Geochemical and strontium isotopic characteristics of parental Aleutian arc magmas: evidence from the basaltic lavas of Atka

Eighteen flows from a basal stratigraphic sequence on the Aleutian Island of Atka were analyzed for major elements, trace elements and initial ⁸⁷Sr/⁸⁶Sr ratios. Petrographically, these lavas contain abundant plagioclase (24–45%) and lesser amounts of olivine (<7%), magnetite and clinopyroxene phenocrysts. Compositionally, the lavas are high-alumina (20wt%) basalts (48–51 wt% SiO₂) with low TiO₂ (<1%) and MgO (<5%). Within the section, compositional variations for all major elements are quite small. While MgO content correlates with olivine phenocryst contents, no such relationship exists between the other oxides and phenocryst content. These lavas are characterized by 8–10 ppm Rb, high Sr (610–669 ppm), 308–348 ppm Ba and very constant Zr (23–29 ppm) and Sc (23–29 ppm) abundances. Ni and Cr display extremely large compositional ranges, 12–118 ppm and 12–213 ppm, respectively. No correlation exists between trace element concentrations and phenocryst contents. Strontium isotopic ratios show a small but significant range (0.70314–0.70345) and are slightly elevated with respect to typical MORB. No systematic correlation between stratigraphic position and petrography or geochemistry is evident. REE abundances measured on six samples are LREE enriched ((La/ Yb)_N = 2.20–2.81) and display similar chondrite normalized patterns. One sample has a slight positive Eu anomaly but the other lavas do not. Compared to other Aleutian basalts of similar silica content, these lavas are less LREE enriched and have lower overall abundances. The geochemical characteristics of these basalts suggest they represent true liquid compositions despite their highly porphyritic nature. Published phase relations indicate fractionation of a more MgO-rich magma could not have produced these lavas. The high Al₂O₃ and low MgO and compatible element abundances suggest a predominantly oceanic crustal source for parental high-alumina basalts.     

Geochemical evidence for the Trindade hotspot trace: Columbia seamount ankaramite

The Columbia seamount 825 km offshore from Brazil at 20°S lies on the east–west ‘trace’ of the Trindade hotspot. Continental and oceanic magmatism believed to have originated with this hotspot is alkalic and SiO₂-undersaturated, and dates from 85 Ma in southern Brazil to <3 Ma on the islands of Trindade and Martin Vaz 1100 km offshore. An ankaramite (clinopyroxene 16 vol%) dredged from Columbia seamount (est. 10 Ma) conforms to this geochemistry with SiO₂-undersaturated Al-rich clinopyroxene (8–13 wt.% Al₂O₃) and rhönite. Clinopyroxene isotopic compositions are ⁸⁷Sr/⁸⁶Sr=0.703900, ¹⁴³Nd/¹⁴⁴Nd=0.512786, ²⁰⁶Pb/²⁰⁴Pb=19.190, ²⁰⁷Pb/²⁰⁴Pb=15.045, and ²⁰⁸Pb/²⁰⁴Pb=39.242 — resembling those for Trindade, except for slightly higher ²⁰⁷Pb/²⁰⁴Pb. The isotopic composition and abundance ratios among weathering-resistant Nb, La, and Yb suggest that Columbia seamount magmatism represents the present-day Trindade plume, but 10 million years earlier and perhaps when the plume manifested a signature of ‘contamination’ from subducted sediments. The Columbia seamount analyses provide the first quantitative assessment for the Trindade hotspot trace existing between the Brazil margin and Trindade, strengthening the case for a continuum of magmatism extending from the 85 Ma Brazilian igneous provinces of Poxoréu and Alto Paranaiba.     

Geochemical characteristics of lavas from Broken Ridge, the Naturaliste Plateau and southernmost Kerguelen Plateau: Cretaceous plateau volcanism in the southeast Indian Ocean

