Deformation and Magma Transport in a Crystallizing Plutonic Complex, Coastal Batholith, Central Chile GEOSPHERE; V

Research Paper

GEOSPHERE Deformation and magma transport in a crystallizing plutonic complex, Coastal Batholith, central Chile GEOSPHERE; v. 11, no. 5 Jeffrey R. Webber1,*, Keith A. Klepeis1, Laura E. Webb1, José Cembrano2,4, Diego Morata3,4, Gabriela Mora-Klepeis1, Gloria Arancibia2,4 1Department of Geology, University of Vermont, Delehanty Hall, 180 Colchester Avenue, Burlington, Vermont 05405-0122, USA doi:10.1130/GES1107.1 2Departamento de Ingeniería Estructural y Geotécnica, Pontificía Universidad Católica de Chile, Avenida Vicuña Mackenna 4860, Santiago 7820436, Chile 3Departamento de Geología, Facultad de Ciencia Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Casilla 13518 Correo 21 Santiago, Chile 13 figures 4Centro de Excelencia en Geotermia de los Andes (CEGA, Fondap-Conicyt, 15090013)

CORRESPONDENCE: [email protected] ABSTRACT INTRODUCTION CITATION: Webber, J.R., Klepeis, K.A. Webb, L.E., Cembrano, J., Morata, D., Mora-Klepeis, G., and Arancibia, G., 2015, Deformation and magma The Carboniferous–early Permian Santo Domingo complex in coastal Studies of the structure and deformation history of batholiths are essen- transport in a crystallizing plutonic complex, Coastal Chile (33.5°S) preserves magmatic structures that allowed us to partially tial to our understanding of arc magmatism, orogenesis, and the evolution Batholith, central Chile: Geosphere, v. 11, no. 5, reconstruct and compare the deformation histories of two intrusive units of continental lithosphere. Batholiths record magma transport and emplace- p. 1–26, doi:10.1130/GES01107.1. within a mid-upper crustal zoned pluton. The oldest history is preserved ment processes, which are primary mechanisms of transferring heat and mass

in the Punta de Tralca tonalite, where microgranitoid enclaves record the through the lithosphere. Key questions include (1) how the constituent mag- klepeis_01107 1st pages / 1 of 26 Received 23 July 2014 Revision received 20 February 2015 emplacement and partial assimilation of mostly mafic magma into an in- mas of batholiths interact, differentiate, and grow and (2) how different styles Accepted 10 July 2015 termediate host. Enclaves record early foliation development by a mechani- of deformation influence magma movement and emplacement. Ultimately, the cal sorting and alignment of minerals during hypersolidus flow in melt-rich link between deformation and magma transport in a crystallizing pluton may magma currents, followed by diffusion creep and sliding along melt-coated provide insight into the timing, volumes, and styles of silicic arc volcanism. crystals. Structures in a weaker, tonalitic matrix record compaction, flatten- A great deal of research over the past decade has focused on the physi ing, and near-solidus deformation as porous flow, aided by brittle defor cal, petrologic, and temporal relationships between plutonic and volcanic mation, drained residual melts. These processes produced penetrative magmas, including the conditions necessary for large volumes of magma to S > L fabrics (i.e., planar more dominant that linear fabric) in an increas- exist in subvolcanic magma chambers (Bachmann et al., 2002; Bachmann and ingly viscous, crystal-rich mush and promoted folding, fracturing, shearing, Bergantz, 2004, 2006; Huber et al., 2011; Hodge and Jellinek, 2012; Caricchi and crystal-plastic deformation as the mush approached its solidus. The et al., 2012; Pistone et al., 2013; Coint et al., 2013). Many studies have concluded deformation disrupted igneous layering and helped mobilize and concen- that large zoned intrusions are assembled incrementally with small, distinct trate melt-rich aggregates, forming diffuse patches and dikes that intruded batches of magma that are emplaced over several million years (e.g., Coleman previously deformed enclaves and matrix and aided pluton differentiation. A et al., 2004; Glazner et al., 2004; Bartley et al., 2006; Schaltegger et al., 2009; different deformation history is recorded by the Estero Córdoba dike, which Coint et al., 2013). Nevertheless, there remains substantial disagreement on intruded and interacted comagmatically with the Punta de Tralca tonalite. whether these small magma batches interact with one another in different set- The dike records how magma flow near stiff boundaries resulted in veloc- tings and, if they do, the nature of these interactions. ity gradients that drove deformation during magma replenishment. This One common assumption in some studies of magmatic processes is that deformation reset inherited enclave fabrics, increased ductile stretching magmas move and differentiate mainly as crystal-poor liquids and are the and winnowing, and formed linear (L>S) fabrics. This example illustrates products of an evolution linked to simple cooling prior to volcanic eruption how different styles of deformation assisted magma movement through a (Bachmann and Bergantz, 2006). However, a growing body of work provides mid-upper crustal magma chamber and highlights the diverse origins and evidence that magmas can crystallize to nearly solid crystal-rich mushes that significance of structures generated by deformation in magmas of variable are then reheated, partially remelted, and remobilized before eruption (Bach- crystal-melt ratios. mann et al., 2002; Bachmann and Bergantz, 2004, 2006; Yoshinobu et al., 2009; Pistone et al., 2013; Coint et al., 2013). These latter studies suggest that the indi vidual magma batches that make up large zoned magma chambers need not crystallize completely, but instead may be reactivated and interact extensively

For permission to copy, contact Copyright *Present address: Department of Geosciences, University of Massachusetts Amherst, 611 North with one another. A primary mechanism by which these reactivations occur Permissions, GSA, or [email protected]. Pleasant Street, Amherst, Massachusetts 01003-9297, USA may involve the intrusion of mafic, or possibly even intermediate, magma

GEOSPHERE | Volume 11 | Number 5 Webber et al. | Deformation and magma transport in the Coastal Batholith, Chile 1 Research Paper

through dikes. The occurrence of microgranitoid enclaves in many magmas (Figs. 1B and 2), where we recorded a wide variety of magmatic structures supports this hypothesis and provides a potential means for evaluating how in detail, including mineral foliations and lineations of different age, igneous the input and resident magmas mixed, mingled, deformed, and differentiated banding, shear zones, folds, sigmoidal fractures, en echelon tension gashes, (Hodge et al., 2012; Hodge and Jellinek, 2012; Caricchi et al., 2012). boudinage, faults, and dikes (Figs. 3–6). These features, and a domainal pres- Another problem related to determining how magmas interact during re- ervation of structures, allowed us to establish a relative sequence of events plenishment events centers on how we use complex igneous structures to and partially reconstruct the deformation histories of the two units. A com- reconstruct the history. Despite their potential value, the use of igneous parison of these histories allowed us to examine the following processes: structures to reconstruct the deformation histories of magmatic bodies is (1) interactions between mafic and intermediate magmas during the replen- commonly difficult. Problems arise because igneous foliations and lineations ishment and remobili zation of a crystal-rich magma chamber; (2) mechanisms are easily reset during cooling and exhumation and may only record the final of crystal-melt segregation and expulsion in a viscous, crystallizing magma increments of strain as crystal-rich mushes approach their solidi (Benn and chamber; (3) microstructures and deformation mechanisms in a crystallizing Allard, 1989; Ildefonse et al., 1997; Paterson et al., 1998). In addition, most of magma as it transitions from flow in melt-rich magma currents to near-solidus the deformation in a magma body may be accommodated by flow in melt, deformation where crystal-plastic deformation occurred in the presence of which can leave little to no record (Paterson et al., 1998; Vernon and Paterson, melt; and (4) patterns of three-dimensional flow and the mechanisms of folia- 2006; Memeti et al., 2010; Mamtani, 2014). In general, most objects in plutons tion development in a crystallizing pluton. and dikes make poor strain markers because their initial shapes are unknown To illustrate the results, we divide our data presentation into three sections. and their final shapes may reflect a wide variety of processes, most of which First, we define the various categories of igneous structures and describe the are spatially and temporally variable (Paterson et al., 2004). The result is that different styles of magmatic deformation that occurred within the two intru-

the origin and significance of structures formed during magmatic flow and the sions (Figs. 2–6). Second, we report microstructures and other mineral tex- klepeis_01107 1st pages / 2 of 26 deformation of crystal-melt aggregates can be difficult to establish in the field. tures that record transitions from hypersolidus flow in melt-rich magmas to In particular, reliable criteria are needed to document the kinds of structures crystal-plastic deformation in crystal-rich mushes near the solidus (Figs. 3 and that form during transitions from hypersolidus flow in melt-rich magmas to 7). We then compare the characteristics of mineral and enclave fabrics at the deformation near the solidus where crystal-plastic deformation occurs in the contact between the two intrusions to evaluate whether they record different presence of migrating melts (Paterson et al., 1989, 1998; Vernon, 2000; Pawley styles and increments of deformation (Figs. 8–11). Our interpretations, and the and Collins, 2002; Vernon et al., 2004; Yoshinobu et al., 2009). These relation- observations that support them, are summarized in six textural zones (Fig. 12) ships, if established, could be combined with thermal and rheological model- that describe areas of the plutonic complex that exhibit similar structures and ing to more precisely characterize magma behavior. processes. These processes include magma movement in dikes, the mingling A potentially promising approach to resolving some of these issues may and partial assimilation of mafic-intermediate magmas with different effective be in comparisons among mesoscale and microscale structures that record viscosities, the fracture and shear of crystal-melt aggregates, melt mobilization different increments of deformation in crystal-melt aggregates, especially if and reintrusion in a crystallizing magma, melt expulsion to forming a viscous their relative sequence and local context can be determined. Although obtain- crystal-rich mush, and the late-stage flattening and compaction of that mush. ing the full rheological and strain history of a crystallizing magma still appears As others have pointed out (e.g., Vernon and Paterson, 2006; Memeti et al., improbable, a close comparison of magma interactions and the deformation 2010; Mamtani, 2014), similar structures and processes may be common in mechanisms that result in mineral fabrics, enclaves, and other structures may granitoids, although many dikes and plutons may not record them. provide some information on the styles and types of magmatic strains and on the rheological transitions that occur in crystallizing magmas (Paterson et al., 1998, 2004; Pawley and Collins, 2002; Huber et al., 2011; Hodge and Jellinek, GEOLOGICAL BACKGROUND 2012; Caricchi et al., 2012; Yoshinobu et al., 2009). One aim of this paper is to test this approach using the Santo Domingo complex (Siña and Parada, The coastal range of central Chile (lat 33°–34°S) is characterized by Paleo- 1985; Siña, 1987a, 1987b; Wall et al., 1996; Parada et al., 1999) of coastal Chile zoic to Mesozoic plutons (Hervé et al., 1988), hypabyssal intrusive rocks (Wall (Fig. 1). The significance of this example is the rich and well-exposed array of et al., 1996), and marine and terrestrial volcaniclastic sedimentary sequences mesoscopic and microscopic structures that preserve different stages of the (Vergara et al., 1995). Three plutonic belts, which decrease in age toward the deformation history of a mid-upper crustal zoned pluton. east (Levi, 1973), dominate the batholith (Fig. 1A), i.e., the Santo Domingo, In this paper we present the results of a field-based analysis of igneous Papudo-Quintero, and Illapel complexes (Parada et al., 1999). Along the coast, structures exposed in a 3 km coastal transect across the Punta de Tralca and the plutonic rocks were emplaced into granitic gneiss and metasedimentary Estero Córdoba intrusions (Parada et al., 1999) between the towns of Isla rock of the Valparaíso metamorphic complex (Wall et al., 1996). Negra and El Tabo (Fig. 1A). As part of this work, we examined outcrops at Isla The Santo Domingo complex (Figs. 1 and 2) includes two main intrusive Negra and completed a 400 m transect across the contacts of the 2 intrusions units (Siña and Parada, 1985; Siña, 1987a, 1987b; Wall et al., 1996) referred to

GEOSPHERE | Volume 11 | Number 5 Webber et al. | Deformation and magma transport in the Coastal Batholith, Chile 2 Research Paper

71° 45′ W 71° 30′ W 71° 15′ W 71° 00′ W 70° 45′ W 71° 41′ 00″ W 71° 41′ 50″ W A N B

33° 00′ S Valparaíso SOUTH C Laguna AMERICA

Coastal Córdoba 33° 26′ 45″ S Chile A Cordillera Study

33° 15′ S Punta de Isla Negra Area Tralca Study Area S poles to mag. fol. (n=60) 11IN01D a 11IN01E n mineral lineations (n=21) to SANTIAGO D (city) N El Tabo om D 11IN01A

i 11IN01C 33° 26′ 55″ S Las ng 33° 30′ S o 11IN01B Cruces com plex central Santo depression Domingo

0 15 km

11.IN.02.A klepeis_01107 1st pages / 3 of 26 33° 45′ S Tertiary Cretaceous volcanics poles to gneissic foliation (n=61) sedimentary rock & volcaniclastic sedimentary rock 33° 27′ 00″ S mineral lineations (n=28) Cretaceous plutonic Jurassic volcaniclastic rock (Illapel complex) sedimentary rock Jurassic granitoids Microgranitoid enclaves, Metapelites 11IN03C (Papudo Quintero granitoid (Punta de Tralca) of VMC 11IN03B 11.IN03A A′ Triassic-Jurassic Carboniferous & complex) Porphyritic granitoid Permian granitoids 11.IN.01.A 100 meters granitoids (Estero Córdoba) Sample location (Santo Domingo complex)

