Sapphirine–quartz granulites from the Cocachacra region of the Arequipa Massif in southern Peru record early Neoproterozoic ultrahigh‐temperature metamorphism. Phase equilibrium modelling and zircon petrochronology are used to quantify timing and pressure–temperature (P–T) conditions of metamorphism. Modelling of three magnetite‐bearing sapphirine–quartz samples indicates peak temperatures of >950°C at ~0.7 GPa and a clockwise P–T evolution. Elevated concentrations of Al in orthopyroxene are also consistent with ultrahigh‐temperature conditions. Neoblastic zircon records ages of c. 1.0–0.9 Ga that are interpreted to record protracted ultrahigh‐temperature metamorphism. Th/U ratios of zircon of up to 100 reflect U‐depleted whole‐rock compositions. Concentrations of heavy rare earth elements in zircon do not show systematic trends with U–Pb age but do correlate with variable whole‐rock compositions. Very large positive Ce anomalies in zircon from two samples probably relate to strongly oxidizing conditions during neoblastic zircon crystallization. Low concentrations of Ti‐in‐zircon (<10 ppm) are interpreted to result from reduced titania activities due to the strongly oxidized nature of the granulites and the sequestration of titanium‐rich minerals away from the reaction volume. Whole‐rock compositions and oxidation state have a strong influence on the trace element composition of metamorphic zircon, which has implications for interpreting the geological significance of ages retrieved from zircon in oxidized metamorphic rocks.

中文翻译：

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秘鲁南部氧化颗粒的岩石年代学

秘鲁南部阿雷基帕地块古柯地区的蓝宝石石英粒记录了新元古代早期的超高温变质作用。相平衡建模和锆石petrochronology被用于量化定时和压力-温度（对-叔）变质的条件。对三个磁铁矿蓝宝石-石英样品的建模表明，峰值温度在〜0.7 GPa时> 950°C，并且沿顺时针方向呈P–T演化。邻二甲苯中Al的浓度升高也符合超高温条件。新生锆石记录了c的年龄。1.0–0.9 Ga被解释为记录了长期的超高温变质。锆石的Th / U比率最高为100，反映了贫铀的完整岩石成分。锆石中重稀土元素的浓度并未显示出随U–Pb年龄的系统变化趋势，但与可变的全岩石成分相关。来自两个样品的锆石中非常大的Ce阳性正异常可能与成原始锆石结晶过程中的强氧化条件有关。钛锆石中的低浓度（<10 ppm）被认为是由于颗粒的强烈氧化性质以及富钛矿物质从反应体积中隔离出来而导致二氧化钛活性降低所致。全岩组成和氧化态对变质锆石的微量元素组成有很大影响，