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首页> 外文期刊>Journal of Metamorphic Geology >Petrological and zircon evidence for anatexis of UHP quartzite during continental collision in the Sulu orogen
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Petrological and zircon evidence for anatexis of UHP quartzite during continental collision in the Sulu orogen

机译：苏鲁造山带陆相碰撞过程中超高压石英岩层状的岩石学和锆石证据

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Petrological evidence is provided for anatexis of ultrahigh-pressure (UHP) metamorphic quartzite in the Sulu orogen. Some feldspar grains exhibit elongated, highly cuspate shapes or occur as interstitial, cuspate phases constituting interconnected networks along grain boundaries. Elongated veinlets composed of plagioclase + quartz ± K-feldspar also occur in grain boundaries. These features provide compelling evidence for anatexis of the UHP quartzite. Zircon grains from impure quartzite are all metamorphic growth with highly irregular shape. They contain inclusions of coesite, jadeite, rutile and lower pressure minerals, including multiphase solid inclusions that are composed of two or more phases of muscovite, quartz, K-feldspar and plagioclase. All zircon grains exhibit steep REE patterns, similar U-Pb ages and Hf isotope compositions with a weighted mean of 218 ± 2 Ma. Most grains have similar δ~(18)O values of -0.6 to 0.1‰, but a few fall in the range -5.2 to -4.3‰. Thus, these grains would have grown from anatectic melts at various pressures. Zircon O isotope differences indicate that anatectic melts were derived from different sources with contrasting O isotopes, but similar Hf isotopes, that is, one from the quartzite itself and the other probably from the country-rock granitic gneiss. Zircon grains from pure quartzite contain relict magmatic cores and significant metamorphic overgrowths. Domains that contain eclogite facies minerals exhibit flat HREE patterns, no Eu anomalies and concordant U-Pb ages of c. 220 Ma. Similar U-Pb ages are also obtained for domains that contain lower pressure minerals and exhibit steep REE patterns and marked negative Eu anomalies. These observations indicate that zircon records subsolidus overgrowth at eclogite facies conditions but suprasolidus growth at lower pressures. Zircon enclosed by garnet gave consistent U-Pb ages of c. 214 Ma. Such garnet is interpreted as a peritectic product of the anatectic reaction that involves felsic minerals and possibly amphibole and titanite. The REE patterns of epidote and titanite also record multistage growth and metasomatism by anatectic melts. Therefore, the anatexis of UHP metamorphic rocks is evident during continental collision in the Triassic.
机译：苏鲁造山带中超高压（UHP）变质石英岩的贫化提供了岩石学证据。一些长石晶粒表现出细长的，高度尖峰的形状，或以间隙，尖峰的形式出现，沿晶界构成相互连接的网络。由斜长石+石英±钾长石组成的细长细纹也出现在晶界。这些特征为UHP石英岩的无毒物提供了令人信服的证据。来自不纯石英岩的锆石晶粒都是变质生长，具有高度不规则的形状。它们包含堇青石，硬玉，金红石和低压矿物的夹杂物，包括由白云母，石英，钾长石和斜长石两相或更多相组成的多相固体夹杂物。所有锆石晶粒均表现出陡峭的稀土元素分布，相似的U-Pb年龄和Hf同位素组成，加权平均值为218±2 Ma。多数晶粒具有相似的δ〜（18）O值，从-0.6到0.1‰，但有一些落在-5.2到-4.3‰的范围内。因此，这些晶粒可能是在各种压力下从高熔点熔体中生长出来的。锆石中O同位素的差异表明，阳极熔体来自不同来源的O同位素，而Hf同位素相似，即一种来自石英岩本身，另一种可能来自于乡村岩石花岗片麻岩。纯石英岩中的锆石晶粒含有残留的岩浆岩心和明显的变质过度生长。含有榴辉岩相矿物的区域显示出平坦的HREE模式，无Eu异常和c的一致U-Pb年龄。 220毫安。对于包含较低压力矿物，表现出陡峭的REE模式和明显的负Eu异常的磁畴，也获得了相似的U-Pb年龄。这些观察结果表明，锆石在榴辉岩相条件下记录了固相线的过度生长，而在较低压力下记录了固相线的过度生长。石榴石包围的锆石给出的U-Pb年龄一致。 214马。此类石榴石被解释为涉及长石矿物以及可能的闪石和钛矿的阳极反应的包晶产物。附子和钛矿的REE模式也记录了由高熔体熔体形成的多阶段生长和交代作用。因此，在三叠纪大陆碰撞过程中，UHP变质岩的明显存在。

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