摘要
穿地壳岩浆系统理论和晶粥模型为研究中国东南部白垩纪岩浆作用提供了新的思路。大衢山岩体位于浙闽沿海东北部,主体由钾长花岗岩组成,其中发育大量暗色微粒包体(MME),局部可见中—基性岩脉穿插其中,潮头门附近出露少量二长岩。MME具细粒结构,发育针状磷灰石。锆石U-Pb定年结果显示,大衢山岩体出露的钾长花岗岩、MME、二长岩、中—基性岩脉均结晶于~100 Ma。钾长花岗岩硅含量较高(SiO_(2)=68.45%~73.82%)。岩体东端可见不含MME的晶洞花岗岩(DQS-7),具有更高硅含量(76.27%),其全岩化学成分与Sr-Nd同位素组成与大衢山周围同期出露的高硅花岗岩体(SiO_(2)>75%,小洋山岩体,普陀山岩体等)类似。大衢山钾长花岗岩中可见斜长石、钾长石聚晶,与大衢山晶洞花岗岩及周边高硅花岗岩具有Ba、Sr、P等微量元素“互补”的地球化学特征。进一步研究显示大衢山钾长花岗岩是由受到岩浆补给的起源于古老地壳基底重熔的长英质岩浆,经分离结晶和高硅熔体抽离后的残余堆晶固结而成,而高硅熔体形成了大衢山晶洞花岗岩及周边高硅花岗岩。大衢山基性岩脉富集大离子亲石元素,亏损Nb、Ta等高场强元素,与同期出露的浙闽沿海镁铁质岩墙具有相似的地球化学特征,起源于俯冲流体交代的富集地幔。电子探针分析结果表明,钾长花岗岩和MME中的斜长石具有核—幔—边结构,核部(花岗岩27~36、MME 25~41,后同)与边部(17~32、18~26)An值较低,幔部An值(28~57、27~65)相对较高,是岩浆混合作用的典型矿物学标志。结合元素地球化学特征和Sr-Nf-Hf同位素组成,二长岩和中性岩脉应该是幔源镁铁质岩浆与长英质岩浆发生均匀混合的产物,而MME为两种岩浆机械混合的产物。角闪石全铝压力计计算结果表明,MME的形成深度为1.8~3.0 km;二长岩中角闪石发育核—幔—边结构,核部和幔部形成深度为17.0~21.2
The models of trans-crustal magmatic system and crystal mush provide new insights into the study of Cretaceous magmatism in northeast China.The Daqushan pluton is located in the northeast of coastal Zhejiang and Fujian.It is mainly composed of K-feldspar granite with abundant melanocratic microgranular enclaves(MME)and is locally traversed by several mafic-intermediate dikes.A small outcrop of monzonite is exposed near the Chaotoumen.MME have a fine-grained texture with acicular apatites.Zircon U-Pb dating results show that the rock samples in the Daqushan pluton(including the K-feldspar granite,MME,monzonite,and mafic-intermediate dikes)crystallized at~100 Ma.The K-feldspar granite are highly silicic(SiO_(2)=68.45%-73.82%).While the miarolitic granite(DQS-7)without MME has the higher silica(76.27%),and its whole-rock geochemical and Sr-Nd isotope compositions are similar to those of coeval high silica granites(SiO_(2)>75%)exposed around the Daqushan pluton.Daqushan K-feldspar granite bearing aggregates of plagioclase and K-feldspar exhibit“complementary”trace element geochemical characteristics with Daqushan miarolite and surrounding high silica granites.Further researches show that the Daqushan K-feldspar granite and miarolite were formed by felsic magma which originated from the partial melting of the ancient crustal basement and was recharged by mantle-derived magma.Such felsic magma underwent fractional crystallization and the extraction of high silica melt.Then,the residual silicic cumulate of the crystal mush and high silica melt crystallized and formed the Daqushan K-feldspar granite,miarolite and the surrounding coeval high silica granites.The mafic dikes of Daqushan are enriched in LILEs and depleted in HFSEs and are derived from the partial melting of the enriched mantle metasomatized by subducted dehydration fluids.The results of EPMA analyses indicate that the plagioclase in the K-feldspar granite and MME has a core-mantle-rim texture with low-An in the core(27-36,25-41)and rim(17-32,18-26)and re
作者
何晨
夏炎
徐夕生
邱检生
徐航
张志
赵思狄
HE Chen;XIA Yan;XU Xisheng;QIU Jiansheng;XU Hang;ZHANG Zhi;ZHAO Sidi(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;Frontiers Science Center for Critical Earth Cycling,Nanjing University,Nanjing 210023,China)
出处
《高校地质学报》
CAS
CSCD
北大核心
2023年第5期657-678,共22页
Geological Journal of China Universities
基金
国家自然科学基金项目(41930214,42172052)
中央高校基本科研业务费专项资金(0206-14380128)
关键地球物质循环前沿科学中心科研基金(DLTD2105)联合资助。
关键词
穿地壳岩浆系统
晶粥模型
晶体—熔体分离
岩浆混合
角闪石
斜长石
trans-crustal magmatic system
crystal mush
crystal-melt separation
magma mixing/mingling
hornblende
plagioclase
