Origin of a Mesozoic granite with A-type characteristics from the North China craton: highly fractionated from I-type magmas?
Origin of a Mesozoic granite with A-type characteristics from the North China craton: highly fractionated from I-type magmas?
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华北克拉通中生代A型花岗岩的成因：I型岩浆的高度分异？
DOI：
10.1007/s00410-008-0373-2
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发表时间：
2009-01
影响因子：
3.5
通讯作者：
Jiang, N.
中科院分区：
文献类型：
--
作者：
Liu, Y.S.;Zhang, S.Q.;Zhou, W.G.;Jiang, N.
本文报道了华北克拉通北方边缘中生代上水泉花岗岩的年代学、地球化学和同位素资料。花岗岩高度分馏，SiO2> 74%。富碱（K2 O + Na 2 O）、Rb、Y、Nb和重稀土元素，FeOt/MgO高，CaO、Al 2 O3、Ba、Sr含量低，Eu负异常大，与典型的A型花岗岩无明显区别。花岗岩类的地幔成因并不被看好，因为它们的高初始87 Sr/86 Sr（≥0.706）和低εNd（t）（<−15）与岩石圈或软流圈地幔完全不同。其Sr-Nd同位素组成与太古代麻粒岩地体的Sr-Nd同位素组成一致，与中生代壳源I型花岗岩的Sr-Nd同位素组成相当。因此，认为上水泉花岗岩主要来源于古下地壳的部分熔融。其母岩浆被证明是类似于I型岩浆，并在其上升过程中经历了广泛的分馏。附近汉诺坝富辉长岩麻粒岩捕虏体的矿物学、化学、Sr-Nd同位素、锆石U-Pb年龄和Hf同位素特征表明，它们确实是早期的堆积岩。进一步认为，世界范围内的一些高分馏花岗岩，特别是那些具有A型特征而与未分馏岩石关系不密切的花岗岩，实际上可能是分馏的I型花岗岩。这可以解释它们与I型花岗岩密切的时空关系和相似的Sr-Nd同位素组成。我们的研究也为深壳捕虏体的成因提供了新的认识。
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 initial87Sr/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.
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DOI：
10.1016/0024-4937(92)90029-x
发表时间：
1992-07
期刊：
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影响因子：
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通讯作者：
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