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Petrogenesis of the Tampanchi Ultramafic–Mafic Complex (Ecuador): geodynamic implications for the northwestern margin of South America during the late Cretaceous
Gondwana Research ( IF 6.1 ) Pub Date : 2021-10-18 , DOI: 10.1016/j.gr.2021.10.005
F. Villares 1, 2 , I.F. Blanco-Quintero 3 , P.S. Reyes 1 , J.A. Proenza 4 , R. Cartagena 1 , C. Lázaro 2 , A. Garcia-Casco 2, 5
Affiliation  

The Tampanchi Ultramafic–Mafic Complex (TUMC), located in the central segment of the Cordillera Real (Ecuador), is an oval-shaped intrusive body of approximately 18 km2 emplaced within a Cretaceous metavolcano-sedimentary sequence. Field investigations, zircon geochronology, mineral and whole-rock elemental and isotopic compositions constrain the nature of the parental magma as well as the physical conditions of emplacement, age of crystallization and tectonic setting of formation of the TUMC. The Complex consist of wehrlite and olivine-hornblende clinopyroxenite crosscut by hornblende gabbros and minor dikes/veins of diorite and granite. Hornblendites formed mainly at the contact between the olivine-hornblende clinopyroxenite and the intrusive hornblende gabbros by reaction-replacement processes. Geochemical data for both the wehrlites and pyroxenites define a trend with dominantly olivine and clinopyroxene accumulation, whereas a second trend is formed by hornblende gabbros that differentiated to leucocratic rocks, with amphibole as the dominant fractionating mafic phase. The trace elements show enrichment in large-ion lithophile elements, depletion in high field strength elements (Nb, Zr, Ti) and P, and enrichment in Pb, Sr and Ba relative to primitive mantle, indicating subduction-related parental liquids. The Nd and Sr isotopic composition suggests a uniform mantle source metasomatized by subducted crustal components. Thermobarometric estimations constrain emplacement and crystallization at intermediate to shallow continental crust levels (∼12.5 km depth) of hydrated basaltic melt under oxygen fugacity conditions above the nickel-nickel oxide buffer (ΔNNO = 0 to 2). Zircon SHRIMP U-Th-Pb age data constrain crystallization at 75.1−76.0 Ma, with scarce inherited zircons that record limited recycling of the Cordillera Real basement. These results confirm magmatic arc activity at the continental margin of South America during the late Cretaceous as a result of an E-dipping subduction zone prior to the accretion of the Ecuadorian-Colombian-Caribbean oceanic plateau, and support simultaneous double subduction at the northwest margin of South America during the Cretaceous.



中文翻译:

Tampanchi Ultramafic-Mafic Complex(厄瓜多尔)的岩石成因:晚白垩世对南美洲西北边缘的地球动力学意义

Tampanchi Ultramafic-Mafic Complex (TUMC) 位于 Cordillera Real(厄瓜多尔)的中央部分,是一个椭圆形侵入体,长约 18 km 2位于白垩纪变质火山-沉积层序内。野外调查、锆石年代学、矿物和全岩元素和同位素组成限制了母岩浆的性质以及侵位的物理条件、结晶年龄和 TUMC 形成的构造环境。该复合体由橄榄石-角闪石斜辉石岩和角闪辉长岩以及闪长岩和花岗岩的次要脉络/脉组成。角闪石主要形成于橄榄石-角闪石斜辉石与侵入性角闪辉长岩之间的反应-置换过程。Wehrlites 和辉石岩的地球化学数据定义了以橄榄石和单斜辉石为主的积累趋势,而第二个趋势是由角闪辉长岩形成的,它分化为白晶岩,角闪石作为主要的分馏基性相。微量元素与原始地幔相比,大离子亲石元素富集,高场强元素(Nb、Zr、Ti)和P贫乏,Pb、Sr、Ba富集,表明与俯冲相关的母液。Nd 和 Sr 同位素组成表明由俯冲地壳成分交代的均匀地幔源。在氧逸度条件下,在镍-镍氧化物缓冲液(ΔNNO = 0 到 2)之上,热气压估计限制了水合玄武岩熔体在中到浅大陆地壳水平(~12.5 公里深度)的就位和结晶。锆石 SHRIMP U-Th-Pb 年龄数据将结晶限制在 75.1−76.0 Ma,稀有的继承锆石记录了 Cordillera Real 地下室的有限回收。这些结果证实了白垩纪晚期南美洲大陆边缘的岩浆弧活动,这是由于厄瓜多尔-哥伦比亚-加勒比大洋高原增生之前的 E 倾俯冲带造成的,并支持在西北边缘同时发生双俯冲白垩纪时期的南美洲。

更新日期:2021-10-19
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