江西宜黄强过铝质S型花岗岩成因及其对华南早古生代陆内造山运动的制约

Genesis of the Yihuang strong peraluminous S-type granite in Jiangxi Province and its constraints on Early Paleozoic intracontinental orogeny in South China

宜黄花岗岩位于江西省中部宜黄县东南部,属武夷地块,主要岩石类型为二云母二长花岗岩。锆石U-Pb同位素测年表明,宜黄岩体形成于448 Ma。岩石具有高的SiO 2、K 2 O、稀土元素总量(ΣREE=164.29×10^(-6)~256.66×10^(-6))、CaO/Na 2 O值、A/CNK(1.23~1.45)、Rb/Sr值,以及低的P 2 O 5、TiO 2、TFeO/MgO、Al 2 O 3/TiO 2、Nb、Sr等值;轻稀土元素相对富集((La/Yb)N=12.02~34.43),具有中等负Eu异常(δEu=0.38~0.77),低εNd(t)值(-8.22~-13.93),高(87 Sr/86 Sr)i=(0.71283~0.72410)。锆石176 Hf/177 Hf值为0.28155~0.28250,εHf(t)值为-33.15~10.45。全岩Nd同位素二阶段模式年龄为1.99~2.31 Ga,锆石Hf同位素二阶段模式年龄为1.24~3.48 Ga。上述特征表明,宜黄花岗岩具有与强过铝质S型花岗岩类似的特征。宜黄花岗岩中黑云母富含Fe、Mg、Ti;白云母Ti、Al、Na含量高,Fe含量低。综合锆石饱和温度计、黑云母地质温度计、白云母地质压力计、锆石Ce异常等,宜黄花岗岩可能为华南元古宙地壳长石石英质岩石在高温、中等压力(9.5 kbar)和低氧逸度条件下部分熔融而成。在华南早古生代陆内造山作用的背景下,岩石圈拆沉作用引发上涌的地幔岩浆提供热,使华南元古宙地壳岩石发生部分熔融,形成宜黄花岗岩。

The Yihuang granite is located in the southeast Yihuang county of central Jiangxi Province,which belongs to the Wuyi terranes.The main lithology of the Yihuang granitoids is two-mica monzogranite.Zircon LA-ICP-MS U-Pb dating indicates that the Yihuang granitoid formed at 448 Ma.The Yihuang granitoid is characterized by high contents of SiO 2,K 2 O,ΣREE(164.29×10^(-6)~256.66×10^(-6)),CaO/Na 2 O,A/CNK(1.23~1.45),and Rb/Sr,as well as low contents of P 2 O 5,TiO 2,TFeO/MgO,Al 2 O 3/TiO 2,Nb,and Sr.They are enriched in LREE relatively to HREE((La/Yb)N=12.02~34.43)with moderate Eu anomalies(δEu=0.38~0.77).The Yihuang granite displays lowεNd(t)=(-8.22~-13.93)and high(87 Sr/86 Sr)i=(0.71283~0.72410).Zircon 176 Hf/177 Hf andεHf(t)values of the Yihuang granite are 0.28155~0.28250 and-33.15~10.45,respectively,with the corresponding two-stage Nd isotopic model ages of 1.99~2.31 Ga and two-stage Hf isotopic model ages of 1.24~3.48 Ga.The characteristics mentioned above show that the Yihuang granite is similar to the strongly peraluminous S-type granitoid.The biotite in the Yihuang granite is enriched in Fe,Mg,and Ti,and the muscovite has high contents of Ti,Al,Na,and low content in Fe.Combined with zircon saturation thermometers,biotite geothermometer,muscovite geobarometer,and zircon Ce anomalies,the Yihuang granite may be formed by the partial melting of the Proterozoic felsic crust of South China under high temperature,medium pressure(9.5 kbar)and low oxygen fugacity.Under the Early Paleozoic intra-continental Orogeny,the upwelling of mantle caused by the lithospheric delamination provided heat that would have triggered the partial melting of the Proterozoic crust of South China to generate the Yihuang granite.