The link between an anorthosite complex and underlying olivine-Ti-magnetite-rich layered intrusion in Damiao, China: insights into magma chamber processes in the formation of Proterozoic massif-type anorthosites
The link between an anorthosite complex and underlying olivine-Ti-magnetite-rich layered intrusion in Damiao, China: insights into magma chamber processes in the formation of Proterozoic massif-type anorthosites
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中国大庙斜长岩杂岩与底层富含橄榄石-钛磁铁矿的层状侵入体之间的联系：深入了解元古代地块型斜长岩形成过程中的岩浆房过程
DOI：
10.1007/s00410-019-1586-2
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发表时间：
2019
影响因子：
3.5
通讯作者：
Song Zhe
中科院分区：
文献类型：
--
作者：
Li Li-Xing;Li Hou-Min;Zi Jian-Wei;Rasmussen Birger;Sheppard Stephen;Ma Yu-Bo;Meng Jie;Song Zhe
与元古界块状斜长岩共岩浆的镁铁质-超镁铁质侵入岩，可为研究产生大量超长石的母岩浆提供线索。近期在华北克拉通大庙地块型斜长杂岩下发现了一个大型富橄榄钛磁铁矿层状侵入体（大乌苏南沟）。层状侵入体由富含橄榄石-钛磁铁矿的暗层和富含斜长石（约35-80%斜长石）的浅层交替组成，浅层还含有豆荚状或透镜状的辉石-钛磁铁矿集合体。该层状侵入体表现出与上覆大庙斜长杂岩相似的低Mg#和REE模式。Baddeleyite Pb-Pb年代学结果显示，大乌苏南沟层状侵入岩和大庙斜长杂岩的结晶年龄均为约1735 Ma，表明它们是在同一时期侵位的。根据两个侵入体的平均体积组成，通过质量平衡计算，假设30-40%的大乌苏南沟和70-60%的大庙岩浆组成类似于高铝玄武岩岩浆。综上所述，大乌苏南沟层状岩体是大庙斜长岩与高铝玄武质母岩浆分离后的基性残余物。一个短暂的岩浆库被认为提供了这两次侵入。变化成核速率的斜长石原位结晶和镁基性矿物的平衡结晶，形成了大乌苏南沟层状侵入岩的暗、亮重复层。这两个侵入体被解释为是由多次岩浆注入形成的，而不是一次熔体的连续分异。母岩浆来源于枯竭的地幔源，在岩浆演化过程中地壳的贡献较大。Nd-Hf同位素的大变化表明受古太古代到新太古代地壳的污染。
Mafic–ultramafic intrusions comagmatic with Proterozoic massif-type anorthosites can provide insights into the parental magma from which large volumes of hyper-feldspathic rocks are produced. Recent deep drilling has unveiled a large olivine–Ti-magnetite-rich layered intrusion (named Dawusunangou) beneath the Damiao massif-type anorthosite complex in the North China Craton. The layered intrusion is composed of alternating olivine–Ti-magnetite-rich dark layers and plagioclase-rich light layers (ca. 35–80% plagioclase), with the latter also containing pod- or lens-shaped pyroxene–Ti-magnetite-rich aggregates. This layered intrusion shows low Mg# and REE patterns similar to the overlying Damiao anorthosite complex. Baddeleyite Pb–Pb geochronology yielded indistinguishable crystallization ages of ca. 1735 Ma for both the Dawusunangou layered intrusion and the Damiao anorthosite complex, suggesting coeval emplacement. Using the average bulk compositions of the two intrusions, mass balance calculations assuming 30–40% Dawusunangou and 70–60% Damiao would give a composition similar to high-Al basaltic magma. Collectively, these features indicate that the Dawusunangou layered intrusion represents the mafic residues after the segregation of the Damiao anorthosites from high-Al basaltic parental magma. A short-lived magma chamber is thought to have supplied the two intrusions. In situ crystallization with variable nucleation rates for plagioclase combined with the mafic minerals crystallizing in equilibrium proportions resulted in the formation of repeated dark and light layers of the Dawusunangou layered intrusion. The two intrusions are interpreted to have formed by multiple magma injections, instead of continuous differentiation of one melt. The parental magma was derived from a depleted mantle source with significant crustal contribution during magma evolution. The large Nd–Hf isotopic variations suggest contamination by Paleoarchean to Neoarchean crust.