOC. Anorthitic plagioclases in these LOC gabbros therefore unlikely derive from hydrous melting or hydrothermal replacement. The strongly positive correlation between plagioclase anorthite content and whole rock Re concentration of Hualalai LOC gabbros may place further constraints on the origin of anorthitic plagioclase at mid-ocean ridges. Most Hualalai xenoliths represent Hualalai melt-derived cumulates. MELTS modeling and equilibration temperatures suggest Hualalai shield-stage-related gabbros crystallized within local LOC. Therefore, a deep magma reservoir existed within or at the base of the LOC during the shield stage of Hualalai Volcano. Melt–crust interaction between Hawaiian melts and Pacific crust partially overprinted Sr, Nd, and Pb isotope compositions of LOC-derived gabbros. The modified isotope compositions of Pacific LOC (and likely lithospheric mantle) are similar to Hawaiian rejuvenated-stage lavas. Although minor assimilation of Pacific crust by Hawaiian melts cannot be excluded, the range of oxygen isotope compositions recorded in Hawaiian magmas cannot be generated by assimilation of the in situ LOC. The Papoose Canyon (PC) monogenetic eruption sequence in the Big Pine volcanic field, California displays temporal-compositional variations indicating mixing of two distinct melts. PC phenocrysts and xenoliths derive from melt that is more fractionated and enriched than PC lavas. Pressure constraints suggest these phenocrysts and xenoliths crystallized at mid-crust depths. PC lavas also show evidence of crustal contamination. Therefore, PC phenocrysts and xenoliths likely derive from early PC melts that ponded, fractionated and assimilated continental crust in mid-crustal sills, which were mixed with more primitive melts as the eruption began. The temporal-compositional trends thus reflect gradual exhaustion of these sills over time.
Download or read book Partial melting of mafic amphibolitic lower crust by periodic influx of basaltic magma written by N. PETFORD and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Crystallization of Magma written by Richard W. Berry and published by McGraw-Hill Companies. This book was released on 1973 with total page 40 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crystallization of Magma is one of a series of single-topic problem modules intended for use in undergraduate geology and earth science courses. Through problems and observations based on two sets of experiments, this module leads to an understanding of how an igneous rock can form from molten material. Environmental factors responsible for important variations observed in magnetic rocks are stressed. Two fundamental factors affecting or controlling the mineral composition and texture of the resulting rock (initial magma composition and cooling rate) are also stressed. In addition, reasons why scientists classify materials in general and how they classify rocks in particular are explored. However, the ability to name or identify rocks is not a necessary result of attaining the module's goals. Supplemental questions included at the end of the module may prove difficult for the average non-major; they are intended to challenge the superior student. Like other modules in the series, this module is inquiry- and problem-oriented, dealing with interdisciplinary, contemporary, and pragmatic aspects of the subject matter. It is designed to be open-ended so that ideas can be incorporated into higher level classwork. (Author/JN)
Download or read book Melt Inclusion Record of Magmatic Immiscibility in Crustal and Mantle Magmas written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Immiscibility (unmixing of melts and fluids) should be almost inevitable at some point in the evolution of most mantle and crustal magmas during cooling and crystallization. Formation of two immiscible phases "results in a major geochemical fractionation all chemical species present, the elements (and their isotopes), and their various compounds, become distributed between these two phases ... the compositional divergence between the two phases is ... extreme" (Roedder 2003). The variations in compositions of melts undergoing immiscibility, and physical parameters of their evolution in the plutonic environments, mean that each intrusion should be expected to show differences in the processes of exsolution and compositions of exsolving phases. One of the immiscible phases is universally volatile-rich, and this has important consequences for further magma evolution and geological processes related to it. More specifically, volatile-rich phases generally have significant density and viscosity contrasts with parental silicate magmas, and thus rapid separation of the newly exsolved phases is expected. Further, the exsolution of volatile-rich phases exerts major controls on the chemistry of a magmatic system, particularly on metal partitioning between immiscible melts and fluids, so the volatile phase is highly efficient at sequestering the metals (e.g., Candela 1989; Candela & Piccoli 1995; Williams et al. 1995; Heinrich et al. 1999; Webster 2004). Magmatic immiscibility and the related formation of volatile-rich melts and fluids are prerequisites for the origin of mineralized hydrothermal solutions that may transport metals to a suitable depositional site. Immiscible separation, however, is not restricted to magmas that form mineralized rocks. The fugitive nature of magmatic immiscibility involves problems in unraveling physical and chemical characteristics of this fundamental process. If separation of immiscible phases was efficient, the residual magma should be signific.
