Neoproterozoic crustal growth of the Southern Yangtze Block: Geochemical and zircon U-Pb geochronological and Lu-Hf isotopic evidence of Neoproterozoic diorite from the Ailaoshan zone
Neoproterozoic crustal growth of the Southern Yangtze Block: Geochemical and zircon U-Pb geochronological and Lu-Hf isotopic evidence of Neoproterozoic diorite from the Ailaoshan zone
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DOI：
10.1016/j.precamres.2015.05.008
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发表时间：
2015-09
影响因子：
3.8
通讯作者：
Yongfeng Cai;Yuejun Wang;Peter A. Cawood;Yuzhi Zhang;Aimei Zhang
中科院分区：
文献类型：
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作者：
Yongfeng Cai;Yuejun Wang;Peter A. Cawood;Yuzhi Zhang;Aimei Zhang
华南扬子地块边缘新元古代长英质火成岩与基性-超基性岩体伴生，可以用来约束该地区大陆地壳的生长和长期演化。对扬子地块南缘哀老山构造带阿德波石英闪长岩进行LA-ICPMS锆石U-Pb定年，得到新元古代年龄为800±7 Ma， α Hf(t)值在−1.03 ~ +3.75之间，两期模式年龄为1.3 ~ 1.6 Ga。岩体具有低SiO2（60.97 ~ 64.41 wt.%）、低总碱（K2O + Na2O, 7.35 ~ 9.14 wt.%）和高al2o3 （16.98 ~ 18.21 wt.%）的特征，mg值为36 ~ 39。稀土元素归一化模式显示LREE富集，（La/Yb）cn为11.36 ~ 19.77，铕负异常，Eu/Eu* = 0.61 ~ 0.74。样品具有负Nb- ta （(Nb/La)n= 0.18 ~ 0.35）和P、Ti、Sr异常、高Y浓度（33.79 ~ 41.04 ppm）和低Sr/Y比值（5.65 ~ 10.16）的特征。其同位素组成与牢山地区新元古代基性火成岩和扬子地块西南部的基性火成岩相似，表明石英闪长岩是由基性下地壳部分熔融作用形成的。闪长岩的地球化学特征也与增厚下地壳或角闪岩和榴辉岩实验熔体中的埃达质岩石相似。结合该区与弧相关的地球化学特征和与该区同步发育的阿德波石英闪长岩，认为阿德波石英闪长岩体可能是在扬子地块边缘新元古代地壳生长的俯冲构造背景下形成的。
Neoproterozoic felsic igneous rocks associated with mafic-ultramafic bodies along the margins of the Yangtze Block, South China, can be used to constrain the continental crustal growth and secular evolution of the region. LA-ICPMS zircon U–Pb dating of the Adebo quartz diorite pluton in the Ailaoshan tectonic zone on the southern margin of the Yangtze Block gives the Neoproterozoic age of 800 ± 7 Ma andɛHf(t) values in the range of −1.03 to +3.75 with two-stage model age of 1.3–1.6 Ga. The pluton is characterized by relatively low SiO2(60.97–64.41 wt.%) and total alkalis (K2O + Na2O, 7.35–9.14 wt.%) and high Al2O3content (16.98–18.21 wt.%) with mg-number of 36–39. REE-normalized patterns show enrichment in LREE with (La/Yb)cn of 11.36–19.77 and Europium negative anomalies with Eu/Eu* = 0.61–0.74. The samples are characterized by negative Nb-Ta ((Nb/La)n= 0.18–0.35) and P, Ti, Sr anomalies and high Y concentrations (33.79–41.04 ppm) and low Sr/Y ratios (5.65–10.16). Their isotopic composition are similar to those of the Neoproterozoic mafic igneous rocks in the Ailaoshan zone and the southwestern Yangtze Block, indicating that the quartz diorite was produced by partial melting of mafic lower crust. The diorite also shows the similar geochemical characteristics with adakitic rocks from thickened lower crust or amphibolite and eclogite experimental melts. In combination with their arc-related geochemical signatures and synchronous developed adakitic rocks in the region, the Adebo quartz diorite pluton might be produced in a subduction-related tectonic setting during Neoproterozoic crustal growth along the margins of Yangtze Block.