Figure 1. (A) Geologic map of the coastal range of central Chile, modified from Servicio Nacional de Geología y Minería (2002) and Wall et al. (1996). Red box indicates study area. (B) Geologic map of coastal exposures between Isla Negra and El Tabo, modified from Siña (1987a). Sample sites are shown. Cross section A-A’ is shown in Figure 2. VMC—Valparaíso metamorphic complex. (C) Equal area stereographic projection shows orientations of foliations and mineral lineations obtained from igneous rocks of the Santo Domingo complex (mag. fol.—magmatic foliation). (D) Equal area stereographic projection, the VMC.

here as the Punta de Tralca tonalite and the Estero Córdoba dike (Parada et al., ciled with those from the Valparaíso metamorphic complex, which has zircon 1999). The Punta de Tralca tonalite is oldest, and is a layered hornblende-biotite U-Pb ages from gneisses that range from ca. 290 Ma (Godoy and Loske, 1988) intrusion of mostly tonalitic and granodioritic composition that hosts numer- to 214 ± 1 Ma (Gana and Tosdal, 1996). K-Ar ages on biotite, amphibole, and ous fine-grained mafic and microgranitoid enclaves (to 50% by volume) (Figs. plagioclase from the gneisses also have yielded Middle–Late Jurassic ages 3A–3D). The close association of the enclaves with mafic dikes led Parada et al. (Cordani et al., 1976; Hervé et al., 1988; Gana et al., 1996). This range suggests (1999) to suggest that the enclaves represent dismembered dikes that were that the country rock of the batholith records a complex history of magmatism, comagmatic with their tonalite matrix. The younger unit includes a massive, metamorphism, and cooling. relatively enclave-poor tonalite dike that intrudes the Punta de Tralca tonalite. The emplacement depths of plutons within the Santo Domingo complex At its southeastern end, the Estero Córdoba also displays a mix of sheeted remain poorly understood. A single hornblende crystallization pressure of granitic dikes interfolded with layers of country rock (Fig. 2). 700 MPa reported by Siña (1987b) suggests depths of ~26 km. Chlorite- and The Santo Domingo complex appears to range in age from Carboniferous epidote-bearing veins that are cut by the El Tabo mafic dike swarm suggest to early Permian. Berg and Charrier (1987) obtained Carboniferous zircon ages exhumation to upper crustal levels by the mid-Cretaceous (Irwin et al., 1987; from a granitic xenolith in a mafic dike. A U-Pb zircon age of 291 ± 1 Ma (Godoy Creixell et al., 2009). Fission-track thermochronology confirms that the coastal and Loske, 1988) and an Rb-Sr whole-rock isochron age of 292 ± 2 Ma (Hervé rocks were at ~4–5 km depth by 102 ± 4 Ma (Gana and Zentilli, 2000). The mafic et al., 1988) suggest early Permian ages. These ages have yet to be recon- dikes (Creixell et al., 2006, 2009, 2011) have been attributed to an extensional

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Figure 2. Schematic cross section of the study area between Isla Negra and El Tabo (location shown in Fig. 1B), illustrating the structure of the Punta de Tralca and Estero Córdoba tonalites. Inset shows

foliations internal to (SA) and external to

(SB) enclaves. These and two other types

of foliations (SC, SD) are defined in the text. klepeis_01107 1st pages / 4 of 26

tectonic regime that preceded the development of Cretaceous volcaniclastic unit (Fig. 1B), igneous layering (striking 328°, dipping 63°NE) is steeper than at and marine sedimentary basins exposed to the east (Vergara et al., 1995). Thus, its northern end by >10° on average, and locally to 20°. Foliations in the Estero exhumation of the coastal rocks may have occurred concomitantly with sub- Córdoba dike strike more west and dip more gently than the enclave-rich ig- sidence in these basins as arc magmatism migrated eastward. neous layering of the Punta de Tralca by ~15° on average, and locally as much as 30°; this latter discordance results from the truncation of igneous layering by the younger dike. These and other discordances reflect deformation during REGIONAL STRUCTURE OF THE SANTO DOMINGO COMPLEX multiple magma injections that aided in establishing a sequence of events. The alignment of microgranitoid enclaves locally define a northeast-plung- Both the Punta de Tralca and Estero Córdoba intrusions display four cate- ing lineation on foliation planes (e.g., Fig. 3G). Hornblende, biotite, and plagio gories of multiple magmatic foliations and lineations. From oldest to youngest, clase crystals also locally are aligned and plunge 50°–60° to northeast on folia- these include: (1) aligned hornblende, plagioclase and quartz crystals inside tion planes, forming mineral lineations (Fig. 1C). Lineation trends in the Punta

enclaves (SA) (e.g., Figs. 2, 3B, and 3C); (2) a compositional banding defined de Tralca and Estero Córdoba units are statistically identical, although the data by flattened, stretched, and aligned enclave swarms and layers of leucocratic are more scattered at the northern end of the Punta de Tralca unit. This pattern

matrix material (SB) (Figs. 2–5); (3) a preferred alignment (SC) of primary plagio suggests that both units record similar bulk flow directions.

clase, hornblende, and biotite minerals within dikes and intrusions that cut SB

(Figs. 2, 3, and 5); and (4) a magmatic layering (SD) created by sheeted granitoid dikes that are interfolded with layers of country rock at the southeastern FIELD EVIDENCE OF MAGMATIC DEFORMATION end of the Estero Córdoba unit (Figs. 2 and 6). Local crosscutting relationships among these foliations are discussed in the following. Together, all four create Punta de Tralca Tonalite a regional structural grain that strikes to the northwest and dips moderately to the northeast (Figs. 1C and 2). The trend of this structural composite grain is Enclave-Matrix Structures discordant to a gneissic foliation in country rock at Las Cruces by a few tens of degrees (Fig. 1D). Most of the enclaves in the Punta de Tralca tonalite at and south of Isla Inside the batholith, local discordances among the four categories of ig- Negra are composed of plagioclase, hornblende, and interstitial quartz with neous foliations also are common. At the southern end of the Punta de Tralca biotite and minor epidote, titanite, zircon, and apatite. Some mineralogical

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and external foliations (S mineral aggregates inside and outside enclaves. (A) A few evenly distributed grains (white rectangles) in enclaves wrapped by plagioclase accumulations (light gray shading) enclaves (arrows). (C) Enclaves where S (H) Shear zone with asymmetric schlieren recording sinistral displacements. (I) Dike with an internal flow foliation (S and lineation orientations shown in Fig. 1C). Photographs in A–C and G are of surfaces oriented perpendicular to S A–D, F, and H is 15 cm. Notebook width in E and F is 19 with leucocratic material concentrated in fold hinges. (G) Enclave boudinage with felsic material concentrated in boudin necks. Surface parallels magmatic foliation (S of plagioclase-rich felsic segregations and xenolith fragments. (E) Sigmoidal en echelon vein sets and microfaults (dashed lines) affecting enclave swarms. (F) Folded enclaves photographs (except A–C, G) are of surfaces oriented perpendicular to the moderately dipping regional S Figure 3. Photographs and sketches showing styles of magmatic deformation in the Punta de Tralca tonalite from costal outcrops at Isla Negra and areas farther south. All cratic pool and protodike with undulose boundaries and a tapered tip truncate enclaves and S

liation tr liation E fo C A B f tonalit D oliation traces f elsic segregation f phenocr elsic material S e

S a

c B es S B ysts penetrate encalves S accumulations plagioclase Enclav A F oliation trac (amphibolite) xe nolith late frac B S e ). (B) Intermediate stage of assimilation where enclave is partially disintegrated into its matrix. Plagioclase phenocrysts are preserved penetrating

strain shado Fo e trac liation tur tonalit S strain cap e

B e e B w foliations in the matrix are continuous with those inside enclaves (S cm. Coin in G is 2.5 klepeis_01107 1st pages / 5 of 26 cm wide. Fields of view in I and J are 120 cm. Photographs A–C show distributions of plagioclase

G I F

H J fe

c lsic material

o foliatio truncated

v fe e

S r lsic segregatio B

foliation. fel e

C B d sic rich pool felsic segregation ow foliation n Enclave folded encla f oliation trac

B igneous banding and a steeply plunging mineral lineation (foliation f n ol

sheared encla stretche d trac lineation A e ). (D) Xenolith with wedge-shaped strain shadows composed d e ve

e e S s n B C Enclav Fo B c ) that truncates older external foliations (S foliation and parallel to the lineation. Field of view in

d l

lded v

dik prot S e B ve e o- s e B ). (J) Leuco - B ). ).

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bulk transport parallel to regional B L lineation (L) Figure 4. (A) Block diagram summarizing L the geometry of enclave structures in the L Punta de Tralca tonalite. Asymmetric struc- A tures define cells of material that rotated clockwise and counterclockwise about the regional northeast-plunging elongation lineation (L). Boudinage parallel to lineation indicates that it is a true stretching direction. Extension fractures and strain shadows also show extension across the XY plane SB lineation (YZ plane), resulting in a style foliation of deformation characterized by triclinic symmetry. Figure 13 illustrates a type of flow that may explain these patterns. (B) Inset shows the variable alignment of

plagioclase minerals (black) within the SB foliation (XY) plane. For a statistical evalu- ation of the orientations, see Figure 8. W N klepeis_01107 1st pages / 6 of 26 S E YZ plane tonalite host with flow foliation microgranitoid enclave

cells of rotational flow felsic material (plag accumulations) across the regional lineation tonalite dike in the YZ plane

differences, and the presence of xenoliths, suggest that they reflect multiple aligned best along the upper and lower surfaces of a hornblende-rich xenolith, sources rather than a single homogeneous magma batch. forming caps, and less aligned on the ends. The presence of xenolith fragments The tonalite matrix displays greater proportions of euhedral to subhedral within the shadows indicates mechanical plucking during flow. These features plagioclase and biotite crystals and lower abundances of hornblende than demonstrate that the enclaves and xenoliths had a range of effective viscosities the enclaves. Enclave grain sizes are several orders of magnitude smaller during magmatic deformation, most likely as a result of variations in grain size, than the matrix with the exception of large (to 1 cm long) rectangular lathes composition, temperature, and melt concentration (e.g., Blake and Fink, 2000). of twinned plagioclase. Matrix plagioclase forms thin (≤1 cm) accumulations Fractures, folds, and shear zones involving both enclave and matrix provide that surround and penetrate the enclaves by different degrees, ranging from further evidence of the range of viscosity contrasts during magmatic defor- a few evenly distributed grains inside enclaves (Fig. 3A) to examples where mation (cf. Paterson et al., 1998; Yoshinobu et al., 2009). Sigmoidal fractures, plagioclase aggregates dominate and the enclaves have partially disintegrated wedge-shaped en echelon tension gashes, veins, and small faults in enclaves into the matrix (Fig. 3C). Megacrysts frozen at enclave boundaries (arrow in are common (Fig. 3E). Extension fractures display tapered tips and are filled Fig. 3B) record the exchange of material between them prior to their complete with feldspar and quartz aggregations derived from the matrix. Some fractures crystallization (cf. Parada et al., 1999). terminate inside enclaves, suggesting that they initiated at enclave boundaries In addition to forming thin accumulations around enclaves, plagioclase and propagated inward. Others penetrate through the enclaves and merge crystals show preferred orientations that, along with hornblende and biotite, with thin (a few crystals wide) zones of tiled feldspar in the surrounding matrix.

define magmatic foliations. In some cases foliations in the matrix (SB) are These latter varieties form en echelon arrays, the lengths of which exceed half

continuous with those inside the enclaves (SA) (Fig. 3C), indicating that both the width of the enclave and mark the initial stages of boudinage. The sig- enclave and host had similar effective viscosities during deformation. In other moidal varieties show fracture trends ranging from 30° to 60° clockwise from

examples (Fig. 3D), SB foliations are deflected around xenoliths and enclaves, the trace of the SB foliation (Fig. 3E). They are widest and steepest at their forming wedge-shaped strain shadows. Figure 3D shows that minerals are centers, suggesting the tapered tips are youngest and experienced smaller

