A la base du complexe filonien, les fluides réagissent avec le diabase à 400°C et 400 bars pour former des épidosites (roches riches en épidote et quartz). Ces épidosites seraient liées aux dépôts des VMS. Les relations entre la mise en place des dykes, leur altération en épidosite et la déformation régionale restent mal comprises. Des expérimentations sur du métadiabase échantillonné dans le complexe de Troodos (Chypre) ont été réalisées pour, 1) contraindre les conditions P-T-fO2-composition du fluide de la réaction d’épidotisation et 2) quantifier les relations entre la perméabilité et la lithologie au cours de la déformation.A Troodos, deux grands types d’épidosite ont été observés: 1) une épidosite pénétrative au cœur des dykes et parallèle aux bordures figées et 2) des assemblages d'épidote et quartz sous présentant des fronts d'altération dans les joints de refroidissement ou sous forme de veines.De l’épidote a été synthétisée dans un autoclave statique avec un chauffage externe à 500°C et 2500 bars. Deux paramètres sont essentiels à l’épidotisation du métadiabase : la fugacité en oxygène et la composition du fluide (enrichi en Ca et Fe). Cependant, il y a un problème évident de nucléation à 400°C et 400 bars.Des mesures de perméabilité ont été réalisées dans un autoclave dynamique type Paterson par infiltration d’Ar et d’eau durant la déformation coaxiale. La perméabilité du métadiabase avant déformation est d'environ 10-20 m2. Après fracturation de l'échantillon, la perméabilité a augmenté jusqu'à 10-19 m2. En outre, la perméabilité de l’épidosite est d'environ 10-19 m2. Ce qui suggère que l’épidotisation génère de la porosité.Le problème principal est l’initiation de l’écoulement du fluide hydrothermale en raison de l'imperméabilité du diabase. Deux hypothèses sont proposées : 1) le fluide circule via les fractures et les fissures et 2) les fluides circulent dans une roche à l’état subsolidus (importance du dégazage). / In the deepest zone of oceanic crust, the fluids react with the sheeted diabase dikes at 400°C and 400 bars to form epidosites by enrichment in epidote and quartz. These epidosites are suggested to be linked to VMS deposits. The relations and the timing of the emplacement of diabase dikes, their alteration in epidosite and the regional deformation remain unclear. Experiments on metadiabase sampled in the Troodos complex (Cyprus) were performed, 1) to stress the P-T-fO2-fluid composition conditions of the reaction of epidotization and, 2) to quantify interrelations between the permeability and the lithology during deformation.In Troodos, two major types of epidosite were observed: 1) a pervasive epidosite in the core of dikes and a banding which is parallel to chilled margins and, 2) assemblages of epidote and quartz as alteration fronts in cooling joints or in the form of veins cross-cutting non-epidotized dikes.Epidote was synthetized in a static autoclave with external heating at 500°C and 2500 bars. Two parameters are essential to synthesize epidote from metadiabase: the oxygen fugacity and the composition of the fluid (enriched in Ca and Fe). However, there is an obvious problem of nucleation at 400°C and 400 bars.Measurements of permeability during coaxial deformation have been performed in a Paterson apparatus by infiltration of Ar and water. The permeability of the metadiabase prior deformation is about 10-20 m2. After fracturation of the sample, the permeability increased rapidly up to 10-19 m2. Moreover, the permeability of epidosite is about 10-19 m2. So this suggests that epidotization generates porosity.The main problem is the initiation of fluid flow because of the impermeability of diabase. Two hypotheses are proposed: 1) fluids flow via fractures and cracks and, 2) fluids flow into a rock in a subsolidus state (importance of degassing).

Thesis (M.S.)--Indiana University, 2008. / Department of Earh Sciences, Indiana University-Purdue University Indianapolis (IUPUI). Advisor(s): Kathy J. Licht. Includes vita. Includes bibliographical references (leaves 149-154).

