Consideration of the models that have been applied to explain the chemical variations within granitic rock suites shows that most are inadequate to account for the main variations. This stems from a ...variety of model deficiencies, ranging from physical or energetic inadequacies to incompatibility with the chemical data or internal inconsistency between models based on, for example, isotope or trace-element data and major-element data. We contend that any model that fails any of these tests of internal consistency cannot be considered further. Thus, although we can point to examples in which many of the traditionally accepted mechanisms have played secondary roles in producing variation, there presently remains but one viable choice for the primary mechanism by which most granitic magmas acquire compositions beyond the range defined by the compositions of crustal melts. That primary mechanism is peritectic assemblage entrainment (PAE).
We infer that once a partial melt has formed in a crustal protolith it may segregate from its complementary solid residue carrying small crystals of the peritectic phase assemblage formed in the melting reaction, and that the ratios of individual peritectic minerals in the entrained assemblage remains fixed in the ratio decreed by the stoichiometry of the melting reaction. For those elements with low solubilities in granitic melts, PAE (in varying degrees), accompanied by co-entrainment of accessory minerals, is responsible for most of the primary elemental variation in granitic magmas. In contrast, the concentrations of elements with high solubilities in silicic melts reflect the protolith compositions in a simple and direct way. The source is the primary control on granite magma chemistry; it dictates what is available to dissolve in the melt and what will be formed as the entrainable peritectic assemblage. The apparent complexity in granitic rock suites is largely a consequence of these processes in the source. All other mechanisms contribute only as a secondary overlay.
► Most models for chemical variation in granites are inadequate to account for the main variations. ► Many processes can play secondary roles but peritectic assemblage entrainment dominates. ► Partial melt may segregate from its residue carrying crystals of the peritectic assemblage. ► Peritectic crystals are entrained in a ratio decreed by the stoichiometry of the melting reaction. ► Thus, protolith composition is the primary control on granite magma chemistry.
The high-K, calcalkaline granitic rocks of the 370 Ma, post-orogenic Harcourt batholith in southeastern Australia have I-type affinities but are mildly peraluminous and have remarkably radiogenic ...isotope characteristics, with
87
Sr/
86
Sr
t
in the range 0.70807 to 0.714121 and εNd
t
in the range − 5.6 to − 4.3. This batholith appears to be a good example of magmas that were derived through partial melting of distinctly heterogeneous source rocks that vary from intermediate meta-igneous to mildly aluminous metasedimentary rocks, with the balance between the two rock types on the metasedimentary side. Such transitional S-I-type magmas, formed from mainly metasedimentary source rocks, may be more common than is generally realised. The Harcourt batholith also contains mainly granodioritic igneous microgranular enclaves (IMEs). Like their host rocks, the IMEs are peraluminous and have rather radiogenic isotope signatures (
87
Sr/
86
Sr
t
of 0.71257–0.71435 and εNd
t
of − 7.3 to − 4.3), though some are hornblende-bearing. Origins of these IMEs by mixing a putative mantle end member with the host granitic magma can be excluded because of the variability in whole-rock isotope ratios and, for the same reason, the IME magmas cannot represent quench cumulates (autoliths) from the host magmas. Less abundant monzonitic to monzosyenitic IMEs cannot represent accumulations of magmatic biotite and/or alkali feldspar because K-feldspar is absent, and there is no co-enrichment of K
2
O and FeO + MgO, nor can they be mixtures of anything plausible with the host-rock magma. The granodioritic IMEs probably originated through high degrees of assimilation of a range of crustal materials (partial melts?) by basaltic magmas in the deep crust, and the monzonitic IMEs as melts of enriched subcontinental mantle. Such enclave suites provide little or no information on the chemical evolution of their host granitic rocks.
Summary Duchenne muscular dystrophy (DMD) is a severe, progressive disease that affects 1 in 3600–6000 live male births. Although guidelines are available for various aspects of DMD, comprehensive ...clinical care recommendations do not exist. The US Centers for Disease Control and Prevention selected 84 clinicians to develop care recommendations using the RAND Corporation–University of California Los Angeles Appropriateness Method. The DMD Care Considerations Working Group evaluated assessments and interventions used in the management of diagnostics, gastroenterology and nutrition, rehabilitation, and neuromuscular, psychosocial, cardiovascular, respiratory, orthopaedic, and surgical aspects of DMD. These recommendations, presented in two parts, are intended for the wide range of practitioners who care for individuals with DMD. They provide a framework for recognising the multisystem primary manifestations and secondary complications of DMD and for providing coordinated multidisciplinary care. In part 1 of this Review, we describe the methods used to generate the recommendations, and the overall perspective on care, pharmacological treatment, and psychosocial management.