Lavas from several major bathymetric highs in the eastern Indian Ocean that are likely to have formed as Early to Middle Cretaceous manifestations of the Kerguelen hotspot are predominantly tholeiitic; so too are glass shards from Eocene to Paleocene volcanic ash layers on Broken Ridge, which are believed to have come from eruptions on the Ninetyeast Ridge. The early dominance of tholeiitic compositions contrasts with the more recent intraplate, alkalic volcanism of the Kerguelen Archipelago. Isotopic and incompatible-element ratios of the plateau lavas are distinct from those of Indian mid-ocean ridge basalts; their Nd, Sr, ²⁰⁷Pb/²⁰⁴Pb and isotopic ratios overlap with but cover a much wider range than measured for more recent oceanic products of the Kerguelen hotspot (including the Ninetyeast Ridge) or, indeed, oceanic lavas from any other hotspot in the world. Samples from the Naturaliste Plateau and ODP Site 738 on the southern tip of the Kerguelen Plateau are particularly noteworthy, with ε_Nd(T) = − 13 to −7, (⁸⁷Sr/⁸⁶Sr)_T=0.7090 to 0.7130 and high ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb. In addition, the low-ε_Nd(T) Naturaliste Plateau samples are elevated in SiO₂ (> 54 wt%). In contrast to “DUPAL” oceanic islands such as the Kerguelen Archipelago, Pitcairn and Tristan da Cunha, the plateau lavas with extreme isotopic characteristics also have relative depletions in Nb and Ta (e.g., Th/Ta, La Nb > primitive mantle values); the lowest ε_Nd(T) and highest Th/Ta and La Nb values occur at sites located closest to rifted continental margins. Accepting a Kerguelen plume origin for the plateau lavas, these characteristics probably reflect the shallow-level incorporation of continental lithosphere in either the head of the early Kerguelen plume or in plume-derived magmas, and suggest that the influence of such material diminished after the period of plateau construction. Contamination of asthenosphere with the type of material affecting Naturaliste Plateau and Site 738 magmatism appears unlikely to be the cause of low-²⁰⁶Pb/⁰⁴Pb Indian mid-ocean ridge basalts. Finally, because isotopic data for the plateaus do not cluster or form converging arrays in isotope-ratio plots, they provide no evidence for either a quickly evolving, positive ε_Nd, relatively high-²⁰⁶Pb/²⁰⁴Pb plume composition, or a plume source dominated by mantle with ε_Nd of −3 to 0.     

Geochemical characteristics of tin-bearing magnetite-skarns

Geological and geochemical characteristics of tin-bearing magnetite-skarns are reviewed in this paper, together with the author’s opinion with respect to the mechanism of transport of tin in this environment. In addition to cassiterite, the most common form of occurrence of tin in nature, three other forms of occurrence are also of interest in tin-bearing magnetite-skarns: (1) tin present in the form of fine exsolution colloidal grains of cassiterite; (2) tin found as independent tin-bearing minerals, such as malayaite, stokesite, nordenskiöldine, Sn-paigeite, Sn-ludwigite and hulsite in a variety of skarns; (3) tin occurring in the lattice of some skarn minerals, such as garnet, pyroxene, spinel, amphibole, epidote, wollastonite and axinite in the manner of ionic replacement. When Mg²⁺ and Fe²⁺ bearing minerals, in some cases even Sulfides or other mineralizer-containing minerals, replace tin-bearing Fe³⁺ and Ti⁴⁺ skarn minerals during the late stage of skarn alteration, tin in the pre-existing silicates maybe extracted and remobilized, thus contributing to the formation of associated tin deposits.     

坎尔其铜矿地质地球化学特征

坎尔其一带水系沉积物地球化学异常，是国家305项目在开展东天山阿克居里达坂一带1：20万地球化学普查工作中圈定的甲类异常，在对其进行了重点检查，全面踏勘的基础上，布设了土壤地球化学测量和地质地球化学剖面，对重点地段进行了浅表工程揭露，发现了坎儿其铜矿。     

煤中铅的地球化学特征

铅属于重金属元素,也是煤中的有害元素之一,煤中的铅通过风化、燃烧等各种途径转移到大气、水以及土壤中,对环境造成严重危害。本文应用地球化学、矿物学、物理化学和环境化学等方法,对煤中铅的地球化学特征、赋存状态、迁移规律与富集机制进行了详细论述,为环保和脱铅工艺提供了科学依据。     

Geochemical constraints on the contribution of Louisville seamount materials to magmagenesis in the Lau back-arc basin,SW Pacific

