An eclogite from the Early Palaeozoic Fleur-de-Lys Supergroup in Newfoundland was studied because of its biotite porphyroblasts, which very rarely occur in this rock type. Thermodynamic modelling suggests that eclogitic biotite in common metabasite (former basalt–gabbro) is limited to (1) bulk-rock compositions, which are relatively rich in Fe²⁺ and K and poor in Fe³⁺, and (2) the low-pressure range of the eclogite facies. The latter reason is supported by the determination of the pressure–temperature (P–T) path of the Newfoundland eclogite. Chemical zonation of garnet, presence of phengite with Si contents of ~3.4 per formula unit, Zr contents in rutile and petrographic observations resulted in a P–T trajectory starting at medium-pressure conditions. Nearly isothermal burial led to a peak pressure of 18–19 kbar at ~575°C, followed by exhumation and slight heating. Deformation occurred at or close to the peak pressure. Subsequent introduction of hydrous fluids caused the formation of porphyroblasts of biotite and Ca–amphibole in the pressure range of 12–17 kbar at peak temperatures of 625–640°C. Retrogression led to very fine-grained symplectites around omphacite and phengite and marginal replacement of biotite porphyroblasts by plagioclase and titanite. Geodynamic scenarios invoking either a flat subduction of oceanic crust followed by continent–continent collision or intracontinental subduction along a transpressional fault system might best explain the formation of eclogite with biotite porphyroblasts in general. For the Newfoundland eclogite, the latter scenario is preferred.

中文翻译：

---

榴辉岩与黑云母斑叶细胞——哪些条件导致了它们的形成？加拿大纽芬兰北部百合花超群的一个例子

研究人员对纽芬兰早古生代百合花超群的榴辉岩进行了研究，因为它含有黑云母斑片，这种岩石类型中很少出现这种情况。热力学模型表明，常见变碱岩（以前的玄武岩-辉长岩）中的榴辉岩黑云母仅限于（1）块岩成分，其相对富含 Fe ²⁺和 K，而缺乏 Fe ³⁺，以及（2）低-榴辉岩相压力范围。纽芬兰榴辉岩压力-温度 (P-T) 路径的测定支持了后一个原因。石榴石的化学分带、硅含量约为每分子式单位 3.4 的白硅白云母的存在、金红石中的 Zr 含量以及岩相学观察导致了从中压条件下开始的 P-T 轨迹。近等温埋藏导致峰值压力为 18-19 kbar，温度约为 575°C，随后进行折返和轻微加热。在峰值压力或接近峰值压力时发生变形。随后引入含水流体，在 12-17 kbar 的压力范围和 625-640°C 的峰值温度下形成黑云母和 Ca-角闪石的卟啉细胞。退变导致绿辉石和白硅白云母周围出现非常细粒的辛辉石，并且黑云母斑晶被斜长石和钛长石边缘取代。地球动力学场景要么是洋壳平坦俯冲，然后是大陆与大陆碰撞，要么是沿着压断层系统的陆内俯冲，这可能最好地解释一般来说榴辉岩与黑云母斑叶细胞的形成。对于纽芬兰榴辉岩来说，后一种情况是首选。