Mantle metasomatism by P- and F-rich melt/fluids: evidence from phosphate glass in spinel lherzolite xenolith in Keluo, Heilongjiang Province

Spinel lherzolite xenoliths were found in phonolitic alkaline basalt in the Keluo area, Heilongjiang Province. Detailed electron-microprobe study revealed abundant phosphates and associated metasomatic minerals between primary phases in xenolith. The phosphates are considered special residual phases (coagulation) of P- and F-rich mantle melt/fluid, most of which were identified as glass phases based on Raman spectroscopic analyses. Such melt/fluid also further metasomatized primary minerals, thus leading to formation of reaction rims successively composed of Cr-spinel symplectitic zone and olivine diopside zone. Therefore, the P- and F-rich melt/fluid played an important role in the upper-mantle metasomatism in the Keluo area. It is suggested that this kind of metasomstism may occur in some other places of eastern China. The present results may also have significance in study-ing types of metasomatic melt/fluid and its evolution in the lithospheric mantle beneath eastern China.     

Mantle metasomatism by P- and F-rich melt/fluids： evidence from phosphate glass in spinel Iherzolite xenolith in Keluo, Heilonsjiang Province

Spinel Iherzolite xenoliths were found in phonoliUc alkaline basalt in the Keluo area, Heilongjiang Province. Detailed electron-microprobe study revealed abundant phosphates and associated metasomatic minerals between primary phases in xenolith. The phosphates are considered special residual phases （coagulation） of P- and F-rich mantle melt/fluid, most of which were identified as glass phases based on Raman spectroscopic analyses. Such melt/fluid also further metasomatized primary minerals, thus leading to formation of reaction rims successively composed of Cr-spinel symplecUUc zone and olivine ＋ diopside zone. Therefore, the P- and F-rich melt/fluid played an important role in the upper-mantle metasomatism in the Keluo area. It is suggested that this kind of metasomstism may occur in some other places of eastern China. The present results may also have significance in studying types of metasomatic melt/fluid and its evolution in the lithospheric mantle beneath eastern China.     

中国东南部新生代岩石圈地幔研究

利用中国东南部新生代玄武岩中约２００个深源捕虏体,试图认识该区岩石圈地幔的成分特征,了解其经历的地幔作用过程,通过电子探针（ＥＭＰ）和激光探针（ＬＡＭ－ＩＣＰＭＳ）微束技术,对具代表性的深源捕虏体中的矿物进行了主量元素和微量元素地球化学分析,结合全岩主量元素地球化学特征,提出中国东南部元古代地壳之下主要为新的饱满型地幔,而这种新生代岩石圈地幔的形成与该区晚中生代以来软流圈上涌、岩石圈减薄和伸展作用密切相关。     

长白山地区幔源捕虏体的硫化物相及其演化

长白山地区新生代玄武岩的一些层位广布地幔岩捕虏体,在其橄榄石、辉石等矿物内发现有较多的硫化物相,按产出特征可鉴别出3种类型,即早期硫化物颗粒、硫化物包裹体和裂隙中硫化物。硫化物包裹体可以单相硫化物、硫化物－硅酸盐熔体、CO2－硫化物－硅酸盐熔体形式存在。早期硫化物颗粒以磁黄铁矿为主,并发现有方黄铜矿;硫化物包裹体以镍黄铁矿为主,并有黄铜矿、硫铜铁矿出现;裂隙中硫化物均为镍黄铁矿,并具有比硫化物包裹体高的Ni/Fe和（Fe Ni)／S值。地幔岩中存在自早期硫化物颗粒、硫化物包裹体至裂隙硫化物,Ni/Fe和（Fe Ni)/S比值逐渐增加的规律。这种演化不仅受温度和压力制约,而且受Ni,Fe,Cu的地球化学特性和硫逸度的控制。     

Mantle xenoliths from Late Cretaceous basalt in eastern Shandong Province： New constraint on the timing of lithospheric thinning in eastern China

Studies of mantle xenoliths hosted in both the Cenozoic alkali basalt and the Early Paleozoic kimberlite suggest that part of the subcontinental lithosphere as thick as more than 100 km has been lost from the Early Paleozoic to Cenozoic[1—8]. Neither the scale and mechanism nor the accurate timing of the lithospheric thinning has been precisely constrained[7-12]. One of the reasons for this is that there are only a few Mesozoic basalts cropped out, especially, few containing mantle-derived …     

