U/Pb ages of ophiolites and arc-related plutons of the Norwegian Caledonides: implications for the development of Iapetus
U/Pb ages of ophiolites and arc-related plutons of the Norwegian Caledonides: implications for the development of Iapetus
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挪威喀里多尼德斯蛇绿岩和弧相关岩体的 U/Pb 年龄：对土卫八发展的影响
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发表时间：
1988
期刊：
影响因子：
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通讯作者：
Rolf B. Pedersen
中科院分区：
文献类型：
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作者：
G. Dunning;Rolf B. Pedersen
报告了来自挪威喀里多尼德山脉的四颗蛇绿岩和三颗与横切弧相关的岩体的 U/Pb 锆石年龄。从 Karmøy 蛇绿岩的辉长岩中分化出来的斜长花岗岩的年代为 493+7/-4 Ma，而切割该蛇绿岩的与弧相关的长辉长岩则在 485+/-2 Ma 结晶。横切的单斜辉石-辉长岩侵入体的年代为 470+9/−5 Ma，由近协调的岩浆钛矿（榍石）和不一致的富 U（2903-6677 ppm）锆石测得。由斜长花岗岩和单斜辉石-辉长岩最佳拟合线定义的 247+/-68 和 191+/-70 Ma 的较低截距可能反映了真正的低 T 蚀变/裂谷相关事件。Gullfjellet 蛇绿岩杂岩的斜长花岗岩分异物的年代为 489+/-3 Ma，与横切弧相关的英云闪长岩为482+6/−4 Ma。这两个年龄都与 Karmøy 相关岩石的年龄重叠，表明它们是一个具有共同历史的蛇绿岩地体的一部分。与 Leka 蛇绿岩相关的 Trondhjemite 的年代为 497+/-2 Ma，表明那里的俯冲带上岩浆活动可能与形成 Karmøy 轴序列的扩张同时发生。这里报告了挪威蛇绿岩的 U/Pb 锆石年龄，并结合年龄英国和加拿大其他阿巴拉契亚-喀里多尼亚蛇绿岩杂岩的研究表明，特雷马多克-阿雷尼格至少有两个边缘盆地的形成年龄范围很窄。 Karmøy 记录的两个扩散事件在时间上被 485+/-2 Ma 的与弧相关的长角铁矿岩浆的侵入分开，并且可能与其他蛇绿岩中记录的两个独立的扩散事件相关。Solund/Stavfjorden 蛇绿岩，发生于 443+/-3 Ma，是整个阿巴拉契亚-喀里多尼亚造山带中唯一有记录的晚奥陶世蛇绿岩，它可能代表了土卫八洋历史晚期的小型、短暂的边缘盆地。它与威尔士和特隆赫姆地区的卡拉多西亚边缘盆地岩浆作用有关，也与蛇绿岩在大陆边缘就位后以拉张状态侵入纽芬兰蛇绿岩的拉斑辉长闪长岩岩体有关。
U/Pb zircon ages are reported for four ophiolites and three crosscutting arc-related plutons from the Norwegian Caledonides. Plagiogranite differentiated from gabbro of the Karmøy ophiolite is dated at 493+7/-4 Ma whereas arc-related trondhjemite cutting this ophiolite crystallized at 485+/−2 Ma. A crosscutting clinopyroxene-phyric gabbro intrusion is dated at 470+9/−5 Ma by near concordant magmatic titanite (sphene) and discordant U-rich (2903–6677 ppm) zircon. Lower intercepts of 247+/−68 and 191+/−70 Ma defined by the plagiogranite and clinopyroxene-phyric gabbro best-fit lines may reflect a real low-T alteration/rift-related event.A plagiogranite differentiate of the Gullfjellet ophiolite complex is dated at 489+/−3 Ma and a crosscutting arc-related tonalite is 482+6/−4 Ma. Both of these ages overlap with those of the correlative rocks at Karmøy suggesting that they are parts of one ophiolitic terrane with a common history.Trondhjemite associated with the Leka ophiolite is dated at 497+/−2 Ma, indicating that supra-subduction zone magmatism there may be coeval with spreading which formed the Karmøy axis sequence.The U/Pb zircon ages of Norwegian ophiolites reported here, combined with ages of other Appalachian-Caledonian ophiolite complexes in Britain and Canada, indicate a narrow age range for the generation of at least two marginal basins in the Tremadoc-Arenig. Two spreading episodes documented at Karmøy are separated in time by intrusion of arc-related trondhjemite magmas at 485+/−2 Ma and may correlate with two separate spreading events documented in other ophiolites.The Solund/Stavfjorden ophiolite, at 443+/−3 Ma, is the only late Ordovician ophiolite yet documented in the entire Appalachian-Caledonian Orogen and it probably represents a small, short-lived marginal basin late in the history of the Iapetus Ocean. It is correlative with Caradocian ensialic marginal basin magmatism in Wales and the Trondheim region, and with tholeiitic gabbro-diorite plutons that intruded Newfoundland ophiolites in a tensional regime after emplacement of the ophiolites over the continental margin.