伊春地区斑状二长花岗岩锆石U——Pb 年龄及其地质意义

黑龙江伊春南岔-金山屯地区广泛发育斑状二长花岗岩。岩体呈岩基状产出，岩性为肉红色中粗粒斑状二长花岗岩，斑状，斑晶由钾长石和石英组成，基质由钾长石、斜长石、石英和黑云母组成，局部含角闪石。岩石SiO2 含量69. 58% ～ 75. 96%; 富碱，Na2O + K2O 为7. 22% ～ 8. 45%，K2O/ Na2O 为1. 07 ～ 1. 43 ( σ = 1. 58 ～ 2. 47) ，为钙碱性花岗岩。ΣREE 为178. 68 × 10 － 6 ～ 464. 75 × 10--6， ( La /Yb) N = 11. 6 ～ 20. 22，轻重稀土分馏显著，δEu = 0. 17 ～ 0. 34，具铕负异常，相对富Rb、Th、U、 Nd、La、Pr 等元素，贫Ba、Sr、P、Ti 元素等，显示典型的KCG 型( 高钾钙碱性) 花岗岩特征，属于造山后花岗岩( POG) ，为岩浆混合成因。该花岗岩两个锆石U--Pb 年龄值分别为207 ± 2 Ma、197 ± 1 Ma，属晚三叠世-早侏罗世，可能暗示混合后的结晶持续时间，其形成环境与西伯利亚板块和华北板块碰撞对接后的伸展作用有关。

Zircon U-Pb dating of porphyritic monzonitic granite in Yichun and its geological significance

Porphyritic monzonitic granites were widely exposed in Nancha-Jinshantun area of Yichun, Heilongjiang. The rock body occurred as batholiths with porphyry shape, and the rocks were flesh pink medium-coarse porphyritic monzonitic granite. Phenocrysts consisted of potash feldspar and quartz and the matrix was composed of potash feldspar, plagioclase, quartz, biotite and a few amphibole locally. The content of SiO2 was 69.58% - 75.96% , alkaline was rich with Na2o ＋ K2o of 7.22% - 8.45% , K20/Na20 = 1.07 - 1.43 （σ = 1.58 2. 47） , belonging to calc-alkaline granite. The EREE was 178.68 × 10^-6 -464.75 × 10^-6, （La/Yb） N = 11.6 20. 22 with obvious LREE/HREE differentiation and negative Eu anomaly （ 8Eu = 0. 17 - 0.34 ）. Trace elements were relatively rich in Rb, Th, U, Nd, La, Pr, （KCG-types） granite and post-orogenic （POG） The age of zranites were 207± 2 Ma and 197 ± 1 and poor in Ba, Sr, P, Ti, indicating typical high-K calc-alkaline granite in characteristics, and formed with magma mixing origin. Ma, belonging to Late Triass and Early Jurassic, indicating magma crystallization duration after mixing. The formation environment was ralated to the extension fuction after the continental collision between Siberia plate and North China plate.