A New Occurrence of Alkaline Magmatism on the Kola Peninsula: An Agpaitic Dyke in the Kandalaksha Region.
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Abstract:
1125 Alkaline magmatism has been widely abundant on the territory of the Kola Peninsula with the maximal activity in the Paleozoic, when most of the alkaline– ultrabasic complexes, alkaline intrusions of the agpaitic series, and rocks of the dyke series were formed [1–3]. Paleozoic dykes of alkaline rocks were registered (1) in the Khibiny and Lovozero agpaitic massifs and their frames; (2) in the massifs of alka� line–ultrabasic rocks with carbonatite (Kovdor, Turii Mys, Vuorijarvi, Afrikanda, Kandaguba, etc.); (3) in autonomous swarms, which are not spatially related to alkaline intrusions (dykes on the coast of the Kan� dalaksha Bay, swarms of pipes and dykes of kimberlite and melilitite of the Tersk coast, etc.) [3]. A new occurrence of alkaline dyke magmatism was discovered in 2010 during the geological works per� formed by the Murmansk Geological Prospecting Expedition in the “Mokhnatye Roga” area located 55 km to the southeast of the Kovdor massif ( 67°15′ N, 31°30′ E) (Fig. 1). The “Mokhnatye Roga” area is located in the Ensk segment of the northwestern part of the Belomorian mobile belt. We performed a complete petrological and geochemical description of the sections in Holes 19 and 24, which reveal one of the largest dykes in the area. The dyke, with a length of ≈4 km and a width of ≈160 m, has an eastern orientation with steep dipping (60°–90°) to the north. The thickness of Quaternary deposits ranges from 0.8 to 4.0 m; alkaline rocks occur in the range of 4.0–93.9 m being followed by host amphibole–biotite gneiss with interbeds of plagioam� phibolite (AR2 mt) along the section. The contacts with host rocks are sharp, secant, magmatic; there are noKeywords:
Massif
Kola peninsula
Carbonatite
Ultramafic rock
Prospecting
Nepheline
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Phlogopite
Pyroxene
Microprobe
Kola peninsula
Carbonatite
Chromite
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Abstract Abstract The basement complex exposed in the Wright Valley consists of more than 15,000 ft of lolded Precambrian — Lower Cambrian marbles, hornfelses, and schists (Asgard Formation), invaded by acid plutonic rocks. The plutonic rocks comprise three intrusive phases. The oldest intrusives are a strongly foliated granite-gneiss (Olympus) and a porphyritic granite (Dais), cut by pegmatite dykes and veins. The second intrusive phase consists of microdiorite (Loke) and granodiorite (Theseus) dykes intruding the metasediments, granite-gneiss, and granite. The third intrusive phase includes an undeformed homogeneous granite (Vida) containing in a few localities large bodies of amphibolite, and dense swarms of younger lamprophyre and porphyry dykes (Vanda) invading all earlier rocks. The peneplained basement surface is overlain unconformably by more than 4,000 ft of mid-Paleozoic to mid-Mesozoic sediments of the Beacon Sandstone (Group). Ferrar Dolerite sills and dykes intrude the basement complex and the Beacon Sandstone. Late Quaternary deglacierisation has left the Wright Valley ice-free for approximately 30 miles.
Porphyritic
Pegmatite
Basement
Sill
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A dozen ultramafic lamprophyre dykes have been identified in the eastern part of Ungava Bay, Québec. The dark grey dykes are composed of macrocrysts of olivine and phlogopite featuring tetraferriphlogopite rims. These minerals are included in a matrix consisting of fine-grained phlogopite, olivine, spinel, and interstitial carbonate. The geochemical composition, mineral assemblage, chemical analyses of the xenocrysts and phenocrysts and Sm-Nd isotopic signature indicate that these rocks are carbonated ultramafic lamprophyre dykes. The chemical zonation of the micas and the presence of andradite suggest a complex sequence of crystallization. An Ar isotope correlation analysis indicates an age of approximately 550 Ma. The dykes have intruded the Tasiuyak gneiss, a suite of Paleoproterozoic metasedimentary rocks. This unit occupies the Torngat Orogen collision zone between the Rae Province and the Nain Province. The dykes are considered to have been emplaced within tension gashes during reactivation of major Paleoproterozoic structures and fractures associated with the opening of the Iapetus Ocean. They are possibly related to a mantle plume that simultaneously caused both the rupture of the Laurentia and the formation of the ultramafic magma. The Abloviak lamprophyres have quite similar analogues in southwest Greenland. The age, geochemical characteristics, isotopic signature common to all these dykes, the geological environment of the southwest Greenland are all comparable with the data presented here for the Abloviak lamprophyres. Furthermore their pre-drift geographical proximity, prior to the opening of the Labrador Sea, suggests that they are related to a common magmatic event which constitutes a diamondiferous alkaline province located in northeastern North America.
