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Kryštof Verner - One of the best experts on this subject based on the ideXlab platform.
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“Granite tectonics” revisited: insights from comparison of K-feldspar shape-fabric, anisotropy of magnetic susceptibility (AMS), and brittle fractures in the Jizera granite, Bohemian Massif
International Journal of Earth Sciences, 2009Co-Authors: Kryštof Verner, Josef Klomínský, Marta ChlupáčováAbstract:In the Jizera granite of the Krkonoše–Jizera Plutonic Complex, northern Bohemian Massif, contrasting patterns of magmatic K-feldspar fabrics and brittle fractures characterize different structural levels of the Pluton. The uppermost exposed level at ∼800–1,100 m above sea level is dominated by flat foliation that overprints two steep foliations. In contrast, K-feldspar shape-fabric in an underground tunnel (∼660 m above sea level) shows complex variations in orientation and intensity. Magnetic fabric carried by coaxial contributions of biotite, magnetite, and maghemite is homogeneous along the examined section of the tunnel, and is decoupled from the K-feldspar fabric. The Jizera granite is crosscut by two regional sets of subvertical fractures (∼NE–SW and ∼NW–SE) and by near-surface exfoliation joints. The multiple fabrics are inferred to reflect a complex magmatic strain history at different structural levels of the Pluton, bearing little or no relationship to the fracture network. In contrast to the original concept of Hans Cloos (“granite tectonics”), we conclude that no simple genetic relationship exists between fabrics and fractures in Plutons. An alternative classification of fractures in Plutons thus should avoid relationships to magmatic fabrics and should instead consist of cooling, syntectonic, uplift, and post-uplift fractures.
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Forearc deformation and strain partitioning during growth of a continental magmatic arc: The northwestern margin of the Central Bohemian Plutonic Complex, Bohemian Massif
Tectonophysics, 2009Co-Authors: František Dragoun, Kryštof Verner, Marta Chlupáčová, František V. Holub, Václav KachlíkAbstract:Abstract The Late Devonian subduction followed by the Early Carboniferous continental collision of the Saxothuringian and overriding upper-crustal Tepla–Barrandian units led to the growth of a large magmatic arc (the ∼ 354–337 Ma Central Bohemian Plutonic Complex) in the central part of the Bohemian Massif. Far-field tectonic forces resulting from the collision produced ∼WNW–ESE to ∼NW–SE regional shortening across the forearc upper crust above the subduction zone; the shortening was accommodated by predominantly top-to-the-ESE tectonic transport along the southeastern flank of the Tepla–Barrandian unit. Approaching the magmatic arc margin, the regional structural pattern changes and exhibits significant across- and along-strike variations interpreted as a result of strain partitioning, where the Saxothuringian/Tepla–Barrandian convergence interacted in different ways with the intruding magma pulses. Around the voluminous, northeasterly ∼ 354 Ma Sazava Pluton the principal shortening was at high angle to the forearc-facing intrusive contact and the host rocks were significantly thermally softened. The regional top-to-the-ESE tectonic transport converted here into arc-parallel ductile flow within the structural aureole around and above the Pluton. In contrast, a narrow to nonexistent ductile strain aureole is preserved in the host rocks around discordant sheet-like Plutons (the southwesterly pre-354 (?) Ma Marginal granite and the Milin granodiorite of unknown radiometric age). Our AMS study of the Marginal granite and Milin granodiorite, and mapping of mesoscopic magmatic foliations and lineations in another neighboring sheet-like Pluton (the ∼ 346 Ma Kozarovice granodiorite), reveals sigmoidal map-scale fabric patterns consistent with dextral transpression. We thus suggest that the thin sheet-like Plutons were oriented obliquely to the principal shortening and were rheologically weaker than the host rocks prior to final crystallization, producing dextral transpression recorded by the internal fabrics of these Plutons. Our study shows that the far-field plate kinematics during Pluton emplacement is not the only factor that controls strain partitioning in continental magmatic arcs. The two contrasting styles of Pluton emplacement documented here indicate that the Pluton shape, orientation of intrusive contacts with respect to the background plate convergence vector, and heat budget of intrusions (magma volume, composition, and proportion of hot mantle component) may also govern strain partitioning.
