摘要
随着造山带从俯冲、同碰撞阶段向碰撞后伸展阶段演化,造山带岩浆的性质也从钙碱性转变为超钾质。造山带钾质-超钾质岩浆的成因及钾的来源成为一个关键问题。并且,这一显著的岩浆性质转变,可能反映了地幔源区性质的改变。因此,揭示造山带岩浆K富集机制的关键在于理清:(1)岩浆K的来源;和(2)岩浆源区的岩石特征。本研究从K和Fe同位素的视角分别示踪造山带岩浆K的来源和源区特征,并结合已有文献中的资料,详细分析了造山带岩浆K的富集过程。结果发现,钙碱性岩浆的K可以来源于俯冲板片释放的流体和沉积物熔体,其中,“冷俯冲”环境下以流体为主,而“热俯冲”环境下以沉积物熔体为主;其源区的岩石性质为橄榄岩。超钾质岩浆中K的来源与钙碱性岩浆相似,但其流体可能由更富K的俯冲组分提供(如沉积物),而沉积物熔体在发挥作用时则在更高的压力下产生。且与钙碱性岩浆不同的是,超钾质岩浆的源区岩石类型主要为含金云母的辉石岩。因此,本研究认为,在造山带伸展背景下,交代流体与沉积物熔体K含量显著提升以及源区岩石性质从橄榄岩转变为含金云母的辉石岩是导致造山带岩浆K富集和岩浆性质转变的重要原因。
As orogenic belts evolve from subduction/syn-collisional to post-collisional stages,magma compositions transition from calc-alkaline to ultrapotassic,accompanied by significant potassium enrichment.However,the sources of K in ultrapotassic magmas and associated K-enrichment mechanism are still unclear.Furthermore,the nature of the mantle source of these K-rich magmas remains uncertain.Thus,deciphering the K-enrichment processes centers on addressing two fundamental aspects:(1)the origin of K,and(2)the lithology of the magmatic sources.This study employs a novel approach by utilizing K and Fe isotopes to trace K sources and source lithologies of orogenic magmas,respectively.Integrating our previous work with published data,we provide a detailed analysis of K enrichment processes in orogenic magmas.Results reveal that K in calc-alkaline magmas can be contributed by either subducted slab-derived fluids or sediment melts-fluids dominate in cold subduction systems while sediment melts prevail in hot subduction systems-with a peridotitic source lithology.Ultrapotassic magmas share similar K sources but involve fluids from K_(2)O-richer subducted components(e.g.,sediments)and sediment melts generated at higher pressures,yielding elevated K_(2)O concentrations.Crucially,ultrapotassic magmas originate primarily from a pyroxenitic source lithology,contrasting with the peridotitic sources of calc-alkaline magmas.Consequently,the substantial K_(2)O increase delivered by metasomatic agents(fluids and sediment melts),coupled with the source lithology transition from peridotite to pyroxenite,drives significant K enrichment and the compositional shift in orogenic magmas.
作者
杜德宏
王孝磊
李伟强
DU DeHong;WANG XiaoLei;LI WeiQiang(State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits,School of Earth Sciences and Engineering,Nanjing University,Nanjing)
出处
《岩石学报》
北大核心
2025年第12期4126-4136,共11页
Acta Petrologica Sinica
基金
国家自然科学基金青年基金项目(42302065)资助.
关键词
造山带
超钾质岩浆
钙碱性岩浆
K和Fe同位素
钾富集
Orogenic belts
Ultrapotassic magmas
Calc-alkaline magmas
K and Fe isotopes
Potassium enrichment
