Magnetic fabrics and compositional evidence for the construction of the Caleu pluton by multiple injections, Coastal Range of central Chile

Parada, Miguel A.; Roperch, Pierrick; Guiresse, Claudio; Ramírez, Ernesto

doi:10.1016/j.tecto.2004.12.032

Cited by 13 publications

(5 citation statements)

References 38 publications

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“…Using field and geophysical evidence, Glazner et al (2004) and Parada et al (2005) also concluded that large and broadly homogeneous plutons can accumulate incrementally, from many smaller magma batches. Such pulses were predicted by Clemens & Mawer (1992), based on consideration of the mechanics of dyke ascent of granitic magma.…”

Section: Discussionmentioning

confidence: 99%

Chemical structure in granitic magmas – a signal from the source?

Clemens¹,

Helps

Stevens³

2009

Earth and Environmental Science Transactions of the Royal Socie

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Though typically exhibiting considerable scatter, geochemical variations in granitic plutons and silicic volcanic deposits are commonly modelled as products of differentiation of originally homogeneous magmas. However, many silicic igneous bodies, particularly those classified as S-types, are internally heterogeneous in their mineralogy, geochemistry and isotope ratios, on scales from hundreds of metres down to one metre or less. The preservation of these heterogeneities supports recent models for the construction of granitic magma bodies through incremental additions of numerous batches (pulses) of magma derived from contrasting sources. Such pulses result from the sequential nature of the melting reactions and the commonly layered structure of crustal magma sources. Internal differentiation of these batches occurs, but not generally on the scales of whole magma chambers. Rather than being created through differentiation or hybridisation processes, at or near emplacement levels, much of the variation within such bodies (e.g. trace-element or Mg# variation with SiO2 or isotope ratios) is a primary or near-source feature. At emplacement levels, the relatively high magma viscosities and slow diffusion rates of many chemical components in silicic melts probably inhibit processes that would lead to homogenisation. This permits at least partial preservation of the primary heterogeneities.

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Section: Discussionmentioning

confidence: 99%

Chemical structure in granitic magmas – a signal from the source?

Clemens¹,

Helps

Stevens³

2009

Earth and Environmental Science Transactions of the Royal Socie

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“…Fabric development may result from internal (e.g., flow, mixing, thermal convection) or external (regional strain) processes. Previous workers have interpreted magmatic fabrics in plutons as a record of either magmatic processes at the emplacement level (Cruden and Launeau, 1994;Tobisch and Cruden, 1995;Archanjo et al, 1999;Ferré et al, 1999;de Saint-Blanquat et al, 2001Parada et al, 2005;Stevenson et al, 2007;Naibert et al, 2010;Archanjo and Campanha, 2012;Gutiérrez et al, 2013;Morgan et al, 2013) or regional strain during syntectonic emplacement (Brun and Pons, 1981;Brun et al, 1990;Archanjo et al, 1995;Leblanc et al, 1996;Benn et al, 1997Benn et al, , 1999Benn et al, , 2001Sen et al, 2005;Mamtani et al, 2013). Solid-state (or subsolidus) fabrics in granitic intrusions are formed by crystal-plastic deformation of phases in the absence of melt.…”

Section: Introductionmentioning

confidence: 99%

Internal fabrics of the Idaho batholith, USA

et al. 2016

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The Idaho batholith of the North American Cordillera is a large and long-lived silicic intrusive center. We studied fabrics at the regional scale within the different intrusive suites of the Idaho batholith, using microstructural characterization, anisotropy of magnetic susceptibility measurements, and shape preferred orientation analyses. Each studied outcrop was collocated with existing U-Pb zircon geochronology and ongoing (U-Th)/He zircon thermochronology results. Three new 40 Ar/ 39 Ar biotite ages, collocated with the existing U-Pb zircon ages, constrain the cooling rates within the batholith. The presence of dominantly magmatic microstructures allows us to interpret the results relative to the U-Pb zircon ages and observe spatial and temporal patterns of fabric development. The early (pre-80 Ma) intrusive suites exhibit solid-state microstructures that show a consistent orientation only in the western part of the batholith. Fabrics in the 83-67 Ma Atlanta peraluminous suite are weak and inconsistent in orientation, despite emplacement during regional contraction. We hypothesize that the lack of consistently oriented fabrics in the Atlanta lobe results from either: (1) topographic effects that caused local extensional/neutral strain environments in the upper parts of a crustal plateau; or (2) emplacement in thin, horizontal magmatic sheets. In contrast, fabrics within the 66-53 Ma Bitterroot peraluminous suite are well developed and consistently oriented (NW-striking; NE-dipping), recording localized contraction during magmatism.

