Deciphering magmatic processes in calc-alkaline plutons using trace element zoning in hornblende

Schlieren-Bound Magmatic Structures Record Crystal Flow-Sorting in Dynamic Upper-Crustal Magma-Mush Chambers

“…Regionally extensive magmatic fabrics (e.g., Figure 1A), recycling of older units into younger, compositional evidence for widespread magma mixing and recycling in bulk rocks and in minerals, geochronologic studies, and thermal models all suggest that TIC magma chambers (interconnected melt regions) in the Cathedral Peak unit, and in each of the older units, were volumetrically extensive (∼1000 km 3 ) and long-lived (up to 1.5 m.y.) (e.g., Matzel et al, 2005Matzel et al, , 2006Solgadi and Sawyer, 2008;Memeti et al, 2010Memeti et al, , 2014Paterson et al, 2011Paterson et al, , 2016Barnes et al, 2016). Together with the above-listed evidence, outcropscale flow features, domain-scale clustering and regional-scale outward-younging schlieren-bound structure patterns presented here require a magma emplacement model where incrementally emplaced new magma pulses can interact with older pulses dynamically by magmatic flow, transferring mass and energy to the larger-scale interconnected-melt region, or magma mush.…”

“…However, the relationship between pairs of related samples is not the same for all samples studied or compiled; in most cases (five samples out of six), Sr i is more radiogenic in schlieren, but εNd i is variable. In addition, the preservation of textural and compositional zoning in Rb-bearing phases such as K-feldspar, and Sm and Nd-bearing phases such as hornblende (and apatite) demonstrates that diffusion of fast-and slow-diffusing elements was limited in the TIC (Memeti et al, 2014;Barnes et al, 2016;Werts et al, 2020). Thus, isotopic differences between schlieren and host are interpreted as primary magmatic features of the samples resulting from processes (1) and (2), rather than secondary features (3).…”

“…TIC rocks are metaluminous to locally peraluminous, calcalkaline compositions, spanning a wide range of SiO 2 contents (48-79 wt.%) (Bateman and Chappell, 1979;Bateman, 1992;Memeti et al, 2014). Hornblende analyses indicate that all units experienced crystal accumulation and/or melt loss to varying degrees, contributing to the wide variation in rock type (Barnes et al, 2016;Werts et al, 2020). The considerable compositional overlap between units in major and trace elements, as well as isotopes, has been attributed to a combination of fractionation and mixing processes involving multiple magma sources; the depth that these processes occur is debated (e.g., Kistler et al, 1986;Bateman, 1992;Gray et al, 2008;Coleman et al, 2012;Memeti et al, 2014;Barnes et al, 2016).…”

“…Solgadi and Sawyer (2008) demonstrated, using hornblende Mg-number, that schlieren lacked any compositional gradients from base to top, which either a thermal or chemical gradient should impose. In-situ mineral analyses of samples across all TIC units reveal complex zoning patterns, which suggests that thermochemical diffusion did not re-equilibrate the mineral compositions (Memeti et al, 2014;Barnes et al, 2016;Werts et al, 2020). In a liquid immiscibility model, a form of chemical diffusion (e.g., Glazner et al, 2012;Bartley et al, 2019), isotope compositions should be identical between schlieren and host, and the felsic component to the mafic schlieren should be enriched in alkalis, Rb, Cs, Sr, and Ba (Ryerson and Hess, 1978;Hurai et al, 1998), neither of which are observed in TIC samples.…”

Extraction of high-silica granites from an upper crustal magma reservoir: Insights from the Narusongduo magmatic system, Gangdese arc

“…Amphibole major and trace element compositions have been utilized to decipher magmatic processes and conditions of crystallization (e.g., Putirka 2016;Barnes et al 2016; Zhou et al 2020), and the SiO 2 content in coexisting liquids can be estimated reliably using only amphibole chemistry(Ridolfi et al 2010;Ridolfi and Renzulli 2012;Erdmann et al 2014;Zhang et al 2017;Humphreys et al 2019). Amphibole in the crystal aggregates(Figure 4a) within the andesites have Si atoms of 6.8 to 7.1 per 23 O atoms and they are crystallized from high-silica melts (74.8-75.7 wt% SiO 2 ;Fig.…”