Silicate Units Research Articles

Detrital zircon geochronology of the Fredericton Trough, New Brunswick, Canada: Constraints on the Silurian Closure of remnant Iapetus Ocean

The Fredericton Trough in the Appalachians of southwestern New Brunswick is filled by the Silurian Kingsclear Group, consisting mainly of turbidites, deposited during convergence of Laurentia with components of the peri-Gondwanan domain Ganderia. Its tectonic setting has been interpreted as a successor basin, trench, foredeep or foreland basin. We present new detrital zircon U-Pb data from four formations of the Kingsclear Group, collected north and south of the Fredericton Fault, which bisects the trough. South of the Fredericton Fault, detrital zircon ages from an early Silurian (Llandovery) unit show a late Neoproterozoic peak, typical of peri-Gondwanan provenance. Detrital zircons from a younger Silurian unit (Wenlock - Ludlow, intruded by the Pocomoonshine pluton, 422.7 ± 3 Ma) display a distinctive asymmetric peak at ∼1.0 Ga with a tail of older Proterozoic zircons, suggesting Laurentian provenance. North of the Fredericton Fault, a Llandovery sample also shows a signature consistent with Laurentian sources. In a mid-Silurian (Wenlock) unit zircon peaks indicate mixed Laurentian and peri-Gondwanan sources, consistent with exhumation of the Miramichi terrane to the north. The absence of Laurentian material in Llandovery strata south of the fault, contrasted with a strong Laurentian signature in rocks to the north, suggests that a remnant of the Iapetus Ocean, in which turbidites of the Kingsclear Group were deposited, persisted until at least the mid-Silurian. The timing of its closure is constrained by the arrival of Laurentian detritus south of the Fredericton Fault before 422.7 ± 3 Ma, and probably by the mid-Wenlock.

Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province

The impetus for this research was the enigma regarding the origin of the extensive silicic volcanic units in the Parana-Etendeka Igneous Province. Are they rheoignimbrites, lava flows, or a combination of both? The Sao Joaquim silicic eruptive sequence is comprised of Palmas-Type aphyric dacites and is located in the northern segment of Torres Trough, a dissected mountainous region in southern Brazil. These dacite outcrops form plateaus and remnant hills that are scattered above a basaltic andesitic landscape. The original morphology of the silicic volcanic flows was constrained based on the internal architecture, geometry, and cyclicity of the lithofacies, in conjunction with petrographic and geochemical information. The data suggests the presence of ancient large tabular and lobate silicic lava flows (~100 m thick and ~10–40 km extents). No pyroclastic features were found. Eight interdigitating units were mapped. These large aspect ratios are similar to ones for basaltic flows and those of Snake River-type rhyolites, and they suggest high effusion rates and high temperatures as well as the presence of well-insulated cooled crusts. Lavas would have overflowed from long fissure vents that had created an extensive volcanic silicic surface body composed of conjugated and interdigitated flows above the north segment of the Torres Trough region.

Structural and Dielectric Studies on Na2O-PbO-SiO2 Glasses

Structural studies on x Na2O.(50-x)PbO.50SiO2 glasses have been carried out by different spectroscopic techniques. FTIR, EDX, NMR and dielectric spectroscopies are applied to follow the change in glass structure in terms of bridging oxygen (BO), non-bridging oxygen (NBO), and cluster species upon adding of Na2O at expense of PbO. NBOs are formed in the silicate network upon Na2O addition, since Na2O plays the role of glass modifier. Changes in relative area of Q2 (obtained from IR analysis) and NMR chemical shift of silicon nuclei with increasing Na2O are indicative for formation of the less shielded silicate units. While in sodium rich silicate glasses, the structural role of Na2O is changed due to changing Na coordination. FTIR analysis could be used to elucidate the changes related to changing the role of Na2O. The data obtained are correlated with that obtained from EDX spectroscopy. Moreover, the role of Na2O on the process of cluster formation when it substitutes PbO is determined. NBOs only are formed in the silicate network upon Na2O addition up to 30 mol%. On the other hand, in sodium rich silicate glasses an additional type of oxygen (free oxygen O2−) is present. The free oxygen is required for sodium to form aggregated cluster, specially at high concentration of Na2O (50 mol%). An increase in Na2O concentration in Na2O-rich silicate network results in increasing Na coordination instead of breaking more silicon–oxygen bonds. Scanning electron micrographs (SEM) and EDS spectroscopy in correlation with FTIR results confirm the presence of Na cluster species. The effect of clusters formation on AC conductivity was discussed according to jump relaxation model. Some parameters related to AC conductivity are found to be affected by the presence of cluster species in the glass network.

