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对造山带中岩浆作用的研究可以为构造演化提供约束.兴蒙造山带中段乌兰敖包图一带出露一套早古生代早期的闪长质侵入岩(石英闪长岩和闪长岩),具有俯冲带型侵入岩的岩石组合和地球化学特征,标志着早古生代古亚洲洋的俯冲事件.通过锆石LA-MC-ICPMS U-Pb定年,在石英闪长岩和闪长岩中分别获得了474.0±1.8Ma和487.8±1.9Ma的年龄,属于晚寒武世-早奥陶世.锆石原位Hf同位素分析表明,乌兰敖包图侵入岩具有富集的Hf同位素组成,~(176) Hf/~(177) Hf范围为0.282 123~0.282 304,εHf(t)均为负值(两件样品的平均值分别为-10.84和-8.53),二阶段模式年龄为古元古代(范围为1 851~2 250Ma),表明这套侵入岩源于古元古代中期再循环地壳物质.岩石地球化学分析显示,石英闪长岩和闪长岩具有中等SiO_2含量(56.52%~66.06%),较高的Na_2O(2.60%~6.81%)、Al_2O_3(14.69%~18.35%)、CaO(0.57%~6.58%,平均值为3.97%)含量,低的K_2O(0.73%~2.94%)、TFeO、MgO含量,Na_2O/K_2O比值较高(0.92~5.66,平均值为3.19);微量元素具有Rb、Ba、Th、U、Sr、K等大离子亲石元素的富集以及Nb、Ta、P、Ti等高场强元素的亏损;稀土总量较低,轻稀土富集,具有较弱的Eu负异常(δEu范围为0.76~0.99).地球化学特征以及锆石Hf同位素组成表明,乌兰敖包图早古生代侵入岩在主动大陆边缘的构造背景之下,由古老地壳物质熔融形成的,代表了兴蒙造山带中段早古生代早期的俯冲事件,将兴蒙造山带中段早古生代北部岩浆岩带向东延伸,并且佐证了锡林浩特地区存在前寒武纪基底.
A study of magmatic activity in the orogenic belt can provide constraints for tectonic evolution: a set of dioritic intrusive rocks (quartz diorite and diorite) were exposed in the early stage of the Early Paleozoic in the Ulan Aobao map in the middle of the Xingmeng orogenic belt, The rock assemblages and geochemical characteristics of the subduction zone intrusive rocks indicate the subduction events of the Paleozoic Paleo-Asian Ocean. The zircon LA-MC-ICPMS U-Pb dating was obtained in quartz diorite and diorite respectively The ages of 474.0 ± 1.8Ma and 487.8 ± 1.9Ma belonged to the Late Cambrian to Early Ordovician.The in-situ Hf isotopic analysis of zircons showed that the intrusive rocks in the Wulan Ooobao map have enriched Hf isotopic composition, The Hf / ~ (177) Hf ranged from 0.282 123 to 0.282 304 and εHf (t) was negative (the average of the two samples was -10.84 and -8.53, respectively). The second-stage model was of Paleoproterozoic 1 851-2 250 Ma), indicating that the intrusive rocks originated from the recycle of crustal materials in the middle Paleoproterozoic. Geochemical analysis showed that quartz diorite and diorite have medium SiO 2 content (56.52% -66.06%) High content of K2O (2.60% ~ 6.81%), Al_2O_3 (14.69% ~ 18.35%), CaO (0.57% ~ 6.58%, average value of 3.97% 0.73% ~ 2.94%). The ratios of TFeO, MgO and Na2O / K2O were relatively high (0.92-5.66, average 3.19). Trace elements such as Rb, Ba, Th, U, Sr, Enrichment and depletion of high-field elements such as Nb, Ta, P and Ti; the total amount of rare earths is low and the light rare earths are enriched, with weaker Eu anomalies (δEu ranges from 0.76 to 0.99) .Geochemical characteristics and zirconium The Hf isotopic compositions of the rocks show that the Paleozoic intrusive rocks of the Wulan Ooobao Formation formed by the melting of the ancient crustal material under the tectonic setting of the active continental margin represent the early Paleozoic subduction events in the middle of the Xingmeng orogenic belt. The middle part of the Early Paleozoic northward magmatic belt extends eastward, and it proves the existence of Precambrian basement in Xilinhot area.