摘要
库车河流域小提坎里克组火山岩主要为一套流纹岩建造,富碱(Na_2O+K_2O=6.89~8.46%)、高钾(K_2O/Na_2O=1.6~2.1)、铝含量12.83~14.78%(平均为14.18%),低钙(1.06~2.51%,平均为1.50%)、低镁(MgO=0.27~0.44%,平均为0.37%),Fe_2O_3~*=1.29%~2.68%(平均为2.17%)。其铝饱和指数A/CNK为0.98~1.15,为过铝质高钾钙碱性—钾玄质花岗岩类。流纹岩的轻稀土强烈富集,重稀土亏损,明显富集Rb、Th、U、K、Pb等大离子亲石元素,亏损Sr、Nb、Ta、P、Ti等元素,具明显的铕负异常(δEu为0.46~0.54)。主微量元素特征显示其壳源成因,原岩为变质杂砂岩,源区有石榴石、角闪石、斜长石的残留。对两个流纹岩样品中的锆石进行LA-ICP-MS U-Pb年龄测定,获得288.3 Ma和290.3 Ma的形成年龄,与西部温宿和拜城地区的小提坎里克组火山岩为同期火山活动产物。该套火山岩具有同碰撞过铝质S型花岗岩特征,结合区域上广泛分布的二叠纪后造山花岗岩,认为西南天山洋至少在早二叠世已经闭合。
There are debates on the tectonic setting of the acid volcanic rocks of Xiaotikanlike Formation exposed along Kuqa River in Southwest Tianshan, and precise U-Pb ages of these rocks have not been reported yet. 7 geochemical samples and 2 samples for zircon U-Pb dating from this volcanic suit are analyzed. Geochemical data indicate that the Xiaotikanlike Formation volcanic rocks are mainly rhyolites. They are characterized by high alkali( Na20+K20 = 6.89% - 8.46% ) , potassium ( K^O/Na20 = 1.6 - 2. 1 ) and A1203 ( 12.83%~ 14.78% ) content, while low CaO ( 1.06%- 2.51% ) , MgO ( 0.27%- 0.44% ) and Fe203 ( 1.29%- 2.68 % ) eontent. They are strongly enriched in LREE and depleted in HREE,and have medium negative Eu anomaly (SEu = 0.46- 0.54) in the chondrite-normalized REE-patterns diagram. They are also enriched in LILE elements like Rb, Th, U, K, Pb, and depleted in Sr, Nb, Ta, P and Ti. Based on the geochemical features and CaO/Na20, (La/Yb)N ratios, we suggest that the rhyolites were derived from partial melting of metagreywackes. The residual minerals were with garnet, hornblende and plagioclase. In situ U-Pb LA-ICP-MS dating on magmatic zircons from the two samples yield ages of 288.3 Ma and 290.3 Ma respectively. Integrating previous studies, especially the extensive distributed post-orogenic granites of Permian in southwest Tianshan,we conelude that the Xiaotikanlike Formation volcanic rocks have the features of peraluminous S-type granite formed in a syn-collisional setting, and we believe that the southwest Tianshan Ocean has been closed at least in Early Permian.
出处
《地质科学》
CAS
CSCD
北大核心
2014年第1期242-258,共17页
Chinese Journal of Geology(Scientia Geologica Sinica)
基金
中国地质调查项目(编号:12120113096500,12120113094000,1212011120135)
石油重大专项(编号:2011ZX05029001-002)资助
关键词
锆石U-Pb年代学
地球化学
小提坎里克组
火山岩
南天山
Zircon U-Pb geochronology, Geochemistry, Xiaotikanlike Formation,Volcanic rocks,South Tianshan