Möwe Bay Dykes, Northwestern Namibia: Geochemical and geochronological evidence for different mantle source regions during the Cretaceous opening of the South Atlantic
Möwe Bay Dykes, Northwestern Namibia: Geochemical and geochronological evidence for different mantle source regions during the Cretaceous opening of the South Atlantic
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纳米比亚西北部莫韦湾堤坝：南大西洋白垩纪开放期间不同地幔源区的地球化学和年代学证据
DOI：
10.1016/j.chemgeo.2016.08.040
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发表时间：
2016
期刊：
影响因子：
3.9
通讯作者：
Pfänder
中科院分区：
文献类型：
--
作者：
Frimmel;Pfänder
在纳米比亚西北部的巴拉那-埃滕德卡火山作用过程中，岩墙侵位被认为是一个与大约135-130 Ma的特定岩浆源有关的短暂事件。新的地球化学、全岩Sr-Nd-Pb同位素数据和40 Ar/39 Ar年龄表明，纳米比亚西北部骨架海岸Möwe湾地区至少可划分出三个地球化学和同位素特征不同的拉斑玄武岩岩墙世代，其侵入年龄分别为135.2 ± 0.7，124.1 ± 0.8，113.0 ± 0.5Ma。不同的地幔源成分被确定在岩石成因的各个岩墙世代。岩浆成分的两个老岩墙套房，这两个都是侵位在一个构造环境为主的东西向延伸，从板内丰富的洋中脊玄武岩类型。238 U/204 Pb值（= μ2）高达9.97，表明受到大陆地壳和/或岩石圈地幔的污染，这是典型的喀拉哈里盆地。第三代岩墙形成于SE-NW向伸展为主的构造体制，其同位素组成为高Ti洋岛型玄武岩，来源于地幔源区，μ2值为9.35。这种异常很可能是由地幔柱的外围部分撞击岩石圈的底部，造成次大陆地幔岩石圈的侵蚀和熔融以上的羽头。冈瓦纳西南部的初始裂解和早期洋壳的形成最有可能是由于被动而不是主动裂谷作用。持续的羽流上涌促进了西南冈瓦纳地壳的逐渐变薄，导致形成年轻的，c。113 Ma的古老岩墙，其化学和同位素特征与沃尔维斯海岭东北部的同时代岩石相同，因此被解释为当时特里斯坦-高夫羽流头的陆上表现。老年人和年轻的堤坝一代的主导延伸方向的差异可以解释由旋转引起的Aptian/Albian开放的赤道中大西洋，伴随着南大西洋扩张率大幅增加。
Dyke emplacement in the course of Paraná-Etendeka volcanism in northwestern Namibia has been considered as a short-lived event related to a specific magma source at approximately 135–130 Ma. New geochemical, whole rock Sr-Nd-Pb isotope data and40Ar/39Ar ages reveal that at least three geochemically and isotopically different tholeiitic dyke generations, with intrusion ages of 135.2 ± 0.7, 124.1 ± 0.8 Ma and 113.0 ± 0.5 Ma, can be distinguished in the Möwe Bay area, Skeleton Coast of northwestern Namibia. Distinct mantle source components were identified in the petrogenesis of the various dyke generations. Magma composition of the two older dyke suites, both of which were emplaced in a tectonic setting dominated by E-W extension, evolved from a within-plate to an enriched mid-ocean ridge basalt type. Contamination by continental crust and/or lithospheric mantel is suggested by a high238U/204Pb-value (= μ2) of 9.97, which is typical of the Kalahari Craton. The third dyke generation, which intruded in a tectonic regime dominated by SE-NW extension, corresponds to high-Ti ocean island-type basalt with unradiogenic isotopic compositions derived from a mantle source with a μ2-value of 9.35.The formation of the older dykes is attributed to the presence of a thermal anomaly in the upper sublithospheric mantle. This anomaly was most likely caused by the peripheral part of a mantle plume that impinged at the base of the lithosphere and caused erosion of the subcontinental mantle lithosphere and melting above the plume head. The initial break-up of SW Gondwana and the formation of early oceanic crust were most likely due to passive rather than active rifting. Continued plume upwelling facilitated by progressive thinning of SW-Gondwana crust led to the formation of the younger, c. 113 Ma old dykes, which are chemically and isotopically identical to coeval rocks from the northeastern portion of the Walvis Ridge and thus are interpreted as onshore expressions of the Tristan-Gough plume head at that time. The difference in the dominant extension directions of the older and the younger dyke generations can be explained by rotation induced by the Aptian/Albian opening of the Equatorial Central Atlantic, accompanied by a substantial increase in the South Atlantic spreading rate.
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影响因子：
5.3
作者：
Gibson, SA;Thompson, RN;Dickin, AP
通讯作者：
Dickin, AP
影响因子：
3.8
作者：
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通讯作者：
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影响因子：
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作者：
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影响因子：
2.3
作者：
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通讯作者：
P. Ledru
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影响因子：
2.9
作者：
Joana Rohde;P. Bogaard;K. Hoernle;F. Hauff;R. Werner
通讯作者：
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