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引用本文:苏扣林,丁兴,郭宇,石晓龙. 广州增城地质公园安山质-流纹质火山岩地球化学特征及Rb-Sr年龄测定[J]. 中国地质, 2021, 48(1): 161-172.
SU Koulin,DING Xing,GUO Yu,SHI Xiaolong. Rb-Sr dating and geochemistry of andesitic-rhyolitic volcanics in the Zengcheng Geopark, Guangzhou, Guangdong Province[J]. Geology in China, 2021, 48(1): 161-172(in Chinese with English abstract).
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广州增城地质公园安山质-流纹质火山岩地球化学特征及Rb-Sr年龄测定
苏扣林1, 丁兴2, 郭宇1, 石晓龙1
1.广州市地质调查院, 广东 广州 510440;2.中国科学院广州地球化学研究所同位素地球化学国家重点实验室, 广东 广州 510640
摘要:
广州市增城地质公园发育有大量的燕山期安山岩和流纹岩,由于缺少详细的岩石地球化学研究,这些火山岩的成因和所代表的大地构造意义一直未明确。文章对上述火山岩进行了较为系统的全岩地球化学以及同位素地球化学分析。研究结果显示,安山岩具有安第斯型火山岩特点,显示Nb、Ta、Sr和Ti的亏损,Isr值介于0.70332~0.7144,平均值0.7092,岩石稀土总量较低(ΣREE=158.9×10-6~215.0×10-6),平均值186.8×10-6,轻重稀土元素分异较弱((La/Yb)N5.06~9.87),平均值7.01,Eu负异常不明显(δEu=0.80~1.38),平均值δEu=0.94。流纹岩具有高钾特点,有明显的Ba、Sr、P、Eu、Ti负异常和Pb、Yb正异常,其Isr值介于0.71393~0.73650,平均值0.72615,岩石稀土总量较低(ΣREE=93.4×10-6~481.5×10-6),平均值285.7×10-6,轻重稀土元素分异弱((La/Yb)N=0.65~9.51),平均值4.35,Eu负异常很明显(δEu=0.01~0.03),平均值δEu=0.02,全岩Rb-Sr同位素年龄为(112±12)Ma。综合的地球化学研究表明,增城地质公园安山质-流纹质火山岩均属壳幔混合成因,其中安山岩以幔源为主,而流纹岩则以壳源为主,分别形成于早侏罗世和早白垩世太平洋板块俯冲碰撞挤压的构造背景下。这对华南地区中生代构造演化的深入认识具有重要的地质意义。
关键词:  火山岩  安山岩  流纹岩  地球化学特征  构造环境  地质调查工程  增城地质公园  广州  广东
DOI:10.12029/gc20210112
分类号:P588.144;P597.3
基金项目:广州市国土资源和规划委员会调查项目(212019906)资助。
Rb-Sr dating and geochemistry of andesitic-rhyolitic volcanics in the Zengcheng Geopark, Guangzhou, Guangdong Province
SU Koulin1, DING Xing2, GUO Yu1, SHI Xiaolong1
1.Guangzhou Geological Survey institute, Guangdong Guangzhou 510440;2.State Key Laboratory of Isotope Geochemistry Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Abstract:
A large number of Yanshanian andesite and rhyolite rocks are developed in the Zengcheng Geopark in Guangzhou. Due to the lack of detailed petrogeochemical studies, their genesis and the tectonic significance have not been clarified. Therefore, a more systematic analysis was conducted for the whole-rock geochemistry and isotopic geochemistry of these volcanic rocks. The results show that the andesitic rocks are somewhat analogous to the Andes-type volcanic ones, with obviously depleted Nb, Ta, Sr and Ti and low Isr values (0.70332-0.7144, averaging 0.7092), lower rare earth ΣREE(ΣREE=158.9×10-6-215.010-6, averaging 186.8×10-6), with obvious LREE and HREE differentiation((La/Yb)N5.06-9.87,averaging7.01)and negative Eu anomalies (δEu=0.80-1.38, averaging 0.94) in the chondrite-normalized REE distribution patterns. The rhyolitic rocks have high potassium contents with significant negative Ba, Sr, P, Eu, Ti anomalies and positive Pb and Yb anomalies. They are characterized by the Isr values ranging from 0.71393 to 0.73650(averaging 0.72615), lower rare earth ΣREE(ΣREE=93.410-6-481.510-6,averaging 285.710-6)with obvious LREE and HREE fractionation((La/Yb)N 0.65~9.51,averaging 4.35) and negative Eu anomalies (δEu=0.01-0.03, averaging 0.02) in the chondrite-normalized REE distribution patterns. The whole rock Rb-Sr Isotopic age is 112 ±12 ma. The integrated geochemical studies demonstrate that both the andesitic and rhyolitic magmas are of crust-mantle mixing origin, of which the andesitic magma was mainly originated from the mantle and the rhyolitic one mostly from the crust. The andesite rocks and rhyolitic volcanics were formed under the tectonic background of Pacific plate subduction and collision in early Jurassic and early Cretaceous respectively.
Key words:  volcanic rocks  andesite  rhyolite  geochemistry  tectonic environment  geological survey engineering  Zengcheng Geopark  Guangzhou  Guangdong Province