崂山花岗岩岩石地球化学与成因

崂山花岗岩是中国东部晚中生代较典型的由钙碱性岩碱和碱性岩套构成的复合花岗岩体，可划分石英二长岩、黑云二长花岗岩、正长花岗岩和碱性花岗同夺四个单元，结晶年龄分别为１４６．８、１２６．２、１１３．０和１１０．８Ｍａ。岩石地球化学研究表明：钙碱性岩套自石英二长岩→黑云二长花岗岩→正长花岗岩 呈现向富硅、富碱、低铝、低钙、低镁方向的演化特征；碱性花岗岩总体呈现出高硅、高碱、低铝、低钙、低镁的特征，其大离子亲石元素和高场强元素Ga、Nb、Hf、Zr、Y及Ga／Al、F／Cl比值等明显偏高，与国内外典型的A型花岗岩成分相当。同位泰示踪及成岩机理研究揭示出崂山花岗岩起源于下地壳基底变质岩的部分熔融。两套岩石分别与两次熔融事件有关，钙碱性岩套各单元是岩浆不同分离结晶程度的产物，而碱性花岗岩可能起源于经先前熔融事件(形成钙碱性岩套)萃取过的残留源岩，其形成与AFC过程有关。基于一系列地球化学图解的判别，结合区域构造演化，指出崂山花岗岩是胶北地体－胶南地体陆－陆碰撞剪切造山带构造发展演化至特定阶段的产物，钙碱性岩套形成于造山晚期压性或压性向张性转化的应力环境，而碱性花岗岩则形成千造山期后的剪切张性(transtension)构造环境．后者成为苏北－胶南地区燕山晚期造山作用结束的标志。

THE GEOCHEMISTRY AND GENESIS OF THE LAOSHAN GRANITOIDS,SHANDONG PROVINCE

The Laoshan granitoids, distributed in the middle part of the Northern Jiangsu-Southeastern Shandong tectonic zone, is a typical Mesozoic granitic complex composed of calc-alkaline and peralkaline groups. The calc-alkaline group includes three units of ganitic rocks: quartz monzonitic granite, biotite monzonitic granite and syenogranite unit, while the peralkaline group comprises a series of alkaline or peralkaline granites characterized by occurrence of alkaline melanic minerals such as arfvedsonite and aegirine. The emplacement ages determinated by zircon U-Ph method of the four above units are 146.8, 126.2. 113.0 and 110.8Ma respectively. There exists evident evolutionary trend indicated by increasing Si, alkaline and decreasing Al, Ca, Mg from quartz monzonitic granite, biotite monzonitic granite to syenogranite unit in the calc-alkaline group, while the alkaline granite is generally of higher Si, alkaline and lower Al, Ca, Mg and especially rich in Ga, Nb, Hf, Zr, Y and of high F/Cl, Ga/Al ratio, similar to typical A-type granite in the world. Based on the data of Sr, Nd, Ph, O isotope and the study of rock-forming mechanism, the authors presented that both groups of the Laoshan granitoids were derived from the similar source of metamorphic rocks of the lower crust basement, the Jiaonan Group, but related to two different partial melting events. In the first event, the calc-alkaline magma was generated to form three units by different degrees of fractional crystallization, while the alkailine granite was possibly generated from the remelting of the “restite” in the second event and through AFC process. Based on the results from a series of geochemical diagram and the regional tectonic development, it is suggested that the Laoshan granitoids are the products of a special period of tectonic evolution in the continent-continent collision transpression orogenic zone between Jiaobei terrane and Jiaonan terrane, of which the talc-alkaline group was formed at the compressive environment transpreesion or the transitiona1 environment from transpression to transtension, while the alkaline granite was definitely formed at the tensional environment. The latter can be considered as a mark of the ending of Mesozoic orogenic movement in the eastern Shandong area.