苏鲁造山带大规模岩浆活动的证据:新元古代多成因花岗质片麻岩

花岗质片麻岩是苏鲁超高压变质带中分布最为广泛的岩石单元,其岩石形成于新元古代。苏鲁超高压变质带中段——山东胶—莒南地区的花岗质片麻岩主要由以细粒白云母二长花岗质片麻岩为代表的荣成片麻岩套、以粗粒含角闪二长花岗质片麻岩为代表的月季山片麻岩套和以含霓石碱长花岗质片麻岩为代表的岚山头片麻岩套等组成。花岗片麻岩主体属于高K钙碱性系列。相比而言,荣成片麻岩套碱质较低、贫钠,月季山片麻岩套相对富碱质、富钠、富铁镁、低硅,岚山头片麻岩套则富硅钾、贫铝铁镁。荣成岩套具有S型花岗岩的特点,月季山岩套具有I型花岗岩的特点,岚山头岩套具有A型花岗岩的特点。苏鲁超高压变质带新元古代花岗质片麻岩构成了较完整的碰撞造山型花岗岩系列:陆陆碰撞主造山期,形成同碰撞双花岗岩,其中荣成岩套形成时间略早,深俯冲到地幔中遭受了超高压变质作用,而月季山岩套是在超高压岩片快速折返过程中形成的;碰撞造山后期地壳伸展,形成岚山头片麻岩套。

DIVERSIFIED ORIGIN GRANITIC GNEISS IN THE SULU ULTRA-HIGH PRESSURE METAMORPHIC BELT:EVIDENCE FOR NEOPROTEROZOIC LARGE SCALE MAGMATISM

Granitic gneiss is the most extensive geologic unit in the Sulu ultra-high pressure metamorphic belt and the age of protoliths of granitic gneiss is Neoproterozoic era.The granitic gneiss in Jiaoan-Junan area of Shandong province consist of Rongcheng gneiss SUIT,Yuejishan gneiss suit and Lanshantou gneiss SUIT.Representative rocks of the three gneiss SUIT respectively are fine muscovite-bearing monzogranitic gneiss,coarse hornblende-bearing monzogranitic gneiss and aegirite-bearing alkali feldspar granitic gneiss.Chemical compositions of the granitic shows that it gneiss belongs to high-K calcalkaline series.Comparatively,alkali and Na content of Rongcheng gneiss suit is low,alkali and femic content of Yuejishan gneiss SUIT is high with low Si,whereas Si and K content of Lanshantou gneiss SUIT is high with low Al and femic.The three gneiss SUITS belong to S-type granite,I-type granite and A-type granite respectively.The Neoproterozoic granitic gneiss in the Sulu ultra-high pressure metamorphic belt are continent collision granite series.Syn-collision I-type and S-type granite formed at main orogenic phase.Because the formation of Rongcheng gneiss suit is relatively ealier,so the deep subduction into mantle leads to ultra-high pressure metamorphism.While Yuejishan gneiss suit formed at the phase of ultra-high pressure metamorphic terrane during fast upwelling.Lanshantou gneiss suit formed under the crust extensional environment at post collision setting.