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首页> 外文期刊>Contributions to Mineralogy and Petrology >Origin of a Mesozoic granite with A-type characteristics from the North China craton: highly fractionated from I-type magmas?
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Origin of a Mesozoic granite with A-type characteristics from the North China craton: highly fractionated from I-type magmas?

机译：来自华北克拉通的具有A型特征的中生代花岗岩的起源：高度分离自I型岩浆吗？

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We report geochronological, geochemical and isotopic data for the Mesozoic Shangshuiquan granite from the northern margin of the North China craton. The granite is highly fractionated, with SiO2 > 74%. Occurrence of annitic biotite, high contents of alkalis (K2O + Na2O), Rb, Y, Nb and heavy rare earth elements, high FeOt/MgO, low contents of CaO, Al2O3, Ba, and Sr, and large negative Eu anomalies, makes it indistinguishable from typical A-type granites. A mantle-derived origin for the rocks of the granite is not favored because their high initial 87Sr/86Sr (≥0.706) and low εNd (t) (<−15) are completely different from either those of the lithospheric or asthenospheric mantle. In fact, their Sr–Nd isotopes fall within the range of Sr–Nd isotopic compositions of the Archean granulite terrains and are comparable to those of Mesozoic crustal-derived I-type granitoids in the region. Therefore, the Shangshuiquan granite is considered to be dominantly derived from partial melting of the ancient lower crust. Its parental magmas prove to be similar to I-type magmas and to have undergone extensive fractionation during its ascent. This is supported by the fact that some of the nearby Hannuoba feldspar-rich granulite xenoliths can be indeed regarded as the early cumulates in terms of their mineralogy, chemistry, Sr–Nd isotopes and zircon U–Pb ages and Hf isotopes. It is furthermore argued that some of highly fractionated granites worldwide, especially those with A-type characteristics and lacking close relationship with unfractionated rocks, may in fact be fractionated I-type granites. This suggestion can explain their close temporal and spatial associations as well as similar Sr–Nd isotopes with I-type granites. Our study also sheds new light on the petrogenesis of deep crustal xenoliths. Keywords Fractionation - I-type granite - A-type granite - North China craton - Lower crustal xenoliths Communicated by T.L. Grove.
机译：我们报告了华北克拉通北缘中生代上水泉花岗岩的地质，地球化学和同位素数据。花岗岩高度分馏，SiO 2 2 O + Na 2 O），Rb，Y，Nb和重稀土元素，FeO t高 / MgO，CaO，Al 2 O 3 ，Ba和Sr的含量低，且Eu负值较大，使其与典型的A型没有区别。花岗岩。由于花岗岩的初始 87 Sr / 86 Sr（≥0.706）高而ε Nd低，地幔起源于花岗岩岩石并不受欢迎。 sub>（t）（<−15）与岩石圈或软流层地幔完全不同。实际上，它们的Sr-Nd同位素处于太古代花岗岩地带的Sr-Nd同位素组成范围内，并且与该地区中生代地壳衍生的I型花岗岩类相当。因此，上水泉花岗岩被认为主要来源于古代下地壳的部分熔融。它的亲代岩浆被证明与I型岩浆相似，并且在上升过程中经历了广泛的分离。从附近的汉诺巴长石富含粒状异种岩中可以看出，从矿物学，化学，Sr-Nd同位素，锆石U-Pb年龄和Hf同位素的角度来看，它们确实可以被视为早期堆积物。此外，有人认为，世界范围内一些高度分馏的花岗岩，特别是那些具有A型特征且与未分馏岩石缺乏紧密关系的花岗岩，实际上可能是I型分馏花岗岩。这个建议可以解释它们在时间和空间上的紧密联系，以及与I型花岗岩相似的Sr-Nd同位素。我们的研究也为深地壳异岩的成岩提供了新的思路。分馏-I型花岗岩-A型花岗岩-华北克拉通-T.L.树林。

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