Origin of lamprophyres from the northern margin of the North China Craton: implications for mantle metasomatism
Origin of lamprophyres from the northern margin of the North China Craton: implications for mantle metasomatism
复制标题
DOI：
10.1144/jgs2016-044
复制
发表时间：
2016-11
影响因子：
2.7
通讯作者：
Xiaolu Niu;Bin Chen;Guangying Feng;Fei Liu;Jingsui Yang
中科院分区：
文献类型：
--
作者：
Xiaolu Niu;Bin Chen;Guangying Feng;Fei Liu;Jingsui Yang
华北陆块北方边缘附近发育丰富的地幔岩墙，为研究地幔源区的性质提供了一个独特的机会。脉岩为由金云母、透长石和方解石组成的矿物岩。~（40）Ar/~（39）Ar定年结果为234 ± 2和222 ± 6 Ma。层状岩浆是近原生的幔源超钾质熔体，具有低SiO_2（31.0 - 41.5wt%）和高K_2O（4.40 - 7.12wt%）含量，高Mg#（62 - 84）和高相容元素含量。其特征是稀土元素分馏模式、放射成因Sr和非放射成因Nd同位素组成（87 Sr/86 Sr = 0.7070 - 0.7075; εNd（t）= −12.8-−9.2）。少量的镁铁质地壳岩石（<4.4%）可能在岩浆上升过程中被同化，187 Os/188 Osi比值为0.4548 - 0.8068。这些数据表明，层状岩石起源于一个低程度的部分熔融富集的次大陆岩石圈地幔源丰富的金云母，单斜辉石和碳酸盐。该源区被碳酸盐和富钾流体所交代，这些碳酸盐和富钾流体来自于通过古蒙古洋板俯冲到华北板块之下而再循环的碳酸盐沉积物。补充材料：大同层状岩的黑云母、长石和碳酸盐的微探针分析、40 Ar-39 Ar分析数据以及金云母斑晶和基质的36 Ar/40 Ar v.39Ar/40 Ar逆等时线图可在www.example.com上获得https://doi.org/10.6084/m9.figshare.c.3574265。
Abundant lamprophyre dykes occur near the northern margin of the North China Craton and offer a unique opportunity to study the nature of the mantle source. The dykes are minettes composed of phlogopite, sanidine and calcite. 40Ar/39Ar dating yields ages of 234 ± 2 and 222 ± 6 Ma. The lamprophyres are near-primary, mantle-derived ultrapotassic melts, having low SiO2 (31.0 – 41.5 wt%) and high K2O (4.40 – 7.12 wt%) contents, high Mg# (62 – 84) and high contents of compatible elements. They are characterized by fractionated rare earth element patterns, radiogenic Sr and unradiogenic Nd isotope compositions (87Sr/86Sri = 0.7070 – 0.7075; εNd(t) = −12.8 to −9.2). A small amount of mafic crustal rocks (<4.4%) may have been assimilated during magma ascent, as revealed by 187Os/188Osi ratios of 0.4548 – 0.8068. These data suggest that the lamprophyres originated from a low degree of partial melting of an enriched subcontinental lithospheric mantle source with abundant phlogopite, clinopyroxene and carbonate. The source has been metasomatized by carbonate- and potassium-rich fluids derived from carbonated sediments recycled via subduction of Palaeo-Mongolian oceanic slab beneath the North China Craton. Supplementary material: Microprobe analyses of biotite, feldspar and carbonate, 40Ar–39Ar analytical data, and 36Ar/40Ar v. 39Ar/40Ar inverse isochron diagrams for phlogopite phenocrysts and groundmass from the Datong lamprophyres are available at https://doi.org/10.6084/m9.figshare.c.3574265.