Petrogenesis of Cretaceous shoshonitic rocks in the northern Wuyi Mountains, South China: A result of the roll-back of a flat-slab?
Petrogenesis of Cretaceous shoshonitic rocks in the northern Wuyi Mountains, South China: A result of the roll-back of a flat-slab?
复制标题
华南武夷山北部白垩纪钾玄岩的岩石成因：平板回滚的结果？
DOI：
10.1016/j.lithos.2017.06.014
复制
发表时间：
2017
期刊：
影响因子：
3.5
通讯作者：
Yang Dong Sheng
中科院分区：
文献类型：
--
作者：
Li Wu Xian;Li Xian Hua;Wang Xuan Ce;Yang Dong Sheng
钾质岩浆活动通常与造山后/晚期环境有关，如大陆岩石圈的沉降或对流减薄。它们的岩石成因是制约残留的次大陆岩石圈地幔的化学和物理性质的关键。本文报道了武夷山北方大安、应城、资溪和红宫四个钾质岩体的SHRIMP锆石U-Pb年龄、全岩地球化学结果和Sr-Nd、锆石Hf同位素数据。SHRIMP锆石U-Pb分析表明，这些钾质岩石形成于139-126 Ma。它们的特征是高SiO2（56-73%）和K2 O（3.8-6.7%），K2 O/Na 2 O比值为2.18-2.04，位于高SiO2钾玄岩范围内。它们的IS和εNd（t）值分别为0.7077 ~ 0.7162和-5.66 ~-10.52。初始锆石εHf（t）值介于2.3 ~ − 13.1之间，对应的TDM模式年龄介于707 ~ 1330 Ma之间。这些地球化学和同位素特征表明，这些钾玄岩起源于俯冲改造的古陆岩石圈地幔，然后在岩浆上升过程中经历了显着的分离结晶的钾长石，斜长石，副矿物，如磷灰石和Fe-Ti氧化物。我们解释了软流圈地幔上涌（由板块向东回滚引起的？）触发了早白垩世武夷山北方岩石圈地幔的部分熔融，形成了钾玄质岩浆活动。结合华南陆块内部的地球化学资料，发现华南陆块内部的弧形地球化学特征仅限于武夷山地区，而向华南内陆则变得很小甚至不可见。这意味着早中生代俯冲作用的远场效应仅到达武夷山，约。距离海沟500公里，与平坦或浅俯冲模型一致。
Potassic magmatism is commonly linked to post-/late-orogenic environments, such as foundering or convection thinning of continental lithosphere. Their petrogenesis is crucial for constraining the chemical and physical properties of the remnant sub-continental lithospheric mantle. Here we report new SHRIMP zircon U–Pb ages, whole rock geochemical results and Sr–Nd and zircon Hf isotope data from four potassic plutons (the Da'an, Yingcheng, Zixi and Honggong plutons) in the northern Wuyi Mountains, South China. SHRIMP U–Pb zircon analyses indicate that these potassic rocks formed at 139–126 Ma. They are characterized by high SiO2(56–73%) and K2O (3.8–6.7%), with a K2O/Na2O ratio of 2.18–2.04, plotting within the field of high-SiO2shoshonites. TheirISrand εNd(t) values vary from 0.7077 to 0.7162 and − 5.66 to − 10.52, respectively. The initial zircon εHf(t) values range from 2.3 to − 13.1, corresponding to TDMmodal ages between 707 and 1330 Ma. These geochemical and isotope characteristics indicate that these shoshonites derived from a subduction-modified ancient subcontinental lithospheric mantle, and then underwent significantly fractional crystallization of K-feldspar, plagioclase, and accessory minerals, such as apatite and Fe–Ti oxides during magma ascent. We interpret that asthenospheric mantle upwelling (caused by eastward roll-back of a flat-slab?) triggered partial melting of the metasomatized lithospheric mantle to result in the Early Cretaceous shoshonitic magmatism in the northern Wuyi Mountains. An integration of our new results with compiled data from the interior of the South China Block reveals that the arc-like geochemical signature is confined to the Wuyi Mountains region, but becomes little or even invisible toward inland in South China. This implies that the far-field effects of the early Mesozoic subduction only reached the Wuyi Mountains, ca. 500 km away from the trench, consistent with flat or shallow subduction models.