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Magmatic fabrics and emplacement of the cone-sheet-bearing Knížecí Stolec durbachitic Pluton (Moldanubian Unit, Bohemian Massif): implications for mid-crustal reworking of granulitic lower crust in the Central European Variscides
International Journal of Earth Sciences, 2008Co-Authors: Kryštof Verner, Radmila Nahodilová, František V. HolubAbstract:The ∼340 Ma Knížecí Stolec durbachitic Pluton was emplaced as a deep-seated cone-sheet-bearing ring complex into the Křišt’anov granulite body (Moldanubian Unit, Bohemian Massif). Prior to the emplacement of the durbachitic magma, the steep sub-concentric metamorphic foliation in the granulite formed due to intense ductile folding during high-grade retrograde metamorphism. Subsequently, the durbachitic Pluton intruded discordantly into the granulite at around ∼340 Ma. The steep margin-parallel magmatic fabric in the durbachitic rocks may have recorded intrusive strain during emplacement. After the emplacement, but prior to the final solidification, the Pluton was overprinted by the regional flat-lying fabric under lower pressure–temperature conditions ( T = 765 ± 53°C; P = 0.76 ± 0.15 GPa). Based on this study and comparison with other ultrapotassic Plutons, we suggest that the flat-lying fabrics, widespread throughout the exhumed lower to middle crust (Moldanubian Unit), exhibit major variations in character, intensity, kinematics, and shape of the fabric ellipsoid. These fabrics may have formed at different structural levels and in different parts of the root prior to ~337 Ma. Therefore, we suggest that this apparently “single” orogenic fabric recorded multiple deformation events and heterogenous finite deformation rather than reflecting a single displacement field within the orogenic root.
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Tectonic evolution of a continental magmatic arc from transpression in the upper crust to exhumation of mid-crustal orogenic root recorded by episodically emplaced Plutons: the Central Bohemian Plutonic Complex (Bohemian Massif)
International Journal of Earth Sciences, 2005Co-Authors: František V. Holub, Kryštof VernerAbstract:The Central Bohemian Plutonic Complex (CBPC) consists of episodically emplaced Plutons, the internal fabrics of which recorded tectonic evolution of a continental magmatic arc. The ~354–350 Ma calc-alkaline Plutons were emplaced by multiple processes into the upper-crustal Teplá-Barrandian Unit, and their magmatic fabrics recorded increments of regional transpression. Multiple fabrics of the younger, ~346 Ma Blatná Pluton recorded both regional transpression and the onset of exhumation of mid-crustal orogenic root (Moldanubian Unit). Continuous exhumation-related deformation during Pluton cooling resulted in the development of a wide zone of sub-solidus deformation along the SE margin of the CBPC. Finally, syn-exhumation tabular durbachitic Pluton of ultrapotassic composition was emplaced atop the intrusive sequence at ~343–340 Ma, and the ultrapotassic Tábor Pluton intruded after exhumation of the orogenic root (~337 Ma). We suggest that the emplacement of Plutons during regional transpression in the upper crust produced thermally softened domain which then accommodated the exhumation of the mid-crustal orogenic root, and that the complex nature of the Teplá-Barrandian/Moldanubian boundary is a result of regional transpression in the upper crust, the enhancement of regional deformation in overlapping structural aureoles, the subsequent exhumation of the orogenic root domain, and post-emplacement brittle faulting.
František V. Holub - One of the best experts on this subject based on the ideXlab platform.
