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Middle Eocene to early Oligocene intrusions, widespread in the Ruby Mountains– East Humboldt Range metamorphic core complex, Nevada, USA, provide insights into a major Paleogene magmatic episode and its relation to tectonism in the northeastern Great Basin. These intrusions, well-exposed in upper Lamoille Canyon, range in composition from gabbro to leucomonzogranite. They form small plutons, sheets, and dikes that intrude the metamorphic and granitic infrastructure of the core complex. Two types of Paleogene monzogranite were recognized. The first is exemplified by two of the larger intrusive bodies, the Snow Lake Peak and Castle Lake intrusions, which occur as sheet- like bodies near and at the structural base of metamorphosed Neoproterozoic and Cambrian Prospect Mountain Quartzite where it is inverted above Cambrian and Ordovician marble of Verdi Peak in the Lamoille Canyon nappe. Swarms of dikes are associated with these intrusions. U-Pb (zircon) ages range ca. 40– 33 Ma and typically display relatively simple and minor inheritance. The rocks have the lowest εHf (zircon) and εNd (whole rock) of any of the middle Cenozoic granites. The second type of monzogranite, Overlook type, typically occurs as thin, isolated dikes and leucosome- like bodies in Late Cretaceous granites of the infrastructure, with no obvious relationship to the large monzogranite bodies. Overlook- type monzogranite displays complex zircon inheritance, yields igneous ages ca. 37– 32 Ma, and has εHf (zircon) and εNd (whole rock) identical to those of Late Cretaceous granites in the core complex. These isotopic and field data indicate that Overlook- type monzogranite formed in situ through anatexis of host Cretaceous granites. A pervasive thermal event was required to stimulate this crustal melting. Gabbros from Lamoille Canyon and quartz diorite dated from 32 km away signal mantle- derived magmatism ca. 39– 37 Ma (U-Pb, zircon) was a driver of crustal melting and hybridization. Eocene 40Ar/39Ar apparent ages on hornblende and biotite are consistent with syn- to post- magmatic extensional exhumation and decompression. Thus, the core complex provides a window into trans- crustal magmatism and insight into how such magmatism affected the Nevadaplano orogenic plateau. This Paleogene thermal pulse, which may relate to removal of the Farallon slab by delamination of mantle lithosphere, involved partial melting of the upper mantle and transfer of magma and heat to the Nevadaplano crust. Lower- crustal melting of Archean(?) to Paleoproterozoic rocks resulted in Snow Lake Peak– type magmas, and middle- crustal melting of granite in the infrastructure yielded Overlook- type magmas. This crustal magmatism, as exemplified by the intrusions in the core complex, likely played a role in destabilizing the Nevadaplano and its later collapse during middle Miocene extension. The Paleogene intrusions and associated structural features also provide insight into the evolution of the core complex through either the buoyant upwelling of a melt- rich diapir (gneiss- dome model) or buoyant upwelling of the melt- rich middle crust synchronous with a west- rooted mylonitic shear zone (extensional shear- zone model). We favor a hybrid that incorporates both models. [ABSTRACT FROM AUTHOR]

The concept of defrosting, heating and partially melting a crystal-rich, weakly mobile or immobile magma (magmatic mush) has gained wide support from volcanological studies. This process has been called on as a means to promote eruption of crystal-rich (monotonous) dacites and also to permit extraction of felsic magmas, which may accumulate in the upper crust and erupt as crystal-poor rhyolite or trachyte. Most studies of the latter type of defrosting call on a conjugate plutonic part of the system from which the felsic melt was extracted. Although petrographic and geochemical features of defrosting are well described for eruptive rocks, few studies have investigated petrographic and geochemical features of plutons that indicate defrosting. The Jurassic Ashland pluton is a tilted intrusive complex exposed in southern Oregon and northern California, USA. The central part of the pluton, quartz monzodiorite (QMD), displays petrographic features (crystal fragmentation, widespread resorption, local concentrations of refractory minerals) characteristic of partial melting. This unit is intruded and overlain by biotite granite, which displays plagioclase cores identical in composition to plagioclase in the underlying QMD, resorbed titanite cores in plagioclase, and local subhedral to anhedral cores of alkali feldspar in poikilitic alkali feldspar crystals. Hornblende and biotite in the biotite granite display enrichments in Ti and Nb relative to these minerals in QMD, negating fractional crystallization as a petrogenetic process. Instead, these high Ti and Nb contents reflect significant partial melting of titanite in the QMD, thereby releasing high field strength elements to the defrosted biotite granite melt. The biotite granite magmas are thus interpreted as the melt-rich products of defrosting caused by intrusion of mafic–intermediate magmas into the QMD magma column. [ABSTRACT FROM AUTHOR]