Seamounts are an integral part of element recycling in global subduction zones. The published trace element and Pb-Sr-Nd isotope data for basaltic lavas from three key segments (Central Lau Spreading Ridge (CLSR), Eastern Lau Spreading Ridge (ELSR), and Valu Fa Ridge (VFR)) of the Lau back-arc basin were compiled to evaluate the contribution of Louisville seamount materials to their magma genesis. Two geochemical transitions, separating three provinces with distinct geochemical characteristics independent of ridge segmentation, were identified based on abrupt geochemical shifts. The origin of the geochemical transitions was determined to be the result of drastic compositional changes of subduction components added into the mantle source, rather than the transition from Indian to Pacific mid-ocean ridge basalt (MORB) mantle, or due to variable mantle fertilities. The most likely explanation for the drastic shifts in subduction input is the superimposition of Louisville materials on ‘normal’ subduction components consisting predominantly of aqueous fluids liberated from the down-going altered oceanic crust and minor pelagic sediment melts. Quantitative estimation reveals that Louisville materials contributed 0–74% and 21–83% of the Th budget, respectively, to CLSR and VFR lavas, but had no definite contribution to the lavas from the ELSR, which lies farthest away from the subducted Louisville seamount chain (LSC). The spatial association of the subducted LSC with the Louisville-affected segments suggests that the Louisville signature is regionally but not locally available in the Tonga subduction zone. Besides, the preferential melting of subducted old Cretaceous LSC crust instead of the old normal Pacific oceanic crust at similar depths implies that elevated temperature across the subduction interface or seamount erosion and rupture were required to trigger melting. A wider implication of this study, thus, is that seamount subduction may promote efficiency of element recycling in subduction zones.     

Geochemical characteristics of Cretaceous carbonatites from Angola

The Early Cretaceous (138–130 Ma) carbonatites and associated alkaline rocks of Angola belong to the Paraná-Angola-Etendeka Province and occur as ring complexes and other central-type intrusions along northeast trending tectonic lineaments, parallel to the trend of coeval Namibian alkaline complexes. Most of the Angolan carbonatite-alkaline bodies are located along the apical part of the Moçamedes Arch, a structure representing the African counterpart of the Ponta Grossa Arch in southern Brazil, where several alkaline-carbonatite complexes were also emplaced in the Early Cretaceous. Geochemical and isotopic (C, 0, Sr and Nd) characteristics determined for five carbonatitic occurrences indicate that: (1) the overall geochemical composition, including the O---C isotopes, is within the range of the Early and Late Cretaceous Brazilian occurrences from the Paraná Basin; (2) the La versus relationships are consistent with the exsolution of CO_i2-rich melts from trachyphonolitic magmas; and (3) the and initial ratios are similar to the initial isotopic ratios (129 Ma) of alkaline complexes in northwest Namibia. In contrast, the Lupongola carbonatites have a distinctly different initial ratio, suggesting a different source.The Angolan carbonatites have Sr---Nd isotopic compositions ranging from bulk earth to time-integrated depleted sources. Since those from eastern Paraguay (at the western fringe of the Paraná-Angola-Etendeka Province) and Brazil appear to be related to mantle-derived melts with time-integrated enriched or B.E. isotopic characteristics, it is concluded that the carbonatites of the Paraná-Angola-Etendeka Province have compositionally distinct mantle sources. Such mantle heterogeneity is attributed to ‘metasomatic processes’, which would have occurred at ca 0.6–0.7 Ga (Angola, northwest Namibia and Brazil) and ca 1.8 Ga (eastern Paraguay), as suggested by Nd-model ages.     

Geochemical variations in lavas from Kahoolawe volcano,Hawaii: evidence for open system evolution of plume-derived magmas

The Kahoolawe shield volcano produced precaldera and caldera-filling tholeiites and mildly alkalic post-caldera lavas that petrographically and compositionally resemble such lavas from other Hawaiian shield volcanoes. However, Kahoolawe tholeiites display wide ranges in incompatible trace element ratios (e.g., Nb/Th=9–24, Th/Ta=0.6–1.3), ⁸⁷Sr/⁸⁶Sr (0.70379–0.70440), ¹⁴³Nd/¹⁴⁴Nd (0.51273–0.51298), and ²⁰⁶Pb/²⁰⁴Pb (17.92–18.37). The isotopic variation exceeds that at any other Hawaiian shield volcano, and spans about half the range for all Hawaiian tholeiites. Quasi-cyclic temporal evolution of Kahoolawe tholeiites is consistent with combined fractional crystallization and periodic recharge by primitive magmas. Ratios of highly incompatible trace elements and Sr, Nd, and Pb isotopic ratios from coherent sub-trends that reflect recurrent interactions between variably evolved magmas and two other mantle components whose compositions are constrained by intersections between these trends. The most MgO-rich Kahoolawe tholeiites are partial melts of a high Nb/Th (23.5) ascending plume, possibly comprising ancient subducted oceanic lithosphere. Slightly evolved tholeiites experienced combined crystal fractionation and assimilation (AFC) of material derived from a distinct reservoir (Nb/Th 9) of asthenospheric derivation. The most evolved tholeiites display compositional shifts toward a third component, having mid ocean ridge basalt-like isotopic ratios but enriched OIB-like trace element ratios, representing part of the lithospheric mantle (or melts thereof). Periodic recurrence of all three magma variants suggests that eruptions may have tapped coeval reservoirs distributed over a large depth range. Kahoolawe provides new evidence concerning the nature of the Hawaiian plume, the distribution of compositional heterogeneities in the suboeanic mantle, and the processes by which Hawaiian tholeiites form and evolve.     