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Forearc deformation and strain partitioning during growth of a continental magmatic arc: The northwestern margin of the Central Bohemian Plutonic Complex, Bohemian Massif
Tectonophysics, 2009Co-Authors: František Dragoun, Kryštof Verner, Marta Chlupáčová, František V. Holub, Václav KachlíkAbstract:Abstract The Late Devonian subduction followed by the Early Carboniferous continental collision of the Saxothuringian and overriding upper-crustal Tepla–Barrandian units led to the growth of a large magmatic arc (the ∼ 354–337 Ma Central Bohemian Plutonic Complex) in the central part of the Bohemian Massif. Far-field tectonic forces resulting from the collision produced ∼WNW–ESE to ∼NW–SE regional shortening across the forearc upper crust above the subduction zone; the shortening was accommodated by predominantly top-to-the-ESE tectonic transport along the southeastern flank of the Tepla–Barrandian unit. Approaching the magmatic arc margin, the regional structural pattern changes and exhibits significant across- and along-strike variations interpreted as a result of strain partitioning, where the Saxothuringian/Tepla–Barrandian convergence interacted in different ways with the intruding magma pulses. Around the voluminous, northeasterly ∼ 354 Ma Sazava Pluton the principal shortening was at high angle to the forearc-facing intrusive contact and the host rocks were significantly thermally softened. The regional top-to-the-ESE tectonic transport converted here into arc-parallel ductile flow within the structural aureole around and above the Pluton. In contrast, a narrow to nonexistent ductile strain aureole is preserved in the host rocks around discordant sheet-like Plutons (the southwesterly pre-354 (?) Ma Marginal granite and the Milin granodiorite of unknown radiometric age). Our AMS study of the Marginal granite and Milin granodiorite, and mapping of mesoscopic magmatic foliations and lineations in another neighboring sheet-like Pluton (the ∼ 346 Ma Kozarovice granodiorite), reveals sigmoidal map-scale fabric patterns consistent with dextral transpression. We thus suggest that the thin sheet-like Plutons were oriented obliquely to the principal shortening and were rheologically weaker than the host rocks prior to final crystallization, producing dextral transpression recorded by the internal fabrics of these Plutons. Our study shows that the far-field plate kinematics during Pluton emplacement is not the only factor that controls strain partitioning in continental magmatic arcs. The two contrasting styles of Pluton emplacement documented here indicate that the Pluton shape, orientation of intrusive contacts with respect to the background plate convergence vector, and heat budget of intrusions (magma volume, composition, and proportion of hot mantle component) may also govern strain partitioning.
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Magmatic fabrics and emplacement of the cone-sheet-bearing Knížecí Stolec durbachitic Pluton (Moldanubian Unit, Bohemian Massif): implications for mid-crustal reworking of granulitic lower crust in the Central European Variscides
International Journal of Earth Sciences, 2008Co-Authors: Kryštof Verner, Radmila Nahodilová, František V. HolubAbstract:The ∼340 Ma Knížecí Stolec durbachitic Pluton was emplaced as a deep-seated cone-sheet-bearing ring complex into the Křišt’anov granulite body (Moldanubian Unit, Bohemian Massif). Prior to the emplacement of the durbachitic magma, the steep sub-concentric metamorphic foliation in the granulite formed due to intense ductile folding during high-grade retrograde metamorphism. Subsequently, the durbachitic Pluton intruded discordantly into the granulite at around ∼340 Ma. The steep margin-parallel magmatic fabric in the durbachitic rocks may have recorded intrusive strain during emplacement. After the emplacement, but prior to the final solidification, the Pluton was overprinted by the regional flat-lying fabric under lower pressure–temperature conditions ( T = 765 ± 53°C; P = 0.76 ± 0.15 GPa). Based on this study and comparison with other ultrapotassic Plutons, we suggest that the flat-lying fabrics, widespread throughout the exhumed lower to middle crust (Moldanubian Unit), exhibit major variations in character, intensity, kinematics, and shape of the fabric ellipsoid. These fabrics may have formed at different structural levels and in different parts of the root prior to ~337 Ma. Therefore, we suggest that this apparently “single” orogenic fabric recorded multiple deformation events and heterogenous finite deformation rather than reflecting a single displacement field within the orogenic root.