Bulk-rock compositions are commonly used as proxies for melt compositions, particularly in silicic plutonic systems. However, crystal accumulation and/or melt loss may play an important role in bulk-rock compositional variability (McCarthy and Hasty 1976; McCarthy and Groves 1979; Wiebe 1993; Wiebe et al. 2002; Collins et al. 2006; Deering and Bachmann 2010; Miller et al. 2011; Vernon and Collins 2011; Lee and Morton 2015; Lee et al. 2015; Barnes et al. 2016a; Schaen et al. 2018). Recognizing and quantifying the effects of crystal accumulation and melt loss in these silicic systems is challenging. Hornblende-melt Fe/Mg partitioning relationships and hornblende (Hbl) chemometry are used here to test for equilibrium with encompassing bulk-rock and/or glass compositions from several plutonic and volcanic systems. Furthermore, we assess the extent to which these tests can be appropriately applied to Hbl from plutonic systems by investigating whether Hbl from the long-lived (~10 Ma) Tuolumne Intrusive Complex preserves magmatic crystallization histories. On the basis of regular zoning patterns, co-variation of both fast- and slow-diffusing trace elements, Hbl thermometry, and compositional overlap with volcanic Hbl we conclude that Hbl from plutons largely preserve records supporting the preservation of a magmatic crystallization history, although many compositional analyses yield calculated temperatures <750 °C, which is unusual in volcanic Hbl. Hornblende is only rarely in equilibrium with host plutonic bulk-rock compositions over a wide range of SiO2 contents (42–78 wt%). Hornblende chemometry indicates that the majority of Hbl from the plutonic systems investigated here is in equilibrium with melts that are typically more silicic (dacitic to rhyolitic in composition) than bulk-rock compositions. These results are consistent with crystal accumulation and/or loss of silicic melts within middle- to upper-crustal plutons. Although the processes by which melts are removed from these plutonic systems is uncertain, it is evident that these melts are either redistributed in the crust (e.g., leucogranite dikes, plutonic roofs, etc.) or are instead erupted. In contrast, Hbl from volcanic rocks is more commonly in equilibrium with bulk-rock and glass compositions. In most cases, where Hbl is out of equilibrium with its host glass, the glasses are more evolved than the calculated melts indicating crystallization from a less fractionated melt and/or mixed crystal populations. Where Hbl is not in equilibrium with volcanic bulk-rocks, the bulk-rock compositions are typically more mafic than the calculated melts. In some intermediate volcanic samples, the occurrence of wide-ranges of calculated melt compositions is indicative of magma mixing. The general absence of Hbl with temperatures <750 °C from volcanic systems suggests that magmatic mushes below this temperature are unlikely to erupt. Our results indicate that bulk-rock compositions of granitic plutonic rocks only rarely approximate melt compositions and that the possibility of crystal accumulation and/ or melt loss cannot be ignored. We suggest that detailed assessments of crystal accumulation and melt loss processes in magmatic systems are crucial to evaluating magma differentiation processes and discerning petrogenetic links between plutonic and volcanic systems. [ABSTRACT FROM AUTHOR]