Permian A-type rhyolites of the Muráň Nappe, Inner Western Carpathians, Slovakia: in-situ zircon U–Pb SIMS ages and tectonic setting

AbstractThree representative A-type rhyolitic rock samples from the Muráň Nappe of the inferred Silicic Unit of the Inner Western Carpathians (Slovakia) were dated using the high-precision SIMS U–Pb isotope technique on zircons. The geochronological data presented in this paper is the first in-situ isotopic dating of these volcanic rocks. Oscillatory zoned zircon crystals mostly revealed concordant Permian (Guadalupian) ages: 266.6 ± 2.4 Ma in Tisovec-Rejkovo (TIS-1), 263.3 ± 1.9 Ma in Telgárt-Gregová Hill (TEL-1) and 269.5 ± 1.8 Ma in Veľká Stožka-Dudlavka (SD-2) rhyolites. The results indicate that the formation of A-type rhyolites and their plutonic equivalents are connected to magmatic activity during the Permian extensional tectonics and most likely related to the Pangea supercontinent break-up.

The role of Ni2+ ions on structural and spectroscopic properties of Li2O–ZrO2–Y2O3–SiO2 glass system

The glasses of composition (35–x) Li2O–5ZrO2–10Y2O3–50SiO2: x NiO (0 < x < 0.5) have been synthesized. The amorphous nature of the samples is verified by XRD studies and DTA studies. The information on of various structural vibrational units (viz., zirconate, silicate) and their compositional dependence of is evaluated by FT–IR and Raman studies. The results of these studies have indicated that there is a growth of asymmetrical bands at the expense of symmetrical bands of silicate units with increasing concentration of NiO. The optical absorption (OA) and photoluminescence (PL) spectral of Li2O–ZrO2–Y2O3–SiO2: NiO glasses indicated gradual increase of octahedral occupancy of Ni2+ ions in the glass network with the increase in the concentration of NiO in the glass network.

Structural Role of Cerium Oxide in Lead Silicate Glasses and Glass Ceramics

Silicate glasses and glass ceramics in the system CeO2-PbO-SiO2 have been studied as a function of the structure factors R and K. The latter two factors are defined as: R = (CeO2 + PbO)/SiO2 and K = (SiO2/CeO2) molar ratios. In this glass, PbO is fixed at 50 mol% and CeO2 increases at the expense of SiO2. NMR investigations have revealed that increasing R which is accompanied with decreasing K leads to reasonable decrease in the shielding of silicon atoms. The chemical shift (δ) showed an increasing behavior due to increasing non-bridging oxygen atoms (NBO) in silicate network. It is evidenced that NBO in cerium free glass is much lower than that of glasses containing CeO2. Increasing R is clearly leading to higher chemical shift and higher NBO. This reflects that CeO2 has an effective structural role, since it would be consumed in all cases as an intermediate oxide. The main portions from CeO2 and PbO inter as glass modifiers which are consumed to form NBO atoms. A limited portion of CeO2 acts as glass former which consumed to form tetrahedral cerium containing NBO due to modification by PbO as a modifier oxide. Increasing R = [(CeO2 + PbO)/SiO2] from 1 to 2.34 leads to a frequent increase of NBO in the average glass network. FTIR spectroscopy of the glasses showed a clear shift of the main absorbance peak toward the low wavenumber with increasing R which confirms the increasing silicate units containing NBO atoms. XRD of the investigated materials revealed the presence of some nanostructures from cerium silicate crystalline phases. Formation of separated phases containing micro clusters is found to depend on NBO concentration, since NBO can facilitate process of phase separation. Majority of modifier are consumed to form NBO in the glass network and the rest are aggregated or separated to form silicate phase riches with cerium cations. In such case, some of silicon atoms are electrically compensated with both Pb and Ce cations.

