Mafic Microgranular Enclaves Formed by Gas-driven Filter Pressing During Rapid Cooling: an Example from the Gangdese Batholith in Southern Tibet
Mafic Microgranular Enclaves Formed by Gas-driven Filter Pressing During Rapid Cooling: an Example from the Gangdese Batholith in Southern Tibet
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快速冷却过程中气体驱动压滤形成的镁铁质微粒包体：以藏南冈底斯岩基为例
DOI：
10.1093/petrology/egab003
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发表时间：
2021-03
期刊：
影响因子：
--
通讯作者：
Zhidan Zhao
中科院分区：
文献类型：
--
作者：
Wei Xu;Di-Cheng Zhu;Qing Wang;Roberto F. Weinberg;Rui Wang;Shi-Min Li;Liang-Liang Zhang;Zhidan Zhao
基性微颗粒包体（MMEs）广泛分布于中-长英质弧深岩体中，携带着弧岩浆成因和演化的重要信息，但其起源仍有争议。在这里，我们研究了来自c的mme -寄主闪长岩对。在杂岩中，mme -寄主闪长岩基本上与它们的寄主闪长岩相似，具有相似的就位年龄（~ 200 Ma）、矿物组合和矿物组成，以及全岩Sr-Nd-Hf和锆石Hf同位素组成。而mme中角闪石和黑云母的模态含量较高，相容元素富集，不相容元素亏缺。某些MME样品的锆石具有暗阴极发光（CL）岩心和不同厚度的亮阴极发光边缘的特征。深cl岩心的Th、U和稀土元素丰度高于浅cl岩心。通过与同成因基性熔体的比较和质量平衡计算，我们认为MMEs是与其寄主闪长岩相关的早结晶堆积（自长岩）。冷质结构、流动微观结构和枕形表明，MMEs在被宿主岩浆捕获之前经历了快速冷却。快速冷却可能是上升的闪长岩岩浆与较冷的围岩接触的结果。当岩浆迅速结晶时，它们达到第二次沸腾和泡化，并分离成细粒的富含晶体的边缘和富含熔体的中心。结晶度和压力的梯度将间隙熔体从富含晶体的边缘驱逐到缺乏晶体的中心，导致晶体-液体分离（气体驱动的过滤压力）。具有高Th和U丰度的深cl锆石芯可能在富晶边缘高度演化的间隙熔体中结晶。细粒富晶边缘随后被后期上升的寄主岩浆在完全结晶之前捕获并拖拽为MMEs。这一分异过程可能发生在岩浆上升数公里的过程中，并在翠久火成岩杂岩的多压分异结晶过程中发挥了重要作用，为上地壳浆液提供了更多分异的安山岩岩浆。
Abstract Mafic microgranular enclaves (MMEs), widespread in intermediate to felsic arc plutons, carry significant information on the genesis and evolution of arc magmas, yet their origin remains debatable. Here, we examine MME-host diorite pairs from the c.200 Ma Cuijiu Igneous Complex in the eastern Gangdese Batholith, southern Tibet, to constrain the petrogenesis of MMEs and the evolution of arc magmas. Within the complex, MMEs are essentially similar to their host diorites with similar emplacement ages (∼200 Ma), mineral assemblages and mineral compositions, as well as whole-rock Sr–Nd–Hf and zircon Hf isotopic compositions. However, MMEs have higher modal contents of hornblende and biotite, and are enriched in compatible elements and depleted in incompatible elements. Zircons from some MME samples are characterized by dark cathodoluminescence (CL) cores overgrown by light-CL rims of varying thickness. The dark-CL cores show higher Th, U and rare earth elements (REE) abundances than the light-CL rims. Based on comparison with co-genetic mafic melts and mass-balance calculations, we propose that the MMEs were early-crystallized cumulates (autoliths) related to their host diorites. The chilled textures, flow microstructures and pillow shapes suggest that the MMEs experienced rapid cooling before being captured by the host magmas. The rapid cooling may result from contact between ascending diorite magmas and cooler wall rocks. As the magmas quickly crystallized, they reached second boiling and vesiculation, and separated into fine-grained crystal-rich margins and melt-rich centres. Gradients in crystallinity and pressure expelled interstitial melts from the crystal-rich margins to the crystal-poor centres, leading to crystal-liquid separation (gas-driven filter pressing). The dark-CL zircon cores with high Th and U abundances may crystallize from highly evolved interstitial melts within the crystal-rich margins. The fine-grained crystal-rich margins were subsequently captured and dragged as MMEs before their complete crystallization by later ascending host magmas. This differentiation process could have occurred over several kilometres of magma ascent, and have played an important role in the polybaric fractional crystallization of the Cuijiu Igneous Complex, feeding more differentiated andesitic magmas to upper crustal mushes.
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影响因子：
64.8
作者：
Charles E. Lesher
通讯作者：
Charles E. Lesher
影响因子：
3.1
作者：
H. Holland;K. Turekian
通讯作者：
H. Holland;K. Turekian
藏南冈底斯深部弧的构建：古新世岩成作用与麻粒岩相变质作用
影响因子：
3.9
作者：
Zhang ZM;Dong X;Xiang H
通讯作者：
Xiang H
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影响因子：
2.3
作者：
Dong, Xin;Zhang, Zeming;Santosh, M.;Wang, Wei;Yu, Fei;Liu, Feng
通讯作者：
Liu, Feng
影响因子：
2.4
作者：
Te-Hsien Lin;Sun‐Lin Chung;Anil Kumar;Fu-Yuan Wu;H. Chiu;I. Lin
通讯作者：
Te-Hsien Lin;Sun‐Lin Chung;Anil Kumar;Fu-Yuan Wu;H. Chiu;I. Lin