The Wooley Creek batholith is a Late Jurassic, arc-related, calc-alkaline plutonic complex in the Klamath Mountain province of California. Post-emplacement tilting and erosion have exposed ~12 km of structural relief. The complex consists of an older (~159.1 Ma) lower zone (pyroxenite to tonalite) assembled by piecemeal emplacement of many magma batches, a younger (~158.2 Ma) upper zone (quartz diorite to granite), and a transitional central zone. In the lower zone, pyroxenes are too Fe rich to be in equilibrium with a melt whose composition was that of the host rock. Mass-balance calculations and simulations using rhyolite-MELTS indicate that these rocks are cumulates of pyroxenes and plagioclase ± olivine and accessory apatite and oxides. Percentages of interstitial melt varied from ~7.5-83%. The plagioclase/pyroxene ratios of cumulates vary considerably among the most mafic rocks, but are relatively uniform among quartz diorite to tonalite. This near-constant ratio results in compositional trends that mimic a liquid line of descent. In the upper zone, bulk-rock compositional trends are consistent with differentiation of andesitic parental magmas. Upward gradation from quartz dioritic to granitic compositions, modeled via mass-balance calculations and rhyolite-MELTS simulations, indicate that structurally lower parts of the upper zone are cumulates of hornblende and plagioclase ± biotite and accessory minerals, with 37-80% trapped melt. In contrast, the structurally higher part of the upper zone represents differentiated magma that escaped the subjacent cumulates, representing differentiated melt fractions remaining from 92-54%. The ratio of cumulate plagioclase/(plagioclase + mafic minerals) is ~0.48 among upper-zone cumulates, mimicking a liquid line of descent. The results suggest that compositional variation in many calc-alkaline plutons may be at least as representative of crystal accumulation as of fractional crystallization. If so, then the assumption that arc plutons geochemically resemble frozen liquids is dubious and should be tested on a case-by-case basis. Moreover, comparisons of plutonic rock compositions with those of potentially comagmatic volcanic rocks will commonly yield spurious results unless accumulation in the plutons is accounted for. [ABSTRACT FROM AUTHOR]

The Late Jurassic English Peak plutonic complex was emplaced in an upper crustal retro-arc setting in the central Klamath Mountains province, northern California. Emplacement of the main, central pluton was preceded by intrusion of two satellite bodies: the Uncles Creek pluton crystallized from H2O-rich quartz dioritic magma with hornblende as the liquidus mafic phase; in contrast, the Heiney Bar pluton is a c. 25km diameter body zoned from gabbro to granodiorite. Al-in-hornblende barometry from these two plutons indicates a stage of magma storage at c. 600- 500 MPa. The central English Peak pluton is a c. 15km diameter body composed of early and late stages. Early stage rocks range from gabbro to tonalite, with variable proportions of augite, orthopyroxene, hornblende and biotite. The early stage lacks discernible zoning and rock types vary at the outcrop scale. This diversity is reflected in bulk-rock compositions, which do not form a compositional array. The late-stage intrusion consists of three concentric units that are zoned from outer, more mafic rocks (quartz diorite, tonalite, quartz monzodiorite) to inner, compositionally evolved rocks (granodiorite and granite). Late-stage samples plot in smooth, typically linear arrays for most major and trace elements. Al-in-hornblende pressures indicate that late-stage hornblende cores grew in a reservoir at c. 400MPa and that rims grew at the level of final emplacement (c. 250 MPa). The mid-crustal reservoir was the site of late-stage magma evolution, including episodic magma mixing. Oxygen and Sr isotopes indicate initial evolution of English Peak pluton magmas in a deep crustal region of mixing, assimilation, storage, and homogenization (MASH zone), where they were contaminated by metasedimentary rocks. Thus, the English Peak pluton represents a crustalscale system, with mantle-derived magmas that differentiated near the Moho, storage and crystallization of satellite-pluton magmas in the middle crust (c. 600-500 MPa), development of a large, episodically recharged, magma chamber in the upper middle crust (c. 400 MPa) and final emplacement in the upper crust. [ABSTRACT FROM AUTHOR]