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Folded enclaves (Fig. 3F) occur in clusters. The folds are asymmetric and A 2.5 meters NW SE filled with crescentic zones of felsic material that are widest in hinges and nar- Estero Córdoba rowest on limbs. This felsic material is distinguished from the matrix tonalite Punta Tralca tonalite by an assemblage of quartz and feldspar minerals, and contains significantly tonalite smaller modal abundance of mafic minerals such as hornblende and biotite. Leucocratic These segregations widen into strain shadows and grade smoothly into the dike S C rotated surrounding matrix. The shadows, plus the presence of prongs, ears, and tails, enclaves record winnowing and stretching during folding and magmatic flow. Elongated SC and boudinaged enclaves formed on the limbs of some tight folds. Felsic ma- channel terial fills the interboudin partitions (Fig. 3G). Lithic fragments in the partitions, derived from fracturing and ductile flow, record the partial disaggregation of S B rotated enclaves during boudinage. These patterns suggest that pressure gradients enclaves SC transferred melt into dilational sites around enclaves as they deformed in a crystal-rich mush. Asymmetric schlieren occur in mesoscopic shear zones as long as several meters (Fig. 3H). The shear zones show across-strike gradients defined by increases in the degree of attenuation of enclaves, decreases in layer thick- SB ness, and a deflection of layering and enclaves into thin (1–5 cm) bands where

strains appear highest. Within these high-strain zones, the deformation mech- klepeis_01107 1st pages / 7 of 26 anism does not appear to be largely crystal-plastic when observed in outcrop due to the subhedral to euhedral phenocryst forms. Both sinistral and dextral B C sets occur within subdomains of the tonalite. In high-strain areas, individual enclaves are rotated into alignment with flow banding that truncates older en-

claves and SB foliations. This diversity and the asymmetry of these structures allowed us to partially reconstruct the kinematics of flow and cross-check senses of shear. These structures include (1) the sense of rotation of S foliations and the asymmetry SSCC B S of schlieren and matrix strain shadows in shear zones, (2) fault offsets, (3) sig- B channelchannel moidal fracture sets, (4) en echelon vein arrays, and (5) asymmetric folds. In all cases, the asymmetries are preserved on surfaces oriented perpendicular to

both the dominant SB foliation and the regional, northeast-plunging elongation lineation (Figs. 1C and 4). Few to no asymmetric structures were observed on Figure 5. (A) Sketch of outcrop at site 11IN01B (Fig. 1B) showing the contact between the Punta de Tralca (left) and Estero Córdoba (right) tonalites. View is surfaces perpendicular to foliation and parallel to lineation. Boudinage parallel

of a surface oriented perpendicular to the SB foliation and the regional north- to the lineation (Fig. 3G) confirms that it is a true stretching direction, although east-plunging lineation (YZ plane). Note different shapes, orientations, and align- plagioclase minerals often locally show only a weak preferred alignment in ment of enclaves in each unit. Dashed lines highlight S foliation surfaces. Small C this plane where they tumbled around enclaves (Fig. 4B). Extension fractures box in the Estero Córdoba dike shows the location of C. (B) Photograph of SB

foliation in the Punta de Tralca tonalite. (C) Photograph of SC foliation and narrow and strain shadows also show extension across the lineation, indicating that channels that record the flow and an exchange of material between the two there were two directions of extension during foliation development. The units parallel to SB. asymmetric structures delineate zones as much as tens of meters wide where shear sense indicators match one another. These zones alternate with one an- rotations compared to the centers. Faults that offset enclave boundaries by other, defining small cells where material rotated both clockwise and coun- a few centimeters show no evidence of cataclasis. High-angle fractures (~60° terclockwise about the northeast-plunging mineral lineation (Fig. 4). Areas of

relative to the trace of the SB foliation) show offsets that are antithetic to the convergence and divergence between cells tend to be steeper than adjacent deflections of shear zones. Low-angle fractures (0°–30° from foliation) exhibit areas, possibly forming cylindrical pipes. These patterns, and the partitioning synthetic offsets. These features formed late in the history of deformation in of displacements both parallel to and across the lineations, result in a style the unit and when enough solid material had crystallized to accommodate of deformation characterized by triclinic symmetry (Lin et al., 1998; Iacopini shearing and fracturing (Paterson et al., 1998; Vigneresse and Tikoff, 1999). et al., 2007).

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Figure 6. (A) Photograph of the southeastern contact of the Estero Córdoba tonalite with metasedimentary rock of the Valparaíso metamorphic complex at site ribbons of isolated schlieren 11IN03 (location in Figs. 1B and 2). Section B migmatitic biotite-rich exposes granitoid sheets interfolded with country rock. (B) Profile of A. Horizontal porphyritic granitoids country rock klepeis_01107 1st pages / 8 of 26 late mafic dikes scale of photo and profile is 15 m. synmagmatic folds biotite-rich pods microgranitoid, enclave-rich granitoids

magmatic foliations

enclaves and xenoliths

Melt Reintrusions and Dike Networks previously deformed enclaves and matrix, including those involved in folds and shear zones, indicating that they are among the youngest features in the unit. Virtually all of the structures that affect both enclave and matrix in the Punta The felsic concentrations exhibit systematic changes in geometry and tex- de Tralca tonalite (e.g., Figs. 3E–3H) exhibit accumulations of the leucocratic ture with increasing size. Accumulations between 1 cm and 1 m long truncate matrix in dilational sites, including strain shadows, fold hinges, interboudin both enclaves and matrix material at one end while grading smoothly into the partitions, tension gashes, and faults. Many of these accumulations are distin- host matrix without sharp boundaries at the other end. Their margins typically guished texturally and compositionally from other matrix material by higher show undulating, scalloped geometries and most do not entrain enclaves, sug- abundances of K-feldspar, plagioclase, and quartz, and lower abundances of gesting only minor flow. In contrast, meter-scale dikes and accumulations en-

biotite and hornblende. These concentrations display a variety of shapes and train enclaves and display new flow foliations (SC) that truncate older external sizes, ranging from diffuse globular patches to thin (≤2 m) dike networks with ones everywhere along their length (Fig. 3I). Many of the large concentrations irregular margins (Fig. 3J) to dikes with straight, planar boundaries. All intrude form approximately planar zones, although their margins locally are undulose

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and scalloped. The ends of these zones display apophyses with tapered ends Tralca tonalite. Most contacts are sharp and truncate enclaves. Long (1–2 cm) (Fig. 3J), suggesting that they propagated as fractures within the crystallizing clots of hornblende form flow foliations within the dikes at high angles to folia- host. A continuum appears to exist between these incipient dikes with diffuse, tions in host rock. Some dikes show drag along their margins, further suggest- undulating boundaries and well-developed dike networks with straight planar ing that they intruded when both older units mostly had solidified. boundaries that cut across the foliation defined by igneous layering and en-

claves (SB). The youngest dikes show few enclaves and granodioritic composi- Southeastern Contact tions. These observations suggest that the small patches record the pooling of melt-crystal aggregates during the early stages of mobilization. Transportation The southeastern end of the Estero Córdoba unit is characterized by sheeted away from these pools via dike propagation likely occurred during the last granitoid dikes interlayered and interfolded with screens of country rock (sites stages of crystallization. 11IN03A–11IN03C; Figs. 1B, 2, and 6). Megacrystic granodiorites, granites, and hornblende-biotite tonalites make up the granitoid sheets. Xenoliths, which ap- Estero Córdoba Dike pear to be derived from the wall rock, occur throughout this zone. The incorpora- tion of xenoliths that are completely disconnected and surrounded by intrusive Northwestern Contact rock in Estero Córdoba unit suggests that stoping could have been an important process late in the history of the pluton. The wall rock, which is best exposed at At site 11IN01B (Figs. 1B, 2, and 5) a diffuse, nonplanar contact between Las Cruces (Fig. 1A), is a combination of gneiss, slate, biotite schist, and calcar- the enclave-rich Punta de Tralca tonalite and the younger Estero Córdoba dike eous gneiss that forms part of the Valparaíso metamorphic complex (Fig. 1B). is well exposed (Fig. 5A). The Estero Córdoba dike contains inclusions of the The orientations of deformed dikes and the alignment of minerals within

Punta de Tralca tonalite, and in a few places truncates igneous layering (SB) in the granitoid sheets define a magmatic layering (SD) that is distinct from later klepeis_01107 1st pages / 9 of 26

the older rocks. Foliations composed of tiled plagioclase and aligned biotite stage crosscutting dikes containing SC foliations observed elsewhere in the

locally parallel the contact and truncate some enclaves while flowing around unit (Fig. 6). SD foliations are deflected around flattened schlieren with pressure others. Leucocratic dikes emanate from the younger tonalite (Fig. 5A), cutting shadows. Inside xenoliths, older mineral foliations are tightly folded and trun- through the Punta de Tralca tonalite. In other places along the same contact, cated at their margins, indicating that they were more viscous than the matrix. both the young intrusion and its enclave-rich host share a common magmatic At site 11IN03A (Figs. 1B, 2, and 6), the dikes and layers show various stages

foliation that parallels SB. These zones form narrow channels (Figs. 5A, 5C) of boudinage, from pinch-and-swell to broken, isolated biotite-rich pods. Felsic where enclaves and plagioclase crystals are preserved crossing the cuspate segregations fill the hinges of folds, and even the most highly stretched and boundary between the two units, suggesting that they were conduits for ma- attenuated layers exhibit little mesoscopic evidence of crystal-plastic deforma- terial exchange. Inclusions of the Punta de Tralca tonalite within the dike sup- tion. These features, including synmagmatic folds of granitic dikes and country

port this conclusion. These observations imply that temperatures were high rock and the SD layering, compose a structural style that is absent in the unit enough and emplacement rates were slow enough to allow the two units to farther north. The interfolding and parallel mineral lineations (Figs. 1C, 1D) exchange material as they crystallized and deformed together. suggest that the Estero Córdoba dike and Valparaíso metamorphic complex A comparison of structures within the two units reveals differences in the locally shared a history of ductile deformation during intrusion. relative age and character of foliations. In the Punta de Tralca tonalite, the domi

nant foliation is a pervasive, relatively uniform igneous layering (SB) (Fig. 5B).

Foliations inside (SA) and outside (SB) the enclaves are parallel (e.g., Figs. 3C and DEFORMATION MICROSTRUCTURES 5B). The enclaves are all aligned and display uniformly oblate shapes. These observations indicate that the enclaves and their matrix share deformation his- Enclaves in the Punta de Tralca Tonalite tory and had similar effective viscosities at the time the foliations formed.

In contrast, inside the Estero Córdoba dike, schlieren and tiled feldspar ac- Enclaves in the Punta de Tralca tonalite display continuous foliations (SA)

cumulations align into foliations (SC) that are discordant to foliations in chan- of dark green and brown hornblende intergrown with plagioclase-quartz

nels that parallel SB (Figs. 5A, 5C), implying a clockwise (top to the southeast) aggregates. The boundaries between these phases commonly are irregular rotation of material about an axis parallel to the mineral lineation. The en- with rounded corners, mutual indentations (arrows, Fig. 7A), and protru- claves are stretched, winnowed, and broken, implying a combination of semi- sions that disrupt the strong shape-preferred orientations exhibited by large rigid rotation, fracturing, and ductile distortion within a weak, melt-rich matrix. plagioclase phenocrysts. The aggregates consist of polygonal grains that The youngest features include late, hornblende-bearing felsic dikes that cut contain smaller rounded grains and inclusions of quartz and feldspar within

SC foliations. Some dikes display undulose contacts but, unlike the older Estero them (Figs. 7A, 7B). Concentrations of quartz inclusions at plagioclase grain Córdoba dike, do not record mixing or mingling with the enclave-rich Punta de boundaries indicate that the two minerals grew together (arrows, Fig. 7B).

GEOSPHERE | Volume 11 | Number 5 Webber et al. | Deformation and magma transport in the Coastal Batholith, Chile 9 Research Paper for discussion and significance of arrows. tonalite. All images are shown with crossed polars except F, which is in plane light. Boxes in E and H show location of images in G and I, respectively. See text cline. (D) Tonalitic matrix of the Punta de Talca tonalite. Box shows tapered pressure shadows of biotite on plagioclase crystals. (E–I) The Estero Córdoba Figure 7. (A–C) Deformation microstructures in an enclave of the Punta de Talca tonalite. Q—quartz, pl—plagioclase, hb—hornblende, bt—biotite, ks—micro - H E C A hb hb hb hb pl pl quartz beads quartz beads pl pl pl pl pl pl pl pl pl pl pl pl pl Q Q Q Q ks pl pl Q Q Q Q Q ks ks Q Q Q Q hb hb pl pl Q pl pl pl pl Q Q ks ks pl pl late fractur ks ks pl pl hb hb pl pl klepeis_01107 1st pages / 10 of 26 pl pl 1 mm 1 mm pl pl Q Q pl pl Q Q e pl pl B D hb hb pl pl F G I bt pl pl pl pl ks Q Q pl pl b. b. Q Q pl pl Q pl pl 0.5 mm pl pl Q Q late fractur Q Q pl pl pl pl pl Q Q bt bt bt bt 1 mm pl pl pl pl ks ks Q Q hb hb Q Q a. es hb hb bt bt pl pl Q Q Q Q Q hb hb 0.5 mm bt bt pl pl Q Q

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Many grains also are internally strain free and exhibit no crystallographic pre- tured plagioclase crystals are visible as irregular quartz crystals with cuspate ferred orientations. These microstructures suggest that crystal-plastic adjust- boundaries and low dihedral angles in triple junctions with plagioclase grains ments of grain boundaries changed the shapes of aggregates initially aligned (Fig. 7D). However, most of these pseudomorphs of melt have been destroyed by magmatic flow. The rounded corners and amoeboid shapes indicate that by late hydrothermal mineral reactions, resulting in the growth of biotite. Late the adjustments did not take place when the crystals were suspended freely biotite crystallized as aggregates that partly to completely infill large pores in a magma body; instead, they appear to have occurred by diffusion along between fractured plagioclase grains. This style contrasts with the infilling of grain boundaries, through crystals, and/or by diffusion-accommodated sliding pores exhibited by the Estero Córdoba dike, many of which are infilled by small (Vernon, 1970; 2004). quartz and K-feldspar crystals (e.g., Fig. 7E). Biotite shows few inclusions, and Differences in the dihedral angles formed by triple junctions between commonly is chloritized. Cuspate embayments along some boundaries be- plagioclase, quartz, and hornblende crystals suggest disequilibrium among tween plagioclase and biotite suggests possible late-stage hydrothermal alter- phases and provide additional evidence that grain boundary adjustments by ation (cf. Eggleton and Banfield, 1985). Late fractures cut across multiple grains crystal-plastic deformation modified the shapes of aggregates in the presence and are filled with small quartz and feldspar crystals (Fig. 7D). Plagioclase is of melt. Some quartz on quartz grain boundaries show 120° dihedral angles at sericitized along its edges in fractured zones. These microstructures record triple junctions (Fig. 7B), indicating that these aggregates were hot long enough fluid infiltration accompanied by brittle deformation and the growth of sec- for crystal interfaces to adjust to minimize their interfacial free energy (Ver- ondary minerals late in the history of solidification. non, 2004). Boundaries involving plagioclase-quartz, hornblende-quartz, and The biotite that fills spaces between plagioclase grains forms tapered over- hornblende-plagioclase crystals show small dihedral angles (arrows, Figs. 7A, growths on lenticular and bent plagioclase crystals (box in Fig. 7D). The over-