Structures and lithofacies of inferred silicic conduits in the Paraná-Etendeka LIP, southernmost Brazil

Extensive silicic units in the Paraná-Etendeka LIP have been long interpreted as pyroclastic density currents (rheomorphic ignimbrites) derived from the Messum Complex in Namibia. In recent literature, however, they have been characterized as effusive lava flows and domes. In this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at Mato Perso, São Marcos and Jaquirana-Cambará do Sul areas in southern Brazil. Inferred conduits are at least 15–25m in width and the lithofacies include variably vesicular monomictic welded and non-welded breccias in the margins to poorly vesicular, banded, spherulitic and microfractured vitrophyres in the central parts. Flat-lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits. Large-scale, regional tectonic structures in southern Brazil include the NE-SW aligned Porto Alegre Suture, Leão and Açotea faults besides the Antas Lineament, a curved tectonic feature accompanying the bed of Antas river. South of the Antas Lineament smaller-scale, NW-SE lineaments limit the exposure areas of the inferred conduits. NE-SW and subordinate NW-SE structures within this smaller-scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub-vertical banding in the widespread banded vitrophyre lithofacies. Upper lava flows display flat-lying foliation, pipe-like and spherical vesicles and have better developed microlites. Petrographic characteristics of the silicic vitrophyres indicate that crystal-poor magmas underwent distinct cooling paths for each inferred conduit area. The vitrophyre chemical composition is defined by the evolution of trachydacitic/dacitic vitrophyres with 62–65wt% SiO2 to rhyodacite and rhyolite with 66–68wt% SiO2. The more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits. Degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions. Based on the documented lithofacies architecture, we attribute the source of the silicic lava flows in the studied localities to tectonic-controlled, local conduits, rather than pyroclastic density currents from distant vent areas.

An AMS study of different silicic units from the southern Paraná-Etendeka Magmatic Province in Brazil: Implications for the identification of flow directions and local sources

In the Southern portion of the Paraná-Etendeka Magmatic Province in Brazil, extensive silicic (dacite-rhyolite) deposits occur at the top of a sequence of low-Ti pahoehoe to rubbly basalts. The internal architecture of the silicic deposits and their eruptive style, as well as the location of their sources are still unsatisfactorily known. In an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive, and test the hypothesis of local sources, we carried out anisotropy of magnetic susceptibility (AMS) studies on the two main silicic units (Caxias do Sul dacites and Santa Maria Rhyolites) with the best exposures in an area previously mapped in detail.Magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites. Rock magnetism properties indicate that “pseudo-single-domain” magnetite carries the fabrics and the remanence. Magnetic fabrics were determined by applying anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). Both AMS and AARM tensors are coaxial, indicating that the AMS fabric is not affected by the effect of magnetite single-domain grains.Magnetic data from several dacitic coulées (Caxias do Sul unit) indicate flows from SE to NW. The location and spatial distribution of these lavas support the hypothesis of local sources, aligned along a NE-SW trend. These data are in agreement with the alignments of structures (dome-shaped hills) observed in field work and DEM images. On the other hand, magnetic data obtained in Santa Maria rhyolites indicate that flow directions in two different areas are distinct (towards NW/NE and W), suggesting that they derived from different emission centers.So, regarding the silicic volcanism in the studied region, our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit. In contrast, we propose the occurrence of local volcanic events, implying in the existence of different sources, possibly characterized by local emission centers.

Presentation of the 2016 Harrell L. Strimple Award of the Paleontological Society to Samuel J. Ciurca, Jr.

Among the hosts of amateur fossil collectors, very few attain the status of “world authority” or “living legends.” But this year’s Strimple Award winner, Mr. Samuel J. Ciurca, Jr., deserves both of these titles. Google eurypterids and you will find an image of a wiry man up to his knees in water, hauling a “living eurypterid” from the sea: meet Sam Ciurca, posing with a cleverly crafted model of one of the largest eurypterids, he discovered, a 1.3 m Pterygotus . I have known of Sam for nearly four decades. I got to know him quite well when I began teaching at the University of Rochester and I am still working with him to this day. Indeed, in some ways he was already mentoring students when I arrived at Rochester. My first Master’s student, Richard Hamell (who did a study of the famed eurypterid-bearing upper Silurian Bertie Dolostone), was a disciple of Mr. Ciurca, who, even then, was nicknamed “Sam the eurypterid man.” At the time, Sam worked as a chemist for the Eastman Kodak Company, but his true passion was field study of eurypterid beds. Sam began his geological pursuits as a teenager in the early 1960s with initial interests in minerals and petrified wood. Sam started to document and disseminate his findings early on: he wrote an article on celestite in upper Silurian units in 1962, and even had a “petrified wood museum” for public view. It …

