Solubility of titanium dioxide in ultrahigh-temperature metamorphic minerals at high pressures and high temperatures to calibrate the geothermobarometer for ultrahigh-temperature granulites

在压力7-25kbar，温度850-1300℃条件下，研究了二氧化钛在石榴石和斜方辉石中的溶解度。实验中使用了两种麻粒岩：(1)纳皮尔杂岩麦金太尔的斜方辉石麻粒岩；(2)伦德维谢塔的硅线石-堇青石-蓝宝石麻粒岩。以麦金太尔麻粒岩粉+8wt%SiO_2+16wt%TiO_2+8wt%Al_2O_3为原料，在10kbar、1500℃下熔融1min后冷却。另一种陈述材料是含有2wt%1102(RVH)的Rundvolshetta麻粒岩粉末。运行时间为至952小时。我们使用的是钼铂双胶囊或AuPd胶囊。研究结果表明：(1)石榴石和斜方辉石中的钛取代了四面体的硅，而不替代了镁、铁和铝；(2)二氧化钛的溶解度随着温度的升高而增加，如(X^&lt；Grt&gt；_T√X^&lt；Grt&gt；_&lt；Si&gt；)=-15366/T+5.962(GARN…)斜方辉石的Et和In(X^&lt；opx&gt；_T√X^&lt；opx&gt；_Ti)=-11367/T+3.107较高；(3)这些温度计对估算金红石析出的逆行温度非常有用；(4)石榴石中的钛随着压力的增加而减少，而斜方辉石中的钛随着压力的增加而增加。这些报告发表在加利福尼亚大学圣巴巴拉举行的第十届南极地球科学国际研讨会(ISAES2007)上。从描述岩石学的角度，提出了石英中钛的经验温度计为T(℃)=-5895/(INX〓_&lt；Ti02&gt；+1.729)-273。该温度计现已在《伦敦地质学会杂志》特刊上发表。详细分析了超高温麻粒岩的变质过程。在岩相学分析中，我们发现石英中的Fe~(2+)~(3+)随着温度的升高而增加。在990-1440℃温度范围内，对Fe~(2+)~(3+)~(3+)在硅石矿物中的溶解度进行了实验。结果表明，石英中铁的含量随压力和温度的升高而增加：Inx&lt；Fe&gt；=(-1092-5.254T+7.75P)IT，其中X&lt；Fe&gt；，T和P分别是按2-氧原子归一化(Fe的阳离子摩尔分数)、温度(开尔文)和压力(Kbar)计算的石英中Fe原子的个数。将这种新型地温计应用于马鞍山超高温变质石英磁铁矿岩石。在东南极纳皮尔杂岩的Riiser-Larsen地区，在5-15Kbar的压力下，变质温度估计为994-1095℃。较少

The solubility of titanium dioxide of garnet and orthopyroxene was investigated at pressures 7-25 kbar and temperatures 850-1300℃. The two granulites: (1) orthopyroxene granulite from McIntyre, Napier Complex; and: (2) the silimanite-cordierite-sapphirine granulite from Rundvagshetta, Lutzow-Holm Complex, were used in the present experiments. A glass starting material was prepared as: the mixture of the powdered McIntyre granulite + 8 wt% SiO_2 + 16 wt% TiO_2 + 8 wt% Al_2O3 was fused at 10 kbar and 1500℃ for 1 minute and quenched (MCTQ). Another stating material was a powdered Rundvagshetta granulite containing 2 wt% of 1102 (RVH). Run durations were 64 to 952 hours. We used the Mo/Pt double capsule or AuPd capsule. The present investigation provided following results: (1) Ti in garnet and orthopyroxene substitutes for the tetrahedral Si and never substitutes for Mg, Fe and AI; (2) the solubility of TiO_2 increases with temperature as In(X^<Grt>_T√X ^<Grt>_<Si>)=-15366/T+5.962 for garn … More et and In(X^<opx>_T√X^<opx>_Ti)=-11367/T+3.107 for orthopyroxene; (3) these thermometer is very useful to estimate the retrograde temperatures where rutile would exsolve; (4)Ti in garnet decreases with pressure although Ti in orthopyroxene increases with pressure. These were published at The 10th International Symposium on Antarctic Earth Science (ISAES2007), Santa Barbara, University of California. From the aid of the descriptive petrology, we proposed the empirical thermometer Ti in quartz as T(℃)=-5895/(InX〓_<TiO2>+1.729)-273. This thermometer is now in press in the Journal of the Geological Society of London, Special Issue. We analyzed the metamorphic processes of the ultrahigh-temperature granulites in detail. During the petrographic analyses we found the Fe^<3+> in quartz increases with temperature. Experiments on the solubility of Fe^<3+> in silica minerals were carried out at temperatures 990-1440℃ in the air. We obtained the found the content of ferric iron in quartz increases with increasing pressure and temperature: InX_<Fe> =(-1092-5.254T +7.75P)IT, where X_<Fe>, T and P are the number of Fe atoms in quartz per formula unit based on a 2-oxygen atom normalization(cationic mole fraction of Fe), temperature in Kelvin and pressure in kbar, respectively. This new geothermometer is applied to the ultrahigh-temperature metamorphosed quartz-magnetite rock from Mt. Riiser-Larsen area, Napier Complex, East Antarctica, resulting that the metamorphic temperatures are estimated as about 994-1095℃ for pressures 5-15 kbar. Less