摘要
根据其岩石化学特征,广东吴川—四会断裂带燕山期强过铝质花岗岩可以分为两类。第一类SiO2含量较低,Al2O3/TiO2比值低(<100)、CaO/Na2O比值高(>0.3),具中等程度的66轻稀土富集。第二类SiO2含量较高,Al2O3/TiO2比值高(>100)、CaO/Na2O比值(<0.3),不具明显的轻稀土富集。这种特征暗示,第一类强过铝质花岗岩其源区成分为镁铁质正变质岩,熔融温度较高,来源相对较深。第二类强过铝质花岗岩其源区为泥岩质成分,熔融温度较低,来源相对较浅。该地区强过铝质花岗岩形成的大地构造背景是古太平洋板块向亚洲大陆东缘俯冲形成的活动大陆边缘带靠近内陆的一侧。吴川—四会断裂带燕山期岩浆活动(包括这些强过铝质花岗岩)的深部热源是由活动海岭俯冲所导致的高温地幔楔所生成的底侵岩浆。吴川—四会断裂带燕山期的深部热机制类似于欧洲海西造山带,属于“热”造山带。
The northeastern trending Wuchuan Sihui fracture belt is an important tectonic and metallogenic belt in Guangdong Province, China. There are many Yanshanian strongly peraluminous granitoids (SPGs) occurring in the belt. As revealed by their petrochemical feature, they can be grouped into two types. According to the geochemical classification suggested by Frost et al. (2001), the first group SPGs belong to the magnesian class granitoids, but the second group SPGs belong to the ferroan class. The first group is characterized by their lower SiO2 content (less than 74%mostly) and Al2O3/TiO2 ratio (< 100) but higher CaO/Na2O ratio (>0.3), as well as moderate LREE enrichment. However, the second group exhibits higher SiO2 content (more than 74%), Al2O3/TiO2 ratio (>100), higher CaO/Na2O ratio (< 0.3) and no significant LREE enrichment. These features imply that the first group SPGs are generated by melting of mafic metamorphic rocks in a hot and deep source, but the second group SPGs are originated from a relative 'cold'and shallow source with pelitic composition. The tectonic setting of these SPGs is the inboard portion of continental arc that is formed by the subduction of palaeo Pacific plate underneath the eastern margin of Asia. The deep heat source for Yanshanian magmatism (including these SPGs) in the belt is the underplating magma derived from a hot mantle wedge, which is caused by the active ridge subduction. The simple modeling on the thermal structure of crust in peak period of orogeny shows that the temperature can reaches 1 000-1 300 ℃at 60 km depth. Therefore, the Wuchuan-Sihui belt belongs to the 'hot'orogen; its thermal regime during Yanshanian period is similar to that of Hercynian orogen in Europe.
出处
《大地构造与成矿学》
EI
CAS
CSCD
北大核心
2003年第1期56-63,共8页
Geotectonica et Metallogenia
基金
国家自然科学基金项目(编号:40104003)
国土资源部科技发展计划"华南地区岩石圈三维结构及其演化"(20001010206)
"华北地区岩石圈三维结构及其演化"(20001010202)
中国博士后科学基金
中国地质调查局地质调查项目(K1.4-1-2)
基础地质综合研究课题“燕山造山带花岗岩与大陆地壳改造和生长”联合资助.
关键词
强过铝质花岗岩
岩石化学特征
燕山期
吴川—四会断裂带
广东
Strongly peraluminous granitoid
Petrochemical characteristics
Yanshanian cycle
Wuchuan Sihui fracture belt
Guangdong Province