Geochemical evolution of historical lavas from Askja Volcano, Iceland: Implications for mechanisms and timescales of magmatic differentiation

The mechanisms and the timescales of magmatic evolution were investigated for historical lavas from the Askja central volcano in the Dyngjufjöll volcanic massif, Iceland, using major and trace element and Sr, Nd, and Pb isotopic data, as well as ²³⁸U-²³⁰Th-²²⁶Ra systematics. Lavas from the volcano show marked compositional variation from magnesian basalt through ferrobasalt to rhyolite. In the magnesian basalt-ferrobasalt suite (5-10 wt% MgO), consisting of lavas older than 1875 A.D., ⁸⁷Sr/⁸⁶Sr increases systematically with increasing SiO₂ content; this suite is suggested to have evolved in a magma chamber located at ∼600 MPa through assimilation and fractional crystallization. On the other hand, in the ferrobasalt-rhyolite suite (1-5 wt% MgO), including 1875 A.D. basalt and rhyolite and 20th century lavas, ⁸⁷Sr/⁸⁶Sr tends to decrease slightly with increasing SiO₂ content. It is suggested that a relatively large magma chamber occupied by ferrobasalt magma was present at ∼100 MPa beneath the Öskjuvatn caldera, and that icelandite and rhyolite magmas were produced by extraction of the less and more evolved interstitial melt, respectively, from the mushy boundary layer along the margin of the ferrobasalt magma chamber, followed by accumulation of the melt to form separate magma bodies. Ferrobasalt and icelandite lavas in the ferrobasalt-rhyolite suite have a significant radioactive disequilibrium in terms of (²²⁶Ra/²³⁰Th), and its systematic decrease with magmatic evolution is considered to reflect aging, along with assimilation and fractional crystallization processes. Using a mass-balance model in which simultaneous fractional crystallization, crustal assimilation, and radioactive decay are taken into account, the timescale for the generation of icelandite magma from ferrobasalt was constrained to be <∼3 kyr which is largely dependent on Ra crystal-melt partition coefficients we used.     

北京周口店岩体地球化学特征及物源分析

通过对周口店岩体地球化学特征和构造环境及其与埃达克岩对比的分析，发现该岩体具有C型埃达克岩的地球化学特征。^143Nd／^144Nd-^87Sr／^86Sr图解发现该岩体的锶、钕同位素投影点均落在EMI型富集地幔区域内，表明其物质来源与EMI型富集地幔有关。而εNd（t）-ISr图解中，其投影点正好落在汉诺坝二辉麻粒岩包体范围内（汉诺坝二辉麻粒岩包体是幔源基性岩浆在晚古生代-中生代底侵到下地壳底部构成的年轻下地壳的一部分）。由此推测认为，周口店岩体是中生代新增生的华北克拉通下地壳的部分熔融的产物。     

Fractal characteristics of resource quantity of cobalt crusts and seamount topography, the West Pacific

This paper presents the fractal distribution of topography of seamounts from the West Pacific and the resource quantity of cobalt crust therein. The cobalt resource quantity has three to four variable fractal dimensions, corresponding to the distinct slopes and water depths of the seamount. The multiple fractal property of resource quantity may have resulted from various factors, such as types and components of cobalt crusts and ages of oceanic crusts hosting the seamounts. Individual seamounts display complex topography and quantity of cobalt crust, both in the same and different regions. Translated from Acta Sedimentologica Sinica, 2006, 24(5): 705–713 [译自: 沉积学报]     

