Prograde P–T–t paths of eclogites are often ambiguous owing to high variance of mineral assemblages, large uncertainty in isotopic age determinations and/or variable degree of retrograde equilibration. We investigated these issues using the barroisite eclogites from the Lanterman Range, northern Victoria Land, Antarctica, which are relatively uncommon but free of retrogression. These eclogites revealed three stages of prograde metamorphism, defining two distinctive P–T trajectories, M_1–2 and M₃. Inclusion minerals in garnet porphyroblasts suggest that initial prograde assemblages (M₁) consist of garnet+omphacite+barroisite/Mg‐pargasite+epidote+phengite+paragonite+rutile/titanite+quartz, and subsequent M₂ assemblages of garnet+omphacite+barroisite+phengite+rutile±quartz. The inclusion‐rich inner part of garnet porphyroblasts preserves a bell‐shaped Mn profile of the M₁, whereas the inclusion‐poor outer part (M₂) is typified by the outward decrease in Ca/Mg and X_Fe (=Fe²⁺/(Fe²⁺+Mg)) values. A pseudosection modelling employing fractionated bulk‐rock composition suggests that the eclogites have initially evolved from ~15 to 20 kbar and 520–570°C (M₁) to ~22–25 kbar and 630–650°C (M₂). The latter is in accordance with P–T conditions estimated from two independent geothermobarometers: the garnet–clinopyroxene–phengite (~25 ± 3 kbar and 660 ± 100°C) and Zr‐in‐rutile (~650–700°C at 22–27 kbar). The second segment (M_3A–B) of prograde P–T path is recorded in the grossular‐rich overgrowth rim of garnet. Apart from disequilibrium growth of the M_3A garnet, ubiquitous overgrowth of the M_3B garnet permits us to estimate the P–T conditions at ~26 ± 3 kbar and 720 ± 80°C. The cathodoluminescence (CL) imaging of zircon grains separated from a barroisite eclogite revealed three distinct zones with bright rim, dark mantle and moderately dark core. Eclogitic phases such as garnet, omphacite, epidote and rutile are present as fine‐grained inclusions in the mantle and rim of zircon, in contrast to their absence in the core. The sensitive high‐resolution ion microprobe U–Pb dating on metamorphic mantle domains and neoblasts yielded a weighted mean ²⁰⁶Pb/²³⁸U age of 515 ± 4 Ma (tσ), representing the time of the M₂ stage. On the other hand, overgrowth rims as well as bright‐CL neoblasts of zircon were dated at 498 ± 11 Ma (tσ), corresponding to the M₃. Average burial rates estimated from the M₂ and M₃ ages are too low (<2 mm/year) for cold subduction regime (~5–10°C/km), suggesting that an exhumation stage intervened between two prograde segments of P–T path. Thus, the P–T–t evolution of barroisite eclogites is typified by two discrete episodes with an c. 15 Ma gap during the middle Cambrian subduction of the Antarctic Ross Orogeny.

中文翻译：

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南极维多利亚州北部兰特曼山脉的钡铁矿榴辉岩中PT演化和片状锆石生长

由于矿物组合的高度变化，同位素年龄确定的不确定性和/或逆行平衡程度的变化，榴辉岩的PTt -t前进路径通常是模棱两可的。我们使用南极维多利亚州土地北部的兰特曼山脉的钡铁矿榴辉岩调查了这些问题，这种榴辉岩相对罕见，但没有倒退。这些榴辉岩揭示了三个阶段的渐进变质作用，定义了两个不同的P–T轨迹：M _1–2和M ₃。石榴石成卟啉细胞中包含的矿物表明，最初的前进组合（M ₁）由石榴石+辉石+钡铁矿/镁-辉石粉+锂辉石+钠钙石+钠钙石+金红石/钛铁矿+石英组成，随后是M石榴石+辉石+铁矿石+辉石+金红石±石英的_2个组合。石榴石成叶细胞的内含物丰富的内部保留了M ₁的钟形锰分布，而内含物贫乏的外部部分（M ₂）则以Ca / Mg和X _{F e}（= Fe ²）的向外减少为特征。⁺ /（Fe ²⁺ + Mg））值。利用分段的碎石成分进行的伪剖面模拟表明，榴辉岩最初从约15至20 kbar和520–570°C（M ₁）演化为约22–25 kbar和630–650°C（M ₂）。后者符合PT根据两个独立的地热气压计估算的条件：石榴石-斜茂铁-辉石（约25±3 kbar和660±100°C）和金红石（约650-700°C，22 – 27 kbar）。前进P–T路径的第二个部分（M _3A–B）记录在石榴石的富含眼球的过度生长边缘中。除了M _3A石榴石的不平衡生长之外，M _3B石榴石的泛滥也使我们能够估计P–T温度在〜26±3 kbar和720±80°C下。从钡铁矾榴辉岩中分离出的锆石的阴极发光（CL）成像显示出三个不同的区域，它们具有明亮的边缘，深色的地幔和中等深色的核心。石榴石，绿辉石，附子和金红石等浮生相以细粒夹杂物形式存在于锆石的地幔和边缘，而岩心中则没有。敏感的高分辨率离子微探针U–Pb在变质地幔域和成胚细胞上的年代，加权平均²⁰⁶ Pb / ²³⁸ U年龄为515±4 Ma（tσ），代表了M ₂期的时间。另一方面，锆石的过度生长轮缘和明亮CL新生代的日期为498±11 Ma（tσ），对应于M ₃。从M ₂和M ₃年龄估计的平均埋葬率太低（<2 mm /年），对于冷俯冲状态（〜5–10°C / km）而言，表明在P– 2的两个前进阶段之间有一个掘尸阶段。 T路径。因此，P-T-吨的冻蓝闪石榴辉进化是通过用两个分立的集为代表Ç。南极罗斯造山带中寒武纪俯冲过程中的15 Ma间隙。