黑龙江伊春红星地区碱性花岗岩的地球化学及其构造指示意义

黑龙江省伊春红星地区大地构造上位于布列亚-佳木斯地块和张广才岭造山带结合部位，区内出露晚三叠世碱性花岗岩，其岩石组合为正长花岗岩、碱长花岗岩、含钠闪石、霓石碱性花岗岩。地球化学上，该套岩石具有富硅、富碱，铁镁比值较高，CaO、MgO含量低，富含F、Zr、Nb、Ce、Ga、稀土元素（REE）、Y和Zn等元素，贫Sr、P、Ti，镓铝比值高，轻重稀土分馏显著，具有强的Eu负异常等特点。在花岗岩成因类型判别图解中，它们均投影在A型花岗岩区，结合岩石具有过碱和相对贫铝的化学组成特征，表明它们应属过碱性A型花岗岩。在微量元素蛛网图上，这套岩石表现出较明显的Ba、Sr、P、Ti的负异常，保留有先期“弧”岩浆作用的地球化学印记，其Y／Nb和Y／Ta比值也较高，分别为1．55—3.27和13．5～44．00，在A型花岗岩岩石学亚类判别图解中，它们均投影在产于后造山环境的A2花岗岩区。根据对岩石地球化学的组成及产出地质背景的分析，表明这套岩石应形成于造山期后的张性构造环境。

Gelchemical Characteristics and Tectonic Significance of Alkali-Granites in Hongxing Area, Yichun, Heilongjiang Province

Hongxing area which is locating in Yichun, southeast Heilongjiang province, is geologically at the binding site of Bulieya -Jiamusi block and Zhangguangcailing orogenic belt. The late Triassic alkali - granite of this area is composing of syenogranite, alkali - feldspar granite and sodium - amphibole and aegirine bearing alkali - granite. In terms of geochemistry, those alkali - granites are rich in silicon and alkali, and poor in CaO and MgO, with high iron to magnesium ratios; rich in F, Zr, Nb, Ce, Ga, rare earth elements （REE）, Y, Zn, and poor in Sr, P, Ti, with high gallium to aluminum ratio, obviously fractionated light REE to heavy REE and intensive Eu negative anomaly. In the discriminate diagram for genesis of granites, those rocks are all fall in the A - type granite area, and combined with the rich in alkali and poor in alu- minum characters, indicating they should belong to ultra - alkali A - type granite. On the trace elements spider diagram, those rocks have got obviously negative anomalies of Ba, Sr, P and Ti, reserving arc magma geochemical affinity, with high Y/Nb and Y/Ta ratios （ 1.55 - 3.27 and 13.5 -44.00, respectively）. In the sub -category diagram for A -type granite rocks, those rocks fall in A2 granite area. All the above geochemical evidence indicated that those alkali -granites are formed in the post -orogenic extensional tectonic setting.