Under the right circumstances, fluid-fluxed crustal melting occurs, as demonstrated by some amphibolite-facies migmatites, but the relatively low temperatures involved make this mode of formation an ...unsatisfactory model for most silicic magma genesis in arcs. The concept of silicic arc magma formation through either partial melting of metabasalts or fractionation of hydrous basaltic parent magmas should also be treated with scepticism, as both these processes produce sodic and moderately to strongly peraluminous liquids that are chemically unlike most arc silicic rocks and glasses. Furthermore, if the silicic magmas are formed in the deep crust, the fractionation model predicts evolved liquids with extreme H
2
O contents. Thus, the answer to the question posed in the title is that neither of these two models, in isolation, seems likely for the formation of the majority of the more silicic magmas in arc environments. Given the totality of the evidence, we favour models in which high-
T
processes dominate. These could include fluid-absent partial melting of older non-basaltic arc crust, entrainment of source-derived crystal cargos, hybridisation with mantle-derived magmas and, in some cases, crystal fractionation of andesitic magmas at shallow crustal levels.
Despite a perception that it represents a perverse divergence, it is perfectly possible to believe in the existence of S- and I-type granites (and the implications for the nature of their ...protoliths), and to disbelieve in the applicability of the restite-unmixing model for chemical variation in granitic magmas. White and Chappell erected the S–I classification with impeccable validity. The isotopic evidence demands contrasting source reservoirs for S- and I-type granitic magmas. However, the major advance was not the classification, but the recognition that highly contrasting parental materials must be involved in the genesis of granitic magmas.
The restite-unmixing model is commonly seen as a companion to the S–I classification, but it is really a separate issue. This model implies that the compositions of granites ‘image’ those of their source rocks in a simple way. However, there are other equally valid models that can explain the data, and none of them represents a unique solution. The most cogent explanation for the high-grade metasedimentary enclaves in most S-type granites is that they represent mid-crustal xenoliths; restitic enclaves are either rare or absent. Inherited zircons in S-type rocks are certainly restitic. However, the occurrence of a substantial restitic zircon population does not imply an equally substantial restitic component in the rest of the rock. Zircon and zirconium behaviours are controlled by disequilibrium and kinetics, and Zr contents of granitic rocks can rarely be used to infer magma temperatures.
Since the dominant ages among inherited zircons in Lachlan Fold Belt (LFB) S-type granites are Ordovician and Proterozoic, it seems likely that crust of this age, but geochemically different from the exposed rocks, not only underlies much of the LFB but also forms a component in the granite magma sources. The evidence is overwhelming that the dark, microgranular enclaves that occur in both S- and I-type granites are igneous in origin. They represent globules of quenched, more mafic magma mingled and modified by exchange with the host granitic magma. However, magma mixing does not appear to be a significant process affecting the chemical evolution of the host magmas. Likewise, the multicomponent mixing models erected for some granitic rock suites are mathematically nonunique and, in some cases, violate constraints from isotopic studies. S- and I-type magmas commonly retain their distinct identities. This suggests limited source mixing, limited magma mixing and limited wall-rock assimilation. Though intermediate types certainly exist, they are probably relatively minor in volume.
Crystal fractionation probably plays the major role in the differentiation of very many granitic magmas, including most S-types, especially those emplaced at high crustal levels or in the volcanic environment. Minor mechanisms include magma mixing, wall-rock assimilation and restite unmixing. Isotopic variations within plutons and in granite suites could be caused by source heterogeneities, magma mixing, assimilation and even by isotopic disequilibrium. However, source heterogeneity, coupled with the inefficiency of magma mixing is probably the major cause of observed heterogeneity.
