论文部分内容阅读
龙王花岗岩岩体产于华北克拉通南缘,岩石类型主要为黑云母钾长花岗岩,局部见有霓辉石花岗岩。岩体高硅(SiO2=72.17%～76.82%)、富碱(K2O+Na2O=8.28%～10.22%,K2O/Na2O>1),碱性指数AI(agpaitic index)=0.84～0.95,分异指数DI=95～97,铝指数ASI(aluminium saturation index)=0.96～1.13。含铁指数高(FeO/(FeO+Mg)=0.90～0.99),岩石为准铝质至弱过铝质、碱性—碱钙性、铁质A型花岗岩。岩石富集大离子亲石元素,稀土元素含量很高(854～1572μg/g);高场强元素(Nb、Ta、Zr、Hf)的富集程度明显低于大离子亲石元素,因此在微量元素蛛网图上呈相对亏损特征;岩石显著亏损Ba、Sr、Ti、Pb;εNd(t)=-4.5～-7.2,Nd模式年龄为2.3～2.5Ga。εHf(t)=-1.11～-5.26,模式年龄tHf1=2.1～2.3Ga,tHf2=2.4～2.6Ga。黑云母钾长花岗岩中的锆石主要为无色透明柱状晶体,CL图像多数显示清晰的岩浆成因的韵律环带结构,锆石LA-ICPMSU-Pb年龄为(1602.1±6.6)Ma,MSWD=0.48。岩石化学、微量元素及Nd、Hf同位素地球化学特征表明,龙王岩体形成于板内伸展构造环境,其形成可能与约1.8Ga古大陆碰撞拼合之后岩石圈地幔及下地壳拆沉和玄武质岩浆底侵有关,岩体可能主要为富集地幔部分熔融的玄武质岩浆经强烈结晶分异的产物,在其形成和上升过程中可能有地壳物质的混染。龙王岩体的形成与Columbia超大陆裂解过程有关,是华北克拉通古元古代末-中元古代早期已知最年轻的非造山岩浆活动,可能代表华北克拉通古元古代末期自Columbia超大陆裂解出来的时间。
Longwang granite rock produced in the southern margin of North China Craton, the rock type is mainly biotite potassium long granite, locally see the Ni-hui granite. The contents of high silicon (SiO2 = 72.17% ~ 76.82%), alkali - rich (K2O + Na2O = 8.28% ~ 10.22%, K2O / Na2O> 1) DI = 95-97, aluminum index (ASI) = 0.96-1.13. The iron index is high (FeO / (FeO + Mg) = 0.90 ~ 0.99). The rocks are quasi-aluminum to weakly peraluminous, alkaline-alkali calcium and iron type A granites. The rocks are enriched in large ion lithophile elements with a high content of rare earth elements (854-1572 μg / g). The enrichment of high-field elements (Nb, Ta, Zr, Hf) Trace elemental cobweb maps showed relative depletion characteristics; rocks were significantly depleted in Ba, Sr, Ti, Pb; εNd (t) = -4.5 ~ -7.2, Nd mode age was 2.3 ~ 2.5Ga. εHf (t) = - 1.11 ~ -5.26, the model age tHf1 = 2.1 ~ 2.3Ga, tHf2 = 2.4 ~ 2.6Ga. The zircons in biotite k-long granites are mainly colorless and transparent columnar crystals. Most of the CL images show a clear magmatic causative ring structure. The zircon LA-ICPMSU-Pb ages are (1602.1 ± 6.6) Ma and MSWD = 0.48 . The petrochemistry, trace elements and Nd, Hf isotope geochemical characteristics show that the Longwang pluton was formed in an intraplate extensional tectonic setting and may form after lithospheric mantle and crustal delamination and basaltic magma Intrusion, the rock mass may be the product of strong crystallization differentiation of the basaltic magma partially enriched in the mantle, and there may be contamination of the crustal material during its formation and ascent. The formation of the Longwang pluton is related to the Columbia supercontinent pyrolysis process and is the youngest orogeny magma activity of the late Paleoproterozoic-Mesoproterozoic in the North China Craton. It may be representative of the Paleoproterozoic Paleocene from the Columbia supercontinent Out of time.