7B), including 60° angles in three grain junctions between quartz, plagioclase, growths exhibit oblate shapes and form a part of the SB foliation. In some of and hornblende (Fig. 7B). These small angles indicate that these grains were the overgrowths, and along the boundaries between large plagioclase crystals, not in textural equilibrium and suggest the presence of residual interstitial biotite and chlorite are sheared, suggesting that they accommodated relative klepeis_01107 1st pages / 11 of 26 melt (Jurewicz and Watson, 1985). Hornblende also shows an interstitial motion between grains. The shear bands are defined by shredded cleavage, geometry consisting of arms and panhandles that partially surround quartz broken fragments, and subgrains, suggesting slip on cleavage planes. The crystals (arrow, Fig. 7A). Other evidence of melt includes beads of equant, presence of oblate shapes and the alignment of pressure shadows on plagio randomly oriented, strain-free quartz and feldspar grains that formed along clase crystals suggest that flattening, compaction, and mineral growth contrib-

grain boundaries and fill the intervening spaces between fractured primary uted to the development of SB foliations as interstitial liquids were removed plagioclase crystals (Fig. 7C). Dihedral angles of the tips of grain boundary from crystalline networks. melt films are <60°. This string-of-beads texture results from the crystallization of melt as cooling rates slow, which creates melt rims on quartz and feldspar Estero Córdoba Dike grain boundaries that are replaced by aggregates of equigranular, randomly oriented feldspar and quartz grains (Holness and Isherwood, 2003). These ob- The Estero Córdoba dike (Figs. 1 and 2) contains plagioclase and biotite servations indicate that the enclaves record the transition from hypersolidus with variable amounts of quartz, microcline, hornblende and epidote. At site

flow in a melt-rich magma to near solidus deformation where crystal-plastic 11IN01B (Figs. 1B, 2, and 5), biotite aggregates form foliations (SC) that wrap deformation occurred in the presence of migrating melts. twinned plagioclase crystals. Most of the biotite is bladed and shows little to Evidence of some low-temperature brittle deformation is also preserved. no optical evidence of kinks, bent lattices, or other internal deformation, even Late minor fractures (Fig. 7C) filled with quartz and other late magmatic min- where they bend around large plagioclase crystals. The exception to this occurs eral cut across multiple grains. Alteration zones with sericite surround clusters in a few small areas between large, unstrained plagioclase grains where biotite of these microfractures in plagioclase. Biotite, which crystallized after horn- shows slip along cleavage planes and local shear band boudinage. The shear blende, is mostly unaligned and shows habits ranging from amorphous to bands form tapered aggregates where biotite crystals are thinned, shredded, small blades. These observations indicate that biotite growth, fracturing, and and stretched (arrow a in Fig. 7F). Similar microstructures have been reported hydrothermal alteration occurred late in the history of the enclaves. in other deformed tonalites where they have been used to infer sliding along grain boundaries, possibly aided by the presence of melt (Vernon et al., 2004). Matrix in the Punta de Tralca Tonalite Plagioclase crystals are variably aligned. Some of the largest grains display two different types of fractures. One type occurs entirely within single

The leucocratic matrix surrounding enclaves shows spaced foliations (SB) plagioclase crystals, ending at their boundaries (Figs. 7E, 7F). A second type defined by clots of coarse-grained, primary hornblende between plagioclase forms pull aparts (arrow and box in Fig. 7E). Many of these fragments display aggregates. Hornblende forms dark green and dark brown blades with many irregular edges that match other grains on the opposite side of the fracture. small quartz and feldspar inclusions. Remnants of melt pockets between frac- Quartz, microcline, and minor hornblende and epidote filled the intervening

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pockets between the grains. This texture, the granitic composition of the fill, geneous over the scale of the measurements, (2) markers deform passively and the interstitial relationships among adjoining plagioclase megacrysts sug- with their matrix, (3) the initial three-dimensional shapes and orientations of gest that these pockets collected residual melts (e.g., Vernon et al., 2004). markers can be reasonably established, (4) marker shapes are relatively uni- Highly irregular, cuspate grain boundaries and small (<120°) dihedral angles form, and (5) all markers share a common deformation history. In addition, (Figs. 7G, 7H) in aggregates involving plagioclase, quartz, microcline, and the use of minerals is complicated because their orientations are easily reset hornblende indicate disequilibrium, also suggesting that these phases crys- and they do not record deformation accommodated by melt (Paterson et al., tallized from residual melts (Jurewicz and Watson, 1985; Holness and Sawyer, 1998). Enclaves carry another set of problems related to temporal and spatial 2008). Other evidence includes straight crystal faces of coexisting plagioclase variations in how they form and respond to deformation. Their final shapes and K-feldspar against quartz (Fig. 7H), overgrowths of late K-feldspar on pri- and orientations are influenced by many processes, including initial shapes, mary, twinned plagioclase (arrow, Fig. 7E), and plagioclase pieces stranded as variable viscosities, a competition between strain and interfacial energies, and inclusions in melt pockets between fractured plagioclase crystals (arrows, Fig. deformation that may involve internal strain or rigid rotations in a magma 7I) (Vernon, 2004). These microstructures suggest the formation of cracks by body (Paterson et al., 2004). These and other problems preclude the use of melt-enhanced hydrofracturing and the pseudomorphing of granitic melts in mineral and enclave populations as accurate strain markers. pockets by late magmatic phases. In a detailed consideration of these issues, Paterson et al. (2004) suggested A number of pockets between fragments of plagioclase show lobes where that comparisons among the characteristics of igneous layering, mineral fab- vermicular intergrowths of quartz and potassium feldspar replaced plagioclase rics, and enclave fabrics, including internal mineral alignment, may provide (arrows, Fig. 7I). These myrmekites record mineral reactions in low-strain sites qualitative information on the changing styles and kinematics of magmatic that were sheltered by large, rigid grains of plagioclase (Hanmer, 1982). The strains. We tested this approach at site 11IN01B (Figs. 1B and 5) by comparing dendritic grain shapes suggest a slowing of diffusion rates (Vernon, 1968) rela- the orientations and distributions of two populations of enclaves and plagio tive to those that accompanied changes in the shapes of plagioclase and quartz clase minerals in the Punta de Tralca and Estero Córdoba units using three klepeis_01107 1st pages / 12 of 26 aggregates in the enclaves. Plagioclase also shows evidence of crystal-plastic different techniques. The techniques included raw measurements of mineral recrystallization while new crystals of quartz and potassium feldspar were alignment in three dimensions and analyses of the preferred orientations (f)

growing from melt in low strain pockets. Grain boundary bulging and groups and shape fabrics (Rf) using the center to center (Fry, 1979; Erslev, 1988) and

of small, strain free grains concentrated along grain boundaries (arrows, Fig. Rf /f (Dunnet, 1969; Lisle, 1985) methods (see Appendix 1). Rather than attempt 7H) suggest that some melt crystallized along grain boundaries and may re- to calculate true finite strains, our goals were to evaluate (1) whether plagio flect sliding on melt-coated grains (Vernon, 2004). clase and enclave orientations and distributions in the Punta de Tralca tonalite In the melt pseudomorphs, K-feldspar shows subgrains, deformation are compatible with interpretations of the late compaction and flattening of bands, and scalloped grain boundaries (arrow, Fig. 7G), suggesting that re- a crystal-rich mush, and (2) if inherited enclave fabrics in the Estero Córdoba crystallization occurred by dislocation creep at temperatures >500 °C (Tullis dike were reset during magma emplacement or if they retained some memory et al., 2000). Large quartz grains in melt pockets show chessboard extinction, a of their previous history within the Punta de Tralca tonalite. The application blocky subgrain structure that is common in granulites and migmatites (Kruhl, of these techniques in this context highlights systematic variations that may 1996; Garlick and Gromet, 2004) and granitoids (Paterson et al., 1989; Vernon, reveal differences in the deformation history between the two units. 2000) deforming near solidus temperatures. The exact temperatures this pat- Achieving these goals appears possible at site 11IN01B because the relative tern records is dependent on water content, strain rate, and other factors, but age, relative viscosities, three-dimensional shapes, and structural context of generally ranges from 400 to 700 °C (Vernon, 2004). Other relatively low tem- the mineral and enclave fabrics are clear. The presence of narrow channels perature, subsolidus deformation textures include deformation lamellae in (Figs. 5A, 5C) where enclaves and plagioclase crystals are preserved crossing quartz (Fig. 7I), lenticular deformation twins in plagioclase (Figs. 7E, 7H), and the cuspate boundary between the two units, and inclusions of the Punta de K-feldspar and tartan twinning in K-feldspar (Fig. 7G). The concentrations of Tralca tonalite within the dike, indicates that enclaves in the Estero Córdoba the latter microstructures vary with local strain. dike were derived from the Punta de Tralca tonalite. This relationship allowed us to evaluate how entrainment in the dike affected the shapes of enclaves FABRIC ANALYSIS whose initial conditions could be reasonably established. The relative uniformity of enclave shapes and parallel mineral and enclave lineations in each unit Approach also simplified the comparisons. The three techniques used, which emphasize different aspects of the fabrics, provided a means to evaluate sensitivities. The Most attempts to measure magmatic strains in granitoids encounter prob- goals we chose also allowed us to avoid assumptions of passive deformation lems because the assumptions required to use standard methods of strain and permitted us to compare fabrics that incompletely record different incre- analysis frequently are violated (Paterson et al., 2004), i.e., (1) strain is homo- ments of deformation.

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Applications Results

We measured the orientations of 1729 plagioclase crystals in 2 hand sam- For the mineral fabrics in the Punta de Tralca tonalite, all three analytical tech- ples that show the typical characteristics of each unit at site 11IN01B. These niques yielded similar results (Fig. 8). The raw measures of plagioclase alignment included a penetrative S > L fabric shared by both enclaves and matrix ma- (Figs. 8D–8F) show a slightly more pronounced peak and lower circular standard terial in the Punta de Tralca tonalite and stretched and aligned minerals and deviation in the XZ plane, indicating the minerals are slightly more aligned on enclaves in the Estero Córdoba dike (Fig. 5). The measurements were obtained from polished rock surfaces (Fig. 8A). Code modified in Webber (2012, 2014) statistically fit ellipses to the traces of grain outlines (Fig. 8B) and tabulated their eccentricities and orientations. Orientations were measured from three A Sample (XZ face) B Fitted ellipses C Reference frame mutually perpendicular planes, defined with respect to foliations and lineations measured in the field (Fig. 8C). The results are plotted as probability den- XY plane sity functions (Figs. 8D–8F and 9A–9C), which describe the relative likelihood foliation Z that each mineral will take on a given orientation within each plane. Circular X standard deviations (Fisher, 1996) of the distributions provide a measure of the e degree of mineral alignment for each plane. n Y c mineral & XZ plane l For the center to center technique, we created normalized Fry (1979) plots a elongation lineation (Erslev, 1988) from the centroids of plagioclase minerals on three perpendic- v e 0 5 ular faces (Figs. 8G–8I and 9A–9C). For each plot, the apogee and perigee of the central voids were selected to determine the axial ratio of the sectional centimeters klepeis_01107 1st pages / 13 of 26 fabric ellipse. Three sectional ellipses (Figs. 10D, 10E) allowed us to construct a fabric ellipsoid using algebraic methods described by Owens (1984), Robin D XY face E XZ face F YZ face n=701 n=362 CSD = 0.6051 n=274

(2002), and Launeau and Robin (2005). This ellipsoid provided a measure of 0.02 0.02 CSD = 0.8958 0.02 CSD = 0.7809 the distribution of the grains in three dimensions. Several fits were compared 0.01 0.01 to assess errors (Appendix 1). 0.01

We applied the Rf /f method (Lisle, 1985) to both mineral and enclave popu- 0.00 0.00 0.00 Probability density lations in the two units. For minerals, we used the same grains as those used in −90 09φ 0 −90 09φφ0 −900 90 the Fry analyses and probability density functions. Measurements of enclaves GH I were completed from photographs of outcrop surfaces of known orientation. All photographs were taken perpendicular to, and at the same distance from, the outcrop using a customized camera mount (Webber, 2012). This procedure minimized edge distortions and other data collection errors. The absence of prongs, ears, and other irregularities allowed us to reasonably approximate enclave shapes and orientations with ellipses. Harmonic means of shape ratios

(Rs) and vector means of their orientations (Figs. 8J–8L) were used to compare fabric ratio 1.3 results (Webber, 2012, 2014). A series of fabric ellipsoids were obtained using fabric ratio 1.1 fabric ratio 1.5 the same methods described above. J K L ratio=1.5 0

0 n=51 0 n=50 ratio=1.6 ratio=1.2 n=54 51 51 51 Figure 8. (A) Photograph of plagioclase crystals surrounding a small enclave in a sample of the H =1.8 f H =1.7 m Punta de Tralca tonalite (XZ face shown). Dashed red line shows trace of SB foliation. (B) Fitted m R Hm=1.9 ellipses. (C) Block diagram illustrating the three perpendicular planes used as a reference frame in the analysis. (D–F) Probability density histograms of plagioclase populations measured on the three perpendicular faces. Plots show the greatest mineral alignment in the XZ plane, the weakest alignment in the XY (foliation) plane, and moderate alignment in the YZ plane. 12 12 (G–I) Results of a normalized center to center (Fry) analysis of plagioclase populations on the 12

three perpendicular faces. (J–L) A sectional Rf/ϕ analysis of the same mineral populations. Re- –90 090 –90 090 –90 090 sults of the two methods are nearly identical and show similar oblate fabric ellipsoids (plotted φ φ φ in Fig. 10C). CSD—circular standard deviation; Hm—harmonic mean.