Normal geothermal gradients are seldom sufficient to provide the necessary heat for partial melting of the crust, and crustal thickening likewise fails to provide sufficient heat. Generally, the mantle must be the major heat source. This might be provided through mantle upwelling and crustal thinning, and possibly through the intra- and underplating of mafic magmas. Upper crustal extension seems to have been common in regions undergoing granitic magmatism. Migmatites probably provide poor analogues of granite source regions because they are mostly formed by fluid-present reactions. Granitic magmas are mostly formed by fluid-absent processes. Where we do see rare evidence for arrested fluid-absent partial melting, the melt fraction is invariably concentrated into small shear zones, veinlets and small dykes. Thus, it seems likely that dyking is important in transporting granitic magma on a variety of scales and at many crustal levels. However, one major missing link in the chain is the mechanism by which melt fractions, in small-scale segregations occurring over a wide area, can be gathered and focused to efficiently feed much wider-spaced major magma conduits. Answers may lie in the geometry of the melting zones and in the tendency of younger propagating fractures to curve toward and merge with older ones. Self-organization almost certainly plays a role.
There is little dispute about the sources of peraluminous, crustally evolved, S-type, granitic magmas. These are derived through partial melting of metasedimentary rocks that had a significant ...fraction of Al-rich clays in their protoliths. However, the origins of I-type magmas are, and always have been, in dispute. From isotope geochemistry, we know that I-types are not generally produced through fractionation of normal, juvenile, mantle-derived, mafic magmas. In addition, we can demonstrate that the chemical diversity among most I-type series is not primarily due to magma mixing. Thus, we start from the premise that most I-type magmas are dominantly crustal in origin, as reflected in their O isotope ratios. Experimental work on a range of potential hornblende- and/or biotite-bearing source rocks, as well as studies of felsic I-type rocks, indicate that the parent felsic melts for I-type magmas are mildly peraluminous. However, the rocks themselves are commonly metaluminous, especially at the more mafic end of the compositional spectrum. Chemically and mineralogically, the best explanation for this is that peraluminous melt left the I-type source terranes with entrained peritectic clinopyroxene. In detail, the chemistry of most I-type series is controlled by differential entrainment of this pyroxene, together with peritectic plagioclase, ilmenite/titanomagnetite and restitic apatite and zircon. So, what sorts of sources partially melt to produce the peraluminous I-type melts with peritectic clinopyroxene and ilmenite, while imparting a distinctly crustal isotope signature to the magmas? From experimental and theoretical perspectives (and with the exception of the uniquely Archean tonalite–trondhjemite–granodiorite TTG series), the best candidates for I-type protoliths are not mafic igneous rocks but arc volcanic rocks of intermediate composition (dacites to andesites), and possibly some relatively mafic granodiorites and tonalites, rich in biotite and hornblende. Thus, the S–I dichotomy in granite typology is unlikely to reflect simple sedimentary versus igneous sources, but rather the nature of the peritectic minerals entrained by the ascending granitic melts. There should be granitic rocks transitional between S- and I-type, depending on the balance between clay-rich and clay-poor rocks in the protolith. The fact that equivocal or transitional types appear to be uncommon is telling us that the packages of rocks that give rise to S- and I-type magmas are generally spatially separated from each other, and may also be separate in terms of their ages and tectonic environments. Additionally, melting of biotite + sillimanite assemblages in evolved metapelitic sources will occur significantly earlier during a crustal heating cycle than will that of the hornblende + biotite assemblages that will predominate in I-type sources. Thus, even where interlayered sources do exist, S- and I-type magmas may be produced as temporally separate batches.
► I-type granitic rocks are not differentiates of more mafic magmas. ► They are not generally the products of mixing between crustal and mantle magmas. ► The magmas are formed by the breakdown of biotite–hornblende mineral assemblages. ► Their compositions are controlled by entrainment of peritectic Cpx, Pl, and Ilm. ► They are melts of arc crust, which gives them connexions with both the mantle and the crust.