Hornblende in the Kuna Crest lobe (KCL) of the Tuolumne Intrusive Complex (TIC) and the upper zone of the Wooley Creek batholith (WCB) precipitated over a temperature range of ~835 to 700 °C, and thus has the potential to record magmatic processes. We measured trace element concentrations in hornblende from the WCB, from the KCL of the TIC, and from one sample from an adjacent interior unit of the TIC to compare and contrast magmatic processes in these two mid-crustal intrusions. In both systems the magmatic amphibole is magnesiohornblende in which Ti, Zr, Hf, Nb, Sr, Ba, and rare earth elements (REE) typically decrease from crystal interiors to rims, an indication of compatible behavior of these elements, and the size of the negative Eu anomaly decreases. In the Kuna Crest lobe, hornblende from individual mapped units differs in trace element abundances and zoning trends. Some samples contain at least two distinct hornblende populations, which is particularly evident in the shapes of REE patterns. In contrast, compositions of hornblende from all structural levels of the upper WCB and related dacitic roof-zone dikes form a single broad array and the REE patterns are essentially indistinguishable, regardless of rock type, from quartz diorite to granite. In the WCB, Zr/Hf ratios in hornblende are consistent with crystallization from a melt with chondritic Zr/Hf values. In contrast, most hornblende in the KCL has Zr/Hf values lower than expected from crystallization from a melt with chondritic values, suggesting that zircon fractionation occurred before and during crystallization of the hornblende. Simple fractional crystallization models indicate that REE, high field strength elements, Sr, and Ba were compatible in KCL and WCB magmas as hornblende grew; these trends require removal of hornblende + plagioclase + zircon ± ilmenite ± biotite. The uniform variations of trace element concentrations and patterns in the upper WCB and roofzone dikes indicates crystallization from a large magma body that was compositionally uniform; probably stirred by convection caused by influx of mafic magmas at the base of the zone (Coint et al. 2013a, 2013b; cf. Burgisser and Bergantz 2011). In contrast, in the KCL, each analyzed sample displays distinct hornblende compositions and zoning patterns, some of which are bimodal. These features indicate that each analyzed sample represents a distinct magma and that individual magmas were variably modified by fractionation and mixing. Hornblende trace element contents and zoning patterns prove to be powerful tools for identification of magma batches and for assessing magmatic processes, and thereby relating plutonic rocks to hypabyssal and volcanic equivalents. [ABSTRACT FROM AUTHOR]

The 465 Ma Svarthopen pluton in northcentral Norway was emplaced under middle-crustal conditions (∼700 MPa) into metasedimentary rocks of the Helgeland Nappe Complex. The pluton is characterized by zones of mingling and mixing of gabbro/ diorite with peraluminous, garnet-bearing biotite granite. Variation in bulk-rock Sr and Nd isotope ratios are consistent with simple mixing; however, nonuniform enrichment of Zr and the rare earth elements (REEs) suggests that individual magma batches underwent postmixing fractionation. Hybrid intermediate rocks are characterized by Ca-rich garnet. Such garnet is absent in possible mafi c end members, and garnet in felsic end members is Ca poor. Evidently, the ferroan , peraluminous hybrid rocks promoted garnet stability, and we interpret these garnets to be igneous in origin. Garnets in the hybrids have low Zr contents, positive light REE slopes, and fl at to negative heavy REE slopes with lower REE abundances than in typical igneous garnet. These trace-element data combined with textural evidence suggest that garnet formed near the solidus, after fractionation of zircon, allanite, and possibly xenotime. The Svarthopen pluton is not unique: similar intermediate rocks with Ca-rich garnets crop out adjacent to three other plutons in the region. Formation of garnet-bearing hybrid rocks in the Svarthopen pluton provides an analog for mixing of peraluminous and ferroan endmember magmas in the deep crust, where such mixing should be widespread, particularly in continental arcs and zones of continental collision. Postmixing fractionation of hybrid magmas could greatly increase the diversity of major- and trace-element abundances yet retain an isotopic signature of mixing. Moreover, formation of garnet-rich hybrids could result in lower-crustal rocks dense enough to delaminate from the arc crust. [ABSTRACT FROM AUTHOR]

The Hortavær intrusive complex consists of a wide range of plutonic rocks, from gabbro (calcic) to alkali feldspar syenite (alkalic). Emplacement at 456 ± 8 Ma (U-Pb, titanite) was primarily as a series of dikes that range from tens of cm to many meters in width. Magma mingling structures are ubiquitous and magma mixing occurred locally. Therefore, the intrusive complex can be considered to be a zone of magma transfer and storage rather than a single pool of magma. The complex is characterized by CaO-rich rock compositions and by the presence of minerals typical of assimilation of carbonate-rich metasedimentary rocks, such as calcite, titanite, scapolite, nepheline, Ca-garnet, and idocrase. These features have been interpreted as the result of intense assimilation of host calc-silicate rocks. However, major and trace element compositions show inflections in the magmatic trend, which argues for crystal-liquid separation processes. Furthermore, some syenites are quartz bearing, which suggests a quartzofeldspathic component in the contaminant.When combined, these observations suggest that the Hortavær magmas evolved by assimilation-fractional crystallization of parental gabbroic magmas to evolved syenitic ones. Fractionation was initially dominated by separation of clinopyroxene, which was stabilized at the expense of olivine because of assimilation of carbonate components of the host rocks. The excessive fractionation of clinopyroxene forced melt compositions to alkali-rich, silica-undersaturated compositions, rather than SiO2-rich ones expected with olivine fractionation. Such assimilation was possible because of the open-system behavior of the intrusive complex (magma transfer zone) such that CO2 was lost before it could stop assimilation reactions. Development of evolved quartz syenitic magmas required a shift to assimilation of the quartzofeldspathic component of the host rocks, which occurred because carbonates are insoluble in such evolved magmas. [ABSTRACT FROM AUTHOR]