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A XY face B XZ face C YZ face We measured the axial lengths and orientations of 203 enclaves on three n=127 n=130 CSD = 0.4600 n=135 faces in each unit (Fig. 5A). Each face contained a population size of between CSD = 0.8809 0.02

0.02 CSD = 0.7405 0.02 30 and 44 enclaves (Fig. 11). The sectional ellipses in both units all show the highest degree of alignment and distortion on surfaces oriented parallel to 0.01 0.01 0.01 lineation and perpendicular to foliation. In the Punta de Tralca tonalite, all enclaves show preferred alignments and 0.00 0.00 0.00 Probability density Probability density Probability density −90 09φ 0 −90 09φ 0 −900φ 90 oblate shapes, and a fabric ellipsoid that is more distorted than those recorded DE F by the mineral fabrics (Figs. 10C, 10D, 10F). Like the raw mineral measurements and Fry analyses, the Rf /f plots also show maximum alignment in the XZ plane and weak alignment in the other two planes (Figs. 11A–11C). In contrast, enclaves in the Estero Córdoba dike display highly distorted prolate shapes, even though their orientations are the same as both mineral and enclaves in the Punta de Tralca tonalite (Fig. 10). The axial ratios of sectional ellipses are generally higher in the dike than in the older tonalite, especially in the XZ plane (Fig. 11). fabric ratio 1.1 fabric ratio 1.6 fabric ratio 1.3 The differences in the two units are illustrated in the Nadai plot in Figure 10C. The low dispersions (Fig. 11) and reasonable ellipsoid fitting errors (Fig. 10C) Figure 9. (A–C) Probability density histograms of plagioclase mineral populations in the (Appendix 1) in each unit reflect the relatively uniform populations. The fabric Estero Córdoba tonalite. CSD—circular standard deviation. (D–F) Results of a normalized center to center (Fry) analysis of plagioclase mineral populations in the Estero Córdoba ellipsoid from the Punta de Tralca tonalite plots within the oblate field u( = 0.46)

tonalite. Plots show the greatest mineral alignment in the XZ plane and subordinate align- and has a low magnitude of distortion (es = 0.73). The fabric ellipsoid from the

ment in the other two planes. The results define an oblate fabric ellipsoid that is similar to klepeis_01107 1st pages / 14 of 26 dike plots within the prolate field u( = –0.24) and is more distorted (es = 1.36). This that in the Punta de Tralca tonalite (plotted in Fig. 10C). result is surprising because of the textural evidence from the outcrop showing that enclaves in the dike were derived from the older tonalite and yet they record no evidence of their prior oblate shape. This suggests that the enclave fabric in sections oriented parallel to lineation and perpendicular to foliation. The YZ plane the dike has been reset by flow during intrusion. The differences between the shows weak alignment and the XY (i.e., foliation) plane shows none. The lack mineral and enclave fabrics in both units also suggest that they record different of alignment in XY suggests that the plagioclase orientations partly reflect local increments of the deformation, most likely as a result of viscosity contrasts. tumbling and flow around semirigid enclaves, such as that illustrated in Figure 4B. Alignment in both the XZ and YZ planes is compatible with late compaction. DISCUSSION The normalized Fry (Figs. 8G–8I) and Rf /f (Figs. 8J–8L) plots both show that the most mineral alignment occurs in the XZ plane, little to no alignment The data we report in this paper, combined with the work of others (Siña occurs in the YZ plane, and no detectable alignment occurs in the XY plane. and Parada, 1985; Siña, 1987a, 1987b; Wall et al., 1996; Parada et al., 1999), The fabric ellipsoids using both techniques show similar slightly oblate shapes allowed us to reconstruct the history of magmatism and deformation in the (Fig. 10C). A comparison of the orientations of foliation (XY) planes and linea- Punta de Tralca tonalite and the Estero Córdoba dike (Figs. 1B and 2). We use tions (X directions) calculated from the mineral fabric (Fig. 10B) approximately structural relationships preserved within the two units to examine the fol- match those measured in the field (Fig. 10A), suggesting that the ellipsoids are lowing processes: (1) interactions between mafic and intermediate magmas, reasonably oriented. The shapes also are compatible with a small increment of (2) mechanisms of melt segregation and expulsion from a crystallizing pluton, late near-solidus, melt-present, compaction. (3) microstructures that record rheological transitions as the magmas crystal- Plagioclase mineral orientations in the Estero Córdoba dike (Figs. 9A–9C) are lized, and (4) flow patterns and igneous fabric development during magma similar to those in the Punta de Tralca tonalite (Figs. 8G–8I), except with slightly chamber replenishment and reactivation. better alignment in the YZ and XY faces. The better alignment could reflect the smaller population size. The Fry technique (Figs. 10D–10F) was not sensitive to Mafic and Intermediate Magma Interactions During these subtle differences and yielded an oblate fabric ellipsoid similar in shape Magma Chamber Rejuvenation and orientation to that in the Punta de Tralca tonalite (Fig. 10C). Calculated foliations and lineations (Fig. 10B) also match measured ones (Fig. 10A) reasonably The Punta de Tralca unit (Figs. 1B and 2) records the intrusion of multiple well and mimic the slight discordances observed at the outcrop. These similar- batches of mostly mafic magma into an intermediate host and the variable ities and the weak distortions suggest that the mineral foliations, like those in mixing and mingling of those magmas. The mafic intrusions, which are now the Punta de Tralca, mostly are sensitive to the last increments of compaction. represented by enclave swarms, depict the replenishment, thermal rejuvena-

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A) Measured attitudes B) Calculated attitudes

Es ter o C P ór u d n ob t a a d e

T ( r e a n l c c l a a Z (PdT enclave) ( v e e n p Z (EC enclave) c l o a o Figure 10. (A) Equal area stereographic pro- v r Z (PdT mineral) e ) jection showing that S and S foliations B C r i c measured in the Punta de Tralca (PdT)

h ) Z (EC mineral) and Estero Córdoba (EC) tonalites, respec- n (foliations) = 83 tively, are slightly discordant. Mineral lineations are indistinguishable. (B) Foliation n (lineations) = 21 planes (XY) calculated for each unit at site

pole to SB foliation (Punta de Tralca) Punta de Tralca (enclave) XY plane 11IN01B using enclave and mineral populations approximately match the measured pole to S foliation (Estero Córdoba) Estero Córdoba (enclave) XY plane C foliations. Calculated elongation linea- mineral lineations (both units) Punta de Tralca (mineral) XY plane tions (X) are identical to one another and Estero Córdoba (mineral) XY plane to measured mineral lineations. (C) Nadia mean vector (95% conf. cone) klepeis_01107 1st pages / 15 of 26 plot summarizing results of fabric analy- C) fabric parameters E) enclave ellipsoid ses. Error contours are 1σ and 2σ. Enclave D) enclave ellipsoid shape fabrics in each unit are distinct from (Punta de Tralca) (Estero Córdoba) one another and from mineral shape fabrics. (D–G) Three-dimensional renderings of fabric ellipsoids with normalized X, Y, Z values. Orientations are indistinguishable. All ellipsoids are oblate except for E, which EC is prolate. (enclave)

PdT (enclave) G) mineral ellipsoid Ln (R ) = 1.5, F) mineral ellipsoid f (Punta de Tralca) (Estero Córdoba) Rf= 4.5

Fry PdT (mineral) EC (mineral) Rf/φ Ln (Rf) = 0, Rf= 1

tion, and remobilization of a crystal-rich magma chamber by the injection of by enclaves to interpret how the input and resident magmas interacted as the magma through dikes. This process is important in arc systems because it pluton differentiated and crystallized. governs how magma bodies in the middle and upper crust grow and differ- Some of the principle features of the Punta de Tralca unit include (1) en- entiate (Couch et al., 2001; Bachmann et al., 2002, 2007; Hodge et al., 2012; claves that show strong preferred orientations and variable degrees of defor- Hodge and Jellinek; 2012; Caricchi et al., 2012). In addition, the injection of hot mation and assimilation with their tonalitic and granodioritic host (Figs. 3A– mafic magma into cooler, more silicic magma chambers may trigger erup- 3C); (2) multiple generations and types of foliations that record deformation tions in shallow magma reservoirs (Feeley and Dungan, 1996; Bachmann and processes ranging from the rotation and alignment of crystals suspended in Bergantz, 2004, 2006; Huber et al., 2011). We use the mineral textures recorded melt-rich magma currents to near-solidus deformation in crystalline aggre-

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Punta de Tralca enclaves: categories of foliations are represented in zones 1–3: (1) the preferred alignment of hornblende, plagioclase, and quartz minerals (S ) inside enclaves A XY plane B XZ plane C YZ plane A (Figs. 3B, 3C), (2) flattened and stretched enclaves entrained in the leucocratic

20 ratio= 2.6 ratio = 2.0 n=30 ratio = 1.5 n=32 n=44 matrix of their host, forming alternating light and dark colored bands (SB) (e.g.,

Fig. 5B), and (3) mineral foliations (SC) composed of aligned hornblende, bio- 10 tite, and plagioclase crystals within leucocratic dikes and other intrusions that

cut SA and SB (e.g., Fig. 3I). Crosscutting relationships among these foliations, 5 and comparisons of features inside and outside enclaves, allowed us to define f three different types of interactions between the enclaves and their matrix. R H = 2.7 Zone 1 (Fig. 12) represents areas where enclaves display the lowest viscos- 2 m ity contrasts and highest crystal contents, and are mostly assimilated into their tonalitic matrix (Fig. 3C). Foliations internal (S ) and external (S ) to the en- H = 2.4 A B

1 m Hm = 2.1 claves are parallel and grade smoothly into one another across enclave bound-

−90 090 −90 090 −90090 aries, forming the regional SB layering (Fig. 5B). This parallelism indicates that φ φ φ the two foliations formed together under similar conditions, most likely during Estero Córdoba enclaves: final deformation of the matrix. The zone records the fewest number of plagio clase-rich, leucocratic dikes and patchy accumulations in the unit. Stretched XY plane XZ plane YZ plane unit circle D E F and flattened enclaves form a penetrative oblate S > L shape fabric (Figs. 5B,

20 n=30 ratio= 2.4 n=31 ratio = 4.4 n=36 ratio = 2.0 10C, and 10D), which forms the dominant structure. Most prongs, ears, and other protrusions on enclaves (in the XZ plane) appear to have been removed klepeis_01107 1st pages / 16 of 26

10 by winnowing during flow and/or flattening. Microstructures indicate that both enclaves and matrix share a history of late-stage crystal-plastic recrystalliza- Hm = 5.1 5 tion that accompanied flattening and occurred in the presence of melt. These f features suggest that both the enclaves and their matrix in this zone share R Hm = 2.4 Hm = 2.4 a similar, mostly ductile deformation history. This history was acquired at a

2 stage when both magmas were highly viscous, crystal rich, and deforming near their solidi.

1 Zone 2 displays enclaves with moderate to high viscosity contrasts rela-

−90 090 −90 090 −90090 tive to their matrix (Figs. 3A, 3D, 3G). Foliations internal to the enclaves (SA) φ φ φ commonly are oblique to, and cut by, matrix foliations (SB). Some late crystal-plastic recrystallization of quartz-feldspar aggregates occurred but was Figure 11. (A–C) Results of sectional R / analyses of enclave populations in the Punta de Tralca f ϕ weak enough to avoid obliterating evidence of earlier hypersolidus flow in a tonalite. Hm—Harmonic mean. (D–F) Results for Estero Córdoba tonalite. melt-rich magma. Evidence of brittle and ductile deformation affecting both enclaves and matrix material is abundant, and includes shear zones, folds, gates where crystal-plastic deformation mechanisms occurred in the presence fractures, boudinage, and faults (Fig. 3E–3H). Collections of plagioclase-rich of melt; (3) variable histories of brittle fracturing, ductile shearing, and flatten- leucocratic material are preserved in pressure shadows, fold hinges, shear

ing that affected both enclaves and their matrix (Figs. 3E–3H); (4) asymmetric zones, and boudin necks, some of which truncate SB. These features indicate structures recording the rotational flow of magmas about a plunging mineral that most of the enclaves in this zone behaved as rigid or semirigid objects lineation (Fig. 4); (5) felsic and tonalitic accumulations that intrude older en- during deformation and magma mingling. Although some deformation, such clave swarms and show systematic changes in abundance, geometry, and tex- as fracturing and shearing, was shared by both enclaves and matrix, the en- ture with increasing size; and (6) granodioritic and granitic compositions in the claves mostly record a deformation history that differs from that of their matrix. youngest dikes and patches. Zone 3 is marked by the appearance of mesoscale (from several centime- The geometric relationships among these features are summarized in tex- ters to several meters wide) leucocratic felsic and tonalitic accumulations and

tural zones 1–3, shown in the lower half of Figure 12; zones 4–6, in the upper dikes with internal flow foliations (SC) that truncate enclaves and other (SA and

part of the diagram, show the Estero Córdoba dike and the Valparaíso meta- SB) foliations (Figs. 3H–3J). The largest dikes form interconnected networks morphic complex. The stacked arrangement of the zones is conceptual and is and channels, and are among the youngest features that make up the unit. The used to illustrate areas with similar structures and crystal-melt ratios. Three variety of orientations and angles created by dike apophyses suggests that

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Structures Processes 0.5 km - interfolded granitic sheets - diking, folding and mixing of 6 and country rock granitic sheets and country rock - sheet orientations in uenced Fig. 6 -granitic sheets, stretched xenoliths, by country-rock structure 5 magmatic mineral foliation (SD)

