山西吕梁山中段元古代花岗质岩浆活动和变质作用

对吕梁山中段花岗质岩石的年代学和地球化学研究表明，研究区存在两期古元古代花岗质岩浆活动，分别形成于2063Ma和1806Ma；它们具有不同的地球化学特征：早期石英二长岩具有埃达克质岩浆特点，低SiO2，MgO，Y和Yb，高Al2O3，Na2O，Sr，Ba和Sr／Y比值，没有明显的Eu异常；后期二长花岗岩则具高SiO2，Rb，Nb，Y，Yb和低Na20，Al2O3，Sr的特点，并具低的Sr／Y比值和明显的Eu负异常。结合同位素特征，道仁沟石英二长岩被解释为古老的地壳物质在地幔深部发生部分熔融形成，并与地幔围岩发生了物质交换。而宽坪花岗岩则由石榴子石麻粒岩在地壳深度分解熔融产生。岩石学和地球化学特征显示它们分别形成于同碰撞和造山后两种不同的构造背景。吕梁群主变质作用与第二期花岗质岩浆活动几乎同时发生，它们具有等温降压的顺时针PTt轨迹，表明它们经历了快速抬升的变质过程。这一期花岗质岩浆活动和变质作用与华北地块许多岩浆活动和变质作用同时发生，暗示从这个时间开始华北地块处于拉张构造背景。

Paleoproterozoic Granitic Magmatism and Metamorphism in Middle Part of Luliang Range,Shanxi Province

The studies on geochronology and geochemistry of granitoid rocks in Middle Laliang Mountain，Shanxi Province indicate that there are two periods of granitic magmatism in Paleoproterozoic，occurring at ca．2 063 Ma and 1 806 Ma，respectively．The earlier adamellites are characterized by low Si02，MgO，Y and Yb concentration，high AI203，Na20，Sr，Ba concentration and high Sr／Y ratio．The later monzonitic granites are characterized by high Si02,Rb,Nb，Y and Yb concentration，low Na20,AL2O3，Sr concentration and low Sr／Y ratio．The later also exhibit lower(La／Yb)n ratio and markedly negative Eu anomalies，implying their different origins．Combined with the Sr-Nd isotopic characteristics，the Daorengou adamelites are interpreted as resulting from partial melting of Paleo-to Meso-Archean crustal materials within mantle depth，and interacting with mantle wall rocks．The Kuanping granites were produced by partial melting of the garnet granulite and decomposing of garnets in the lower crust．Geological and geochemical evidences indicate that these two periods of magmatism took place in different tectonic settings．The early adamellites were related with collision setting，and the later monzonitic granites were formed in post-orogenic setting．T-P estimates for middle-high-grade metamorphic rocks of Laliang Group indicatethat the Laliang Group experienced isothermal decompression(ITD)metamorphism with clockwise FFt paths at near same time as second granitic magmatism，indicating a rapid ascending process．The later post-orogenic granite and the metamorphism with ITD path occurred at about 1 800 Ma，when magmatism and middle-high-grade metamorphism were widespread and strong in whole North China，implying that the North China Block was in extension tectonic setting from then．