A new jadeitite jade locality (Sierra del Convento, Cuba): first report and some petrological and archeological implications
A new jadeitite jade locality (Sierra del Convento, Cuba): first report and some petrological and archeological implications
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DOI：
10.1007/s00410-008-0367-0
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发表时间：
2009-07
影响因子：
3.5
通讯作者：
A. Garcia‐Casco;A. Rodríguez Vega;J. Cárdenas Párraga;M. Iturralde-Vinent;C. Lázaro;I. Blanco Quintero-I.-Blanco-Quint
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文献类型：
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作者：
A. Garcia‐Casco;A. Rodríguez Vega;J. Cárdenas Párraga;M. Iturralde-Vinent;C. Lázaro;I. Blanco Quintero-I.-Blanco-Quint
在古巴东部康托山（Sierra del Convento）的蛇纹岩基俯冲带中发现了一种新的翡翠玉石产地，与石榴绿绿闪长角闪岩、调性绿绿绿片麻岩和蓝片岩等构造块体有关。翡翠玉石和翡翠岩的矿物组合多种多样，包括在P-T演化不同阶段形成的翡翠、辉长石、钠长石、paragonite、铝石、斜殖石—绿帘石、磷灰石、云母、云母、绿泥石、绿帘石、钛矿、金红石、锆石和石英的组合。野外关系尚不清楚，但一些几乎完全由硬玉制成的样品显示出来自静脉液体结晶的证据。在详细研究的其中一个样品中，翡翠显示出复杂的结构和化学特征（包括振荡带），表明在变化的化学介质中生长。认为富Al-Na流体与超镁铁质岩石相互作用产生了不同组成的Al-Na - mg - ca流体。由于静脉的不定期开放，这些流体的不定期浸润，通过流体的直接沉淀和流体与预先存在的翡翠的反应，形成了振荡带。最新的渗透流体中Mg-Ca含量较丰富，有利于在开放孔洞中形成红辉石和富Mg-Ca的硬玉，并在550 ~ 560℃时由细粒红辉石+硬玉取代早期的硬玉。古巴新发现的翡翠为加勒比地区前哥伦布时期玉器的考古研究开辟了重要的视角。
A new jadeitite jade locality has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento (eastern Cuba) in a context associated with tectonic blocks of garnet-epidote amphibolite, tonalitic–trondhjemitic epidote gneiss, and blueschist. The mineral assemblages of jadeitite jade and jadeite rocks are varied and include combinations of jadeite, omphacite, albite, paragonite, analcime, clinozoisite-epidote, apatite, phlogopite, phengite, chlorite, glaucophane, titanite, rutile, zircon, and quartz formed during various stages in their P–T evolution. Field relationships are obscure, but some samples made almost exclusively of jadeite show evidence of crystallization from fluid in veins. In one of these samples studied in detail jadeite shows complex textural and chemical characteristics (including oscillatory zoning) that denote growth in a changing chemical medium. It is proposed that interaction of an Al–Na rich fluid with ultramafic rocks produced Al–Na–Mg–Ca fluids of varying composition. Episodic infiltration of these fluids, as a result of episodic opening of the veins, developed oscillatory zoning by direct precipitation from fluid and after reaction of fluid with pre-existing jadeite. The latest infiltrating fluids were richer in Mg–Ca, favouring the formation of omphacite and Mg–Ca rich jadeite in open voids and the replacement of earlier jadeite by fine-grained omphacite + jadeite at 550–560°C. This new occurrence of jadeite in Cuba opens important perspectives for archeological studies of pre-Columbian jade artifacts in the Caribbean region.