Near-infrared (NIR) fluorescence imaging has the potential to improve sentinel lymph node (SLN) mapping in breast cancer. Indocyanine green (ICG) is currently the only clinically available ...fluorophore that can be used for SLN mapping. Preclinically, ICG adsorbed to human serum albumin (ICG:HSA) improves its performance as a lymphatic tracer in some anatomical sites. The benefit of ICG:HSA for SLN mapping of breast cancer has not yet been assessed in a clinical trial. We performed a double-blind, randomized study to determine if ICG:HSA has advantages over ICG alone. The primary endpoint was the fluorescence brightness, defined as the signal-to-background ratio (SBR), of identified SLNs. Clinical trial subjects were 18 consecutive breast cancer patients scheduled to undergo SLN biopsy. All patients received standard of care using
99m
Technetium-nanocolloid and patent blue. Patients were randomly assigned to receive 1.6 ml of 500 μM ICG:HSA or ICG that was injected periareolarly directly after patent blue. The Mini-Fluorescence-Assisted Resection and Exploration (Mini-FLARE) imaging system was used for NIR fluorescence detection and quantitation. SLN mapping was successful in all patients. Patient, tumor, and treatment characteristics were equally distributed over the treatment groups. No significant difference was found in SBR between the ICG:HSA group and the ICG alone group (8.4 vs. 11.3, respectively,
P
= 0.18). In both groups, the average number of detected SLNs was 1.4 ± 0.5 SLNs per patient (
P
= 0.74). This study shows that there is no direct benefit of premixing ICG with HSA prior to injection for SLN mapping in breast cancer patients, thereby reducing the cost and complexity of the procedure. With these optimized parameters that eliminate the necessity of HSA, larger trials can now be performed to determine patient benefit.
This study provides new constraints on the causes of the chemical and isotopic variability in the central Victorian, Devonian, silicic, magmatic rocks and relates these to crustal architecture in the ...region. Synthesising present and previous work, it is concluded that the Selwyn Block, which forms the main source region for the Devonian silicic magmas (granitic and silicic volcanic rocks), is heterogeneous in three dimensions, on scales of 1 km and less. The sources of both the I- and S-type magmas were formed in Paleoproterozoic to Mesoproterozoic times, in the distal back-arc region of an Andean-type margin, in a basin that was extending and deepening eastward with time. The prominent rock types are high-grade metamorphosed greywackes, potassic andesites and dacites, with smaller volumes of pelitic rocks. The metasediment-dominated source rocks generally lie at deeper levels and reached higher metamorphic grades than the sources of the I-type magmas. This means that the I-type magmas were generally at lower temperatures and were also more hydrous than the S-type magmas. Heat for the metamorphism and partial melting of the source rocks of the silicic magmas was advected into the crust by mantle-derived magmas. These probably formed an underplate, to drive the regional metamorphism, but numerous, scattered, sill-like mafic bodies caused local contact anatexis and silicic magma production. Along with the emplacement of mafic magma bodies, the ascent of the silicic magmas to the upper crust rendered the deeper parts of the Selwyn Block denser and more mafic.
The largely unexposed Selwyn Block, which forms the crustal basement in central Victoria, is heterogeneous in three dimensions, on scales of 1 km and less.
The sources of the Devonian I- and S-type silicic magmas here formed in the Paleoproterozoic to Mesoproterozoic distal back-arc of an Andean-type margin.
The metasedimentary S-type source rocks lie at deeper levels and reached higher metamorphic grades than the sources of the I-type magmas.
Heat for the metamorphism and partial melting was advected by both underplating and numerous sill-like mafic bodies scattered throughout the deep crust.
Age distributions among the detrital zircon populations in western and central Victorian Paleozoic metasedimentary rocks suggest that most were deposited in Andean-type back-arc environments, with ...variable proportions of arc and continental sediment sources. Notable exceptions are the upper Cambrian Knowsley East Shale and the Silurian(?) sample of 'Glen Creek Lithic Sandstone', which both contain unimodal zircon populations. In the case of the Knowsley East Shale, this age is very close to the inferred depositional age, implying a possible forearc environment, with sediment derived directly from the contemporary volcanic arc. On the other hand, the implied trench environment for the 'Glen Creek Lithic Sandstone' is most likely inherited from its very local sediment source in the fault-bounded and mainly Cambrian Glen Creek erosional window. The only analysed rock units that may have been deposited in non-arc settings are the middle Silurian Humevale Siltstone and the Lower Devonian Norton Gully Sandstone. The zircon populations in these units carry strong continental signals, and they may have been deposited in an extensional marine basin bounded by continental blocks. The upper Silurian Grampians Group may have been deposited in a similar rift setting, but the zircon age histogram for this unit suggests that it was more proximal to an arc terrane. These assignments of depositional/tectonic environment should be regarded as indicative only, particularly since the method provides only subtle distinctions between some extensional and convergent settings. However, if the assignments are correct, there are some important implications for the geological history of this part of the Lachlan Orogen. For example, contrary to present perceptions, the Stawell Zone rocks may not have been prominently uplifted during the Ordovician, and the basin in the Bendigo Zone may have been receiving sediment input from further west in the Grampians-Stavely Zone.
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