摘要
为探讨甘肃北山造山带晚古生代-中生代的构造演化特征,对该区前红泉地区的斑状花岗闪长岩开展了年代学和地球化学研究。通过高精度的LA-ICP-MS锆石U-Pb测年,获得了该区斑状花岗闪长岩的加权平均年龄为(264.2±1.2) Ma、(249.3±1.1) Ma和(234.3±1.1) Ma,表明其为中二叠世-晚三叠世岩浆活动的产物。地球化学数据表明,岩体为准铝质、高钾钙碱性系列,主量元素表现为高硅(SiO_(2)为64.03%~72.23%)、高铝(Al_(2)O_(3)为14.01%~16.60%)、富碱(Na_(2)O+K_(2)O为7.20%~8.36%)和低钙(CaO为1.87%~3.43%)、贫镁(MgO为0.55%~1.53%);轻稀土富集,轻重稀土分馏明显,具负Eu异常(δEu为0.56~0.87);微量元素富集强不相容元素Th、U和大离子亲石元素Rb、K,显著亏损高场强元素Nb、P、Ti,表现出I型花岗岩的特点。结合区域地质背景,认为北山洋盆在早二叠世已经闭合,中二叠世-晚三叠世北山南带处于后碰撞伸展的大地构造环境。
In order to explore tectonic evolution characteristics of the Beishan orogenic belt in Gansu province during the Late Paleozoic to Mesozoic periods, a study on chronology and geochemistry of porphyritic granodiorites in the Qianhongquan area of the Beishan orogenic belt has been carried out in this paper. The high precision LA-ICP-MS zircon dating results show that porphyritic granodiorites in the Qianhongquan area have weighted average ages of(264.2±1.2) Ma,(249.3±1.1) Ma and(234.3±1.1) Ma, respectively, indicating that they are products of Middle Permian to Late Triassic magmatic movements. Geochemical data show that these rocks belong to metaluminous and high potassium calc-alkaline series with characteristics of high Si(SiO_(2) contents of 64.03%-72.23%), high Al(Al_(2)O_(3) contents of 14.01%-16.60%), alkaline-rich(Na_(2)O+K_(2)O contents of 7.20%-8.36%), low Ca(CaO contents of 1.87%-3.43%), Mg-poor(MgO contents of 0.55%-1.53%), LREE-enriched, obvious fractionation of LREE and HREE, negative Eu anomalies(δEu values of 0.56-0.87), enriched strongly incompatible elements of Th, U and large ionophile elements of Rb and K, obviously depleted high field strength elements(HFSE) of Nb, P, and Ti, indicating that they have characteristics of the I-type granite. Combined with regional geological setting, it is believed that the Beishan oceanic basin could be closed in the Early Permian, whereas the southern part of the Beishan area was in a tectonic environment of post-collisional extension during the Middle Permian to Late Triassic periods.
作者
杨镇熙
赵吉昌
荆德龙
赵青虎
张晶
樊新祥
YANG Zhen-xi;ZHAO Ji-chang;JING De-long;ZHAO Qing-hu;ZHANG Jing;FAN Xin-xiang(Fourth Institute of Gological and Mineral Exploration of Gansu Provincial Bureau of Geology and Mineral Resources,Jiuquan Gansu 735000,China;Xi'an Geological Survey Center of China Geological Survey,Xi'an 710054,China)
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2021年第1期228-241,共14页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
甘肃省基础地质调查项目(甘财经二[2017]105号,甘国土资勘发[2018]45号,甘资勘发[2019]66号,甘资财环[2020]28号)
陕西省自然科学基础研究计划(2019JQ-934)。