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Tectonic evolution of a continental magmatic arc from transpression in the upper crust to exhumation of mid-crustal orogenic root recorded by episodically emplaced Plutons: the Central Bohemian Plutonic Complex (Bohemian Massif)
International Journal of Earth Sciences, 2005Co-Authors: František V. Holub, Kryštof VernerAbstract:The Central Bohemian Plutonic Complex (CBPC) consists of episodically emplaced Plutons, the internal fabrics of which recorded tectonic evolution of a continental magmatic arc. The ~354–350 Ma calc-alkaline Plutons were emplaced by multiple processes into the upper-crustal Teplá-Barrandian Unit, and their magmatic fabrics recorded increments of regional transpression. Multiple fabrics of the younger, ~346 Ma Blatná Pluton recorded both regional transpression and the onset of exhumation of mid-crustal orogenic root (Moldanubian Unit). Continuous exhumation-related deformation during Pluton cooling resulted in the development of a wide zone of sub-solidus deformation along the SE margin of the CBPC. Finally, syn-exhumation tabular durbachitic Pluton of ultrapotassic composition was emplaced atop the intrusive sequence at ~343–340 Ma, and the ultrapotassic Tábor Pluton intruded after exhumation of the orogenic root (~337 Ma). We suggest that the emplacement of Plutons during regional transpression in the upper crust produced thermally softened domain which then accommodated the exhumation of the mid-crustal orogenic root, and that the complex nature of the Teplá-Barrandian/Moldanubian boundary is a result of regional transpression in the upper crust, the enhancement of regional deformation in overlapping structural aureoles, the subsequent exhumation of the orogenic root domain, and post-emplacement brittle faulting.
Scott R Paterson - One of the best experts on this subject based on the ideXlab platform.
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Roof and walls of the Red Mountain Creek Pluton, eastern Sierra Nevada, California (USA): implications for process zones during Pluton emplacement
Journal of Structural Geology, 2006Co-Authors: Scott R PatersonAbstract:Abstract The Red Mountain Creek Pluton has a sub-circular outline in map section, generally flat roof, and steep sides. The Pluton roof sharply truncates host rock markers, has a highly irregular geometry with rectangular steps, and passes continuously into a steep wall. The roof–wall transition is not offset by faults and shows no evidence of extensive diking or synemplacement ductile strain, which requires that the Pluton roof and its wall remained attached to each other and were not faulted or ductilely deformed during emplacement of the Pluton. We propose that the exposed section through the Red Mountain Creek Pluton may represent the crestal portion of a vertically extensive piston-shaped Plutonic system, the upper part of which was largely emplaced by magmatic stoping although other material transfer processes may have previously operated during emplacement. Characteristics of the Pluton roof presented in this paper as well as in other papers on Pluton roofs directly rule out some emplacement models commonly applied to Plutons in the Sierra Nevada, place limitations on other models, and fit well the expected characteristics of visco-elastic diapirs around which variable material transfer processes largely displace host rock downwards. In the upper-crustal Plutons, the most widespread preserved process of downward transport of host rock was magmatic stoping.
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Is there a close spatial relationship between faults and Plutons
Journal of Structural Geology, 1999Co-Authors: Scott R Paterson, Keegan L. SchmidtAbstract:Abstract Using spatial relationships between individual Plutons and faults to support genetic correlations between faulting and magmatism is meaningless since even random magmatic or tectonic processes will result in some Plutons adjacent to faults. Our initial analyses of populations of faults and Carboniferous Plutons in the Armorican Massif, France and faults and Alleghanian Plutons in the southern Appalachians, USA indicate that Plutons have broad distributions with respect to faults but with a tendency for Plutons to occur away from faults. Maxima of integrated Pluton areas occur at 1/4 (Appalachians) and 1/2 (Armorican) of the distance between the average fault spacing in these orogens. Although there is a great need for statistical evaluations of relationships between populations of igneous bodies and structures in a wide variety of settings and crustal depths, our initial studies suggest that faults do not preferentially channel magma during ascent or emplacement and that these are relatively unfocused processes within orogenic belts.
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The Ardara Pluton, Ireland: deflating an expanded intrusion
Lithos, 1993Co-Authors: Ron H. Vernon, Scott R PatersonAbstract:Abstract The Ardara Pluton, north-western Ireland, is a circular monzodiorite-granodiorite intrusion with a “tail.” It has been regarded as a typical example of a Pluton emplaced entirely by expansion (“balloning”) after initial intrusion. Most of the foliation in the Pluton is magmatic, with weak superimposed solid-state features, apart from a thin rind of strong solid-state deformation. The solid-state deformation in the Pluton appears to be largely, if not entirely, of post-intrusive, tectonic origin. Flattened microgranitoid enclaves, a concentric magmatic flow foliation and compositional zoning in the Pluton are consistent with some expansion of magma prior to crystallization. However, strains in the wall rocks indicate that only a small amount (25%–38%) of the volume of the Pluton can be ascribed to ballooning. This relatively small amount of expansion could account for (a) observed structural concordance and strong syn-metamorphic deformation in the aureole, (b) flattening of microgranitoid enclaves (magma globules) in the Pluton and possibly (c) a small amount of solid-state deformation in the Pluton during “lock-up” of magmatic flow. Evidence of solid-state deformation superimposed on a strong magmatic flow foliation in the tail of the Pluton implies that a fault was active during emplacement and may have assisted the intrusion. Further space for the Pluton may have been made by a complex interaction of processes, many of which cannot be constrained from a two-dimensional cross-section through the area. These possibilities highlight the limitations of attempting to constrain emplacement mechanisms on the sole basis of structures adjacent to Plutons.