The sheeted complex of the ~92 Ma Tenpeak pluton, in the Northern Washington Cascades crystalline core, forms a <1.5-km wide zone with a moderate, NE-dip at the SW margin of the pluton. Sheeted magmatic complexes, such as the one in the Tenpeak pluton, are common in plutons and represent examples of incremental growth of plutons. Though it is widely accepted that plutons are constructed incrementally over prolonged timescales of several million years, it is not clear if and to what degree individual batches of magma interact, the timing and size of each magma pulse, and the role, timing, and location of magmatic differentiation. This project uses a combination of field evidence, bulk rock chemistry, and mineral geochemistry to address the (1) role of magma mixing and fractionation, (2) constraints on the relative timing of magma differentiation, (3) diversity of mixing styles preserved, and (4) physical properties that dictate how individual batches of magma interact within this sheeted complex. Rock samples were collected throughout the complex from mafic, felsic, dioritic, thinly-banded, and gradational sheets. Field evidence shows a range of sheet contacts that vary from sharp to diffuse, strong prevalence of mafic enclaves, and localized cases of mechanical mixing in which plagioclase feldspars from a felsic sheet are incorporated into a mafic sheet. In general, sheet thickness increases farther from the contact with the White River shear zone. The bulk rock and mineral chemistry suggests that the felsic magmas in sheets formed independently from the more mafic and hybridized sheets. The composition of the felsic sheets cannot be modeling by binary mixing processes involving mafic and felsic magmas or result from fractionating the most mafic magmas. However, mass-balance calculations using a linear least-squares mass balance calculation and Rayleigh fractionation models indicate that it is possible to explain the range of felsic compositions by internal, crystal fractionation driven mostly by plagioclase crystallization (~40-58%). Negative Eu anomalies in amphiboles from the felsic sheets imply that plagioclase fractionation commenced prior to the onset of amphibole crystallization. With the exception of the most primitive mafic sheet sampled, the mafic and hybridized sheets represent variable proportions of the mafic parental magma and the range of felsic differentiated magmas. Efficient mixing that resulted in these mafic to hybridized magmas must also have occurred prior to mineral growth as the mineral chemistry reflects intermediate, mixed compositions. The bulk rock and mineral chemistry of the most primitive, mafic sheet suggest that it did not mix with any felsic magmas. However there is evidence that the mafic sheet underwent plagioclase fractionation prior to emplacement. This is evident by lower bulk rock Sr/Ba relative to calculated Sr/Bamelt of plagioclase that cannot be reconciled without removing ~40-58% plagioclase. In contrast to the felsic sheets, the amphiboles from this mafic sheet lack Eu anomalies implying that amphibole crystallization occurred prior to major plagioclase fractionation. Chemical evidence reveals that magma mixing played an important role in controlling the chemical composition of individual sheets and field observations suggesting that there was a range of mixing styles. Throughout the sheeted complex, there are localized sites of mechanical mixing where plagioclase phenocrysts from adjacent felsic sheets are mechanically mixed into mafic sheets. Evidence for mechanical mixing is present across both sharp and gradational contacts. This implies varying rheological and viscosity contrasts between different sheets, though in both cases crystallinity and viscosity appears sufficiently low to allow crystals to migrate across sheet contacts. Variability in sheet thickness and contact type suggests that the physical parameters (i.e. temperature, viscosity, rheology, and magma flux) of the system continue to evolve throughout the formation of the sheeted complex. Near the White River, sheets are thin and more heterogeneous but become progressively thicker (>302 m) and more felsic in composition up-section. The composition of plagioclase and amphibole is remarkably uniform in all of the felsic sheets suggesting that each sheet formed from an array of felsic parental magmas. Thicker, felsic sheets most likely reflect hotter conditions where larger magma fluxes could be accommodated or viscosity-temperature contrasts that were low enough to allow for efficient mixing between two adjacent sheets and therefore erase sheet contacts. / Graduation Date: 2013

Hydrothermal fluid circulation is an important process in the formation and evolution of ocean crust. A tectonic window located at Pit Deep (NE corner Easter Microplate) provides an ideal location to examine a 3-dimensional view of ocean crust formed at the fast-spreading East Pacific Rise. This study focuses on the base metal (Cu, Ni, Mn, Co, Zn, and Pb) content of the bulk rock and mineral components in the sheeted dike complex. There is no observable trend of metal mobility with depth, geographic location, or dominant alteration phase. Secondary mineral analyses (using LA-ICP-MS) show that metals are redistributed throughout the sheeted dikes, entering into secondary sulphides, chlorite, and amphibole. Temperature and mineral stability is a primary control of metal mobility in these rocks. Due to highly variable metal concentrations and observed temperatures of alterations, the hydrothermal cell is suggested to be a continuously evolving system, and can cause the large variability observed in the metal distribution in the sheeted dikes. / Graduate / 0996 / 0411 / 0372

Indiana University-Purdue University Indianapolis (IUPUI) / Differential exhumation within the eastern Transverse Ranges of southern California has revealed a tilted crustal section that provides a unique view into the architecture of the Mesozoic arc. At the base of this crustal section is a group of well-exposed sheeted plutons. Well-developed, gentle to moderately dipping magmatic and solid-state fabrics within these plutons are regionally consistent, margin-parallel, discordant to internal sheeting and layering, and are generally parallel to equivalent host rock structures and fabrics. In some plutons, magmatic foliations define regional fold structures, thus recording regional contraction during chamber construction. Collectively, field mapping and fabric analyses within these sheeted plutons show that the observed fabric patterns are better explained by regional deformation rather than internal magma chamber processes. This interpretation is in direct contrast to previous mapping in the region. The host rocks also record complex processes during sheeted pluton emplacement. Deflection of host rock foliations and structures into parallelism with pluton contacts suggest that downward ductile flow played a role in making space for these plutons. However, evidence of regional faulting and shearing is not observed, suggesting that they did not play a significant role. Although there is considerable microstructural variability within each pluton, the observed microstructures are generally consistent with a transition from magmatic to submagmatic/ high-temperature solid-state deformation. Magmatic microstructures are defined by euhedral to subhedral plagioclase, hornblende, and biotite that do not show significant internal crystal-plastic deformation. Evidence for high-temperature solid-state deformation includes high-temperature grain boundary migration in quartz, plagaioclase, potassium feldspar, and hornblende; chessboard extinction in quartz; and ductile bending in plagioclase and hornblende. Microstructural observations also indicate that mafic and intermediate compositions record stronger magmatic fabrics than felsic compositions. Based on the structural and microstructural observations presented in this study, I interpret that these sheeted plutons were emplaced into an active continental arc setting that was undergoing regional contraction. The strong magmatic fabrics and high-temperature solid-state overprinting is likely a consequence of regional deformation during crystallization. The weak fabrics within upper crustal plutons relative to the strong fabrics within the mid-crustal plutons suggest that deformation was largely localized to the more compositionally heterogeneous mid-crustal portions of the arc structure.