Fig. 6 - intrusion truncates SA, SB in some melt-rich magma areas, shared foliation in others - material exchange between enclave- SD - high viscosity contrasts between rich host and melt-rich intrusion enclaves and matrix magma replenishment S - rotated and stretched enclaves SC C - formation of new mineral foliations zone 4 record prolate, L>S shape fabric Fig. 5 - enclave deformation by fracturing, (SC) dened by aligned plagioclase ductile distortion and a semi-rigid and biotite rotation within a melt-rich host

mixture of crystal-rich and melt-rich magmas - dikes with tapered tips and internal ow foliations (SC) - dike apophyses and melt-pools truncate older (SA, SB) foliations begin to link and merge SA - zones of leucocratic magma are - combination of porous ow, brittle zone 3 commonly linked together deformation and channel ow in Figure 12. Left: Illustration of structures Figs. 3I, 3J dikes

observed in six textural zones viewed on klepeis_01107 1st pages / 17 of 26 surfaces oriented perpendicular to the crystal-rich magma regional northeast-plunging elongation - internal (SA) and external (SB) lineation (YZ plane). References to figures foliations commonly oblique - mobilization and pooling of melt by with example relationships are shown SB - moderate-high viscosity contrasts porous ow, enhanced by brittle and on left axis. Center: Summary of struc- between enclaves and matrix ductile deformation, including the tures that characterize each zone. Right: - abundant leucocratic plagioclase shear and fracture of crystal-rich Summary of processes interpreted from the analyses and observations. Enclaves Figs. 3A, accumulations in fold hinges, en aggregates echelon fractures, shear zones and - melt accumulation in low pressure have been enlarged to emphasize their 3D-3H zone 2 pressure shadows sites as enclaves deform structure. Magmatic foliations (SA, SB, SC, SD) and other relationships are described in the text. S crystal-rich magma A - internal (SA) and external (SB) foliations commonly parallel - mingling and mixing of S - low viscosity contrasts between B mac-intermediate magmas enclaves and matrix - draining of melt-rich components - stretched and attened enclaves leaves a crystal-rich magma mush form oblate S>L shape fabric that - low viscosity contrasts between Figs. 3B, dominates the unit enclaves and host 3C, 5B - enclaves and matrix share a late zone 1 - compaction increases attening crystal-plastic deformation history and melt expulsion 0 Legend country rock with foliation Estero Córdoba tonalite dike enclave with internal foliation (SA), surrounded by plagioclase-rich accumulations megacrystic granite with xenoliths Punta de Tralca host tonalite, folded granite sheets with flow foliation (SB) interlayered with country rock enclave-poor tonalitic dikes late crosscutting leucocratic dike and pools with flow foliation (SC)

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these intrusions did not undergo most or all of the flattening, compaction, and fractures may have occurred by a process similar to that described by Huber crystal-plastic deformation that dominated zone 1, and do not share the same et al. (2011); in their model, density differences between melts and crystals, deformation history as the enclaves and matrix. We interpret the abundant and the low compressibility of both, lead to a local increase of pressure where leucocratic accumulations in this zone to represent residual crystal-melt ag- melts are concentrated. Microfracturing relieves the overpressure because of gregates that were separated from their tonalitic host and remobilized during the high density of cracks that leads to a loss of strength. This process unlocks synmagmatic deformation. Similar features have been reported in other zoned the rigid mush and promotes the movement of melt. The tapered tips (Fig. magma chambers (Vernon and Paterson, 2006; Yoshinobu et al., 2009; Pignotta 3J), sigmoidal shapes (Fig. 3E), and en echelon geometries of the fractures we et al., 2010; Coint et al., 2013). observed imply an increasingly viscous host where local increases in magma On the basis of these relationships, we interpret zones 1–3 to record differ- pressure and/or strain rate promoted further brittle deformation and fracture ent degrees of mafic-intermediate magma assimilation. The variable interac- propagation (Blake and Fink, 2000; Paterson et al., 2004). Pressure gradients, tions most likely were controlled by differences in the density, temperature, generated as melts accumulated and enclaves deformed, also aided in the composition, and effective viscosity of the enclaves and their tonalitic host (cf. transfer of melt into dilational sites around folds. Hodge et al., 2012; Hodge and Jellinek, 2012; Caricchi et al., 2012). The varieties Melt mobilization and removal was accompanied by compaction and flat-

of leucocratic felsic and tonalitic accumulations that surround and intrude the tening. In zone 1, mineral reactions that occurred during near-solidus, H2O-sat- enclaves to varying degrees record different stages in the mobilization and urated crystallization or late hydrothermal alteration formed oblate biotite expulsion of melt from the magma chamber. This removal of melt resulted pressure shadows around large plagioclase lathes and destroyed most melt

in a differentiated, viscous crystal-rich magma mush. In the following we use pseudomorphs within SB (Fig. 7D). Some biotite crystals are sheared, suggesting mesoscale structures in zones 1–3 to examine some of the physical processes that they accommodated sliding between the larger plagioclase grains as melt that facilitated magma differentiation and melt expulsion in the unit. was extracted. Strain shadows and fracture sets show two perpendicular direc- klepeis_01107 1st pages / 18 of 26 tions of extension within the XY plane of SB (Fig. 4), further suggesting flatten- Melt Mobilization and Expulsion From a Crystallizing Pluton ing. In addition, the S > L mineral fabrics (Figs. 10C, 10F) and the uniformly oblate enclave shapes (Figs. 10C, 10D) in zone 1 evoke flattening. Because enclaves and The mechanisms by which felsic and tonalitic melts in the Punta de Tralca mineral fabrics commonly record different deformation increments, and enclave unit were mobilized and expelled are recorded well by mesoscale structures shapes can reflect a variety of processes (Paterson et al., 2004), the uniform pat-

that affect both enclaves and the regional SB layering in zone 2 (Fig. 12). In terns in zone 1 suggest that the flattening occurred late, at a time when enclaves

this zone, fractures, folds, and shear zones all disrupt SB (Figs. 3E–3H), indi- and matrix shared foliations and viscosity contrasts between them were low. cating that they formed late in the deformation history of the magma. These The occurrence of crystal-plastic deformation mechanisms in both enclaves and structures reflect deformation in viscous, crystal-rich mushes where enough matrix in this zone also suggests that the flattening occurred when the magma solid material (~45–50 vol% crystal) was present to enable fractures and shear had mostly crystallized and was deforming close to its solidus. zones to form and be preserved (Paterson et al., 1998; Vernon and Paterson, In summary, the mobilization and removal of residual felsic and tonalitic 2006; Bachmann and Bergantz, 2004; Yoshinobu et al., 2009; Huber et al., 2011). melts from within the Punta de Tralca unit was accomplished through a com- This is because aggregates of touching feldspar crystals with an interstitial bination of compaction, porous flow, internal fracturing, synmagmatic ductile liquid allow the transmission of differential stresses (Vigneresse and Tikoff, deformation, and flow within dikes. These processes all helped drain melts 1999). The crystal concentrations most likely resulted from a combination of into dilational sites of folds, boudins, fractures, and other structures and recrystallization below the rigid percolation threshold (Vigneresse et al., 1996), sulted in the formation of the highly viscous, crystal-rich magma mush that a mechanical sorting of crystals at rheological boundaries, and the removal of dominates zone 1. These interpretations agree well with those of other studies interstitial melt. All of these processes would have increased the viscosity of (e.g., Bachmann et al., 2002; Bachmann and Bergantz, 2004; Yoshinobu et al., the mush, allowing the folds, fractures, and shear zones to form. 2009; Huber et al., 2011) suggesting that significant portions of some plutons The results from other field studies, experiments, and numerical model- in arc settings are compacted, high-strength cumulate-rich bodies that can be ing indicate that a variety of brittle and ductile deformation mechanisms can reactivated through a combination of synmagmatic brittle and ductile defor- promote the draining of melts from between crystals (Jurewicz and Watson, mation mechanisms. 1984; Dell’Angelo and Tullis, 1988; Gleason et al., 1999; Rosenberg and Berger, 2001; Sawyer, 2001; Yoshinobu et al., 2009; Huber et al., 2011). In the Punta de Rheological Transitions in Crystallizing Magmas Tralca unit, fractures (Fig. 3E), the collection of leucocratic material in low-pressure sites around enclaves (Figs. 3D, 3F, 3 G), and remnants of melt pockets The rheological transitions that occur as magmas mingle, crystallize, and between broken plagioclase crystals (Figs. 7E, 7I) suggest that this process differentiate play important roles in how these materials migrate and solid- involved porous flow aided by microfracturing. The initial formation of micro ify within the crust. A comparison of mineral microstructures in the Punta de

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Tralca and Estero Córdoba units highlights the different transitions these two research would be to combine the microstructures we describe and flow laws magmatic bodies underwent. Both units preserve a progression from hyper- for high-temperature creep in quartz and plagioclase to estimate how magma solidus flow in melt-rich magmas to deformation close to the solidus where rheology changes as plutons crystallize. Some studies utilized this approach crystal-plastic processes occurred in the presence of melt. However, the Estero for various continental (Pawley and Collins, 2002) and oceanic (Yoshinobu and Córdoba dike preserves a richer array of deformation structures that suggest Hirth, 2002) settings. The approach could significantly augment current meth- high melt fractions and less evidence of crystal-plastic recrystallization than ods, which mostly employ combinations of field observations and information the Punta de Tralca rocks. The dike shows an abundance of crystallization on the temperature, chemical composition, and volatile content of the mag- microstructures, including microfractures (Figs. 7E, 7F), melt pseudomorphs mas (Yoshinobu et al., 2009; Caricchi et al., 2012; Hodge and Jellinek, 2012). (Figs. 7E–7H), K-feldspar overgrowths on primary plagioclase (Fig. 7E), and inclusion-rich melt pockets between fractured grains (Fig. 7I). These and many other features are well preserved and lack the late hydrothermal reactions Magma Flow Patterns and Fabric Development that destroyed most of the crystallization microstructures and melt pseudomorphs in the Punta de Tralca tonalite. This suggests that the Estero Córdoba Punta de Tralca Tonalite dike was less viscous, richer in melt, cooled more quickly, and underwent less late-stage flattening and compaction than the viscous crystal-rich mush into Mesoscale structures preserved within the Punta de Tralca tonalite provide which it intruded. Some of the best evidence of magma flow involving the ro- information on the three-dimensional geometry of flow patterns that accom- tation and alignment of crystals suspended in a melt-rich magma is preserved panied pluton crystallization and the draining of melts to form a crystal-rich inside enclaves in the Punta de Tralca tonalite. Plagioclase accumulations that mush. Figure 13 illustrates conceptually how some of this flow may have oc- surround and penetrate enclaves by varying degrees (Figs. 3A–3C) record the curred. The diagram shows a pattern whereby material rotated about the re- comagmatic exchange of material between matrix and enclaves during flow. gional northeast-plunging mineral lineation during bulk transport parallel to klepeis_01107 1st pages / 19 of 26 Thin (≤1 cm) layers of tiled crystals between enclaves and matrix (Figs. 3A, the lineation through a network of rigid or semirigid enclaves and crystals. The 3G) connote the presence of an interstitial liquid (Vernon and Paterson, 2006). These textures, and evidence of initially high viscosity contrasts, suggest that mechanical sorting by the addition of crystals at and across enclave bound

aries during magma flow contributed to mineral alignment within AS . Other microstructures preserved inside enclaves, especially in zone 1, record the transition to near-solidus deformation in crystalline aggregates where crystal-plastic deformation occurred in the presence of small amounts of migrating melt. Amoeboid grain shapes, strain-free quartz and plagioclase, rounded grains, and other features (Figs. 7A–7C) indicate that the shapes of quartz-plagioclase aggregates initially aligned by magmatic flow were modified by diffusion creep (Vernon, 1970, 2004), dislocation creep, and finally late hydrothermal mineral reactions. Interstitial hornblende between feldspar and quartz (Fig. 7A), small dihedral angles in three-grain junctions between quartz, plagioclase, and hornblende (Fig. 7B), and the string-of-beads textures (Fig. 7C) suggest that melt crystallized along plagioclase grain boundaries and that some sliding occurred on melt-coated grains (Garlick and Gromet, 2004; Hol-

ness and Sawyer, 2008). Thus, the minerals that define SA inside enclaves also record a transition from flow in a melt-rich magma to near-solidus deformation, where crystal-plastic deformation mechanisms contributed to the forma-

tion of SA as melt was expelled. These observations are important because they demonstrate that crystal-plastic deformation in quartz-plagioclase aggregates occurred while the Punta de Tralca tonalite, and to some degree the Estero Córdoba dike, were deforming above their solidi. Their occurrence suggests the possibility of us- Figure 13. Diagram illustrating a type of helicoidal flow resulting in cells of material that rotate about the direction of bulk transport illustrated in Figure 4. The bulk transport direction parallels ing experimentally-derived flow laws to estimate the rheologies of magmas a steeply plunging mineral lineation. Displacements occur parallel to and across this lineation, with variable crystal-melt fractions in natural granitoids. An interesting area of resulting in a style of deformation that exhibits triclinic symmetry.

