Origin of Cretaceous aluminous and peralkaline A-type granitoids in northeastern Fujian, coastal region of southeastern China
Origin of Cretaceous aluminous and peralkaline A-type granitoids in northeastern Fujian, coastal region of southeastern China
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闽东北、东南沿海白垩纪铝质和过碱性A型花岗岩成因
DOI：
10.1016/j.lithos.2019.05.009
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发表时间：
2019-09
期刊：
影响因子：
3.5
通讯作者：
Zhang Ji Heng
中科院分区：
文献类型：
--
作者：
Chen Jing Yuan;Yang Jin Hui;Zhang Ji Heng
本文报道了福建东北部六个花岗岩类岩体的地球化学、全岩Sr、Nd、Hf同位素、锆石U-Pb年龄和Hf-O同位素组成，以阐明该地区铝质和过碱性A型花岗岩的成因。这些岩石（包括斑状正长岩、斑状花岗岩、碱长花岗岩和钠铁闪石花岗岩）的锆石U-Pb年龄为94-98 Ma。矿物组合和地球化学特征表明，钠铁闪石花岗岩属过碱性A型，而斑状正长岩、斑状花岗岩和碱长花岗岩属铝质A型。全岩Nd-Hf同位素（εNd（t）= −5.5 ~ −4.0，εHf（t）= −3.6 ~ 0）和锆石Hf-O同位素（εHf（t）= −3.0 ~+1.4，δ 18 O = 5.4‰ ~ 6.0 ‰）表明，斑状正长岩是由下地壳地壳岩石部分熔融而成。斑状花岗岩和碱长花岗岩与斑状正长岩具有相似的地球化学特征和锆石Hf-O同位素组成，表明它们是在地壳浅部水平下，由深源壳源正长岩浆以辉长岩为主的结晶分异作用形成的。与铝质A型花岗岩相比，过碱性A型花岗岩的Al 2 O3、MgO、CaO、Ba和Sr丰度较低，SiO2和HFSE丰度较高，总FeO/MgO、Ga/Al和Rb/Sr比值较高，但全岩Nd、Hf和锆石Hf-O同位素组成相似。过碱性A型花岗岩是由含铝A型花岗岩岩浆经结晶分异作用形成的。由于研究的A型花岗质侵入体与中国东南沿海地区的双峰式火山岩和拉张盆地同时代，它们可能产生于拉张环境，可能是在岩石圈减薄过程中，导致在中国东南部的古太平洋板块俯冲。
In this work, we report the geochemical, whole-rock Sr-, Nd-, and Hf-isotopes, and zircon U–Pb age and Hf–O isotopic compositions for six granitic intrusions in northeastern Fujian, coastal region of southeastern China, to elucidate the petrogenesis of aluminous and peralkaline A-type granites in this region. Zircon U–Pb dating of these rocks (including porphyritic syenites, porphyritic granites, alkali-feldspar granites, and arfvedsonite granites) yielded Late Cretaceous ages of 94–98 Ma. Mineral assemblage and geochemical features suggested that the arfvedsonite granites were peralkaline A-type but the porphyritic syenites, porphyritic granites, and alkali-feldspar granites were aluminous A-type. Geochemical data, whole-rock Nd–Hf isotopes (εNd(t) = −5.5 to −4.0, εHf(t) = −3.6 to 0), and the zircon Hf–O isotopes (εHf(t) = −3.0 to +1.4, δ18O = 5.4‰–6.0‰) indicated that the porphyritic syenites were produced by partial melting of crustal rocks in the lower crust. The porphyritic granites and alkali-feldspar granites had similar geochemical features and zircon Hf–O isotopic composition with the porphyritic syenites, suggesting that they were formed by feldspar-dominant crystal fractionation of deep crust derived syenitic magma under shallow crustal level. Compared with the aluminous A-type granites, the peralkaline A-type granites had lower abundance of Al2O3, MgO, CaO, Ba, and Sr, higher abundance of SiO2and HFSE, as well as higher ratio of total FeO/MgO, Ga/Al, and Rb/Sr. However, the whole-rock Nd-, Hf- and zircon Hf–O isotopic compositions of the peralkaline and aluminous A-type granites were similar. It could be inferred that the peralkaline A-type granites were formed by crystal fractionation of aluminous A-type granitic magmas. Since the studied A-type granitic intrusions were coeval with the bimodal volcanic rocks and the extensional basins in the coastal region of southeastern China, they were likely produced in an extensional setting, possibly during lithospheric thinning that resulted from the subduction of the paleo-Pacific plate beneath southeastern China.
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