Abstract

Geological-structural and petrological data acquired by the authors on the most widely spread metamorphic associations of the Belomorian Mobile Belt in northern Karelia, Russia, indicate that the rocks belong to five age groups (0–IV), which were produced by metamorphism of protoliths of different composition and genesis. The Paleoproterozoic metamorphic associations were formed by three successive metamorphic episodes, which corresponded to discrete evolutionary episodes of the Lapland–Karelian Orogen. The first episode of Paleoproterozoic metamorphism was high-pressure transformations that produced steep zones of ductile flow of submeridional and northeastern trend. The second episode was high-temperature metamorphism at intermediate and high pressure, which was triggered by the development of gently sloped ductile flow zones and tectonic mélange of roughly latitudinal trend. The third metamorphic episode involved amphibolization of the rocks during high-temperature decompression cooling and was likely related to the development of randomly oriented fractures when the rocks of the Belomorian Mobile Belt were brought to middle and upper crustal levels. Each of the episodes was characterized by different P–T parameters of metamorphism, which are recorded in the compositions of the rock-forming minerals. The former two episodes corresponded to the prograde metamorphic evolution, and the third one was a retrograde evolution. The beginning of the first episode was responsible for the origin of amphibolites at Т = 560–640°C and Р = 6.7–9.5 kbar, with the metamorphic peak producing eclogites at Т = 600–690°C and Р = 11.3–12.9 kbar and eclogite-like rocks at higher temperatures of Т = 650–780°C and Р = 10.3–13.0 kbar. The peak of the second metamorphic episode corresponded to the origin of abundant plagiomigmatite leucosomes, which were formed within a broad temperature range (640–840°C) and a narrow pressure range (9.0–11.9 kbar). The widespread amphibolization of the metabasites of all types occurred only during the third metamorphic episode, whose P–T parameters broadly varied: 590–740°C and Р = 7.5–10.8 kbar. All dike varieties of the complex of eclogitized garnet metagabbro were formed at the metamorphic peak at the same P–T parameters as the host metamorphic rocks in the corresponding structures: metagabbro I was formed in steep ductile flow zones, and metagabbro II was produced in the gently sloped zones.

中文翻译：

---

俄罗斯北卡累利阿中部Belomorian移动带古元古代变质事件的热压法

摘要

作者从俄罗斯北部卡累利阿州Belomorian移动带最广泛分布的变质协会获得的地质结构和岩石学数据表明，这些岩石属于五个年龄组（0–IV），它们是由原石变质产生的不同的组成和起源。古元古代变质联系是由三个连续的变质作用形成的，这对应于拉普兰—卡累利阿造山带的离散演化作用。古元古代变质的第一阶段是高压转换，产生了近水下和东北趋势的韧性流的陡峭区域。第二个事件是中高压下的高温变质，这是由缓倾斜的韧性流动带和大致呈纬向趋势的构造混杂岩的发育触发的。第三个变质事件涉及高温减压冷却过程中岩石的两性化，并且可能与将Belomorian移动带的岩石带到中上地壳水平时随机取向的裂缝的发展有关。每个情节都有不同的特点变质的P – T参数，记录在成岩矿物的成分中。前两个事件对应于渐进性的变质演化，第三个事件对应于逆行的演化。第一集的开始是角闪石在Т = 560–640°C和Р = 6.7–9.5 kbar的起源的原因，变质峰产生的榴辉岩在Т = 600–690°C和Р = 11.3-12.9 kbar的情况下在Т = 650–780°C和Р的较高温度下为类似榴辉岩的岩石= 10.3–13.0 kbar。第二次变质峰的峰值对应于丰富的斜长石辉石岩浆体的起源，它们是在较宽的温度范围（640–840°C）和较窄的压力范围（9.0–11.9 kbar）内形成的。仅在第三次变质事件发生期间，所有类型的代谢物都发生了广泛的两亲化，其P – T参数变化很大：590–740°C和Р = 7.5–10.8 kbar。形成在同一变质峰复杂的eclogitized石榴石metagabbro的所有堤防品种P -牛逼 参数是相应结构中的宿主变质岩：变质I形成于陡峭的韧性流动带中，而变质II则形成于缓坡带中。