Petrogenesis of metaluminous A-type granitoids in the Tengchong–Lianghe tin belt of southwestern China: Evidences from zircon U–Pb ages and Hf–O isotopes, and whole-rock Sr–Nd isotopes
Petrogenesis of metaluminous A-type granitoids in the Tengchong–Lianghe tin belt of southwestern China: Evidences from zircon U–Pb ages and Hf–O isotopes, and whole-rock Sr–Nd isotopes
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DOI：
10.1016/j.lithos.2014.11.010
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发表时间：
2015
期刊：
影响因子：
3.5
通讯作者：
Xiaocui Chen;R. Hu;X. Bi;H. Zhong;Jiangbo Lan;Chenghai Zhao;Jing-Jing Zhu-Jing
中科院分区：
文献类型：
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作者：
Xiaocui Chen;R. Hu;X. Bi;H. Zhong;Jiangbo Lan;Chenghai Zhao;Jing-Jing Zhu-Jing
腾冲-两河锡矿带是中国西南三江成矿区锡矿带的重要组成部分。最近在该区发现了两个在空间上与锡矿床有关的A型花岗岩体。这些花岗岩类以黑云母花岗岩为主，具有弱过铝至准铝质成分，高SiO_2含量(73.3-76.2wt.%)，高碱含量(K2O+Na2O=88.3-9.17wt.%)。微量元素蜘蛛图显示，这些花岗岩类也明显富含大离子亲石元素Rb、Th、U和K，但显著亏损BaS和Sr，显著亏损高场强元素Nb和Ti，但富含Zr和Hf。这些岩石具有相对较高的锆石饱和温度(774-833°C)，较高的锆石+Nb+Ce+Y含量(272-416Gppm)，以及10000×10000×Ga/Al比值(几乎为2.7)，这是A型花岗岩的典型特征。稀土元素总量高(174~404ppm)，稀土配分相对平缓，具明显的负Eu异常。LA-ICPMS锆石U-Pb定年结果表明，这两个花岗岩分别侵位于早第三纪(52.7±50.3~53.0±100.4 Ma)和晚白垩世(73.3±100.5~73.3±60.5 Ma)。同位素组成表明，该花岗岩类具有较高的变化(87Sr/86Sr)值(0.7182-0.7457)，相对恒定的低εNd(T)值(−-11.2~−(12.4))，以及古老的Nd和Hf模式年龄(1.56-1.88Ga)，表明它们来自古元古代陆壳的部分熔融。它们的锆石δ18O值(6.6~8.5‰)和εHf值(−=8.6~−=11.3)也表明这些花岗岩类主要来自由镁铁质和变质沉积岩组成的中下陆壳。这些地球化学特征表明，这两个A型花岗岩是在晚白垩世-早新生代新特提斯造山带的后碰撞或同碰撞拉张环境下，古元古代镁铁质和腾冲地块的变质基底部分熔融形成的。晚白垩世花岗岩类可能与新特提斯板块在缅甸西部碰撞后伸展作用下的俯冲以及侏罗纪-早白垩世腾冲微板块的碰撞有关。早第三纪花岗岩类可能是印度与亚洲主碰撞中晚期(55~41 Ma)拉张弛豫的同碰撞产物。
The Tengchong–Lianghe tin belt is the most importantpart of the tin metallogenic belt in southwest China’s Sanjiang Metallogenic province. In this district, two A-type granite plutons that are spatially associated with the tin deposits have recently been discovered. These granitoids are dominated by biotite granites with weakly peraluminous to metaluminous compositions, high SiO2contents (73.3–76.2 wt.%), and high alkali contents (K2O + Na2O = 8.3–9.17 wt.%). Trace element spider diagrams show that these granitoids are also clearly enriched with the large-ion lithophile elements Rb, Th, U, and K, but are markedly depleted in Ba and Sr. They are significantly depleted in the high field-strength elements Nb and Ti, but are enriched with Zr and Hf. These rocks have relatively high zircon saturation temperatures (774–833 °C), high Zr + Nb + Ce + Y contents (272–416 ppm), and 10,000 × Ga/Al ratios (almost > 2.7) that are typical of A-type granites. They also have high total rare earth element (REE) contents (174–404 ppm) and relatively flat chondrite-normalized REE patterns with significantly negative Eu anomalies.LA–ICP–MS zircon U–Pb dating results indicate that the emplacement of these two granite plutons occurred during the early Tertiary (52.7 ± 0.3–53.0 ± 0.4 Ma) and the Late Cretaceous (73.3 ± 0.5–73.3 ± 0.5 Ma) periods, respectively. Isotopic compositions show that the granitoids have highly variable (87Sr/86Sr)iratios (0.7182–0.7457), relatively constant low εNd(t) values (− 11.2 to − 12.4), and ancient Nd and Hf model ages (1.56–1.88 Ga), suggesting that they were derived from the partial melting of the Paleoproterozoic continental crust. Their zircon δ18O values (6.6–8.5‰) and εHfvalues (from − 8.6 to − 11.3) also suggest that these granitoids mainly originated from the middle-lower continental crust consisting of mafic and metasedimentary rocks. Such geochemical characteristics indicate that these two A-type granite plutons were generated by the partial melting of Paleoproterozoic mafic and the metasedimentary basement of the Tengchong block in a post-collisional or syn-collisional extensional setting of the Neo-Tethy anorogenic zone during the Late Cretaceous–Early Cenozoic. The Late Cretaceous granitoids were probably associated with the subduction of the Neo-Tethyan plate under the post-collisional extension of the western Burma and Tengchong microplates’ collision during the Jurassic–Early Cretaceous. The Early Tertiary granitoids might be the syn-collisional product of stretching relaxation during the middle and late main-collisional period (55–41 Ma) between India and Asia.