Ediacaran bimodal volcanism in the southernmost Dom Feliciano Belt, Uruguay: Implications for the evolution of SW Gondwana
Ediacaran bimodal volcanism in the southernmost Dom Feliciano Belt, Uruguay: Implications for the evolution of SW Gondwana
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DOI：
10.1016/j.lithos.2021.106539
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发表时间：
2021-11
期刊：
影响因子：
3.5
通讯作者：
T. Will;C. Gaucher;Xiaoxiao Ling;P. L. le Roux;X.‐H. Li;Q.L. Li
中科院分区：
文献类型：
--
作者：
T. Will;C. Gaucher;Xiaoxiao Ling;P. L. le Roux;X.‐H. Li;Q.L. Li
介绍了乌拉圭Cuchilla Dionisio （CDT）和Nico p录影带雷斯（NPT）地体埃迪卡拉系火山岩的锆石U-Pb-Hf-O、全岩地球化学和Sr-Nd-Pb同位素资料。CDT南部Cerros de Aguirre组高钾钙碱性流纹岩形成于569±5 Ma的活动大陆边缘。流纹岩熔体的形成可以用交代地幔源来解释。同生安山岩和玄武岩安山岩的Sr-Nd同位素组成与富集地幔1的Sr-Nd同位素组成接近，与地壳物质存在下的次大陆地幔熔融形成一致。推断其北部同时期流纹岩形成于活动边缘的远端。NPT中Sierra de Ánimas组流纹岩和粗面岩的形成时间分别为589±3 Ma和586±3 Ma。NPT玄武岩起源于地幔，可能与地幔柱有关。在上升过程中，它们不同程度地受到大陆地壳的污染。NPT流纹岩中的锆石δ18O值非常低，这是由于地壳浅层热液蚀变和熔融作用所致。我们认为，NPT的晚埃迪卡拉纪火成岩活动与板块内的造山和伸展作用有关，而CDT南部大约2000万年的火山活动则发生在俯冲的巴西海之上的超俯冲环境中。我们将NPT地区的双峰型板内火山作用归因于阿拉恰尼亚（Kalahari克拉通的裂离部分）下巴西海的东向俯冲所引起的远场力。因此，提出晚埃迪卡拉世俯冲引起的岩石圈伸展和Río德拉普拉塔克拉通东缘的水平伸展是新元古代末双峰火山作用和同世火山-沉积序列沉积的主要原因。
New zircon U-Pb-Hf-O, whole rock geochemical and Sr-Nd-Pb isotope data of Ediacaran volcanic rocks from the Cuchilla Dionisio (CDT) and Nico Pérez (NPT) terranes in Uruguay are presented. High-K calc-alkaline rhyolite from the Cerros de Aguirre Formation in the southern CDT formed at an active continental margin at 569 ± 5 Ma. A metasomatized mantle source is invoked for the formation of the rhyolitic melts. Cogenetic andesite and basaltic andesite have Sr-Nd isotope compositions that are close to that of enriched mantle 1, which is consistent with melt formation in the subcontinental mantle in the presence of crustal material. Coeval rhyolite in the northern CDT is inferred to have formed distally to the active margin. Rhyolite and trachyte of the Sierra de Ánimas Formation in the NPT formed at 589 ± 3 Ma and 586 ± 3 Ma, respectively. The NPT basalts originated in the mantle and may be related to a mantle plume. During ascent they were variably contaminated by continental crust. Zircon in NPT rhyolite have very low δ18O values that are ascribed to hydrothermal alteration and melting at shallow crustal levels. We propose that the late Ediacaran igneous activity in the NPT was related to anorogenic, extensional processes in an intraplate setting but the c. 20 million years younger volcanic activity in the southern CDT occurred in a supra-subduction setting above the subducting Brazilides ocean. We ascribe the bimodal intraplate volcanism in the NPT to far-field forces caused by slab-pull in response to eastward-directed subduction of the Brazilides ocean underneath Arachania, which is a rifted-off segment of the Kalahari Craton. Thus, late Ediacaran subduction-induced lithospheric stretching and horizontal extension of the eastern margin of the Río de la Plata Craton is proposed as the main cause for bimodal volcanism and the deposition of coeval volcano-sedimentary successions at the end of the Neoproterozoic.