We present new data on crystallized micro-inclusions in zircon from clinopyroxene-bearing felsic stringers within gabbronorite of gabbro-peridotite oceanic core complex at Mid-Atlantic Ridge, 13°34′ N. A relatively large (about 49 × 22 μm) crystallized inclusion exposed in situ in thin section consists of the muscovite + biotite + plagioclase + K-feldspar + quartz assemblage. Smaller inclusions (≤20 μm) found in zircon separates consist of silicate minerals, interstitial water solution, and gas bubbles. At temperature close to 800 °C and estimated pressure about 1.5 kbar the inclusions completely homogenize into a KO-rich (3.9 ± 0.1 wt%), HO-bearing (about 4 wt%) granite (SiO 70 ± 2 wt%) melt. Calculations employed DOMINO software show that complete closed-system crystallization of the analyzed melt exactly reproduces mineral assemblage of the large crystallized inclusion (+HO) at about 1.5 kbar below 600 °C. Granitoid mineralogy of felsic stringers hosting zircon does not correspond to that of the crystallized melt inclusions, with a significantly lower KO in the former. The KO loss might result from interaction of the melt with pyroxenes of the host gabbro. This implies that considering felsic granitoid veins, often present in the oceanic lower crustal sections, as simply “frozen melt” is not always justified. Compositional variations of basalt lava glasses from the 13°25′–14° portion of the Mid-Atlantic Ridge show continuous geochemical trends from -MORB to -MORB with KO enrichment up to 0.9 wt%, suggesting mixing from two sources. The most KO-enriched -MORB composition (KO = 0.9 wt%, HO = 0.7 wt%, KO/TiO = 0.42, (La/Sm) = 2.45) was assumed as a source of the granitoid inclusions. Computer simulation of equilibrium crystallization of this -MORB composition returned a granite residual melt closely matching the average composition of the zircon-hosted melt inclusions at 820 °C, 1.5 kbar and melt fraction 5.2 vol%. The result suggests a direct link between the -MORB magma occurring in the studied area, and the origin of the K-rich granite melt in zircon-hosted inclusions.

中文翻译：

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位于北纬 13°34′ 的大西洋中脊，来自辉长岩长英质纵梁的锆石中富含钾的花岗岩熔融包裹体：E-MORB 连接

我们提出了关于来自北纬 13°34′ 大西洋中脊的辉长橄榄岩洋核杂岩辉长岩内含单斜辉石长英质纵梁的锆石中结晶微包裹体的新数据。相对较大（约 49 × 22 μm）的结晶包裹体原位暴露的薄片由白云母+黑云母+斜长石+钾长石+石英组合组成。锆石分离物中发现的较小包裹体（≤20 μm）由硅酸盐矿物、间隙水溶液和气泡组成。在接近 800 °C 的温度和约 1.5 kbar 的估计压力下，包裹体完全均质化为富含 KO (3.9 ± 0.1 wt%)、含 H2O (约 4 wt%) 花岗岩 (SiO 70 ± 2 wt%) 熔体。采用 DOMINO 软件的计算表明，所分析熔体的完全封闭系统结晶在 600 °C 以下约 1.5 kbar 的压力下准确再现了大结晶夹杂物 (+H2O) 的矿物组合。含有锆石的长英质纵梁的花岗岩矿物学与结晶熔体包裹体的花岗岩矿物学并不对应，前者的 KO 明显较低。KO 损失可能是由于熔体与主体辉长岩的辉石相互作用造成的。这意味着考虑长英质花岗岩脉（通常存在于海洋下地壳部分），因为简单的“冻结融化”并不总是合理的。大西洋中脊 13°25′–14° 部分的玄武岩熔岩玻璃的成分变化显示出从 -MORB 到 -MORB 的连续地球化学趋势，其中 KO 富集高达 0.9 wt%，表明来自两个来源的混合。最富含 KO 的 -MORB 成分（KO = 0.9 wt%，H2O = 0.7 wt%，KO/TiO = 0.42，（La/Sm）= 2.45）被认为是花岗岩类包裹体的来源。对这种 -MORB 成分的平衡结晶的计算机模拟显示，在 820 °C、1.5 kbar 和熔体分数 5.2 vol% 下，花岗岩残余熔体与锆石熔体包裹体的平均成分非常匹配。结果表明，研究区域中发生的 -MORB 岩浆与锆石包裹体中富钾花岗岩熔体的起源之间存在直接联系。