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re examining Pluton emplacement processes
Journal of Structural Geology, 1993Co-Authors: Scott R Paterson, Kenneth T FowlerAbstract:Abstract Previous Pluton emplacement studies have attempted to explain how space is made during Pluton emplacement. In fact, the only means of ‘making space’ during emplacement of mantle-derived magmas in the crust are (1) lowering the Moho or (2) outward displacement of the Earth's surface. Other ‘Pluton emplacement mechanisms’ are material transfer processes (MTPs) that do not increase the volume of the crust. One frequently cited MTP for emplacement of concentrically zoned and ballooning Plutons is ductile flow of wall-rocks around the Plutons. The expected structures and total strains near such Plutons are dependent on the three-dimensional Pluton shape, the width of the deforming aureole, whether the Pluton is a piercing or non-piercing diapir, and, in the latter case, the number of body radii the Pluton travels. We have re-examined a few such Plutons and calculated the amount of material transfer caused by ductile flow. In no case is more than 40%, and in most cases only 15–35%, of the required material transfer accommodated by wall-rock flow. The contact aureoles around these Plutons are too narrow and/or strains too low, indicating that the Plutons are predominantly discordant bodies with narrow (0.1–0.4 Pluton radii) concordant aureoles. A comparison of strains in natural contact aureoles and those made in mechanical models of diapirs indicates that natural strains are at least an order of magnitude less than model strains. We suggest that the similarities between models of diapiric ascent of spherical bodies and concentrically zoned Plutons are superficial because the models are too simplistic. Instead, we argue that the ascent and emplacement of magmas require multiple near-field and far-field MTPs. These MTPs will show gradients with depth, distance from the magma, and with time. Rates of near-field MTPs must be rapid, whereas far-field rates are probably nearer to long-term average rates of orogenic processes.
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Papoose Flat Pluton: Forceful expansion or postemplacement deformation?
Geology, 1991Co-Authors: Scott R Paterson, Tom Brudos, Ken Fowler, Christopher S. Carlson, Kim M. Bishop, Ron H. VernonAbstract:Intense solid-state deformation in the margin of the Papoose Flat Pluton, White Mountians, California, and severe attenuation of nearby wall rocks encouraged earlier workers to suggest that this Pluton was emplaced by blistering or in situ radial expansion. Reexamination of the Pluton and wall rocks indicates that many features present in and around the Pluton are not compatible with this model. These features include the following: (1) lack of compositional zoning or magmatic foliations in the Pluton; (2) lack of high-temperature solid-state deformation or a transition from magmatic to high-temperature solid-state flow; (3) the presence of widespread moderate-to low-temperature deformation in the Pluton; (4) a northwest-southeast-trending stretching lineation and associated kinematic indicators of sinistral shear everywhere within and adjacent to the western half of the Pluton; (5) significant cleavage transposition after the growth of porphyroblasts in the contact-metamorphic aureole; and (6) upright to inclined folds with a steeply dipping axial-planar cleavage in wall rocks that postdate aureole cleavages and porphyroblasts. Many other Plutons in the White and Inyo mountains also have deformed western or northwestern margins and weakly deformed eastern margins. Instead of interpreting all of these Plutons as post-tectonic and inferring that they all expanded in a western direction,more » the authors suggest that significant Cretaceous regional deformation occurred during and after emplacement of these Plutons.« less
Brian S Carl - One of the best experts on this subject based on the ideXlab platform.
