The link between volcanism and plutonism in epizonal magma systems; high-precision U–Pb zircon geochronology from the Organ Mountains caldera and batholith, New Mexico

Abstract

of 36.441 ± 0.020 Ma (Cueva Tuff), 36.259 ± 0.016 Ma (Achenback Park tuff), and 36.215 ± 0.016 Ma (Squaw Mountain tuff). An alkali feldspar granite, which is chemically similar to the erupted tuffs, yielded a synchronous weighted mean 206 Pb/ 238 U date of 36.259 ± 0.021 Ma. Weighted mean 206 Pb/ 238 U dates from the larger volume syenitic phase of the underlying Organ Needle pluton range from 36.130 ± 0.031 to 36.071 ± 0.012 Ma, and the youngest sample is 144 ± 20 to 188 ± 20 ka younger than the Squaw Mountain and Achenback Park tuffs, respectively. Younger plutonism in the batholith continued through at least 34.051 ± 0.029 Ma. We propose that the Achenback Park tuff, Squaw Mountain tuff, alkali feldspar granite and Organ Needle pluton formed from a single, long-lived magma chamber/mush zone. Early silicic magmas generated by partial melting of the lower crust rose to form an epizonal magma chamber. Underplating of the resulting mush zone led to partial melting and generation of a highsilica alkali feldspar granite cap, which erupted to form the tuffs. The deeper parts of the chamber underwent continued recharge and crystallization for 144 ± 20 ka after the final eruption. Calculated magmatic fluxes for the Organ Needle pluton range from 0.0006 to 0.0030 km 3 /year, in agreement with estimates from other well-studied plutons. The petrogenetic evolution proposed here may be common to many small-volume silicic volcanic systems.

AgeSpectraAnalyst: A MATLAB based package to model zircon age distributions in silicic magmatic systems

“…granites, rhyolites) as they source most catastrophic, caldera-forming eruptions [ 17 ] and their near-ubiquitous zircon saturation [ [18] , [19] , [20] ] makes them preferential targets of high-precision zircon geochronology studies (e.g. [ [21] , [22] , [23] , [24] ]).…”

“…(a) Least square regressions (LSQs) for a compiled dataset of recently published (2012-2021) CA-ID-TIMS 206 Pb/ 238 U dates and reported 2σ uncertainties. Data are from: [ [21] , [22] , [37] , [40] , [41] , [42] , [43] , [44] , [45] , [46] , [47] , [48] , [49] , [50] , [51] , [52] , [53] , [54] , [55] , [56] , [57] , [58] , [59] , [60] , [61] , [62] , [63] , [64] , [65] ]. Each line represents a different polynomial fit to the dataset, and points on a line corresponding to interpolated 2σ uncertainties for three magmatic systems of increasing crystallization ages (∼ 7 Ma, Capanne pluton, [ 37 ]; ∼ 95 Ma, Mt.…”

Thermochronological transect across the Basin and Range/Rio Grande rift transition: Contrasting cooling histories in contiguous extensional provinces

“…35 Ma;McIntosh et al, 1992) and the Organ Mountains Caldera (ca. 36 Ma; Zimmerer and McIntosh, 2013;Rioux et al, 2016). In addition, half-grabens are common features above collapsing calderas (e.g., Moore and Kokelaar, 1998), particularly in the early stages of caldera collapse, when subsidence is incremental and collapse occurs in several stages instead of catastrophically (e.g., Walter and Troll, 2001).…”

Constraints on the timescales and processes that led to high-SiO2 rhyolite production in the Searchlight pluton, Nevada, USA

“…Nevertheless, global geochemical data sets suggest compositional parity between volcanic and plutonic rocks (Keller et al, 2015;Glazner et al, 2018) and have been used to question whether any granitoids represent cumulates. Additionally, tests of the temporal relationships between high-SiO 2 rhyolites and potential cogenetic plutons have also provided variable evidence for (Deering et al, 2016;Rioux et al, 2016) and against (Mills and Coleman, 2013) a genetic connection. Consequently, the origin of high-SiO 2 rhyolite through uppercrustal differentiation remains questioned (e.g., Lundstrom and Glazner, 2016).…”

“…Yet, a near 1:1 relationship between the number of inferred increments from high-precision geochronologic data and the number of samples analyzed suggests that the sampling density in most plutonic complexes is rarely high enough to identify the vertical or lateral extent of an individual magmatic pulse or an amalgamated magma reservoir (Schoene et al, 2015). There are only a few examples where overlapping high-precision U-Pb zircon crystallization ages have been used to delineate the extent of a possible fossil, silicic magma reservoir (Matzel et al, 2006;Eddy et al, 2016;Rioux et al, 2016;Ratschbacher et al, 2018;Schaen et al, 2021), hindering our ability to use the geometry and geochemistry of these features to study magmatic processes. Here we present a combined geochemical and geochronologic study focused along a single paleo-vertical transect of the Miocene Searchlight pluton in southern Nevada, USA, with sample spacing of ~100 m. The results enable us to identify a fossil silicic magma reservoir within the larger, incrementally assembled intrusive complex, assess its longevity, and use geochemical gradients within the reservoir to explore potential mechanisms for silicic magma differentiation.…”