scholarly journals A simple and robust method for calculating temperatures of granitoid magmas

2021 ◽  
Author(s):  
Meng Duan ◽  
Yaoling Niu ◽  
Pu Sun ◽  
Shuo Chen ◽  
Juanjuan Kong ◽  
...  
Keyword(s):  
Empirical Equation ◽  
Rock Sample ◽  
Saturation Temperature ◽  
Theory And Practice ◽  
Bulk Rock ◽  
Experimental Calibration ◽  
Granitoid Rocks ◽  
Modal Abundance ◽  
Input Variables ◽  
Zircon Saturation

AbstractCalculating the temperatures of magmas from which granitoid rocks solidify is a key task of studying their petrogenesis, but few geothermometers are satisfactory. Zircon saturation thermometry has been the most widely used because it is conceptually simple and practically convenient, and because it is based on experimental calibrations with significant correlation of the calculated zircon saturation temperature (TZr) with zirconium (Zr) content in the granitic melt (i.e., TZr ∝ ZrMELT). However, application of this thermometry to natural rocks can be misleading, resulting in the calculated TZr having no geological significance. This thermometry requires Zr content and a compound bulk compositional parameter M of the melt as input variables. As the Zr and M information of the melt is not available, petrologists simply use bulk-rock Zr content (ZrBULK-ROCK) and M to calculate TZr. In the experimental calibration, TZr shows no correlation with M, thus the calculated TZr is only a function of ZrMELT. Because granitoid rocks represent cumulates or mixtures of melt with crystals before magma solidification and because significant amount Zr in the bulk-rock sample reside in zircon crystals of varying origin (liquidus, captured or inherited crystals) with unknown modal abundance, ZrBULK-ROCK cannot be equated with ZrMELT that is unknown. Hence, the calculated magma temperatures TZr using ZrBULK-ROCK have no significance in both theory and practice. As an alternative, we propose to use the empirical equation $$T_{SiO_{2}}$$ T S i O 2  (°C) = -14.16 × SiO2 + 1723 for granitoid studies, not to rely on exact values for individual samples but focus on the similarities and differences between samples and sample suites for comparison. This simple and robust thermometry is based on experimentally determined phase equilibria with T ∝ 1/SiO2.

Most Granitoid Rocks are Cumulates: Deductions from Hornblende Compositions and Zircon Saturation

2019 ◽  
Vol 60 (11) ◽  
pp. 2227-2240 ◽  
Author(s):  
Calvin G Barnes ◽  
Kevin Werts ◽  
Vali Memeti ◽  
Katie Ardill
Keyword(s):  
Partition Coefficients ◽  
Granitic Rocks ◽  
Granitic Magma ◽  
Intrusive Complex ◽  
Bulk Rock ◽  
Granitoid Rocks ◽  
Modal Layering ◽  
Zircon Thermometry ◽  
Crystal Accumulation ◽  
Zircon Saturation

Abstract Cumulate processes in granitic magma systems are thought by some to be negligible and by others to be common and widespread. Because most granitic rocks lack obvious evidence of accumulation, such as modal layering, other means of identifying cumulate rocks and estimating proportions of melt lost must be developed. The approach presented here utilizes major and trace element compositions of hornblende to estimate melt compositions necessary for zircon saturation. It then compares these estimates with bulk-rock compositions to estimate proportions of extracted melt. Data from three arc-related magmatic systems were used (English Peak pluton, Wooley Creek batholith, and Tuolumne Intrusive Complex). In all three systems, magmatic hornblende displays core-to-rim decreases in Zr, Hf, and Zr/Hf. This zoning indicates that zircon must have fractionated during crystallization of hornblende, at temperatures greater than 800 °C. This T estimate is in agreement with Ti-in-zircon thermometry, which yields a maximum T estimate of 855 °C. On the basis of this evidence, concentrations of Zr in melts from which hornblende and zircon crystallized were calculated by (1) applying saturation equations to bulk-rock compositions, (2) applying saturation equations to calculated melt compositions, and (3) using hornblende/melt partition coefficients for Zr. The results indicate that melt was lost during crystallization of the granitic magmas, conservatively at least as much as 40 %. These results are in agreement with published estimates of melt loss from other plutonic systems and suggest that bulk-rock compositions of many granitic rocks reflect crystal accumulation and are therefore inappropriate for use in thermodynamic calculations and in direct comparison of potentially consanguineous volcanic and plutonic suites.

scholarly journals Protolith-Related Thermal Controls on the Decoupling of Sn and W in Sn-W Metallogenic Provinces: Insights from the Nanling Region, China