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flow appears helicoidal, but also may simply reflect a type of sluggish convec- Despite these examples, however, there remains a dearth of information tion in a crystallizing intermediate magma body after it was replenished and in the literature on helical and other complex rotational flows in convecting thermally rejuvenated by the input of mafic magma. magma chambers. This suggests that either these flow types are rare, poorly The rotational pattern of flow (Figs. 4 and 13) explains the distribution and preserved, or simply understudied. One potential problem with helical flow is styles of all late asymmetric structures (Fig. 3E–3H) we observed that define that it may be unstable or represent a precursor to turbulent flow (Moffatt and alternating cells of clockwise and counterclockwise displacements across the Tsinober, 1992; Scofield and Huq, 2010). Turbulent convection appears difficult mineral lineation (i.e., in the YZ plane) in zones 2 and 3. This style of flow to achieve in a viscous melt flowing through a framework of solid crystals is reminiscent of deformations that commonly occur in transpressional shear (Bachmann and Bergantz, 2004). Internal fracturing linked to magma overpres- zones where triclinic symmetry is achieved through combinations of flatten- surization, which can break up and weaken the crystalline framework (Huber ing and a kinematic partitioning of displacements both parallel to and across et al., 2011), or the addition of volatiles in wet magmatic systems (Bachmann the mineral stretching lineation (Lin et al., 1998; Marcotte et al., 2005; Iacopini and Bergantz, 2006), may help overcome these problems. These processes et al., 2007). In simple steady-state noncoaxial flow, the vorticity vector is paral- potentially could help promote complex flow in magmas by allowing ther- lel to one of the axes of instantaneous strain, giving the flow monoclinic shape mally rejuvenated mushes to convect. Our study highlights the need for three- symmetry (Iacopini et al., 2007, 2010; Xypolias, 2010). However, if the vorticity dimensional fabric analyses to document the geometry of three-dimensional vector has a direction that is oblique to any of these axes the flow has a triclinic geometries of flow in crystallizing plutons. symmetry (Jiang and Williams, 1998). In the Punta de Tralca unit, the orienta- In addition to rotational flow through a matrix of enclaves, we suggest that

tions of plagioclase crystals within the tonalitic matrix are compatible with a channelized flow in dikes, resulting in the formation of CS foliations and drag type of complex rotational flow: their distribution within the XZ plane and the along dike margins, was important in zone 3 (Fig. 12). Other investigations of lack of preferred orientations in the XY and YZ planes (Fig. 8) are consistent how dikes might be linked to melt segregation in migmatites have produced with the tumbling and rotation of crystals as they move through a matrix of two end-member models. The first, called the rivulets-feeding-rivers model, klepeis_01107 1st pages / 20 of 26 rigid or semirigid enclaves. This process, or something similar to it, could have involves the formation of a self-organized network of veins and dikes operating effectively drained melts, thereby increasing effective viscosities and aiding simultaneously that increases in capacity and decreases in number, forming compaction. a fractal geometry (Weinberg, 1999; Tanner, 1999; Brown, 2004). The second, The geometry of the flow illustrated in Figures 4 and 13, or something simi known as the stepwise accumulation model, forms local melt-conductivity lar to it, may also explain patterns observed in other magmatic and partially pathways through the draining and closure of small veins into larger dikes molten bodies. Hippertt (1994), for example, reported foliation and lineation such that conductivity is spatially and temporally transient (Bons et al., 2009). patterns in migmatitic diapirs in the Baçao complex of southeastern Brazil that Crosscutting relationships among dikes in the Punta de Tralca tonalite suggest depict an internal flow structure with helicoidal geometry. In his model, steep that a single melt conductivity network where magma transportation operated mineral lineations defined the helical geometry in subcells where partially simultaneously at a variety of scales is unlikely. Our observations support a molten material ascended along upwardly flowing spirals. Trubač et al. (2009) stepwise accumulation model while highlight the important role of brittle and observed similar patterns of lineations and foliations they interpreted to re- ductile deformation in segregating and mobilizing increasingly felsic melts cord right-handed helical magma ascent in a steep-sided conduit in the Říčany within a crystallizing host. pluton of the Bohemian Massif. Other, kinematically complex, flow patterns associated with the convective overturning of partially molten and magmatic crust during diapirism were described in Kruckenberg et al. (2011) and Betka Estero Córdoba Dike and Klepeis (2013). Another area that may preserve large cells of convecting material within The Estero Córdoba dike (Figs. 1B and 2) records the intrusion of a melt- a granitoid is in a part of the South Mountain Batholith in Nova Scotia. In the rich tonalitic magma into an already highly viscous crystal-rich mush, repre- Chebucto Head area, Abbott (1989) mapped concentric, subcircular rings to sented by the Punta de Tralca rocks. This intrusion records processes by which 500 m in diameter that he interpreted to be the sides of cylindrical domes in a a rigid crystal-rich mush deforming near its solidus was reactivated and min- compositionally homogeneous monzogranitic body. The domes are defined in gled comagmatically with a melt-rich dike of intermediate composition (Fig. 5). part by steeply plunging, asymmetric folds that show both sinistral and dex- Furthermore, relationships preserved on the southeast side of the dike (Fig. 6) tral shear across a weak, moderately plunging mineral lineation, similar to the record the transfer and ponding of melt-rich material at the margin of the structures we report. Coint et al. (2013) mapped other similar zones of concen- magma chamber near its contact with metamorphic host rock. tric fabrics in the Wooley Creek batholith of the Klamath Mountains in northern The key features of the Estero Córdoba dike include (1) a diffuse, nonplanar California and interpreted them to reflect convective overturn within a crystal northwestern contact with the Punta de Tralca tonalite, into which it intrudes mush prior to its final solidification. (Fig. 5); (2) many local foliation discordances (Fig. 10A) and textural evidence

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of magma mingling and the comagmatic exchange of enclaves and minerals The differences in age and style of deformation recorded by enclaves and in narrow channels (Figs. 5A, 5C); (3) evidence of significant differences in the mineral foliations are even more pronounced in the Estero Córdoba dike. The

viscosities of the two units; (4) L > S flow foliations (SC) that are discordant to orientations and distribution of plagioclase minerals in the unit are identical foliations in the channels (Figs. 5A, 5C); (5) enclaves that record deformation to those in the Punta de Tralca (Fig. 10C). However, enclave shapes are very by ductile distortion, winnowing, and a semirigid rotation of material within different (Figs. 10C, 10D), despite identical orientations and parallelism with a weak, melt-rich host; (6) young dikes that intruded after the main dike had mineral lineations (Figs. 10A, 10B). These patterns illustrate how mineral folia- cooled and mostly solidified; (7) a southeastern contact, representing the mar- tions in crystallizing plutons are easily reset and typically record only the last gin of the magmatic system, where sheeted dikes are interfolded and mixed phase of deformation (e.g., Paterson et al., 1998, 2004; Pignotta et al., 2010; with country rock of the Valparaíso metamorphic complex. Coint et al., 2013).

The geometric relationships among these features are illustrated in tex- A close examination of the size fractions of minerals that make up the SC tural zones 4–6 of Figure 12. Zone 4 includes the northwestern contact and is foliations provides additional information on the mechanisms of fabric reset-

dominated by flow foliations (SC) and other structures that are unique to the ting. Only the largest fraction (0.5–1 cm) of plagioclase crystals are aligned

younger dike. Both zones 5 and 6 show structures at the southeastern end of and contribute to forming SC. In contrast, smaller grains that fill the spaces the unit. Zone 5 exhibits interfolded and stretched granitoids, which form a between megacrysts (e.g., Fig. 7E) are mostly equant, show less alignment,

distinctive magmatic layering (SD) absent in the rest of the unit. Country rock and appear to reflect in situ crystallization. This process, combined with the in zone 6 comprises gneiss, slate, biotite schist, calcareous gneiss. fragmentation of larger grains and mineral rotation in melt, effectively reset On its northwestern side (Figs. 1B and 2), the Estero Córdoba dike records the strain memory of the fabric. This interpretation agrees with the models an exchange of material with the Punta de Tralca tonalite (Figs. 5A, 5C) in of Arbaret et al. (2000), who showed that different size fractions of feldspar narrow channels. This exchange of material, along with the local sharing of in granites record different parts of the strain history. With increasing crystal foliations, indicates that temperatures were high enough and emplacement content, the largest megacrysts tend to evolve closer to the strain ellipsoid klepeis_01107 1st pages / 21 of 26 rates were slow enough to allow the two tonalites to mingle as they crystal- than small grains. We suggest that future work comparing the orientations and lized and deformed together. Parallel lineations formed by both stretched distributions of different mineral size fractions could prove useful for under- enclaves and aligned plagioclase phenocrysts (Fig. 10A) further suggest that standing parts of the strain history. both units record similar bulk flow directions. This interpretation is in agree- Our comparison of enclave populations in the two units also yielded an ment with numerical and analogue models of crystal alignment in a flowing unexpected result. Observations of shared foliations and evidence that both magma that suggest that as crystal contents increase, the heterogeneous enclaves and minerals crossed the contact at site 11IN01B suggest that the size distribution of natural crystals and contact interactions tend to gener- enclaves in the Estero Córdoba were derived from the Punta de Tralca. We ate fabrics with a lineation that tracks directions of magmatic flow (Arbaret therefore expected the enclaves in the former unit to retain some memory of et al., 2000). the oblate shapes and history of flattening in the latter. Viscosity contrasts and A comparison of mineral and enclave fabrics in each unit at site 11IN01B the likelihood that most of the strain accompanying dike emplacement was ac- (Fig. 5) yielded interesting information. In the Punta de Tralca tonalite, these commodated by flow in melt increases the probability of this retention. How- show differences in the age, amount, and style of deformation. As expected ever, the enclaves in the Estero Córdoba record no hint of the oblate shapes (e.g., Vernon and Paterson, 2006), these differences are accentuated in areas and flattening that dominates the Punta de Tralca tonalite. Instead they form where viscosity contrasts are high, such as in zone 2, and are reduced in areas a strong L > S fabric and uniformly prolate shapes (Figs. 10C, 10E). This result of low viscosity contrast, such as zone 1. Zone 2 enclaves record the earli- suggests that the enclaves also were reset, and their prior history erased, by est stages of deformation when mechanical sorting and mineral alignment in ductile stretching, shearing, and winnowing during dike emplacement. The

melt-rich magma currents formed SA. In zone 1, enclaves record a history most evidence of high strains also supports predictions (e.g., Barrière, 1981; Vernon similar to the matrix mineral foliations, which mostly show only the last stage and Paterson, 2006) that magma flow near stiff boundaries drives deformation

of deformation. This shared history is reflected in areas (e.g., Fig. 5B) where AS and sorting. This type of deformation in a flowing, melt-rich magma appears to

and SB foliations are parallel and show fairly uniform oblate (S > L) shape fab- be a primary mechanism for generating linear fabrics in granitoids. rics (Figs. 10C, 10D, 10F). However, even in these latter areas, the shape fabrics One of the pitfalls of using enclave populations to reconstruct deforma- created by the enclaves and mineral populations are significantly different (Fig. tion histories is that statistical averaging can increase errors and mask differ- 10C). These observations support the conclusions of others (Paterson et al., ences if the enclaves exhibited a wide variety of initial shapes (Paterson et al., 2004) who showed that enclaves and mineral foliations in plutons tend to re- 2004). The strong differences we obtained from the two units that persist after cord different parts of the deformation history. The implication is that parallel a consideration of the errors (Fig. 10C) (Appendix 1) appear to partly reflect foliations often record widely different processes, ages, and origins (cf. Pawley the relative uniformity of shapes and orientations in the two populations we and Collins, 2002). selected (note the low dispersions in Fig. 11). The pattern confirms that both

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enclaves and mineral populations have short memories that make them poor CONCLUSIONS strain markers (Paterson et al., 2004). However, the example also shows that the paired use of enclave and mineral structures can be informative because The Punta de Tralca tonalite records the intrusion of multiple batches the combination reveals information on timing and kinematics of flow and the of relatively mafic magma into an intermediate host through dikes. Micro- effects of different processes on the behavior of minerals and the evolution granitoid enclaves in the unit exhibit variable degrees of assimilation with of foliation types. The utility of this approach, as suggested by Paterson et al. a tonalitic and granodioritic host and preserve mesoscale and microscale (2004), demands information on the relative age, initial conditions, and con- structures that record rheological transitions as the crystallizing mush ap- text of the structures. As we illustrate here, some of these properties can be proached its solidus. In areas of high viscosity contrast between enclaves

reasonably established using crosscutting relationships and textural features and matrix, internal (SA) and external (SB) foliations typically are discordant, preserved in outcrops. However, they do not provide a true determination of indicating that the structures record different increments of deformation.