The dioritic Velfjord plutons (∼448 Ma) were emplaced into regional migmatitic metapelitic and metacarbonate rocks at mid-crustal levels, corresponding to pressures of ∼700 MPa. Exhumation to ∼400 MPa began while the migmatites were in a partly molten state. With increasing proximity to the plutons, regional stromatic migmatites change to diatexite, and diatexitic dikes are common within 500 m of the contacts. We interpret these relationships to indicate that heat from the plutons resulted in contact migmatization in a zone up to 1 km wide. Typical residual mineralogy in the diatexites is plagioclase + quartz + biotite + garnet + sillimanite ± K-feldspar, consistent with biotite dehydration melting. Pod- and dike-like leucosomes consist of two types: earlier high-K (granitic) ones with mineral assemblages identical to the migmatites and later low-K (tonalitic) ones in which sillimanite is sparse and garnet absent. The high-K leucosome magmas can be explained by biotite dehydration melting at 700 MPa. Within the aureole, mafic magmas were locally injected into, and hybridized with, the diatexites and the high-K leucosome magmas. In contrast, the low-K leucosomes are thought to result from local, late-stage remelting of H2O-saturated diatexite. The H2O-rich fluid was probably released from intergranular melt trapped in the diatexites during exhumation and solidification. Distinctive porphyritic ‘contact granites’ are common at pluton contacts. Although the mineral assemblage of these granites is identical to that of the diatexites, their isotopic compositions are distinct, with εNd and δ18O in the migmatites from −7·6 to −9·6 and from +10·9‰ to +13·5‰, and in the contact granites from −5·2 to −7·5 and from +9·6‰ to +12·3‰, respectively. Thus, the contact granites could have a source that is isotopically distinct from, but mineralogically similar to the diatexites, or they could result from mixing of magma similar to the high-K leucosomes with dioritic magmas. Mass balance calculations are consistent with the latter interpretation, with proportions of granitic to dioritic magmas from 7:1 to 7:3. Emplacement and solidification of the dioritic plutons provided zones of structural anisotropy along which high-K leucosome magmas and contact granite magmas collected. These magmas were injected by additional dioritic magma and further hybridized. Because the solidi of the plutons were several hundred degrees higher than that of the granitic magmas, the pluton walls acted as long-lived, hot, rigid surfaces along which magmas collected and migrated. [ABSTRACT FROM PUBLISHER]

The late Eocene Harrison Pass pluton was emplaced in the transition zone between the infrastructure and suprastructure of the Ruby Mountains core complex. Emplacement was at ∼3 kbar pressure and was in two stages: early stage tonalitic to monzogranitic magmas, followed by late-stage monzogranites and mafic dikes. The early stage began with emplacement of biotite ± hornblende granodiorite of Toyn Creek, followed by the biotite monzogranite of Corral Creek. Quenched equivalents of these units are preserved as porphyritic dikes in the roof. Leucocratic monzogranite that forms cupolas in the roof zone represents the product of fractional crystallization of the early magmas. Al-in-hornblende barometry and the presence of magmatic epidote suggest that early stage magmas resided at a pressure of ∼5−6 kbar before emplacement in the upper crust. Compositional variation in the Toyn Creek and Corral Creek units is essentially linear, and can be explained by mixing of a tonalitic end member with a monzogranitic end member such as evolved samples of the monzogranite of Corral Creek. The tonalitic end member was itself a hybrid that formed by interaction of mafic magma with crustal melts. The monzogranitic end member is a crustal melt that escaped hybridization. Nd isotopic compositions of the early stage are heterogeneous and do not correlate with degree of differentiation, which is consistent with a compositionally heterogeneous felsic end member. Elemental variation in the early stage of the pluton is unusual because of its essentially linear trends, which suggest a single mixing event before emplacement in the upper crust. Late-stage activity consisted of three pulses of monzogranitic magma plus sparse mafic dikes. The largest and youngest of these pulses, the two-mica monzogranite of Green Mountain Creek, is distinct from all other units in the presence of restitic enclaves, low εNd, and high initial 87Sr/86Sr. Pod-like bodies of leucocratic biotite ± amphibole monzogranite and sheets and dikes of leucocratic two-mica monzogranite make up the other late-stage granites. These rocks display deep negative Eu anomalies and show wide, non-systematic concentrations of high field strength elements; however, their isotopic compositions are identical to those of the early stage rocks. They are thought to be small melt fractions of the lower to middle crust. Their elemental compositions are thought to result from the effects of residual plagioclase and accessory minerals. The variable and non-systematic isotopic compositions of all granitic units in the pluton suggest a heterogeneous source region, such as the Proterozoic Mojave province. [ABSTRACT FROM PUBLISHER]

