Abstract Characterizing island arc and back arc basin system through detailed magmatic profile remains a pivotal task in any regional paleotectonic and supercontinental reconstructions along ancient convergent plate margins, as is of paramount importance for the northern China–southern Mongolia (NCSM) tract along the eastern Central Asian Orogenic belt (CAOB). Here we document episodic Late Carboniferous intermediate to felsic intrusive suites in the West Ujimqin region of central Inner Mongolia, spanning from ca. 315 Ma granodiorites through ca. 310 Ma hornblende diorites to ca. 305–301 Ma diorites. The earlier granodiorites exhibit dominant magnesian-tholeiitic affinity, enrichment in large ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs), and possess whole-rock ISr(t) ratios of 0.707387–0.708799, negative ƐNd(t) of −2.3 to −2.4 and zircon ƐHf(t) values of −0.69 to +4.87 and δ18O of +6.33 to +8.40‰. These features are consistent with the magmatic derivation from dehydration melting of tholeiitic mafic to intermediate lower crustal underplates with obvious high δ18O supracrustal inputs. The ca. 310 Ma pod-like hornblende diorites display high-Ca boninite-like elemental traits and MORB-like isotopic compositions (ISr(t) = 0.704190 to 0.704203, ƐNd(t) = +7.9 to +8.3, zircon ƐHf(t) = +14.7 to +17.5 and δ18O = +4.88 to +6.16‰), indicative of a prior melt-depleted then fluid-enriched mantle source. By contrast, subsequent (301–305 Ma) diorites show arc-like elemental hallmarks, with notable enriched LILEs and depleted HFSEs as well as variable isotopic values (ISr(t) = 0.703690–0.704065, ƐNd(t) = +3.5 to +8.4, zircon ƐHf(t) = +7.10 to +16.4 and δ18O = +3.75 to +6.83‰). They are interpreted to represent the evolved products of hornblende-dominated fractional crystallization from depleted basaltic parental magmas. Given their coincidence with regional back-arc-basin type ophiolitic stratigraphy and detrital zircon age spectra, these intermediate to felsic intrusive suites tend to document the timeline of a back arc basin formation from initial rifting to maturation. In conjunction with Early Carboniferous forearc-type ophiolitic complexes and forearc magmatic records at West Ujimqin and the adjacent region, a Carboniferous island arc and back arc system can be reconstructed from Xilinhot to West Ujimqin. The characterization of this northward (present day coordinates) subduction system in terms of its temporal evolution not only provides overwhelming evidence that modern Pacific-like, archipelago-type arc configuration had prevailed in central Inner Mongolia during the Carboniferous, but also offers vivid insights into the diversity of crustal generation mechanism in a subduction factory that ushered in seminal continental crustal construction in the eastern CAOB.

中文翻译：

---

中亚造山带东部岛弧和弧后盆地系统的构建——从华北内蒙古中部晚石炭世中间侵入体对比看

摘要 通过详细的岩浆剖面表征岛弧和弧后盆地系统仍然是沿古代汇聚板块边缘的任何区域古构造和超大陆重建的关键任务，这对于沿中东部的华北-南蒙古（NCSM）域至关重要。亚洲造山带（CAOB）。在这里，我们记录了内蒙古中部西乌珠穆沁地区的晚石炭纪中期至长英质侵入岩套，从约 约 315 Ma 花岗闪长岩。约 310 Ma 角闪闪长岩 305-301 Ma闪长岩。较早的花岗闪长岩表现出显着的镁-拉斑亲和性，大离子亲石元素（LILEs）富集和高场强元素（HFSEs）耗尽，全岩ISr（t）比为0.707387-0.708799，负 ƐNd(t) 为 -2.3 至 -2.4，锆石 ƐHf(t) 值为 -0.69 至 +4.87，δ18O 值为 +6.33 至 +8.40‰。这些特征与拉斑基性镁铁质脱水熔融到具有明显高δ18O上地壳输入的中下地壳底板的岩浆推导一致。约。310 Ma 豆荚状角闪闪长岩显示出高Ca 钆岩样元素特征和MORB 样同位素组成（ISr(t) = 0.704190 to 0.704203, ƐNd(t) = +7.9 to +8.3, zircon ƐHf(t) = 14.7 至 +17.5 和 δ18O = +4.88 至 +6.16‰），表明先有熔体耗尽然后富含流体的地幔源。相比之下，随后的 (301–305 Ma) 闪长岩显示出弧状元素标志，具有显着的富集 LILE 和耗尽的 HFSE 以及可变同位素值（ISr(t) = 0.703690–0.704065，ƐNd(t) = +3.5 至 + 8.4，锆石 ƐHf(t) = +7.10 至 +16。4 和 δ18O = +3.75 至 +6.83‰)。它们被解释为代表角闪石占主导地位的从枯竭的玄武质母岩浆中分馏结晶的演化产物。鉴于它们与区域弧后盆地类型蛇绿岩地层和碎屑锆石年龄谱相吻合，这些中长英质侵入岩套倾向于记录弧后盆地形成从初始裂谷到成熟的时间线。结合西乌珠穆沁及邻近地区早石炭世前弧型蛇绿岩杂岩和弧前岩浆记录，可重建锡林浩特至西乌珠穆沁石炭世岛弧和后弧系统。这个向北（现代坐标）俯冲系统在时间演化方面的特征不仅提供了压倒性的证据，表明现代太平洋式，