Os isotopic composition of the earth’s primitive upper mantle

The osmium isotopic ratio of¹⁸⁷Os/¹⁸⁸Os ranging from 0.126 to 0.127 for the primitive upper mantle (PUM) is obtained according to the correlation between¹⁸⁷Os/¹⁸⁸Os and Al₂O₃ of mantle-derived xenoliths and orogenic peridotites, which consists with Allegre and Luck’s ALM value and similar to Yin’s nuggets uniform reservoir (NUR) value. It shows that the Os isotope ratio is lower than enstatite or ondinary chondrites, similar to carbonaceous chondrites (CV3).     

安徽女山幔源橄榄岩捕虏体Re-Os 同位素地球化学

Re-Os同位素体系可以为研究大陆岩石圈地幔形成和演化提供重要制约.女山12个地幔橄榄岩全岩样品测得Re含量为19×10-12~306×10-12,Os含量为0.81×10-9~2.42×10-9,187Os/188Os比值为0.114 90~0.131 02,187Re/188Os比值为0.037~1.517.两个石榴子石-尖晶石二辉橄榄岩的Os同位素组成与原始上地幔(PUM)的现代值0.129 6相似,其余的尖晶石二辉橄榄岩、方辉橄榄岩,和角闪石、金云母-尖晶石二辉橄榄岩等的Os同位素组成都低于PUM现代值,Os同位素模式年龄为早元古代.实性和隐性地幔交代作用对女山幔源橄榄岩捕虏体的Os同位素组成没有明显影响.橄榄岩捕虏体代表的女山地区岩石圈地幔是元古代岩石圈地幔经过减薄作用后的残留部分.橄榄岩中Re-Os体系扰动是近期事件.     

玻璃转变区上限的探索研究

分析玻璃转变区上限界定问题,从一个角度讨论了YL方法中玻璃熔接的机理.     

Chondritic osmium isotopic composition of late Archean convecting upper mantle：Evidence from Zunhua podiform chromitites,Hebei, North China

The Os isotopic composition and evolution of con-vecting upper mantle (CUM) are an important and diffi-cult scientific issue related to the distributions of PGEs inearth’s interior and the accretion history of the earth. De-termination of 187Os/188Os of modern CUM has been at-tempted via analyses of abyssal peridotites, mid-oceanridge basalts (MORB), MORB glasses and sulfides. Abyssal peridotites, which are mantle samples re-covered from the ocean ridges, represent the upperm…     

Sr-rich apatite from the Dangzishan leucitite-ijolite xenoliths （Heilongjiang Province）： Mineralogy and mantle-fluid metasomatism

Abundant apatite grains with elevated SrO content were found in leucitite-ijolite xenoliths in the Dangzi Mountain,Heilongjiang Province.Morphological and mineralogical associations,and compositional analysis of the Sr-rich apatite,were carried out using an electron microprobe.Two principal types of apatite were distinguished.One type occurs as short-prismatic crystals with Sr-rich rims,while another type with acicular or finely columnar shapes constitutes Sr-rich apatite element maps and systematic quantitative analysis of apatite revealed great variations in SrO content (0.42%-26.79%).The calculated structural formula of the measured Sr-rich apatite is:(Ca3.15-4.963Sr0.019-1.510Ba0.00-0.030Na0.006-0.108REE0.106-0.153) (P2.84-3.028Si0.009-0.094)O12(F0.675-1.079,Cl0.000-0.256,OH0.084-0.297).Mineralogical textures of apatite implied a replacement mechanism for the Sr-rich apatite.Sr-rich rims of apatite are suggested to have formed after metasomatism (isomorphic replacement) of early fluorapatite in a Sr-,light rare-earth elements (LREE),lithophile light elements (LILE)-and volatile-rich residual melt during late magmatism.However,the acicular apatite probably directly crystallized from a Sr-rich residual melt.The Sr-Nd isotopic composition of the apatite was distinctive from that of leucitite-ijolite and its host rock.These differences,combined with mineralogical features of apatite,imply that Sr-LREE-LILE-volatile-rich components in the residual melt were derived from deep in the asthenosphere,and subsequently were enriched at a late stage in magma evolution.