Temporal evolution of the kerguelen plume: Geochemical evidence from 38 to 82 ma lavas forming the Ninetyeast ridge

Abstract Basaltic basement has been recovered by deep-sea drilling at seven sites on the linear Ninetyeast Ridge in the eastern Indian Ocean. Studies of the recovered lavas show that this ridge formed from ~ 82 to 38 Ma as a series of subaerial volcanoes that were created by the northward migration of the Indian Plate over a fixed magma source in the mantle. The Sr, Nd and Pb isotopic ratios of lavas from the Ninetyeast Ridge range widely, but they largely overlap with those of lavas from the Kerguelen Archipelago, thereby confirming previous inferences that the Kerguelen plume was an important magma source for the Ninetyeast Ridge. Particularly important are the ~ 81 Ma Ninetyeast Ridge lavas from DSDP Site 216 which has an anomalous subsidence history (Coffin 1992). These lavas are FeTi-rich tholeiitic basalts with isotopic ratios that overlap with those of highly alkalic, Upper Miocene lavas in the Kerguelen Archipelago. The isotopic characteristics of the latter which erupted in an intraplate setting have been proposed to be the purest expression of the Kerguelen plume (Weis et al. 1993a,b). Despite the overlap in isotopic ratios, there are important compositional differences between lavas erupted on the Ninetyeast Ridge and in the Kerguelen Archipelago. The Ninetyeast Ridge lavas are dominantly tholeiitic basalts with incompatible element abundance ratios, such as La/Yb and Zr/Nb, which are intermediate between those of Indian Ocean MORB (mid-ocean ridge basalt) and the transitional to alkalic basalts erupted in the Kerguelen Archipelago. These compositional differences reflect a much larger extent of melting for the Ninetyeast Ridge lavas, and the proximity of the plume to a spreading ridge axis. This tectonic setting contrasts with that of the recent alkalic lavas in the Kerguelen Archipelago which formed beneath the thick lithosphere of the Kerguelen Plateau. From ~ 82 to 38 Ma there was no simple, systematic temporal variation of Sr, Nd and Pb isotopic ratios in Ninetyeast Ridge lavas. Therefore all of the isotopic variability cannot be explained by aging of a compositionally uniform plume. Although Class et al. (1993) propose that some of the isotopic variations reflect such aging, we infer that most of the isotopic heterogeneity in lavas from the Ninetyeast Ridge and Kerguelen Archipelago can be explained by mixing of the Kerguelen plume with a depleted MORB-like mantle component. However, with this interpretation some of the youngest, 42–44 Ma, lavas from the southern Ninetyeast Ridge which have²⁰⁶pb/²⁰⁴Pb ratios exceeding those in Indian Ocean MORB and Kerguelen Archipelago lavas require a component with higher²⁰⁶Pb/²⁰⁴Pb, such as that expressed in lavas from St. Paul Island.     

扬子板块北部古被动大陆边缘的地球化学特征

本文初次提出扬子板块北部古被动大陆边缘的地球化学特征是:a、裂陷早期阶段,发育碱性双峰式火山岩,但在裂陷的晚期和移离的早期阶段,发育碱性而不具双峰特征的火山岩、岩脉群;b、发育具两类不同地球化学特征的砂页岩,裂陷阶段形成的砂页岩与活动大陆边缘形成的砂页岩具相似的地球化学特征,移离阶段所形成的砂页岩才真正具被动大陆边缘砂页岩的地球化学特征。     

扬子板块北缘马元铅锌矿床两类矿石地球化学特征及其对成矿作用的制约

对马元铅锌矿白云石-硫化物型和重晶石-硫化物型矿石中的热液矿物白云石和重晶石的同位素和稀土元素地球化学特征对比研究表明,白云石的δ~(13)CPDB为-2.51×10-3~0.93×10-3,δ18OSMOW为17.55×10~(-3)~23.24×10~(-3),说明成矿流体中碳、氧来源于震旦系碳酸盐岩的溶解;锶同位素组成(0.711 46)表明Sr来源以壳源锶为主,可能与富放射性锶的上覆碎屑岩或下伏基底变质火山岩有关;稀土元素具有明显的正Eu异常(δEu平均为1.415),表明白云石-硫化物型矿化流体具有盆地中循环热卤水特点。重晶石的硫同位素(平均为33×10~(-3))具有富重硫且分布均一的特点,暗示硫可能来源于富集重硫的单一海相硫酸盐;Sr同位素(0.709 18~0.709 71)特征表明其来源以海水锶为主,有少量壳源锶加入;稀土元素具有明显负Ce异常(δCe平均为0.255)和正Eu异常(δEu平均为1.43),表明重晶石--硫化物型矿化有关的流体可能是海水(或大气降水)与盆地循环热流体混合的结果。白云石--硫化物型矿石和重晶石-硫化物型矿石的沉淀可能是盆地中循环热卤水与海水(或大气降水)两种端元组分以不同比例混合的结果。     

