Derivation of Mesozoic adakitic magmas from ancient lower crust in the North China craton
Derivation of Mesozoic adakitic magmas from ancient lower crust in the North China craton
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DOI：
10.1016/j.gca.2007.02.018
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发表时间：
2007-05
影响因子：
5
通讯作者：
Neng Jiang;Yongsheng Liu;Wenge Zhou;Jin-Hui Yang;Shuangquan Zhang
中科院分区：
文献类型：
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作者：
Neng Jiang;Yongsheng Liu;Wenge Zhou;Jin-Hui Yang;Shuangquan Zhang
华北克拉通北方缘太古宙麻粒岩区中，在含麻粒岩捕虏体的第三纪汉诺坝玄武岩附近，发现了三个中生代侵入岩体。它们是三叠纪古咀子花岗岩、红花梁花岗岩和早白垩世转枝莲闪长岩。三个岩体的岩石均具有高Sr（576- 1216 ppm）、高Na_2 O（~ 4.0%）、低Y（~ 18 ppm）和重稀土元素（Yb<1.8ppm）的特征。这些特征与岛弧中的现代埃达克岩（高钠、铝、锶、低重稀土和钇含量的硅质岩）和太古代高铝英云闪长岩-奥长花岗岩-花岗闪长岩（TTG）相似。然而，它们明显富钾，其演化的锶，钕，铪同位素组成和继承锆石年龄与太古代麻粒岩和汉诺坝麻粒岩捕虏体相一致。这些特征不能很容易地解释与埃达克岩和TTG的起源以前的模型。我们认为这些埃达克质岩石是由古下地壳的部分熔融形成的，并且以汉诺坝麻粒岩捕虏体为代表的残余岩;我们进一步认为，这可能是华北克拉通东部中生代大量埃达克质岩浆产生的一个主要机制。我们的假说也可以解释麻粒岩地体和捕虏体在年龄和成分上的差异，并暗示地壳深熔作用可能是控制陆壳化学分异的主要过程之一。
Three Mesozoic plutons were intruded into the Archean granulite terrains in northern margin of the North China craton adjacent to the granulite xenolith-bearing Tertiary Hannuoba basalts. They are Triassic Guzuizi and Honghualiang granites and Early Cretaceous Zhuanzhilian diorite. Rocks of the three intrusions are characterized by high Sr (576–1216ppm) and Na2O (⩾4.0%), low Y (⩽18ppm) and heavy rare-earth elements (Yb<1.8ppm). These features are similar to modern adakites (siliceous rocks with high sodium, aluminum and strontium and low heavy rare-earth element and yttrium contents) from island arcs and Archean high-Al tonalite–trondhjemite–granodiorite (TTG). However, they are distinctly potassium-rich and their evolved strontium, neodymium, and hafnium isotopic compositions and inherited zircon ages coincide with those of the Archean granulites and the Hannuoba granulite xenoliths. Such features cannot readily be explained with previous models of the origin of adakites and TTGs. We propose that these adakitic rocks are formed by partial melting of ancient lower crust, and that the restites are represented by some of the Hannuoba granulite xenoliths; we further argue that this could be one major mechanism to generate voluminous Mesozoic adakitic magmas in the eastern North China craton. Our hypothesis can also explain the discrepancies in ages and compositions between the granulite terrains and xenoliths, and implies that crustal anatexis may be one of the major processes controlling the chemical differentiation of the continental crust.