赣杭构造带新路火山盆地粗面斑岩的年代学、岩石成因及其地质意义

Geochronology,petrogenesis and geological significance of the trachyte porphyry from Xinlu Basin,Gan-Hang Belt,SE China

在赣杭构造带上新路盆地中发现有晚期侵入到黄尖组凝灰岩中的粗面斑岩岩脉。本文运用激光等离子质谱(LAICP-MS)对该粗面斑岩中的锆石进行了U-Pb年龄测定,获得了131±1Ma的形成年龄。新路粗面斑岩具有高碱、高钾、高K2O/Na2O,在Si O2-K2O图解中落入橄榄安粗岩(shoshonite)系列岩石的范围之内。新路粗面斑岩还具有贫铁、钛、钙、磷以及富集轻稀土和大离子亲石元素等特征,具有较高含量的高场强元素,亏损Nb、Ta、Sr、P、Ti,以及中等铕负异常(Eu/Eu*=0.32~0.46)和铈负异常(Ce/Ce*=0.64~0.73)的特点。粗面斑岩的全岩εNd(t)值为-5.01^-4.77,锆石的εHf(t)值为-8.3^-3.8(集中在-6^-4之间),两阶段Hf模式年龄集中在1.4~1.6Ga之间。这些地球化学特征表明新路粗面斑岩是幔源岩浆和壳源岩浆混合形成的产物,为赣杭构造带早白垩世幔源岩浆活动提供了重要证据。

A trachyte porphyry dyke was found in the Xinlu Basin from the Gan-Hang Belt,which intruded into the tuff of the Huangjian Formation. LA-ICP-MS zircon U-Pb dating shows that this rock was formed at 131 ± 1Ma. Geochemically,the trachyte porphyry shows high alkali,high K contents and high K2 O / Na2 O ratios,with all samples ploting in the shoshonite field of Si O2-K2 O diagram. The Xinlu trachyte porphyry also has low Fe,Ti,Ca and P contents. The rock is rich in LREE and LILE,and also characterized by high abundances of HFSE,depleted in in Nb,Ta,Sr,P and Ti. The Xinlu trachyte porphyry has moderate negative Eu anomaly（ Eu / Eu＊= 0. 32 ～ 0. 46） and moderate negative Ce anomaly（ Ce / Ce＊= 0. 64 ～ 0. 73）. The εNd（ t） values range from- 5. 01 to- 4. 77,and zircon εHf（ t） values range from- 8. 3 to- 3. 8（ mostly between- 6 and- 4）,with Hf depleted mantle model ages mostly between 1. 4Ga and 1. 6Ga. These geochemical and isotopic data indicate that the Xinlu trachyte porphyry was the product of mixing mantle-derived and crust-derived melts. The occurrence of Xinlu trachyte porphyry provides strong evidence for the Early Cretaceous mantle-derived magmatic activity in the Gan-Hang Belt.