太行山北段王安镇杂岩体岩石学、年代学、地球化学特征及地质意义

Petrology,geochronology and geochemistry characteristics of Wang'anzhen complex in the northern Taihang Mountain and their geological significance

王安镇杂岩体主要由花岗闪长岩、二长花岗岩、花岗岩、石英闪长岩、二长闪长岩组成,LA-ICP-MS锆石U-Pb测年显示,花岗闪长岩和石英闪长岩分别形成于129±2.7Ma和128.3±1.9Ma,说明该杂岩体形成于早白垩世。王安镇杂岩体具有高Sr/Y比值(3.63~83.5),和高Sr(373×10-6~821×10-6),及低Y(7.36×10-6~22.21×10-6)、Yb(0.95×10-6~1.27×10-6)含量的地球化学特征,这与埃达克岩相似。该杂岩体具有相对低的87Sr/86Sr初始比值(0.706538~0.709484)和明显偏低的εNd(128Ma)值(-18.4^-12.8)。结合太行山中生代中-基性侵入岩中地幔包体已有的研究成果,认为具有高Sr/Y特征的王安镇杂岩体是在下地壳发生大规模拆沉的基础上,随着软流圈上涌其所携带的热促使加厚基性下地壳发生部分熔融,之后熔融岩浆在上升的过程中发生了角闪石的结晶分异和岩浆混合作用形成。

The Wang＇anzhen complex in the northern Taihang Mountain mainly consist of granodiorite,monzonitic granite,granite,quartz diorite and monzodiorite. The LA-ICP-MS zircon U-Pb dating shows that the granodiorite and quartz diorites were crystallized at129 ± 2. 7Ma and 128. 3 ± 1. 9Ma,respectively,suggesting that the Wang＇anzhen complex were formed in the Early Cretaceous. The Wang＇anzhen complex are characterized by high Sr = 373 × 10- 6～ 821 × 10- 6,Sr/Y = 3. 63 ～ 83. 5,and low Y = 7. 36 × 10- 6～22. 21 × 10- 6,Yb = 0. 95 × 10- 6～ 1. 27 × 10- 6,similar to adakite. The Wang＇anzhen complex have relatively low initial87 Sr /86 Sr ratios（ 0. 706538 to 0. 709484） and εNd（ t = 128Ma）values（- 18. 4 to- 12. 8）,with Nd model ages from 1. 09 Ga to 1. 89 Ga,indicating that they were mainly derived by partial melting of old continental crustal materials. Combined with the previous results about the mantle xenoliths entrained by the Mesozoic basic-intermediate intrusive rocks in the Taihang Mountains,We considered that the Wang＇anzhen complex was originated from melting of ancient thickened mafic lower crust which was based on large-scale lower crust delaminated into the convecting mantle, triggered by heating from upwelling asthenosphere, subsequently fractionated（ e. g.hornblende） and mixed with felsic magma during rising,produced rocks with high Sr / Y signature.