Palaeomagnetic data from the Lower Cambrian red beds of the Caerfai Group in Pembrokeshire, South Wales have been revisited. Original studies all produced closely similar directional data with the combined results yielding a palaeomagnetic pole at 21.8oS; 355.5°E corresponding to a time of ∼430 Ma when compared with the APWP of Stable Europe and Baltica. The results of this study indicate that remagnetisation occurred during Caledonian metamorphism, prior to Acadian deformation in the area. The magnetic remanence is carried by fine grained hematite distributed throughout the sequence and which appears to have been acquired during the duration of a single chron. This time zone is traditional early Silurian (late Llandovery) and corresponds to the docking of Baltica and east Avalonia with the Laurentian continent. The proposed age of the remagnetisation event is consistent with radiometric ages from epizonal authigenic illites in overlying Middle Cambrian bentonites at Porth-y-Rhaw and elsewhere in the Welsh Basin and other parts of Avalonia including Charnwood block and Brabantia. The Caerfai Group comprises texturally immature litharenites with a mineral assemblage including chlorite, biotite, muscovite, graphite, and epidote consistent with a greenschist facies source area which remains unidentified. A key component of the Caerfai mineral assemblage are magnetite crystals (typically 30–60 μm) deposited during contemporaneous volcanic activity. Deep burial during the drift of Avalonia, indicated by clay transformations and overpressure in the Caerfai Bay Mudstone, was associated with the alteration of iron-bearing minerals and the dissolution of magnetite. During collision of Avalonia/Baltica with Laurentia a geothermal cell with epizonal metamorphic conditions (>300 °C) and fluids enriched in iron, probably in the form of iron chloride complexes was established. The remagnetisation event was triggered when the geothermal cell was cooled, most likely by the infiltration of meteoric water, and the reaction of iron chloride with water produced the widespread precipitation of fine-grained hematite and the formation of a chemical remanent magnetisation (CRM).

中文翻译：

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Caerfai 群（下寒武纪，威尔士西南）在喀里多尼亚（前阿卡迪亚）变质过程中在热地热流体中的再磁化作用


来自南威尔士彭布罗克郡 Caerfai 群的下寒武统红层的古地磁数据已被重新访问。原始研究都产生了非常相似的方向数据，合并结果得出的古磁极为 21.8oS;355.5°E 对应于 ∼430 马 的时间，与稳定的欧洲和波罗的海的 APWP 相比。这项研究的结果表明，再磁化发生在喀里多尼亚变质过程中，在该地区的阿卡迪亚变形之前。剩磁由分布在整个序列中的细粒赤铁矿携带，并且似乎是在单个年代的持续时间内获得的。这个时区是传统的早期志留纪（兰多弗晚期），对应于波罗的海和东阿瓦隆与劳伦森大陆的对接。再磁化事件的拟议年龄与 Porth-y-Rhaw 和威尔士盆地其他地方以及阿瓦隆尼亚其他地区（包括 Charnwood 区块和 Brabantia）上覆的中寒武纪膨润土中外带自生伊利岩的辐射年龄一致。Caerfai 组由质地不成熟的岩砂岩组成，矿物组合包括绿泥石、黑云母、白云母、石墨和绿帘石，与仍未确定的绿片岩相源区一致。Caerfai 矿物组合的一个关键组成部分是在同时期火山活动期间沉积的磁铁矿晶体（通常为 30-60 μm）。Caerfai 湾泥岩中的粘土转变和超压表明了 Avalonia 漂移过程中的深埋，与含铁矿物的蚀变和磁铁矿的溶解有关。 在阿瓦隆尼亚/波罗的海与劳伦西亚碰撞期间，建立了一个具有外带变质条件（x3E300 °C）和富含铁的流体的地热单元，可能以氯化铁络合物的形式存在。再磁化事件是在地热电池冷却时触发的，很可能是由流星水的渗透引起的，氯化铁与水的反应产生了细粒赤铁矿的广泛沉淀和化学剩余磁化 （CRM） 的形成。