Download or read book Magma Envelopes Enclaves and Rogue Crystals in the Atascosa Lookout Lava Flow written by Christine Burrill and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The Atascosa Lookout lava flow is a mid-Tertiary trachyandesite flow that caps the rhyolitic to dacitic volcanic sequence exposed in the Atascosa Mountains of southern Arizona. The flow erupted near the beginning of extension in the southern Basin and Range following the floundering of the Farallon plate and during the development of the San Andreas fault. The flow hosts a variety of disequilibrium crystals and textures including resorbed and overgrown feldspar phenocrysts with inclusion-rich zones, quartz-bearing enclaves, and clusters of plagioclase +/- chromium diopside, magnesian augite, quartz, hornblende, and orthopyroxene crystals and envelopes of contrasting composition with both the groundmass and the enclaves. Current evidence suggests that magma generation and differentiation commonly take place mainly in the lower crust and batches of magma are emplaced and equilibrate across a range of crustal levels. Crystallization depths and temperatures of various phases in the flow were obtained with new and revised geothermometers and geobarometers to examine the petrogenesis of the lava flow. Major elements of parental melts for most of the mineral phases were estimated using thermobarometry equilibrium tests and rare earth and trace element concentrations of parental melts of hornblendes and clinopyroxenes were calculated using known partition coefficients elements. Thermobarometry shows distinct ranges of temperatures and pressures for each component of the flow and calculated parental melts of various phases are distinct from one another. Orthopyroxenes crystallized at depths greater than 25 km, at the highest temperatures from the most mafic parent, estimated to be a picro-basalt. Clinopyroxenes crystallized at 11.5 - 30 km, lower temperatures and a more evolved parent of basalt or trachybasalt composition. Plagioclase crystallized throughout the crust from a range of intermediate melts and hornblendes crystallized 12 - 13 km from a parental melt similar in composition to the groundmass. This study demonstrates the lava flow hosts minerals that crystallized from different parent melts at various crustal levels. Extension and previous magmatism provided a rapid path for magma to ascend, subduing crustal assimilation and enhancing the probability of a diverse crystal cargo that retains the record of the plumbing system beneath a volcanic complex.
Download or read book Using Crystal Zoning Thermobarometry and MELTS to Elucidate Koma Kulshan s Mt Baker Transcrustal Magma Storage System Northern Cascade Arc written by Brendan Michael Garvey and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Koma Kulshan (Mt. Baker) is classified as a high-threat volcano due to its past eruptive history and its proximity to populations, yet its eruptive products are understudied. Combining mineral chemistry from complexly zoned crystals with thermobarometry and thermodynamic modeling (MELTS) is a powerful way to provide constraints on magmatic processes beneath an active volcano. Up to four populations each of pyroxene, plagioclase, and olivine occur as phenocrysts and crystal clusters in the youngest (9.8 ka) lava flow at Koma Kulshan and represent four co-crystallizing assemblages derived from distinct magmas. These co-crystallizing assemblages are defined by petrologic observations and mineral chemistry (An, Fo, Mg#, trace elements). The host lava flow (Sulphur Creek) is composed of two segments: a basalt at the flow toe and a basaltic andesite towards the flow source. The basaltic segment carries three co-crystallizing assemblages; in order of abundance, they are derived from a) the host calc-alkaline basalt (designated as the B3 assemblage), b) a dacite (designated as the D1 assemblage), and c) a high-Mg basalt (designated as the B2 assemblage). The textures and compositions of the D1 and B2 co-crystallizing assemblages suggest entrainment in the host basalt. The up-flow basaltic andesite hosts a distinct native basaltic andesite assemblage (designated as the BA3 assemblage), plus cryptic evidence of the D1 and B2 assemblages. These assemblages, coupled with observed mingling textures in this basaltic andesite part of the lava flow, suggest more-extensive mixing of the magmas that generated the B3 and D1 assemblages to generate a hybridized basaltic andesite magma (parental to the BA3 assemblage). The D1 and B2 assemblages have been previously identified in lavas flows that span the last ~120 ka of eruptive history at Koma Kulshan, suggestive of the presence of long-lived crystal mushes beneath this volcano. Clinopyroxene thermobarometry and olivine thermometry combined with Rhyolite-MELTS models provide quantitative bounds for the storage condition of the native (to the host basalt) and entrained assemblages. The B3 assemblage, native to the basaltic segment, crystallized shallowly at 0-1.5 kbar. The BA3 assemblage, native to the basaltic andesite segment, displays evidence for three distinct episodes of cooling and crystallization within the crust at 0-1.5 kbar, ~2.5 kbar, and ~5 kbar. Storage conditions of the B2 entrained assemblage are constrained from Escobar (2016) and Escobar et al. (in prep.) at 5.8 kbar (22 km). Storage conditions of the D1 assemblage is also unconstrained; however, textural observations suggest the D1 crystal mush is at or below 18 km. These data require a two-stage history for eruption of the Sulphur Creek lava flow with open-system processes culminating in eruption of two distinct magma pulses. The first stage is an early pulse derived from a shallow basaltic system (3.4 km; B3), and the second stage is a later pulse derived from more complex multi-crustal-level mixing of the same basalt (B3) and a dacite (D1) at 3.4 km, 10 km, and 18 km to produce a hybridized basaltic andesite (BA3). This study elucidates magmatic processes occurring in the upper 18 km of a 45-km thick crust; however, the parental melts that drive these processes are generated deeper within and at the base of the crust. This study highlights the instability and reorientation of crystal mushes within arcs and the production of andesites through long lived dacitic reservoirs mixing with rejuvenating mafic magmas.