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sheeted intrusion of the synkinematic mcdoogle Pluton sierra nevada california
Geological Society of America Bulletin, 2003Co-Authors: Kevin H Mahan, Allen F Glazner, John M Bartley, Drew S. Coleman, Brian S CarlAbstract:Field, microstructural, and geochronologic evidence indicates that the Late Cretaceous McDoogle Pluton, located near the eastern margin of the Sierra Nevada batholith, was emplaced as a subvertically sheeted complex into a steep reverse-sense shear zone. Evidence of internal subvertical sheeting includes abundant concordant wall-rock inclusions and screens that separate the Pluton from adjacent Jurassic Plutons, preservation of a ghost tectonostratigraphy in the distribution of the inclusions, and rare interphase contacts. The solid-state tectonic fabric in the wall rocks and the magmatic, submagmatic, and weak solid-state fabrics in the McDoogle Pluton all are concordant and record northeast-southwest horizontal shortening, subvertical extension, and a significant component of northeast-side-up simple shear. Intrusive contacts generally are concordant with the fabrics but, where discordances occur, the wall-rock fabric invariably is truncated by the contact. However, late synkinematic emplacement of the McDoogle Pluton is indicated by synintrusive boudinage of apophyses of the Pluton and by the overall concordance of Pluton fabrics including magmatic lineation. Zircon U-Pb isotope dates were obtained from the quartz monzodiorite central phase of the McDoogle Pluton (94 ± 4 Ma), the mafic granodiorite border phase (94.8 ± 0.6 Ma), and an older hornblende granodiorite included in the central phase (97.6 ± 0.4 Ma). Granodiorite orthogneiss in the wall rock yielded a U-Pb zircon date of 164 +2.1/–6.8 Ma, which we interpret to be the crystallization age and which is indistinguishable from a new age of 164.5 ± 2.3 Ma for the Twin Lakes Pluton. A U-Pb titanite date of 94.4 ± 0.9 Ma from the 164 Ma orthogneiss sample may reflect thermal effects of the intruding McDoogle Pluton, synkinematic growth of titanite in the shear zone, or perhaps both. The age of the Sawmill Lake shear zone that hosts the McDoogle Pluton is bracketed between 148 Ma, the age of the Independence dike swarm, and 92 Ma, the age of the Lamarck Pluton that crosscuts both the McDoogle Pluton and the shear-zone fabrics. Regional evidence suggests a shear-zone age younger than 110 Ma, but older deformation is possible. The predominance of horizontal shortening over transcurrent motion and an age older than 90 Ma exclude a direct relationship to the dextral Sierra Crest shear system, which has been proposed to pass near the study area. The location, age constraints, and kinematics of the shear zone are consistent with both the later stages of movement in the East Sierran thrust system and isostatic sinking of the arc magmatic complex into its substrate.
Giovanni Guglielmo - One of the best experts on this subject based on the ideXlab platform.
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Nested Plutons as megageopetal structures: the Merrimac Plutons, northern Sierra Nevada, California
Geological Journal, 1993Co-Authors: Giovanni GuglielmoAbstract:Contacts within nested Plutons are crucial for constraining the relative timing of Pluton emplacement and the internal geometry of composite Plutons. Exposures in orogenic belts are commonly discontinuous, however, disguising these contacts. In this paper, the Merrimac Plutons in the northern Sierra Nevada of California are used as an example of how composition and foliation patterns can allow the definition of unexposed contacts and identify nested Plutons. Image analysis techniques were used to determine modal compositions of a total of 52 samples from the Merrimac Plutons. The integrated analysis of compositional data and foliations patterns reveals a critical contact within the Plutons, and suggests that the Merrimac Plutons indicate way-up towards the north-east at the time of emplacement 142 ± 3 Ma ago. This paper provides guidelines for recognizing nested Plutons in poorly exposed areas and shows that consistent structural and compositional assymmetries within nested Plutons can be used as regional top-direction indicators.