Geochemical Characteristics of Jinwozi Gold Deposit,Xinjiang

The Jinwozi gold deposit consists of gold-bearing quartz veins in a biotite granodiorite of Hercynian age (zircon U-Pb age ≈ 335.7 Ma). Ore mineralogy is simple. In addition to native gold, there are only small amounts of sulfides, mainly pyrite and minor sphalerite, chalcopyrite and galena. δ³⁴S values average 6.69‰, and δ¹⁸O 13.99‰ Abundant CO₂ is contained in fluid inclusions from quartz. Homogenization temperatures of fluid inclusions are between 186 and 262 °C. REE distribution patterns indicate that the igneous mass may have been derived from a common initial material of calcareous-argillaceous sediments and alkali basalts as the country rocks. In other words, the Jinwozi granodiorite is of remelting origin from crustal material. Isotopic evidence of S, O and Pb shows that the ore-forming material is genetically related to magmatic hydrothermal activity.     

中国七大古都的地球化学环境特征

以全国水系沉积物地球化学调查成果为基础,讨论中国七大古都安阳、西安、洛阳、开封、南京、杭州、北京的环境地球化学背景特征,结果表明,与中国水系沉积物元素含量均值相比,七大古都所在地相对富集镁、钙、硼、锫、银、钴、钡、钠、锶和磷,以人体必需营养元素为主;同时相对贫化镉、钼、锑、铅、钨、铋、砷、锰、铌和汞等,以人体有害元素为主.根据土壤地球化学特征,欧洲的主要国都可分为波罗的海型和地中海型,具有不同的元素分布模式.在中国古都延续时间与元素偶比值之间可建立回归方程Y=0.206X+376,X=(CaO×Fe2O3×V×Co×106)/(SiO2×Pb×Hg×Cd);在欧洲国都与元素偶比值之间也可建立类似的回归方程.充分说明首都的选址还受到地球化学环境的制约.     

白银地区细碧石英角斑岩地球化学特征——兼谈白银板块构造环境

白银地区细碧石英角斑岩具有高钠低钙、富水的特点。地球化学成分与世界其他地区细碧角斑岩基本接近,而明显地区别于正常玄武岩。在里特曼岩系指数图上,细碧岩是一条斜率较大、碱性程度较高的曲线;石英角斑岩是一条斜率较小、碱性程度较低的曲线。从各种岩石的氧化物含量、比值和化学图解看出,其原岩为钙—碱系列岛弧玄武岩。据微量元素含量和图解、稀土元素标准化模式和稀土比值也得出与岛弧大陆拉斑玄武岩一致的结论。因此,该区为弧—沟系敛合型的岛弧及其活动的大陆边缘。     

塔里木板块东北部笔架山东基性-超基性岩体地球化学特征与岩石成因

笔架山东基性—超基性岩体位于塔里木板块东北部的新疆北山地区,是笔架山岩带中最东边的一个岩体,岩体形态为椭圆状,出露面积约5 km2.由含长单辉橄榄岩、橄榄辉长岩、含橄辉长岩、辉长岩以及辉绿岩组成.含橄榄石较多的岩石属拉斑玄武岩系列,而辉长岩属钙碱性系列.岩相学、岩石化学和微量元素地球化学特征表明岩浆演化过程中经历了橄榄石、辉石、斜长石的分离结晶作用.Nd、Sr、Pb同位素组成和岩石地球化学特征反映出岩浆与围岩之间存在物质交换.笔架山东岩体的岩浆源区为OIB型地幔源区,原生岩浆为高镁拉斑玄武岩浆[w(MgO)=11.2％],这些性质与塔里木板块东北部其他基性-超基性岩体的特征相似,表明塔里木板块东北部二叠纪基性—超基性岩体的源区主要为OIB型地幔,可能与地幔柱有关.