2019 ◽  
Vol 114 (5) ◽  
pp. 1005-1012 ◽  
Author(s):  
Shunda Yuan ◽  
Anthony E. Williams-Jones ◽  
Rolf L. Romer ◽  
Panlao Zhao ◽  
Jingwen Mao
Keyword(s):  
South China ◽  
Bulk Rock ◽  
Rare Metals ◽  
The West ◽  
Metallogenic Province ◽  
Peraluminous Granites ◽  
Microgranular Enclaves ◽  
Mafic Microgranular Enclaves ◽  
The World ◽  
Zircon Saturation

Abstract The Nanling region of South China hosts the largest W-Sn metallogenic province in the world, accounting for more than 54% of global tungsten resources as well as important resources of tin and rare metals. An important feature of this province, which is shared by a number of other W-Sn metallogenic provinces, is that W deposits occur separately from Sn and Sn-W deposits, with the latter concentrated in the western part of the region (especially along the deep, NE-trending Chenzhou-Linwu fault) and the W deposits to the east of them. All the deposits are associated with ilmenite series, peraluminous granites. However, the granites associated with the Sn and Sn-W deposits can be distinguished from the W granites by their higher bulk-rock εNd values and their higher zircon εHf values. Most importantly, the Sn and Sn-W granites are characterized by higher zircon saturation temperatures (800 ± 20°C) than the W granites (650°–750°C). The Sn and Sn-W granites also contain abundant mantle-derived mafic microgranular enclaves, whereas such enclaves are rare in the W granites. A model is proposed in which the protolith to the W granites released W to the melt as a result of the breakdown of muscovite. The temperature of melting, however, was too low for biotite to melt. In the west, particularly along the Chenzhou-Linwu fault (the location of the Sn and Sn-W deposits), higher temperatures enabled the breakdown of both muscovite and biotite and the consequent release of both Sn and W to form Sn and Sn-W granites. This model, which is based on differences in the protolith melting temperature and thus mobilization temperatures for Sn and W, is potentially applicable to any Sn-W metallogenic province in which the Sn and Sn-W deposits are spatially separated from the W deposits.

Reconciling zircon and monazite thermometry constrains H2O content in granitic melts

2020 ◽  
Author(s):  
Silvia Volante ◽  
William Collins ◽  
Chris Spencer ◽  
Eleanore Blereau ◽  
Amaury Pourteau ◽  
...  
Keyword(s):  
Water Content ◽  
Volcanic Rocks ◽  
Saturation Temperature ◽  
Granitic Rocks ◽  
Zircon Geochronology ◽  
Bulk Rock ◽  
Independent Evidence ◽  
Water Values ◽  
Host Rocks ◽  
Eastern Domain

<p>In this contribution, we compare and test the reliability of zircon and monazite thermometers and suggest a new and independent method to constrain the H<sub>2</sub>O content in granitic magmas from coeval zircon and monazite minerals. We combine multi-method single-mineral thermometry (bulk-rock zirconium saturation temperature (T<sub>zr</sub>), Ti-in-zircon (T<sub>(Ti-zr</sub><sub>)</sub>) and monazite saturation temperature (T<sub>mz</sub>)) with thermodynamic modelling to estimate water content and P–T conditions for strongly-peraluminous (S-type) granitoids in the Georgetown Inlier, NE Queensland. These granites were generated within ~30 km thick Proterozoic crust, and emplaced during regional extension associated with low-pressure high-temperature (LP–HT) metamorphism.</p><p>SHRIMP U–Pb monazite and zircon geochronology indicates synchronous crystallization ages of c. 1550 Ma for granitic rocks emplaced at different crustal levels—from the eastern deep crustal domain (P = 6–9 kbar), through the middle crustal domain (P = 4–6 kbar), to the western upper crustal domain (P = 0–3 kbar).</p><p>Bulk-rock T<sub>zr</sub> and T<sub>(Ti-zr</sub><sub>)</sub> yielded magma temperature estimates for the eastern domain of ~800°C and ~910–720°C, respectively. Magma temperatures in the central and western domains were ~730°C (T<sub>zr</sub>) and ~870–750°C (T<sub>(Ti-zr)</sub>) in the central domain, and ~810°C (T<sub>zr</sub>) and ~890–720°C (T<sub>(Ti-zr)</sub>) in the western domain, respectively. These temperature estimates were compared with P–T conditions recorded in the host rocks to determine if the magmas had equilibrated thermally with the crust. Similar temperatures were obtained for the middle and lower crust suggesting that the associated magmas thermally equilibrated at their respective depths, whereas the sub-volcanic rocks were, as expected, significantly hotter than the adjacent crust.</p><p>By plotting the results on a P–T–X<sub>H2O</sub> petrogenetic grid, and assuming adiabatic ascent through the crust, the sub-volcanic magmas appear to be drier (~3 wt% H<sub>2</sub>O) than the granitic magmas (~7 wt% H<sub>2</sub>O) which formed at greater depth. Monazite saturation temperatures (which depends on the water content, light–REE content and composition of the granitic melt), are in agreement with the zircon thermometers only if water values of ~3 wt% H<sub>2</sub>O and ~7 wt% H<sub>2</sub>O are assumed for the upper crustal magmas and deeper magmas, respectively. Moreover, melt compositions extracted from a modelled pseudosection of a sillimanite-bearing metapelite, which was interpreted to be the typical source rock for the surrounding granites (P=5 kbar and T=690°C–850°C), show comparable water content values.</p><p>The T<sub>mz</sub> results provide independent evidence for the H<sub>2</sub>O content in magmas, and we suggest that reconciling T<sub>zr</sub> with T<sub>mz</sub> is a new and independent way of constraining H<sub>2</sub>O content in granitic magmas.</p>

