地质论评2019，Vol.65Issue(1)：119-149,31.DOI:10.16509/j.georeview.2019.01.009
内蒙古克什克腾旗大石寨组凝灰岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及其构造意义
LA-ICP-MS Zircon U-Pb Ages, Geochemical Characteristics of the Dashizhai Formation Tuffs in Hexigten Banner, Inner Mongolia and Thier Tectonic Significance
摘要
Abstract
In this essay, we studied the Dashizhai Formation andesitic debris crystal tuffs developed in Changlingzi area, Hexigten Banner, Inner Mongolia, in such aspects as LA-ICP-MS zircon U-Pb isotopic geochronology, Hf isotopic composition analysis and geochemistry.Detrital zircon grains from the Dashizhai Formation tuffs yield seven U-Pb age clusters of 3140～2826 Ma, 2761～2273 Ma, 2025～1673 Ma, 1036～673 Ma, 574～422 Ma, 392～312 Ma and 224～133 Ma.Meanwhile, in situ zircon Hf isotopic analysis yieldεHf (t) values between-18.0 and 16.8, n (176Lu) /n (177Hf) and n (176Hf) /n (177Hf) ratios are 0.000235～0.005759 and 0.280524～0.283022 respectively, and two-stage model ages are 4291～293 Ma.The first group of zircons (3140～2826 Ma) revealed the information of the ancient basements (Mesoarchean to Paleoarchean) in Northeast China;the second group (2761～2273 Ma) recorded the geological event of Kenorland supercontinent convergence, and revealed the information of Archean to Paleoproterozoic ancient basement in Great Hinggan Mountains (Da Xing'an Range) area;the third group (2025～1673 Ma) corresponed to the geological event of Columbia supercontinent formation;the forth and the fifth groups of zircons (1036～673 Ma, 574～422 Ma) may originate from the Northeast China, and these two age groups corresponded to two key tectonic events of the Gondwana and Rodinia episodes, respectively;the peak value of the sixth age cluster (392～312 Ma) is 350 Ma and its weighted mean age is 350.0±6.5 Ma (MSWD=4.0, n=43) , which can be identified as the protolith age of the Dashizhai Formation;the fifth cluster (224～133 Ma) may be related to fluid reformation.Whole-rock major, trace and rare earth elements analyses show that most samples exhibit metaluminous (A/CNK=0.65～1.95) and sub-alkaline (δ=0.88～2.50) characteristics.In the Chondrite-normalized REE patterns, the tuffs show slightly enriched in LREE, depleted in HREE, with no obvious Eu anomalies.In the spider diagram, they show enrichment in large ion lithophile elements (Ba, Rb and K) , and depletion in high field-strengh elements (Nb, Ta, Ti and P) .As shown above, the Dashizhai Formation tuffs exhibited an affinity with Andean active continental margin volcanic rocks.Combined with previous published regional geological data, we concluded that the Dashizhai Formaiton andesitic debris crystal tuffs in Hexigten Banner were formed by the fluids, which derived from dehydration of oceanic crust during the subduction of the Paleo-Asian Ocean, interacting with the overlying mantle wedge.And the tectonic environment for the formation of the tuffs was active continental marginal arc, indicating that the Paleo-Asian Ocean wasn't closed in Early Carboniferous.关键词
克什克腾旗/大石寨组/年代学/岩石地球化学/古亚洲洋Key words
Hexigten Banner (Keshiketeng county)/Dashizhai Formation/geochronology/petrogeochemistry/Paleo-Asian Ocean引用本文复制引用
许强伟,王玭,王志强,王成明,郑义,方京..内蒙古克什克腾旗大石寨组凝灰岩锆石LA-ICP-MS U-Pb年龄、地球化学特征及其构造意义[J].地质论评,2019,65(1):119-149,31.基金项目
国家自然科学基金青年基金资助项目(编号:41602065) （编号:41602065）
克什克腾旗金达矿业开发有限责任公司项目(编号:20150008)的成果 （编号:20150008）
