北阿尔金巴什考供盆地南缘花岗杂岩体特征及锆石SHRIMP定年  

Characteristics of the granitoid complex and its zircon SHRIMP dating at the south margin of the Bashikaogong Basin, North Altun, NW China.

作　　者：吴才来[1] 杨经绥[1] 姚尚志[2] 曾令森[1] 陈松永[1] 李海兵[1] 戚学祥[1] Wooden J L Mazdab F K 

机构地区：[1]中国地质科学院地质所,北京100037 [2]安徽省地质调查院,合肥230001 [3]斯坦福大学

出　　处：《岩石学报》2005年第3期846-858,共13页Acta Petrologica Sinica

基　　金：本文得到国家自然科学基金项目(40472034)国家重点自然科学基金项目(49732070)国家973项目(G1998040800)国土资源部"十五"重点科技项目(20010101)国家地质调查项目(DKD2001003)的资助

摘　　要：北阿尔金巴什考供盆地南缘花岗杂岩体呈近东西向分布,长约49公里,出露面积约90平方公里,与围岩之间为明显的侵入接触关系,接触界线为不规则的渡状、锯齿状。围岩为前寒武纪砂岩、片岩、泥岩及凝灰质砂岩。该杂岩体主要由巨斑花岗岩、红色花岗岩、灰白色似斑状花岗岩和粉红色似斑状花岗岩组成。杂岩体的主元素含量变化不大,SiO2为65．14％- 75．66％,全碱含量为7．49-8．96％,K2O／Na2O比值为1．12-2．68,岩石的里特曼指数平均为2．34,CIPW标准矿物计算均出现刚玉(AC)(平均为1．78),说明岩石铝过饱和;杂岩体的稀土总量变化于89．44×10-6-335．28×10-6之间,不同岩石类型均有负铕异常,且从巨斑花岗岩→灰白色似斑状花岗岩→红色似斑状花岗岩→红色花岗岩,负铕异常越来越明显,表现在Eu／ Eu+值由0．65→0．51→0．48→0．30。在微量元素蛛网图上,所有样品的微量元素丰度均高于原始地幔值,并具有相似的配分模式,即在Ba、Nb、Sr、P、Ti处呈明显的低谷,显示出S型花岗岩的特征。锆石SHRIMP U-Pb定年得出,巨斑花岗岩、红色中细粒花岗岩、灰白色和粉红色似斑状花岗岩的年龄分别为474．3±6．8Ma、446．6±5．2Ma、434．5±3．8Ma和431．1±3．8Ma。结合区域地质特征,我们认为,该杂岩体形成于同碰撞-碰撞后的构造环境。The 49 km long, E-W trending granitic belt with an area of -90 km^2 at the south margin of the Bashikaogong Basin intruded into the Precambrian sandstones, schists, mudstones and tufts. Field observations show that it consists of four types of granites, e. g. , gigantic phenoeryst granites （Ⅰ） , fine to intermediate grained red granites （Ⅱ） , intermediate to coarse grained porphyritic grey granites （Ⅲ） , and intermediate to coarse grained porphyritic pink granites （Ⅳ）. Petrochemically, these granites are peraluminous in that they have （ 1 ） contents of SiO2 and alkaline （ Na2O ＋ K2 O） ranging from 65.14% to 75.66% , and from 7.49%to 8.96%, respectively; （2） K2O/Na2O ratios ranging from 1.12 to 2.68 ; （3） Rittmann index from 1.83 to 2.81, with an average of 2.34; and （4） corundum （AC） （0.77 -3.93% , and average 1.78 ） CIPW normative. These granites have total REE contents of 89.44 -335.28 × 10^-6, and substantial negative Eu anomalies. From type Ⅰ through Ⅲ and Ⅳ to Ⅱ granites, Eu/Eu＊ ratios decrease from 0.65 over 0.51 and 0.48 to 0.30. Trace element compositional data show that （ 1 ） these granites have pronounced negative Ba,Nb, Sr, P and Ti anomalies; （2） their trace element abundances decrease, but the magnitude of Ba, Nb, Sr, P and Ti anomalies increase from type Ⅰ through Ⅲ and Ⅳ to Ⅱ granites. Major element and trace element data indicate that they have an S-type granite affinity. Zircons separated from these four types of granites were used to perform SHRIMP U-Pb zircon dating to constrain their formation ages. Dating results show that their formation ages are 474.3 ±6.8Ma for type Ⅰ granite, 446.6±5.2Ma for type Ⅱ granite,434.5 ± 3.8Ma for type Ⅲ, and 431.1 ± 3.8Ma for type Ⅳ granite, respectively. Combined with field observational data, these data suggest that these granites were derived from partial melting of crustal materials during syn-collision and post collision events between Ahun and Tarim continental bl

关 键 词：花岗岩 锆石SHRIMP定年 巴什考供盆地 北阿尔金 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]