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Ultramafic rock
Phenocryst
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Abstract The northwestern part of southwest Chad is one of the best regions to find exposed Precambrian terrains and their Phanerozoic cover. In this area, it is easy to establish the lithostratigraphic and structural relationships between sedimentary and granitic rocks, greenstone belts and dolerite dykes. Based on petrographic and structural studies, we distinguished the greenstone belts that belong to the Neoproterozoic Zalbi Series. The Neoproterozoic greenstone belts that are intruded by three generations of Pan-African granitoids (gabbro-diorite, biotite monzogranite and leucogranite) host the mineral resources in the region. The Precambrian rocks are covered by Cretaceous shale, sandstone and microconglomerate in the Kebbi Basin, and intruded by dolerite dykes. These late dolerite dykes, have a continental tholeiitic composition, which is supported by the presence of orthopyroxene in the mineralogical assemblage. Structurally, two major deformation events are present in the Zalbi Series. The earliest D1 event is the most intensive and is associated with vertical to subvertical north-trending S1 foliation, a vertical L1 lineation and P1 folds; the metamorphism associated with this phase is equilibrated in greenschist facies conditions. The second D2 event is discrete and is characterised by large-amplitude folds and fractures. 乍得西南的西北部是寻找出露的前寒武纪地体及其显生宇覆盖体的最佳地区之一。在该区，易建立沉积岩和花岗岩石、绿石带和辉绿岩岩墙之间的岩石地层关系和构造关系。根据岩石和构造研究，我们分辨出属于新原生代Zalbi系的绿带。新原生代绿石带被三代泛非洲花岗岩类（辉长-闪长岩、黑云母二长花岗岩和淡色花岗岩）所侵入，因此是该地区矿物资源的载体。在Kebbi盆地，前寒武纪岩石之上覆有白垩纪页岩、砂岩和微砾岩，并有辉绿岩岩墙侵入。这些辉绿岩岩墙具有陆地拉斑玄武岩成分，矿物组合中有斜方辉石类的存在是其证明。在构造方面，Zalbi系中有两个主要变形事件。最早的D1事件最强烈，与垂直和近垂直的北向S1叶理、垂直的L1线理和P1皱褶相关；与这一事件相关的变质作用在绿片岩相环境中呈平衡状态。第二个D2事件以大幅度皱褶和断裂为特征。 KEY WORDS: petrographystructuralNeoproterozoic Zalbi SeriesPan-African plutonic rocksCretaceous sedimentary rocksdolerite dykes关键词: 岩石学构造新原生代 Zalbi系泛非洲深成岩白垩纪沉积岩辉绿岩岩墙 ACKNOWLEDGEMENTS This work was financially supported by the University of N’djamena in Chad and the University of Ngaoundere in Cameroon. We give special thanks to Dr Lanan Wassy Soromou for assistance with this manuscript.
Greenschist
Leucogranite
Greenstone belt
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Abstract Ultramafic dykes associated with dolerites and rhomb porphyries along the northern Skagerrak coast of Sweden seem closely related with the igneous activity in the Oslo Rift zone. On the basis of field evidence, petrography and geochemistry, a cumulus origin of the ultramafic dykes is suggested. Key Words: Ultramafic dykeslamprophyrescumulatespetrographygeochemistryK-ArSkagerrak coastOslo RiftN5818 N5920 E1142 E1058
Ultramafic rock
West coast
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Amphibole
Massif
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Kola peninsula
Peninsula
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Carbonatite
Ultramafic rock
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Phlogopite
Fractional crystallization (geology)
Melt inclusions
Magma chamber
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Carbonatite
Massif
Nepheline
Aegirine
Peralkaline rock
Baltic Shield
Nepheline syenite
Pegmatite
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