华北克拉通基性岩墙成因模式:来自锆石U-Pb年龄、地球化学和Sr-Nd-Pb同位素证据（英文）

Zircon U-Pb age,geochemical and Sr-Nd-Pb isotopic data:Constraints on the genetic model of the mafic dykes from the North China Craton

本研究共涉及来自太行山和郯庐断裂岩浆带的12组基性岩墙群,岩墙群具体出露于河北省、山西省、山东省和安徽省。研究中给出了新的锆石LA-ICP-MS U-Pb年龄、地球化学和Sr-Nd-Pb同位素基性岩墙测试数据。基性岩墙形成于128.1±1.2Ma与115.0±0.8Ma之间,且具有典型的辉绿结构。另外,基性岩墙富集轻稀土元素(LREE)、个别大离子亲石元素(如,Rb、Ba、Sr)、Pb和Th,亏损Nb、Ta和Ti,具有高的初始87Sr/86Sr比值(0.7056~0.7105),负的εNd(t)(-15.5^-12.4)、相对一致的初始Pb同位素比值(206Pb/204Pb=16.45~16.49、207Pb/204Pb=15.44~15.51、208Pb/204Pb=36.49~36.53)及较大的Nd模式年龄(tNd DM2=1.82~2.69Ga)。研究结果表明,基性岩墙来自石榴石二辉橄榄岩地幔源区(类似EM1)一定程度的(1.0%~5.0%)部分熔融,岩浆侵位前经历了橄榄石、单斜辉石和角闪石的分离结晶作用,同时受到少量地壳混染的影响。目前,关于华北克拉通破坏和中生代岩浆作用的成因已有较多可能模式,本研究基性岩墙成因的新模式:古太平洋板块与华北克拉通的持续碰撞,导致华北克拉通岩石圈(地幔和地壳)加厚,并发生可能的榴辉岩化,并在一定时间发生拆沉作用。在新模式的制约下,导致了研究区中生代基性岩墙的产生和侵位。

Twelve mafic dyke swarms crop out in Hebei, Shanxi, Shandong, and Anhui provinces within the Taihang-Da Hinggan Mountains and Tan-Lu （Tan-Lu） magmatie belts, China. Here, we present new zircon LA-ICP-MS U-Pb age, geochemical, and Sr- Nd-Pb isotopic data for these dykes. The dykes formed between 128.1 ± 1.2Ma and 115.0 ± 0. 8Ma, and have typical doleritic textures. They are enriched in the light rare earth elements, some large ion lithophile elements （LILE; e. g. , Rb, Ba, and Sr） , Pb, and Th, and are depleted in Nb, Ta and Ti. The dykes have high initial 87SrJ86Sr ratios （0. 7056 -0. 7105）, negative εNd（t） values （ -- 15. 5 to -- 12. 4）, relatively constant initial Pb isotopic ratios （ 16.45 - 16. 49, 15.44 - 15.51, and 36. 49 - 36. 53 for 206pb/ 204pb, 207 pb/204pb, and 208 pb/204pb, respectively）, and relatively old Nd model ages （tDM2^Nd = 1. 82 - 2. 69Ga）. These results indicate that the dykes were derived from magmas generated by a certain extent partial melting （ 1.0% - 5.0% ） of an EMl-like garnet- lherzolite mantle source. These magmas fractionated olivine, clinopyroxene, and hornblende prior to emplacement, and assimilated minimal amounts of crustal material. Several possible models have been proposed to explain the destruction of the North China Craton （NCC） and the origin of Mesozoic magmatism. Here we propose a new model for the origin of these dykes, involving the foundering of eclogite from thickened lower crust and ongoing collision between the Paleo-Pacific Plate and the NCC.