A study of thermal decomposition of antigorite from dunite and lizardite from peridotite

Two varieties of serpentines, antigorite and lizardite originated from dunite and peridotite, respectively, were previously undergone heat treatment in the range from 396 to 1128 °C and then leached via an original approach to the acid processing of dehydrated serpentines. Because of unsaturated (weak) Si–O(Si) bonds existing in the serpentines structure, ortho- [SiO4]4−, di- [Si2O7]6− and other silicate units are easily leached from dehydrated serpentines in the form of soluble silicic acids along with magnesium compounds via this approach, whereas the more complex fragments largely comprised of metasilicate [(SiO3)2−]n chains remain in the unreacted mass The yields of silicic acids produced from heated serpentines are variable. The influence of thermal treatment on both the serpentinite samples was investigated by thermal, X-ray diffraction and chemical analyses. The data derived from the experimental studies allowed to reveal the distribution of primary ortho- [SiO4]4− and meta- [(SiO3)2−]n silicate units in the silicate layers inherent in these serpentine minerals and to understand its influence on the mechanism of their decomposition including the high-temperature phase transformations into forsterite Mg2SiO4 and enstatite Mg2Si2O6.

Effusive silicic volcanism in the Paraná Magmatic Province, South Brazil: Evidence for locally-fed lava flows and domes from detailed field work

Lava flows and dome complexes of silicic composition were identified in the Lower Cretaceous Paraná Magmatic Province (PMP) at Rio Grande do Sul state, southern Brazil. Detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments, likely representing the fissural systems that fed the three Palmas-type silicic units. Different structures indicative of effusive emplacement (lava domes, lobated flows, sheet flows and autobreccias) are very common in the study area, and are probably also more abundant than previously thought in whole PMP silicic magmatism. In fact, effusive deposits seem predominant in the three distinct silicic units identified in the area, since no remnants of pyroclastic components have been identified. The vitreous dacites that make up the upper flows of the basaltic andesite to dacite Barros Cassal sequence are clearly effusive, as indicated by their occurrence as thin sheet flows. The much thicker early Caxias do Sul dacites occur mostly as lava flow lobes and pancake-like, of low to moderate viscosity, and lava domes. The younger, high SiO2 Santa Maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion, as lobated flows formed by vesicle-rich obsidian. In spite of higher viscosities relative to the previous units (~106Pa·s), it is probable that the very low H2O contents ~1wt% of these rhyolite melts, associated with high discharge rates, resulted in an effusive nature in most to this unit.

Alternating Copolymer of Double Four Ring Silicate and Dimethyl Silicone Monomer-PSS-1.

A new copolymer consisting of double four ring (D4R) silicate units linked by dimethylsilicone monomer referred to as polyoligosiloxysilicone number one (PSS-1) was synthesized. The D4R building unit is provided by hexamethyleneimine cyclosilicate hydrate crystals, which were dehydrated and reacted with dichlorodimethylsilane. The local structure of D4R silicate units and dimethyl silicone monomers was revealed by multidimensional solid-state NMR, FTIR and modeling. On average, D4R silicate units have 6.8 silicone linkages. Evidence for preferential unidirectional growth and chain ordering within the PSS-1 copolymer was provided by STEM and TEM. The structure of PSS-1 copolymer consists of twisted columns of D4R silicate units with or without cross-linking. Both models are consistent with the spectroscopic, microscopic and physical properties. PSS-1 chains are predicted to be mechanically strong compared to silicones such as PDMS, yet more flexible than rigid silica materials such as zeolites.