scholarly journals Reassessing zircon-monazite thermometry with thermodynamic modelling: insights from the Georgetown igneous complex, NE Australia

2020 ◽  
Vol 175 (12) ◽  
Author(s):  
S. Volante ◽  
W. J. Collins ◽  
E. Blereau ◽  
A. Pourteau ◽  
C. Spencer ◽  
...  
Keyword(s):  
Saturation Temperature ◽  
Thermodynamic Modelling ◽  
Accessory Mineral ◽  
Compositional Variation ◽  
Upper Crust ◽  
Middle Crust ◽  
Deep Crust ◽  
Granite Magmatism ◽  
Zircon Thermometry ◽  
Zircon Saturation

AbstractAccessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature (Tzr) and titanium-in-zircon thermometry (T(Ti–zr)) estimate magma temperatures of ~ 795 ± 41 °C (Tzr) and ~ 845 ± 46 °C (T(Ti-zr)) in the deep crust, ~ 735 ± 30 °C (Tzr) and ~ 785 ± 30 °C (T(Ti-zr)) in the middle crust, and ~ 796 ± 45 °C (Tzr) and ~ 850 ± 40 °C (T(Ti-zr)) in the upper crust. The differing averages reflect ambient temperature conditions (Tzr) within the magma chamber, whereas the higher T(Ti-zr) values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H2O, whereas deeper melts contained 7 wt% H2O. Using these H2O contents, monazite saturation temperature (Tmz) estimates agree with Tzr values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO2) melts. At inferred emplacement P–T conditions of 5 kbar and 730 °C, additional H2O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low-T mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.

ARE MOST GRANITOID ROCKS CUMULATES? DEDUCTIONS AND CONUNDRUMS FROM AMPHIBOLE COMPOSITIONS AND ZIRCON SATURATION

2019 ◽  
Author(s):  
Calvin G. Barnes ◽  
◽  
Kevin Werts ◽  
Vali Memeti ◽  
Katie E. Ardill ◽  
...  
Keyword(s):  
Granitoid Rocks ◽  
Zircon Saturation

Addressing the Content Vocabulary With Core: Theory and Practice for Nonliterate or Emerging Literate Students

2012 ◽  
Vol 21 (3) ◽  
pp. 74-81 ◽  
Author(s):  
Debbie Witkowski ◽  
Bruce Baker
Keyword(s):  
Communication Skills ◽  
High Performance ◽  
Theory And Practice ◽  
Written Communication ◽  
Academic Tasks ◽  
Meaningful Participation ◽  
Core Theory ◽  
Communication Needs ◽  
Core Vocabulary ◽  
Personal Success

Abstract In the early elementary grades, the primary emphasis is on developing skills crucial to future academic and personal success—specifically oral and written communication skills. These skills are vital to student success as well as to meaningful participation in the classroom and interaction with peers. Children with complex communication needs (CCN) may require the use of high-performance speech generating devices (SGDs). The challenges for these students are further complicated by the task of learning language at a time when they are expected to apply their linguistic skills to academic tasks. However, by focusing on core vocabulary as a primary vehicle for instruction, educators can equip students who use SGDs to develop language skills and be competitive in the classroom. In this article, we will define core vocabulary and provide theoretical and practical insights into integrating it into the classroom routine for developing oral and written communication skills.

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