finite strain. Mineral microstructures and field relationships show that AS in these zones The southeastern end of the Estero Córdoba dike (zone 5, Fig. 12) exhibits is oldest and formed by a combination of (1) the rotation and alignment of a structural style that is absent farther north. At sites 11IN03A–11IN03C (Figs. crystals suspended in a flowing magma, (2) mechanical sorting during flow 1B, 2, and 6) sheets of compositionally diverse granitoids are interfolded with by the addition of matrix crystals at and across enclave boundaries, and one another and with layers of country rock, suggesting the incremental em- (3) high-temperature diffusion creep and sliding on melt-coated grains as placement of multiple batches of increasingly felsic dikes. The presence of syn- melts crystallized and were expelled. The occurrence of crystal-plastic defor- magmatic folds, xenoliths, and stretched screens of country rock (Figs. 6 and mation suggests the possibility of using experimentally derived flow laws 12) also suggest that the dike and the Valparaíso metamorphic complex locally to estimate the rheologies of magmas with variable crystal-melt fractions in share a deformation history. Pignotta et al. (2010) reached a similar conclu- future studies. sion for the Jackass Lakes pluton in the central Sierra Nevada batholith using In areas of low viscosity contrast, enclaves were mostly assimilated by klepeis_01107 1st pages / 22 of 26

analogous structures. Other work has shown that the differential movement of their matrix. Internal (SA) and external (SB) foliations are parallel and grade magma next to cooler country rock can accentuate deformation along pluton smoothly into one another, forming a regional compositional banding. This margins (Vernon and Paterson, 2006). In this interpretation, magma replen- parallelism indicates that the two foliations formed together during final defor- ishment may cause the magma to expand, resulting in flattening of both the mation of the matrix. Magmatic shear zones, faults, folds, sigmoidal tension pluton margin and its wall rock. gashes, and boudinage disrupt this regional layering, indicating that they also On the basis of these relationships we suggest that most, if not all, of the formed late in the deformation history when enough solid material was pres- structures in zone 5 are the youngest in the Estero Córdoba dike and reflect the ent in a crystal-rich mush to enable fractures and shear zones to form. The last stages of magma emplacement at its margin. In addition, the comagmatic draining of melts to form the crystal-rich mushes increased the mechanical history of the Punta de Tralca and Estero Córdoba units indicates that melt was coupling between enclaves and their matrix and promoted compaction, crys- present in the oldest parts of the system (zones 1–3) as melts near the margin tal-plastic deformation, and flattening, which resulted in in penetrative S > L (zones 5–6) were emplaced. In this context, zone 4 may represent a transfer mineral and enclave fabrics. These structures may provide key insight into the zone that fed dike emplacement in the outer parts of the magma chamber. The mechanisms responsible for the extraction of melt from a crystalline mush type of zonation appears similar to that described by Coint et al. (2013) for the to produce phenocryst-poor rhyolitic eruptions (e.g., Bachmann and Bergantz, Wooley Creek batholith in the Klamath Mountains; this batholith also shows 2004). These mechanisms may partially control the timing, volume, and style three main compositional and temporal zones: a lower zone formed from of Andean volcanism. multiple batches of gabbroic through tonalitic magmas, a central dike-rich Concentrations of leucocratic, quartz-rich material intruded previously zone that underwent mixing with the lower zone, and an upper zone, which deformed enclaves and matrix within the Punta de Tralca tonalite. These is youngest and composed of tonalite to granite. These zones suggest that accumulations exhibit changes in geometry, texture, and composition with large interconnected magma chambers are relatively common in continental increasing size, from small globular patches of tonalite and granodiorite arc systems and provide further evidence that plutons are assembled from that grade smoothly into the tonalite host to granitic dikes with internal

numerous, incrementally emplaced batches (cf. Glazner et al., 2004). However, flow foliations (SC) that entrain and truncate enclaves and older flow folia- the individual magma batches need not crystallize completely, but instead may tions. Gradational contacts between the concentrations and their host indi- interact comagmatically (cf. Coint et al., 2013). In these systems, the injection of cate that melt-rich magma was able to pool within a crystal-rich mush. The intermediate magma into a highly viscous, crystal-rich mush as dikes appears accumulations escaped most or all of the flattening and late near-solidus to be able to provide enough heat, melt, and mechanical energy to sustain the strains are recorded by both enclaves and matrix. We interpret these as magma chamber and help mobilize and expel felsic melts toward the outer or residual melts that were mobilized and concentrated by brittle and ductile upper reaches. deformation. They support a stepwise accumulation model for the pluton

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where melt escaped as the host crystallized and aided compaction of the APPENDIX 1. FABRIC ANALYSES AND ERROR ASSESSMENT crystal-rich mush. The Estero Córdoba dike records the processes by which a rigid, crys- Fabric Analysis Methods tal-rich mush deforming near its solidus was reactivated further and mingled comagmatically with an intrusion of intermediate composition. The dike re- The normalized Fry method (Fry, 1979; Erslev, 1988) produces a polar plot of the center to center distances and angles for each pair of objects that is normalized by the combined lengths of cords a structural style and history that differs from those of the Punta de their mean semiaxial diameters. An undeformed, randomly packed aggregate of objects produces Tralca tonalite, even though the two units were comagmatic. The two intru- a point cloud outside a central void of unit radial length. Through deformation, nearest-neighbor sions display local foliation discordances and evidence of material exchange lengths become closer in shortening directions and farther apart in lengthening directions. This anisotropy is reflected by an elliptical central void that is taken to be a two-dimension strain ratio in thin channels. Parallel lineations formed by both stretched enclaves and if the assumptions described in the text are satisfied.

aligned mineral aggregates suggest that both units record similar bulk flow The Rf /f method (Ramsay, 1967; Dunnet, 1969; Lisle, 1985) determines the axial ratio of a directions. Field relationships and mineral microstructures suggest that the sectional strain ellipse by statistically investigating the relationship between the eccentricities of deformed elliptical objects and their orientations. The method involves determining the orienta- dike was richer in melt and underwent less flattening, less compaction, and tions of deformed objects after iteratively applying a finite increment of inverse strain parallel to less crystal-plastic deformation than the more viscous crystal-rich mush of the vector mean of long axis orientations. This iterative process is carried through a geologically the Punta de Tralca tonalite. The presence of synmagmatic folds, stretched reasonable range of strain ratios, from which a chi-squared test for uniform object orientation also is applied. The inverse strain ratio that produces the most uniformly distribution population of dikes, flattened xenoliths, and deformed screens of gneiss suggest that dike object orientations is taken as the sectional strain ratio, subject to the validity of the assumptions emplacement involved ductile and brittle deformation, sheeting, and the mate- described in the text. rial transfer of country rock. To obtain a three-dimensional ellipsoid, the sectional methods are applied to at least three faces oriented at high angles to each other in order to constrain the inverse shape matrix of Shima Mineral orientations and distributions in the dike are identical to those in moto and Ikeda (1976) and Wheeler (1986), following the method in Robin (2002) and Launeau the Punta de Tralca tonalite and confirm that mineral foliations are easily reset. and Robin (2005). This procedure allows for a parameterization of fabrics using the orientations The in situ crystallization of new minerals, the fragmentation of plagioclase and normalized lengths of a triaxial ellipsoid. These parameters can then be used to investigate klepeis_01107 1st pages / 23 of 26 megacrysts, and crystal rotation within a melt-rich magma were the primary the shape symmetry of the fabric in terms of prolate versus oblate geometry following Lode’s (1926) parameter and the magnitude of distortion given by the octahedral shear strain (Ramsay resetting mechanisms. Different size fractions of minerals in granitoids record and Huber, 1983). different parts of the strain history, with the largest megacrysts recording more strain than smaller grains. Consequently, a comparison of the orientations and distributions of mineral size fractions should prove useful for evaluating these Error Assessment histories in the future. A comprehensive investigation of all errors involved in three-dimensional strain analysis is Field relationships indicate that enclaves in the northwest part of the beyond the scope of this contribution. However, some understanding of the variability of our analy- Estero Córdoba dike were derived from the Punta de Tralca tonalite. Despite ses of enclave fabrics is important for a comparison and interpretation of the results. The approach this origin, and similar orientations, these enclaves retain little evidence of implemented here follows the procedure of Mookerjee and Nickleach (2011), which involves an assessment of how perturbations of sectional data influence the parameters of fitted ellipsoids. their prior history, which was nearly erased by deformation during dike em- Mookerjee and Nickleach (2011) addressed this variability by constructing a random bivariate nor- placement. A comparison of mineral and enclave fabrics in the two units mal distribution of strain ratios and orientations as a function of the variance-covariance of the illustrates how intrusion of the Estero Córdoba dike resulted in velocity sectional Rf and f parameters. Sections that display less dependence between these parameters produce a larger range of strain ratios and orientations. Random samples from these distributions gradients that drove deformation, increased ductile distortion and winnow- then are used to construct a population of ellipsoids that describe the possible analysis error. ing, and resulted in linear (L > S) fabrics. The results highlight the utility of Despite its utility, this approach may be biased in situations involving a comparison of analyses three-dimensional fabric analyses in documenting the geometry of flow in from populations that exhibit different variances in initial axial ratios. To address this scenario, we implemented a modified procedure of the error analysis that involves making two assumptions: crystallizing magmas. (1) the observed distribution of object axial ratios and orientations is representative of the popula- This study provides further evidence that large interconnected intrusive tion for a given section and (2) the sample variance of harmonic means of axial ratios approximates bodies are assembled from many incrementally emplaced batches that need the sample variance of the sectional strain ratio. The first assumption is important because we assessed error by randomly sampling from a two-dimensional kernel density estimation (Venables not crystallize completely and, instead, may interact comagmatically. Relation- and Ripley, 2002) of object ratios and orientations for each section. The kernel density estimation ships preserved in the Punta de Tralca unit suggest that significant portions of grid is evaluated through axial ratios from 1% to 15% beyond the maximum observed axial ratio plutons in arc settings may be compacted, high-strength cumulate-rich bodies at a resolution of 0.05. Object orientations are evaluated through 180° at a 0.5° resolution. This that can be reactivated by the emplacement of magma through dikes and com- distribution is randomly sampled 50 times taking n objects at a time, where n is the original observed population size. Consequently, sectional fabric determinations made from originally larger binations of synmagmatic brittle and ductile deformation. In these systems, populations will reflect lower variance and more confidence about the sectional results. Conversely, the injection of intermediate magmas into highly viscous, crystal-rich mushes sections with fewer objects will display greater variance and lower confidence. From the 50 sample through dikes also appears to be able to provide enough melt and energy to populations a measure of the variance of the strain ratio and lengthening direction is made. Con- sidering that computational efficiency is compromised by applying an iterative destraining and sustain the magma chamber and help mobilize and expel felsic melts upward chi-squared test to each sample population in order to calculate a series of strain ratios, we simply and outward toward the roof and margins of the system. calculated the harmonic mean of axial ratios following assumption two. The variance-covariance

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between the harmonic means and the absolute difference between the sectional vector mean and Coint, N., Barnes, C.G., Yoshinobu, A.S., Chamberlain, K.R., and Barnes, M.A., 2013, Batch-wise as- the sample vector means are used to produce a random bivariate normal distribution, from which sembly and zoning of a tilted calc-alkaline batholith: Field relations, timing and compositional values are randomly sampled and used to construct a population of ellipsoids. The remaining variation: Geosphere, v. 9, p. 1729–1746, doi:10 .1130 /GES00930 .1. methodology parallels Mookerjee and Nickleach (2011) in that a bivariate kernel density estimation Coleman, D.S., Gray, W., and Glazner, A.F., 2004, Rethinking the emplacement and evolution of is used to construct confidence intervals for Lode parameter and octahedral shear strain. zoned plutons: Geochronologic evidence for incremental assembly of the Tuolumne Intrusive Suite, California: Geology, v. 32, p. 433–436, doi:10 .1130 /G20220 .1 . Cordani, U., Munizaga, F., Hervé, F., and Hervé, M., 1976, Edades radiométricas provenientes del basa- mento cristalino de la Cordillera de la Costa de las provincias de Valparaíso y Santiago, Chile, ACKNOWLEDGMENTS in Proceedings, 1st Congreso Geológico Chileno: Santiago, Universidad de Chile, p. 213–221. This paper represents part of Webber’s Master of Science thesis (University of Vermont, Burling- Couch, S., Sparks, R.S.J., and Carroll, M.R., 2001, Mineral disequilibrium in lavas explained by ton). Some funding was provided by National Science Foundation grant EAR-063594 to Klepeis. convective self-mixing in open magma chambers: Nature, v. 411, p. 1037–1039, doi:10 .1038 We gratefully acknowledge reviews by Aaron Yoshinobu and an anonymous reviewer that helped /35082540. improve the manuscript. Creixell, C., Parada, M.A., Roperch, P., Morata, D., Arriagada, C., and Pérez de Arce, C., 2006, Syn- tectonic emplacement of the Middle Jurassic Concón mafic dike swarm, Coastal Range, central Chile (33°S): Tectonophysics, v. 425, p. 101–122, doi:10 .1016 /j .tecto .2006 .07 .005 . Creixell, C., Parada, M., Morata, D., Roperch, P., and Arriagada, C., 2009, The genetic relationship REFERENCES CITED between mafic dike swarms and plutonic reservoirs in the Mesozoic of central Chile (30°– Abbott, R.N., 1989, Internal structures in part of the South Mountain batholith, Nova Scotia, 33°45′S): Insights from AMS and geochemistry: International Journal of Earth Sciences, v. 98, Canada: Geological Society of America Bulletin, v. 101, p. 1493–1506, doi:10 .1130 /0016 -7606 p. 177–201, doi:10 .1007 /s00531 -007 -0240 -9 . (1989)101<1493: ISIPOT>2 .3 .CO;2 . Creixell, C., Parada, M., Morata, D., Vásquez, P., Pérez de Arce, C., and Arriagada, C., 2011, Arbaret, L., Fernandez, A., Ježek, J., Ildefonse, B., Launeau, P., and Diot, H., 2000, Analogue and Middle-Late Jurassic to Early Cretaceous transtension and transpression during arc building numerical modelling of shape fabrics: Application to strain and flow determination in mag- in central Chile: Evidence from mafic dike swarms: Andean Geology, v. 38, p. 37–63. mas: Royal Society of Edinburgh Transactions, Earth Sciences, v. 90, p. 97–109, doi:10 .1130 /0 Dell’Angelo, L.N., and Tullis, J., 1988, Experimental deformation of partially melted granitic aggre- -8137-2350 -7 .97 . gates: Journal of Metamorphic Geology, v. 6, p. 495–515, doi:10 .1111 /j .1525 -1314 .1988 .tb00436 .x . Bachmann, O., and Bergantz, G.W., 2004, On the origin of crystal-poor rhyolites: Extracted from Dunnet, D., 1969, A technique of finite strain analysis using elliptical particles: Tectonophysics, v. 7,

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