Early Paleozoic crust–mantle interaction and lithosphere delamination in South China Block: Evidence from geochronology, geochemistry, and Sr–Nd–Hf isotopes of granites
Early Paleozoic crust–mantle interaction and lithosphere delamination in South China Block: Evidence from geochronology, geochemistry, and Sr–Nd–Hf isotopes of granites
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DOI：
10.1016/j.lithos.2013.11.014
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发表时间：
2014
期刊：
影响因子：
3.5
通讯作者：
Yan Xia;Xi‐sheng Xu;H. Zou;Lei Liu
中科院分区：
文献类型：
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作者：
Yan Xia;Xi‐sheng Xu;H. Zou;Lei Liu
华南地块早古生代造山带为陆内造山带，同步岩浆作用（440~390 Ma）以酸性岩浆作用为主，伴有少量中镁铁质岩浆作用。前期研究表明，华南早古生代花岗岩大部分属于过铝质S型花岗岩，含角闪石的I型花岗岩次之。然而，我们的研究结果表明，大量的早古生代花岗岩同时具有 S 型和 I 型花岗岩的特征。因此，我们建议将这些花岗岩分为两类：较少的是A组，其εHf(t)值相对较高（聚集在−3.0至+9.0范围内）和εNd(t)值（−5.2至+1.3范围内），并且初始温度较高（810–850°C），而大多数是B组，其εHf(t)值相对较低（聚集在−16.0至+1.3范围内）。 − 1.0) 和εNd(t) 值（− 13.2 至− 4.1）以及相对较低的初始温度（700–830 °C）。霞湾二长花岗岩和墩头花岗闪长岩是典型的 A 组花岗岩，其锆石 U-Pb 年龄约为410马。这两种花岗岩的特点是 SiO2 高（重量百分比在 67.59 至 74.87% 之间）、准铝质至过铝质 (A/CNK = 0.96–1.48) 成分以及 P2O5 和 SiO2 之间的负相关性。它们的黑云母属于镁黑云母，表明它们具有I型或S型花岗岩的部分特征。墩头花岗闪长岩表现出较高的εHf(t)值(聚集在+1至+8范围内)和εNd(t)值(-3.0至+1.1)，而霞湾二长花岗岩表现出相对较低的εHf(t)值(聚集在-1至+5范围内)和εNd(t)值(-5.0至-3.7)。 B 组花岗岩以庙儿山-月城岭岩基为代表，其特点是 SiO2 高（重量百分比在 64.57 至 77.37% 之间）、准铝质成分（A/CNK = 0.90-1.24）、P2O5 与 SiO2 呈负相关。该岩基中的月城岭斑状角闪石黑云母花岗岩含有丰富的角闪石，属于I型花岗岩。庙儿山—月城岭岩基也表现出较低的εHf(t)值(−12.7至−1.8)和εNd(t)值(−8.9至−6.7)。对早古生代花岗岩、镁铁质包体和镁铁质至中间岩石的地球化学和同位素分析表明，包括霞湾和墩头花岗岩在内的A组花岗岩可能是由AFC过程是软流圈岩浆与变质沉积岩相互作用的过程，B类花岗岩可能是由同步玄武质岩浆与变质基底相互作用的AFC过程形成的。碰撞后分层和软流圈上升流直接参与A类花岗岩的生成，但间接诱发B类花岗岩的形成。
The early Paleozoic orogen in South China Block is an intracontinental orogen, and synchronous magmatism (440–390 Ma) is mainly acidic with minor intermediate-mafic magmatism. Previous studies suggest that most of the early Paleozoic granites in South China belong to peraluminous S-type genesis while amphibole-bearing I-type granites are subordinate. However, our results indicate that considerable amounts of these early Paleozoic granites have characteristics of both S- and I-type granites. Thus, we propose to divide these granites into two groups: fewer of them are Group A with relatively highεHf(t) values (clustering within − 3.0 to + 9.0) andεNd(t) values (− 5.2 to + 1.3) as well as higher initial temperatures at 810–850 °C, and most of them are Group B with relatively lowεHf(t) values (clustering within − 16.0 to − 1.0) andεNd(t) values (− 13.2 to − 4.1) as well as relatively low initial temperatures at 700–830 °C. The Xiawan monzogranite and Duntou granodiorite are typical Group A granitoids and yield zircon U–Pb ages of ca. 410 Ma. These two granites are characterized by high SiO2(between 67.59 and 74.87 wt.%), metaluminous to peraluminous (A/CNK = 0.96–1.48) compositions, and a negative correlation between P2O5and SiO2. Their biotites belong to magnesium biotites, indicating that they have partial features of either I- or S-type granites. Duntou granodiorites exhibit higherεHf(t) values (clustering within + 1 to + 8) andεNd(t) values (− 3.0 to + 1.1) while Xiawan monzogranites show relatively lowεHf(t) values (clustering within − 1 to + 5) andεNd(t) values (− 5.0 to − 3.7). Group B granitoids are represented by the Miao'ershan–Yuechengling batholith, which are characterized by high SiO2(between 64.57 and 77.37 wt.%), metaluminous compositions (A/CNK = 0.90–1.24), and a negative correlation between P2O5and SiO2. Yuechengling porphyritic amphibole-bearing biotite granites in this batholith contain abundant amphibole, indicating that they are I-type granites. Miao'ershan–Yuechengling batholith also exhibits relatively lowεHf(t) values (− 12.7 to − 1.8) andεNd(t) values (− 8.9 to − 6.7).Geochemical and isotopic analyses on early Paleozoic granites, mafic enclaves and mafic to intermediate rocks demonstrate that the Group A granitoids including Xiawan and Duntou granites may be generated by AFC processes with interactions between asthenosphere-derived magma and metasedimentary rocks, and the Group B granitoids may be formed by AFC processes with interactions between synchronous basaltic magma and metamorphic basement. The post-collisional delamination and asthenospheric upwelling directly participate in the generation of Group A granitoids but indirectly induce the formation of Group B granitoids.