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“…However, the regime and nature of magma flow generating AMS data remains controversial. Some studies have interpreted AMS data as a record of flow during magma emplacement [e.g., McNulty et al ., ; Parada et al ., ; Be Mezeme et al ., ; Stevenson et al ., ], suggesting that magnetic fabrics record the early stages of pluton growth. Indeed, AMS patterns in small magma bodies with high cooling rates (e.g., lava flows, sills, and dikes) are consistent with such emplacement‐related flow [ Dragoni et al ., ].…”

Section: Introductionmentioning

confidence: 99%

“…Both regional tectonic strain (clearly associated with shear and fault zones) and emplacement and/or magma flow‐related strain can be determined through anisotropy of magnetic susceptibility (AMS) fabrics in plutons [e.g., Žák and Paterson , ; Archanjo et al ., ]. Several studies have indicated that AMS data can serve as a record of strain directions in tectonically unperturbed plutons and can provide insight into the dynamics of magma reservoirs, since magnetic fabrics are thought to be produced by magma flow [ McNulty et al ., ; Parada et al ., ; Gil‐Imaz et al ., ]. Interpretations of the AMS data as indicators of magma flow have been based on the following observations [e.g., Knight and Walker , ; Dragoni et al ., ; McNulty et al ., ; Be Mezeme et al ., ; Archanjo et al ., ]: (1) In many cases, magnetic fabrics within plutons do not coincide with regional host rock structures, such as fractures and shear zones; (2) lineation is concordant with measured magma flow directions in dikes and lava flows and coincides with the main elongation of plutons; and (3) foliation is generally parallel to the vertical wall showing a high foliation dip near vertical walls that incrementally decrease in dip toward the upper levels and interior of plutons, yielding a roughly concentric foliation pattern.…”

Section: Introductionmentioning

confidence: 99%

Late‐stage magma flow in a shallow felsic reservoir: Merging the anisotropy of magnetic susceptibility record with numerical simulations in La Gloria Pluton, central Chile

et al. 2013

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[1] La Gloria Pluton is a 10 Myr old epizonal intrusion located in the southern Andes. We present anisotropy of magnetic susceptibility data that indicate a magnetic fabric that is mainly oblate. We find that lineations are weak and have a N-NW trend with a nearly horizontal dip, while foliations are more pronounced, have NW trends, and have dips that vary from vertical at the walls of the intrusion to horizontal at the center and under the roof of the chamber. To interpret these magmatic fabrics, we developed a time-dependent 2-D magmatic fluid dynamic numerical simulation. Our model is calibrated with MELTS and accounts for the coupled processes of cooling, crystallization, and degassing of a magma chamber. Simulations indicate that the resulting convective flow pattern in the crystallizing reservoir is consistent with the magnetic fabric, which is largely produced in the shear zone between the convecting liquid-dominated core and the growing solidification fronts adjacent to the walls. The magnetic fabric records the last increment of strain induced by convective magmatic flow in the cooling reservoir during crystallization at the rheological magma locking point along solidification fronts. Despite the small size of the pluton, the core of the chamber remains thermally insulated from the colder host rocks, surviving up to 20 kyr above the solidus, which allows enough time for the extraction of residual leucogranitic melt and partial late magmatic reactive recrystallization. The results of the simulations are also consistent with the previously determined compositional and mineralogical zonation patterns in the pluton.

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Magnetic fabrics and compositional evidence for the construction of the Caleu pluton by multiple injections, Coastal Range of central Chile

Cited by 13 publications

References 38 publications

Chemical structure in granitic magmas – a signal from the source?

Chemical structure in granitic magmas – a signal from the source?

Internal fabrics of the Idaho batholith, USA

Late‐stage magma flow in a shallow felsic reservoir: Merging the anisotropy of magnetic susceptibility record with numerical simulations in La Gloria Pluton, central Chile

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