The Velfjord plutons are mafic-intermediate plutons in the Bindal Batholith that were emplaced into pelitic and calcareous rocks of the Helgeland Nappe Complex of the Uppermost Allochthon at ∼448 Ma. Al-in-hornblende barometry suggests emplacement in the range of 6 to 8 kbar, which is consistent with the presence of magmatic epidote. Pelitic rocks in the aureoles underwent partial melting and leucosomes locally accumulated adjacent to the plutons to form ''contact granites''. The results of garnetaluminosilicate-silica-plagioclase (GASP) thermobarometry combined with a recently published petrogenetic grid for dehydration partial melting of pelites suggest a clockwise P-T-t path for the wall rocks. The GASP results, plus the presence of early kyanite, suggest initial melting in the 7 to 8 kbar range. Temperatures close to the plutons reached at least 750°C to 800°C. Nearly isothermal decompression to ∼4 to 5 kbar resulted in the hottest wall rocks reaching cordierite stability while they were still partly molten. Cooler wall rocks could not reach conditions of cordierite stability because of the positive slope of the cordierite-in equilibrium. The state of HNC crust prior to pluton emplacement cannot yet be determined. However, rapid exhumation of the plutons and their wall rocks suggests that the youngest plutons of the Bindal Batholith were probably emplaced at lower pressures. [ABSTRACT FROM AUTHOR]

Midcrustal (25–30 km) emplacement of the dioritic Sausfjellet pluton into rocks of the Helgeland Nappe Complex, central Norway, occurred in two stages. Stage 1 consists of two-pyroxene hornblende gabbro and diorite. Stage 2 is asymmetrically zoned, with a modally layered central zone of diorite and anorthosite and a western/annular zone of quartz-bearing monzodioritic rocks. Igneous layering was locally attenuated, folded, and boudinaged in the hyper-solidus state. The magmatic foliation trajectory pattern in the pluton defines a shallowly southwest-plunging synform that crosscuts compositional zones. Mineral lineations plunge shallowly to moderately to the southwest. The pluton intruded a major lithologic boundary within the nappe; migmatitic pelitic gneisses are the main host rocks to the western part of the pluton, whereas the eastern and central parts are hosted predominantly by metacarbonate rocks. Calc-silicate, marble, quartzo-feldspathic, and dioritic xenoliths (up to 200 m in length) are present throughout the pluton; they are most common in Stage 1 and the central zone of Stage 2. Metapelitic xenoliths are conspicuously absent. Ductile flow during emplacement produced an ∼1-km-wide structural aureole in which host-rock structures were deflected into subparallelism with the steeply inward-dipping margin of the pluton. Tight antiforms developed along the northeastern, southeastern, and southwestern margins. Amphibolite-grade shear zones in the host rocks preserve plutonside-up kinematic indicators. In addition to the abundance of dioritic, calc-silicate, and quartzo-feldspathic gneiss xenoliths and geochemical evidence for assimilation in the western/annular zone, regional discordance of the pluton-host-rock contacts indicates that stoping was also an important emplacement process at midcrustal depths. Following magma emplacement, foundering of the central portion of the chamber combined with possible ca. 445 Ma regional contraction produced the map-scale synform defined by magmatic foliations and igneous layers. This study demonstrates that stoping and assimilation may occur simultaneously with host-rock ductile flow during magma chamber evolution at midcrustal levels and offers an explanation of why xenolith preservation may be compositionally dependent. [ABSTRACT FROM AUTHOR]