Pyroxenite–harzburgite sequences in the Dazhuqu ophiolite (Southern Tibet) formed through hydrous melt infiltration and melt–peridotite reaction
Pyroxenite–harzburgite sequences in the Dazhuqu ophiolite (Southern Tibet) formed through hydrous melt infiltration and melt–peridotite reaction
复制标题
DOI：
10.1007/s00410-023-02076-y
复制
发表时间：
2023-11
影响因子：
3.5
通讯作者：
Zhen-Yu Zhang;Chuan-Zhou Liu;Yan Liang;Tong Liu;Chang Zhang;Bo-Da Liu;Yingchun Lin;Wei‐Qi Zhang-We
中科院分区：
文献类型：
--
作者：
Zhen-Yu Zhang;Chuan-Zhou Liu;Yan Liang;Tong Liu;Chang Zhang;Bo-Da Liu;Yingchun Lin;Wei‐Qi Zhang-We
辉石岩脉常见于蛇绿岩的地幔剖面，反映了各种熔体在岩石圈中渗透、反应、结晶的过程。辉石中正辉石和斜辉石均具有高Mg#、低al2o3浓度和不相容微量元素耗尽的特征。这表明辉石岩的母熔体可能是由先前枯竭的地幔源的再融化形成的。我们观察到斜辉石和正辉石的主微量元素组成在辉石岩-辉石岩序列中有系统的变化。通过微量元素模拟，建立了辉石岩脉及其伴生哈尔茨基岩的形成模型。根据这一模型，含水和聚集的熔体从泥质通道顶端排出，随后通过裂缝注入岩石圈。渗透的熔体随后向软流圈内残余的黑锌矿中扩散损失水分，这反过来又促进了黑锌矿的部分熔化。辉石岩脉是由渗透通道熔体和部分熔融辉石形成的基质熔体混合形成的。该构造模型可用于解释雅鲁藏布蛇绿岩和世界其他蛇绿岩中的辉石岩-辉石-辉石-辉石-辉石-辉石-辉石岩序列。
Pyroxenite veins are commonly observed in the mantle section of ophiolites, reflecting a variety of melts that percolate through the mantle, react, and finally crystallize in the lithosphere. To better understand the formation mechanism of the pyroxenite veins and associated peridotites, we conducted an integrated petrological and geochemical study of a suite of orthopyroxenite, websterite, and composite clinopyroxenite–orthopyroxenite veins in residual peridotites from the Dazhuqu ophiolite (Southern Tibet, China). Both orthopyroxene and clinopyroxene in pyroxenites are characterized by high Mg#, low Al2O3concentrations, and depleted patterns of incompatible trace elements. This suggests that parental melts of the pyroxenites could be formed by re-melting of a previously depleted mantle source. We observed systematic variations in the major and trace element compositions of clinopyroxene and orthopyroxene across the pyroxenite–harzburgite sequences. Through trace element modeling, we have established a model for the formation of pyroxenite veins and associated harzburgites. According to this model, hydrous and aggregated melts were expelled from the tip of the dunite channels and subsequently injected into the lithosphere via fractures. The infiltrating melts then underwent diffusional loss of water into the residual harzburgites within the asthenosphere, which in turn promoting partial melting of the harzburgite. The pyroxenite veins were formed by mixing the infiltrating channel melt and matrix melt derived from partially molten harzburgite. This formation model can be applied to explain the pyroxenite–harzburgite and dunite–pyroxenite–harzburgite sequences in the Yarlung-Tsangbo ophiolite and other ophiolites around the world.