Mineralogy, geochronology, and geochemistry of the calc-alkaline Um Takha white granite pluton, South Sinai, Egypt
Mineralogy, geochronology, and geochemistry of the calc-alkaline Um Takha white granite pluton, South Sinai, Egypt
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埃及南西奈半岛钙碱性 Um Takha 白色花岗岩岩体的矿物学、地质年代学和地球化学
DOI：
10.1016/j.lithos.2023.107021
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发表时间：
2023
期刊：
影响因子：
3.5
通讯作者：
Ibañez-Mejia, Mauricio
中科院分区：
文献类型：
--
作者：
Osman, Madiha S.M.;Azer, Mokhles K.;Asimow, Paul D.;Price, Jason B.;Ibañez-Mejia, Mauricio
乌姆塔哈白色花岗岩岩体（UTP）出露于西奈（埃及）中西部，新元古代阿拉伯-努比亚地盾（ANS）的最北端。它是西奈半岛南部最年轻的钙碱性花岗岩系列的一员。UTP侵入变质围岩和闪长岩，并依次被Serbal碱性花岗岩侵入。UTP由单一相的浅色二长花岗岩组成，含有碱性长石、斜长石、石英、黑云母和稀有白云母。两个白色花岗岩样品的锆石U-Pb离子探针测年结果分别为614.9 ± 6.3和581.5 ± 10.9 Ma，但较年轻的样品显示了其锆石受到晚期侵蚀流体（如不一致性和斑片状阴极发光分带），最佳年龄为614.9 ± 6.3Ma。在地球化学上，UTP显示出有限的成分范围（SiO2= 72.9-75.1重量%），主要是高钾钙碱性岩石的变铝质弱过铝质的字符，典型的钙碱性花岗岩类的早期后碰撞阶段的北方ANS。白色花岗岩（n= 22）的稀土元素变化图和平行配分模式表明，它们代表一个同源系列。UTP可能产生的部分熔融的富钠角闪石轴承英云闪长岩源从少年地壳。这与UTP中锆石的Hf同位素比值一致，一致产生正εHf（t）值。UTP形成的触发因素是岩石圈拆沉;它的就位与630 Ma前造山带的广泛剥蚀以及630-600 Ma后碰撞产物、热传递到下地壳和后碰撞岩浆作用有关。虽然UTP是一个同源体，传统的液相线下降分离结晶的方法无法解释大的动态范围内的微量元素含量在一个有限的范围内的主要元素。我们表明，另一种可变比例累积液采样解释的全岩成分，其中最进化的样品代表液体成分和最不进化的样品是一个低熔体分数晶体糊状物，提供了一个物理上合理的方案所观察到的套件。
The Um Takha white granite pluton (UTP) is exposed in west central Sinai (Egypt), in the northernmost segment of the Neoproterozoic Arabian-Nubian Shield (ANS). It is a member of the youngest suite of calc-alkaline granites in south Sinai. The UTP intrudes metamorphosed country rocks and diorites and is in turn intruded by the Serbal alkaline granite pluton. The UTP comprises a single phase of leucocratic monzogranite that contains alkali feldspar, plagioclase, quartz, biotite, and rare muscovite. U-Pb ion probe zircon dating for two samples of the white granite yields ages of 614.9 ± 6.3 and 581.5 ± 10.9 Ma, but the younger sample reveals abundant evidence that its zircons were affected by late corrosive fluids (e.g., discordance and patchy cathodoluminescence zoning); the 614.9 ± 6.3 Ma age is preferred. Geochemically, the UTP displays a limited compositional range (SiO2= 72.9–75.1 wt%) of mostly high-K calc-alkaline rocks of metaluminous to weakly peraluminous character, typical of the calc-alkaline granitoids of the early post-collisional stage of the northern ANS. The variation diagrams and parallel rare-earth element (REE) patterns for the white granite samples (n= 22) suggest that they represent one cogenetic suite. The UTP was likely generated by partial melting of a Na-rich amphibole-bearing tonalite source from the juvenile crust. This is consistent with the Hf isotope ratios of zircons from the UTP, which consistently yield positive εHf(t) values. The proposed trigger for the formation of the UTP is lithospheric delamination; its emplacement was associated with extensive denudation of the pre-630 Ma orogenic edifice as well as the 630–600 Ma post-collisional products, heat transfer into the lower crust, and post-collisional magmatism. Although the UTP is a cogenetic body, the traditional liquid-line-of-descent fractional crystallization approach fails to explain the large dynamic range of trace element contents over a limited range in major elements. We show that an alternative variable-proportion cumulate-liquid sampling interpretation of the whole-rock compositions, in which the most evolved sample represents a liquid composition and the least evolved sample is a low melt-fraction crystal mush, offers a physically reasonable scenario for the observed suite.
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