Effusive silicic volcanism in the Paraná Magmatic Province, South Brazil: Physico-chemical conditions of storage and eruption and considerations on the rheological behavior during emplacement

Expressive occurrences of effusive deposits were identified in silicic units from the Paraná Magmatic Province outcropping in a key area in south Brazil where three units with different compositions occur (Caxias do Sul dacites, CSd, Barros Cassal andesites to dacites, BCs, and Santa Maria rhyolites, SMr). Textural and chemical characteristics of phenocrysts, microphenocrysts and microlites suggest that crystallization started in a shallow magma chamber and continued during ascent to the surface. These magmas had an unique character (e.g., very high temperatures ~1000°C and low H2O contents ~1–2wt%), and formed several types of deposits that are clearly indicative of locally fed lava flows and had physical properties consistent with this mode of eruption (e.g., viscosities as low as 104.2Pa·s at ca. 1000°C for the CSd). The very low estimated H2O contents are a consequence of their petrogenesis (i.e., fractionation from tholeiitic basalts plus assimilation of crustal melts from water-poor granitic sources), and was probably a key factor influencing the non-explosive nature of these deposits. The comparatively higher viscosity calculated for the Santa Maria rhyolite (>1–2 orders of magnitude greater than CSd) would make it a better candidate to generate expressive pyroclastic deposits, but this might be offset by its remarkably low H2O contents (≤1wt%) and low discharge ratios.

Improving the biocompatibility of tobermorite by incorporating calcium phosphate clusters.

In our earlier work, tobermorite containing calcium phosphate (CP) clusters (CP-Tob) was hydrothermally prepared in the CaO-SiO2-P2O5-H2O system for biomedical applications. CP-Tob was used to investigate the influence of CP cluster incorporation on its biocompatibility. Tobermorite samples with and without CP clusters were hydrothermally prepared at 180°C for 40 h. The biocompatibility, structure, and density of states of the tobermorite samples were investigated by experimental and first principles methods. The amounts of lysozyme and bovine serum albumin adsorbed on CP-Tob were higher than those on tobermorite without CP clusters. Cluster incorporation caused a decrease in the solubility, resulting in the enhancement of the cell compatibility. The calculated results indicated that incorporating clusters, which interact with the silicate units of tobermorite, led to a change of the density of states of tobermorite. Incorporation of CP clusters in tobermorite led to improvement of the biocompatibility evaluated by biological and computational analyses.

Water quality variables and pollution sources shaping stream macroinvertebrate communities

In 2015, over 90 percent of German rivers failed to reach a good ecological status as demanded by the EU Water Framework Directive (WFD). Deficits in water quality, mainly from diffuse pollution such as agricultural run-off, but also from wastewater treatment plants (WWTPs), have been suggested as important drivers of this decline in ecological quality.We modelled six macroinvertebrate based metrics indicating ecological quality for 184 streams in response to a) PCA-derived water quality gradients, b) individual water quality variables and c) catchment land use and wastewater exposure indices as pollution drivers. The aim was to evaluate the relative importance of key water quality variables and their sources. Indicator substances (i.e. carbamazepine and caffeine indicating wastewater exposure; herbicides indicating agricultural run-off) represented micropollutants in the analyses and successfully related water quality variables to pollution sources. Arable and urban catchment land covers were strongly associated with reduced ecological quality. Electric conductivity, oxygen concentration, caffeine, silicate and toxic units with respect to pesticides were identified as the most significant in-stream predictors in this order. Our results underline the importance to manage diffuse pollution, if ecological quality is to be improved. However, we also found a clear impact of wastewater on ecological quality through caffeine. Thus, improvement of WWTPs, especially preventing the release of poorly treated wastewater, will benefit freshwater communities.

Resource efficiency of calcium silicate units

AbstractDue to the current importance of sustainability, the federal association of the calcium silicate masonry unit industry has taken intensive interest in the question of the resource efficiency of calcium silicate masonry units and construction and has carried out an extensive investigation to this end. The study subjected all stages of calcium silicate, from raw materials reserves and their extraction, production and use in building to recycling, including all transport routes and energy demands, to detailed analysis and critically examined the sustainability of calcium silicate blocks. The present article explains and evaluates the entire life cycle of calcium silicate masonry units.