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Magmatic strains and foliation triple points of the Merrimac Plutons, northern Sierra Nevada, California: implications for Pluton emplacement and timing of subduction
Journal of Structural Geology, 1993Co-Authors: Giovanni GuglielmoAbstract:Abstract Cross-cutting relationships between regional structures and post-tectonic Plutons of known age are commonly used to date regional deformation in orogenic belts. In order to show that a Pluton is post-tectonic one must demonstrate that the strains within the Pluton are not due to regional tectonic processes. This paper reports strain measurements associated with Pluton emplacement in northern Sierra Nevada. These strain data and a microstructural analysis indicate that strains within the Merrimac Plutons are due to igneous not tectonic processes, which strengthens the hypothesis that the Plutons were emplaced after the formation of regional structures and melanges. Radiometric ages of the Merrimac Pluton, in concert with structural data, place a more reliable upper Jurassic limit on the age of the subduction in the Western Belt of northern Sierra Nevada. This paper also reports constrictional strains around Plutons, and suggests that the Merrimac Plutons contributed significantly to the ductile strains observed in the wall rocks.
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3-D computer graphics in modeling Pluton emplacement
Computer Graphics in Geology, 1992Co-Authors: Giovanni GuglielmoAbstract:Structures which occur around Plutons provide crucial data by which to analyze the deformational history in orogenic belts, and computer modeling is a powerful method by which to study the genesis of these structures. The complex interplay of variables during Pluton emplacement dramatically increases the complexity of the simulation. To overcome these difficulties, a combination of computer techniques such as 3-D viewing, rendering, and an interactive graphical user interface was used. These techniques allow simulation of Pluton expansion in a crust undergoing tectonic deformation. 3-D viewing was critical for establishing the orientation, distribution and position of, structures around the Pluton. The interactive nature of the simulation allowed not only reading of complex input parameters and reliable evaluation of complex output, but also the real-time analysis of progressive deformation. Finally, rendering allowed both the realistic visualization of strain and structures around the Pluton, and the creation of a new strain diagram that integrates the analysis of various strain parameters. As a result of the simulation, the strain patterns and structures which were modeled provided useful insights on the processes and structures related to Pluton emplacement and tectonic deformation in orogenic belts. In addition this simulation demonstrated that computer graphics techniques can be not only convenient but may be required for the proper visualization and interpretation of complex geological simulations.
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Kinematics and strain analysis of Pluton emplacement: field and three-dimensional computer model studies
1991Co-Authors: Giovanni GuglielmoAbstract:Structures within and around Plutons provide crucial data to analyze the deformational history in orogenic belts. However, these structures are often difficult to interpret in part because of insufficient exposures, lack of quantitative measurements of strains within and around Plutons, and the need for quantitative theoretical models to explain these strains and structures. This dissertation tackles these problems by two approaches: (1) a field study of the Merrimac Pluton, northern Sierra Nevada, which addresses structural, strain, and composition measurements, and (2) three-dimensional computer modeling of Pluton emplacement and tectonic deformation. As a result of this study, insights were produced on (1) origins of strains and structures around Plutons in general and deformation history of the Merrimac Pluton in specific; (2) probable timing of Jurassic subduction in northern Sierra Nevada; and (3) computer graphics techniques useful in modeling structures in orogenic belts. Image analysis techniques were used to determine modal compositions of 52 samples within the Merrimac Pluton. The integrated analysis of this composition data with foliation patterns within the Pluton indicates that, contrary to previously believed, the Merrimac Pluton is composed of two independent bodies; the northern Pluton was emplaced after the intrusion of the southern Pluton; and both Plutons were either obliquely emplaced or tilted 30 degrees. This dissertation reports strain measurements associated with Pluton emplacement in northern Sierra Nevada. These measurements indicate that strains within the Merrimac Pluton are due to igneous rather than tectonic processes, which strengthen the hypothesis that the Merrimac was emplaced after the formation of regional structures and melanges. Therefore, the age of the Merrimac Pluton (142 $\pm$ 3 Ma) places an upper limit on the age of the Jurassic subduction in northern Sierra Nevada. In addition, this dissertation reports the occurrence of constrictional strains at ends of a Pluton. These field data constrain 3-D numerical simulation of Pluton emplacement in a regional strain field. This simulation to date has demonstrated that (1) computer graphics techniques, such as interactive modeling and 3-D rendering, is not only convenient but often required to visualize and interpret complex geological simulations, and (2) structures previously believed to be produced by syn-tectonic Pluton expansion under non-coaxial kinematic schemes can also be produced by coaxial tectonic deformation.