九嶷山-铜山岭-都庞岭花岗岩带低钕模式年龄的成因探讨

Genetic study of low neodymium model ages of the Juiningshan-Tongshanling-Dupanling granite belt

九嶷山、都庞岭复式岩体分别由志留纪、中三叠世、中-晚侏罗世和志留纪、晚三叠世、中侏罗世花岗岩组成,源岩主要为壳源物质,钕模式年龄值由早至晚顺序降低,并与花岗岩的酸碱度呈负相关。最晚期的晚侏罗世金鸡岭岩体t2DM 值仅1480～1410Ma,年龄偏低的原因可能是花岗岩浆源岩有部分来自相对较浅、时代较新的地壳和复式岩体区已固结成岩的早时代花岗岩。中三叠世的铜山岭岩体基性程度高,属壳幔同熔型成因,钕模式年龄1480～1380Ma,低钕模式年龄值的成因和幔源物质的加入有关。

Juiningshan and Dupanling composite granite body are composed of Silurian, Triassic and Jurassic intrusions and were primarily derived from the earth's crust. Neodymium model ages of granitic rocks reduce with emplacement age and show negative relationship with contents of acidic and alkali elements. The late Jurassic Jingjiling granite body has a t_2DM) of 1 480~1 410 Ma, which might imply the granitic magma were derived from new shallow crust earlier granites. The middle Jurassic Tongshanling granite body contains more basic materials, belonging to I-type granites and has a lower t_2DM) of 1 480~1 380 Ma, which might be related to adding of mantle materials.