Adoption of the Willam-Warnke Failure Criterion for Describing Behavior of Ca-Si Hollow Blocks

In the paper the proposal of methods to determine the failure surface of masonry made of hollow silicate units has been presented. In order to build the numerical model, the material model based on Willam-Warnke failure criterion has been created. To determine this surface, some tests of silicate cylinder in uniaxial, biaxial and triaxial stress state was conducted. Additionally, some tests of hollow blocks of silicate in triaxial stress state were made. These tests allowed to point of the meridians of the failure surface.

Silurian and Early Devonian ostracods of the Severnaya Zemlya Archipelago

Descriptions and images of reference associations (for formations) of the Silurian and Early Devonian ostracods from the Severnaya Zemlya Archipelago are provided for the first time. They include 105 ostracod taxa, including two new genera and 33 new species and substantially supplement the faunal characteristics of the Silurian and Early Devonian local stratigraphic units of the region. The Silurian and Early Devonian deposits of the Severnaya Zemlya Archipelago are correlated with the beds of adjacent regions of northern Eurasia; a number of reference levels for comparison of the Severnaya Zemlya stratigraphic scheme with the General Stratigraphic Scale are revealed. The material reported in the paper provides a detailed local stratigraphic scheme that increases the efficiency of prospecting and predictive works on hydrocarbons and solid minerals on the islands and shelf of the Kara Sea. The data provided are of interest for survey geologists, stratigraphers, experts in the Paleozoic beds.

Statistics of silicate units in binary glasses.

In this paper, we derive a new model to determine the distribution of silicate units in binary glasses (or liquids). The model is based on statistical mechanics and assumes grand canonical ensemble of silicate units which exchange energy and network modifiers from the reservoir. This model complements experimental techniques, which measure short range order in glasses such as nuclear magnetic resonance (NMR) spectroscopy. The model has potential in calculating the amounts of liquid-liquid phase segregation and crystal nucleation, and it can be easily extended to more complicated compositions. The structural relaxation of the glass as probed by NMR spectroscopy is also reported, where the model could find its usefulness.

Elucidating the magmatic history of the Austurhorn silicic intrusive complex (southeast Iceland) using zircon elemental and isotopic geochemistry and geochronology

The Austurhorn intrusive complex (AIC) in southeast Iceland comprises large bodies of granophyre and gabbro, and a mafic–silicic composite zone (MSCZ) that exemplifies magmatic interactions common in Icelandic silicic systems. Despite being one of Iceland’s best-studied intrusions, few studies have included detailed analyses of zircon, a mineral widely recognized as a valuable tracer of the history and evolution of its parental magma(s). In this study, we employ high spatial resolution zircon elemental and isotopic geochemistry and U–Pb geochronology as tools for elucidating the complex construction and magmatic evolution of Austurhorn’s MSCZ. The trace element compositions of AIC zircon crystals form a broad but coherent array that partly overlaps with the geochemical signature for zircons from Icelandic silicic volcanic rocks. Typical of Icelandic zircons, Hf concentrations are relatively low (<10,000 ppm) and Ti concentrations range from 5 to 40 ppm (Ti-in-zircon model temperatures = 761–981 °C). Zircon δ18O values vary from +2.2 to +4.8 ‰, consistent with magmatic zircons from other Icelandic silicic rocks, and preserve evidence for recycling of hydrothermally altered crust as a significant contribution to the generation of silicic magmas within the AIC. Zircon e Hf values generally range from +11 to +15. This range overlaps with that of Icelandic basalts from off-rift settings as well as the least depleted rift basalts, suggesting that the AIC developed within a transitional rift environment. In situ zircon U–Pb ages yield a weighted mean of 6.52 ± 0.03 Ma for the entire complex, but span a range of ~320 kyr, from 6.35 ± 0.08 to 6.67 ± 0.06 Ma (2σ SE). Gabbros and the most silicic units make up the older part of this range, while granophyres and intermediate units make up the younger part of the complex, consistent with field relationships. We interpret the ~320 kyr range in zircon ages to represent the approximate timescale of magmatic construction of the MSCZ. These U–Pb data suggest that the complex was constructed by multiple short-lived magmatic intrusion events occurring closely spaced in time, allowing periodic re-melting and rejuvenation of mush-like material and a prolonged lifetime for the complex.