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首页> 外文期刊>Contributions to Mineralogy and Petrology >High-resolution Fe-Ti oxide thermometry applied to single-clast pumices from the Bishop Tuff: a re-examination of compositional variations in phenocryst phases with temperature
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High-resolution Fe-Ti oxide thermometry applied to single-clast pumices from the Bishop Tuff: a re-examination of compositional variations in phenocryst phases with temperature

机译：高分辨率Fe-Ti氧化物温度从主教牙龈中施加到单碎屑件：重新检查苯杂交相中温度的组成变化

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摘要

Numerous analyses of multiple ilmenite, titanomagnetite, sanidine, plagioclase, biotite, orthopyroxene, and clinopyroxene crystals (when present) in each of 24 single-clast pumices from the Bishop Tuff (BT), CA are presented, together with whole-rock compositions on the same single clasts. Data from multiple Fe-Ti oxide grains in each sample, coupled with an assessment of analytical uncertainty, show that there is a single population of ilmenite and titanomagnetite in each of 20 samples and no more than two populations of ilmenite and/or titanomagnetite in the remaining four. A statistical evaluation of microprobe uncertainty (for beam conditions of 15 kV and 10 nA) constrains the minimum number of ilmenite (>= 21) and titanomagnetite (>= 56) analyses required to obtain Fe-Ti two-oxide temperatures with propagated uncertainties <= +/- 10 degrees C. Thermometry results confirm a continuous range ( 700-800 degrees C) across the BT deposit. Plagioclase displays a bimodal compositional pattern, where a predominantly sodic (An(14-15)) vs. calcic (An(22-23)) population is found in single clasts where pyroxene is absent vs. present; the latter coincides with geochemical evidence for mixing between high-SiO2 rhyolite and less differentiated melts as previously documented in the literature. When sanidine rims are paired with plagioclase, calculated two-feldspar temperatures ( 690-780 degrees C) are strongly correlated (R-2 = 0.94) with Fe-Ti two-oxide temperatures. Application of plagioclase-liquid hygrometry reveals a systematic decrease in melt water content ( 7.2-4.1 wt%) with increasing temperature across the BT deposit, consistent with experiments from the literature that show cotectic crystallization of quartz-sanidine-plagioclase in rhyolite melt requires a concomitant decrease of 3 wt% H2O between 700 and 800 degrees C at 200 MPa. Single-clast, whole-rock concentrations of some elements (e.g., Rb) correlate strongly with Fe-Ti oxide temperature (R-2 = 0.95). The Mg# in biotite also correlates strongly with temperature (R-2 = 0.97), as do the Mg# values in orthopyroxene and clinopyroxene with whole-rock Mg# (R-2 = 0.6 and 0.8, respectively) and melt water content (R-2 = 0.7 for both). Evidence points to biotite crystallization in all BT samples from high-SiO2 rhyolite melt, which was already continuously zoned in composition and temperature prior to mixing with less differentiated melts, as previously noted in the literature. In contrast, several lines of evidence, including hydrous phase-equilibrium experiments on rhyolites from the literature, show that both pyroxenes in BT pumices co-crystallized with calcic plagioclase ( An(21-29)), in equilibrium with both titanomagnetite and ilmenite, after mixing between less differentiated melt(s) and relatively hot (>= 755 degrees C) high-SiO2 rhyolite.
机译：从主教Tuff（BT），CA，CA中的24个单碎屑厂中的每一个中，多种Ilmenite，钛磁石，静血胺，普拉基酶，生物素，正卵石和临床晶体（当存在时）的许多分析。相同的单碎屑。每个样品中的多个Fe-Ti氧化物颗粒的数据，与分析性不确定性的评估相结合，表明20个样品中的每一个和钛镁镁盐的单一群体，并且在其中不超过两个伊尔梅钛矿和/或钛磁石的群体剩下四个。微探针不确定度的统计评估（对于15kV和10 na的光束条件）约定了获得Fe-Ti两氧化物温度的钛铁矿（> = 21）和钛镁镁镁（> = 56）分析的分析。 = +/- 10度C.测温结果在BT沉积物上确认连续范围（700-800℃）。 Plagioclase显示出一种双峰组成模式，其中主要的碳化钠（An（14-15））与钙（（22-15））群体中发现，其中辉石中不存在与存在的单裂片;后者与在文献中先前记录的高SiO2细流石和较少的分化熔体之间混合的地球化学证据一致。当静嘌呤轮辋与Plagioclase配对时，计算的两性高度（690-780℃）与Fe-Ti两氧化物温度强烈相关（R-2 = 0.94）。 Plagioclase-液体湿法的施用显示熔融含水量（7.2-4.1wt％）随着BT沉积物的温度越来越大的熔融含水量（7.2-4.1重量％），与文献中的实验一致，其显示谷氨石熔体中石英凝聚蛋白蛋白酶的Cotectic结晶需要a在200MPa的200MPa下伴随在700和800摄氏度之间的3wt％H 2 O。单碎屑，一些元素的全岩浓度（例如，Rb）与Fe-Ti氧化物温度强烈相关（R-2 = 0.95）。 Biotite中的MG＃也与温度强烈（R-2 = 0.97）强烈地相关，如整体岩石和Clinopoyroxene中的Mg＃值与全岩石Mg＃（R-2 = 0.6和0.8分别）和熔融含水量（ r-2 = 0.7两个）。从高SiO2菱形熔体中的所有BT样品中的生物素结晶点的证据指向，在与文献中先前注明的熔体相混合，在组合物和温度中已经连续分区，如前所述。相反，几种证据，包括来自文献的毒液相位平衡实验，表明，在BT型钙氏菌酶（AN（21-29））中与钛磁石和Ilmenite的平衡相结晶，吡喃（21-29），在较少分化的熔体和相对热（> = 755℃）的高SiO 2脉灰之间混合后。

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