Lawsonite blueschists are important markers of cold subduction zones, subjected to intense fluid circulation. This is because lawsonite preservation in exhumed blueschists and eclogites is typically linked to cold exhumation paths, accompanied by hydration. In the Catena Costiera (Calabria, southern Italy), lawsonite–clinopyroxene blueschists of the Diamante–Terranova Unit, affected by ductile shearing and retrogression, are exposed. Blueschists contain zoned clinopyroxene crystals, showing core–rim compositional variation from diopside to omphacite and hosting primary inclusions of lawsonite and titanite. Thermodynamic modelling of phase equilibria in the NCKFMASHTO system revealed peak metamorphic conditions of 2.0–2.1 GPa and 475–490°C for the Alpine subduction in Calabria. The subsequent post‐peak metamorphic evolution mainly proceeded along a decompression and cooling path up to ~1.1 GPa and ~380°C. The final exhumation stages are recorded in the sheared blueschists where a mylonitic to ultramylonitic foliation developed at ~0.7 GPa and 290–315°C. Therefore, the P–T evolution of the Diamante–Terranova blueschists mostly occurred in the stability field of lawsonite, sustained by H₂O‐saturated conditions during the exhumation path. The results of this study indicate that the blueschists underwent peak metamorphic conditions higher than previously thought, reaching a maximum depth of ~70 km under a very cold geothermal gradient (~6.6°C/km), during the Eocene subduction of the Ligurian Tethys oceanic crust in Calabria.

中文翻译：

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褐铁矿-斜辉石蓝晶岩揭示了卡拉布里亚北部（意大利）的冷俯冲带

钙钠盐蓝晶岩是冷俯冲带的重要标志，它们经历了强烈的流体循环。这是因为在发掘出的blueschists和榴辉岩中，钠钙矾的保存通常与低温发掘的路径有关，并伴有水合作用。在Catena Costiera（意大利南部的卡拉布里亚），受到韧性剪切和倒退影响的Diamante-Terranova单元的褐铁矿-斜辉石蓝晶岩被暴露出来。Blueschists包含分区的斜辉石晶体，显示出从透辉石到辉绿岩的芯-缘组成变化，并占据了钙钠锰矿和钛矿的主要包裹体。NCKFMASHTO系统中相平衡的热力学模型揭示了卡拉布里亚高山俯冲的峰变质条件为2.0–2.1 GPa和475–490°C。随后的峰后变质演化主要沿减压和冷却路径进行，最高达到〜1.1 GPa和〜380°C。最终的发掘阶段记录在剪切的blueschists中，在约0.7 GPa和290–315°C的温度下，出现了从长链淀粉到超亚扇贝的叶酸。因此，Diamante-Terranova blueschists的P–T演化主要发生在褐铁矿的稳定区域中，在掘尸过程中受到H ₂ O饱和条件的影响。这项研究的结果表明，在利古里亚特提斯洋的始新世俯冲过程中，蓝灰岩经历了比以前认为的更高的峰值变质条件，在非常冷的地热梯度（约6.6°C / km）下达到了约70 km的最大深度。卡拉布里亚的地壳。