Alkaline magmas play a key in understanding crust-mantle interaction and deep carbon recycling. Here, petrography and in situ mineral analyses of evolved alkaline rocks from the North China Craton are reported to decipher mantle metasomatism by recycled carbonated sediments via reconstruction of primary magma composition. The alkaline rocks are nepheline syenites for which new, consistent zircon and titanite UPb ages of ~235 Ma are presented. The rocks are highly evolved (SiO₂ = 58.1–60.0 wt%) with negative anomalies for Sr, Ba, Ti, P and Eu, and relative depletion of MREE, indicating fractional crystallization of feldspar, apatite, titanite and amphibole. Core-rim variation of ⁸⁷Sr/⁸⁶Sr (0.7052–0.7092) of late-crystallized low Mg# clinopyroxene and feldspar are attributed to crustal assimilation.

The origin of primary alkaline magma is recorded in early high Mg# (70–84) clinopyroxenes with weak Eu anomalies (Eu/Eu* = 0.94–1.29), suggesting that they crystallized from a little-differentiated mantle-derived magma (Mg# > 60). Their variable ⁸⁷Sr/⁸⁶Sr ratios (0.7031–0.7060) correlate positively with Sr/Y and (La/Yb)_N and negatively with Ti/Eu ratios, but are not correlated with Mg# or Eu/Eu*. Moreover, the REE patterns of melt equilibrated with high ⁸⁷Sr/⁸⁶Sr clinopyroxene is similar to coeval alkaline rocks from adjacent areas. These features indicate that the primary alkaline magma was derived from the mixing of depleted mantle and enriched mantle metasomatized by carbonatite melts from subducted crustal materials. Low zircon ε_Hf(t) values (−1.4 to −2.8) imply that the subducted crustal material was carbonated sediments. Calcite and CO₂ inclusions occur in early-crystallized olivine, clinopyroxene and zircon, and amphibole and fluorapatite both reveal a volatile-rich (H₂O, F and CO₂) alkaline magma derived from mantle enriched by carbonate metasomatism. The mineral archives of alkaline rocks not only record mantle metasomatism by recycled carbonated sediments, but also fractional crystallization and assimilation during magma evolution.

碱性岩浆在理解地幔幔相互作用和深层碳循环中起着关键作用。在这里，据报道，华北克拉通演化出的碱性岩石的岩石学和原位矿物分析通过重建原生岩浆成分，通过回收的碳酸盐沉积物来解释地幔交代作用。碱性岩石是霞石正长岩，其新的，一致的锆石和钛铁矿的U Pb年龄约为235 Ma。岩石高度演化（SiO ₂  = 58.1–60.0 wt％），Sr，Ba，Ti，P和Eu呈负异常，MREE相对耗竭，表明长石，磷灰石，钛矿和闪石的分步结晶。核心边缘变化为⁸⁷ Sr / ⁸⁶后期结晶的低Mg＃斜向辉石和长石的Sr（0.7052–0.7092）归因于地壳的同化作用。

原始碱性岩浆的起源记录在早期的高Mg＃（70-84）斜向辉岩中，且Eu异常弱（Eu / Eu * = 0.94-1.29），表明它们是从少量分化的地幔衍生岩浆中结晶的（Mg＃ > 60）。它们的可变的⁸⁷ Sr / ⁸⁶ Sr比（0.7031-0.7060）与Sr / Y和（La / Yb）_N正相关，与Ti / Eu比负相关，但与Mg＃或Eu / Eu *不相关。此外，高⁸⁷ Sr / ⁸⁶的熔体的REE模式平衡Sr clinopyroxene与来自邻近地区的同时期碱性岩石相似。这些特征表明，主要的碱性岩浆是由俯冲的地壳物质中的碳酸盐熔岩交代的贫化地幔和富集地幔混合而成的。较低的锆石_εHf（t）值（-1.4至-2.8）表示俯冲的地壳物质是碳酸盐沉积物。方解石和CO ₂夹杂物存在于早结晶的橄榄石，斜辉石和锆石中，而闪石和氟磷灰石都显示出富挥发分（H ₂ O，F和CO ₂）源自岩浆的碳酸盐交代作用富集的碱性岩浆。碱性岩石的矿物档案不仅记录了再循环的碳酸盐沉积物的地幔交代作用，而且还记录了岩浆演化过程中的部分结晶和同化作用。