The North Qilian orogenic belt (NQOB) has been defined as a subduction-collision zone between the Alxa Block and the Qilian Block during the Early Paleozoic. To constrain the post-collisional tectonic evolution of the NQOB, analyses of zircon U-Pb-Hf isotopes, whole-rock major, trace element and Sr-Nd-Pb isotope compositions of the newly discovered Early Devonian lamprophyres and diorites dikes from the Longshoushan area in southwestern margin of the Alxa Block were conducted. Zircon U-Pb dating yields emplacement ages of 400 ± 4 Ma and 403 ± 6 Ma for two lamprophyre dikes and 391 ± 3 Ma for two diorite dikes. The lamprophyres dikes are shoshonitic-high-K (calc-alkaline) in nature, and are characterized by SiO₂ contents of 53.6–56.3 wt %, (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7064 to 0.7072, εNd(t) values of 0.1–1.0, and zircon εHf(t) values of −8.0 to −2.9. The diorite dikes are high-K (calc-alkaline), and are characterized by MgO contents of 6.32–6.98 wt %, (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7089–0.7137, εNd(t) values of −3.8 to −3.5, and zircon εHf(t) values of −9.9–0.4. Both the lamprophyre and diorite dikes show parallel enrichments in LREEs and LILEs and depletions in HREEs and HFSEs and have similar ratios of (²⁰⁶Pb/²⁰⁴Pb)_i (17.587–18.133), (²⁰⁷Pb/²⁰⁴Pb)_i (15.518–15.584) and (²⁰⁸Pb/²⁰⁴Pb)_i (37.676–38.058). Geochemical and isotopic data suggest that the lamprophyre and diorite dikes were derived from low-degrees melts of amphibole- and phlogopite-bearing lherzolite and phlogopite-bearing lherzolite, respectively, in the spinel-garnet transition facies. Their parental magmas both experienced extensive fractional crystallization in a deep magma chamber and negligible crustal contamination during their ascent. Regarding the Palaeozoic tectonic development of the North Qilian orogenic belt, we propose that the Early Devonian lamprophyres and diorites possibly are related to North Qilian orogen unrooting and collapse and marking the end of the North Qilian orogenic events.

北祁连造山带（NQOB）被定义为早古生代Alxa区块与Qilian区块之间的俯冲碰撞带。为了限制NQOB碰撞后的构造演化，对龙首山早期泥盆纪的煌斑岩和闪长岩脉的锆石U-Pb-Hf同位素，全岩主，微量元素和Sr-Nd-Pb同位素组成进行了分析。进行了阿拉善区块西南边缘的区域。锆石U-Pb测年的两个年龄斑岩堤的定位年龄分别为400±4 Ma和403±6 Ma，两个闪长岩堤的定位年龄为391±3 Ma。煌斑岩堤防本质上是含钾高钾（钙碱性），其SiO ₂含量为53.6–56.3 wt％，（⁸⁷ Sr / ⁸⁶ Sr）_i比值为0.7064至0.7072，εNd（t）值为0.1-1.0，锆石εHf（t）值为-8.0至-2.9。闪长岩堤是高K（碱性钙），其特征在于MgO含量为6.32–6.98 wt％，（⁸⁷ Sr / ⁸⁶ Sr）_i之比为0.7089–0.7137，εNd（t）值为-3.8至- 3.5，锆石εHf（t）值为-9.9-0.4。煌斑岩和闪长岩堤在LREE和LILE中都表现出平行的富集，在HREE和HFSE中则表现出损耗，并且具有相似的比率（（²⁰⁶ Pb / ²⁰⁴ Pb）_i（17.587–18.133），（²⁰⁷ Pb / ²⁰⁴ Pb）_i（15.518–15.584） ）和（²⁰⁸ Pb / ²⁰⁴ Pb）_i（37.676–38.058）。地球化学和同位素数据表明，煌斑岩和闪长岩堤坝分别来自尖晶石-石榴石过渡相中含角闪石和金云母的锂铁矿和含金云母的锂铁矿的低度熔融。他们的父母岩浆在深部岩浆室内均经历了广泛的分步结晶，并且在上升过程中地壳污染可忽略不计。关于北祁连造山带的古生代构造发育，我们认为泥盆纪早期的煌斑岩和闪长岩可能与北祁连造山带的解脱和塌陷有关，并标志着北祁连造山事件的结束。