A Highly dynamic hot hydrothermal system in the subduction environment: Geochemistry and geochronology of jadeitite and associated rocks of the Sierra del Convento mélange (eastern Cuba)
J. Cárdenas-Párraga, A. Garcia‐Casco, I. Blanco-Quintero, Y. Rojas‐Agramonte, K. N. Cambra, G. Harlow
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引用次数: 4
Abstract
A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.
俯冲环境中的高动态热液系统:Sierra del Convento mélange(古巴东部)翡翠和伴生岩石的地球化学和地质年代
~ 113 Ma的U-Pb锆石表明,在俯冲相关的Sierra del Convento地块蛇纹岩基msamulange(古巴东部),在高温高压的热俯冲环境下,与MORB变质岩衍生的闪辉质流体几乎同时形成了多种硬玉岩及其相关辉长岩、绿泥岩和富含钠长岩的岩石。野外、岩石学和地球化学资料表明,幼流体引发的热液/交代过程可能是由含水岩浆熔体结晶演化而来的。这些流体与沉积流体的混合程度不同,并沿着上板块地幔的裂缝形成通道,沉淀出相对纯净的翡翠岩和富含绿帘石的翡翠岩,这些翡翠岩的地球化学模式缺乏REE和HFSE,而相对于N-MORB,富含LILE-(特别是Ba)成分。翡翠脉的结晶过程伴随着脉与超镁铁质岩石接触处绿泥岩黑壁的形成和脉外侧红辉质斑块的形成,表明了围岩与流体的相互作用。岩体内部外部流体的进一步普遍流动触发了早期翡翠岩的模态和隐式(地球化学)交代转化,生成了富云母的翡翠岩和钠长绿帘石(-绿泥石)岩石。总的来说,这些岩石记录了上板块地幔中大量流体流动的离散事件,大致与俯冲的MORB变质岩的含水熔融同时发生。
期刊介绍:
The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.