Geochemistry of island arc assemblage in the Eastern Desert of Egypt and the role of Pan-African magmatism in crustal growth of the Arabian–Nubian Shield:A review

Neoproterozoic island arc assemblage of the Arabian–Nubian Shield(ANS)in the Eastern Desert(ED)of Egypt comprises juvenile suites of metavolcanics(MV),large amounts of meta-sedimentary rocks(MS),and voluminous metagabbros-diorites(MGD)and syn-tectonic intrusions of older granitoids(OG).We report here the updates of these four rock units in terms of classification,distribution,chemical characteristics,geodynamic evolution,metamorphism,and ages.In addition,we discuss these integrated data to elucidate a reasonable and reliable model for crustal evolution in the ANS.The main features of these rock units indicate their relation to each other and the geodynamic environment dominated by early immature oceanic island arcs to primitive continental arcs.Integrated information of the island arc metavolcanic and plutonic rocks(gabbros,diorites,tonalites,and granodiorites)furnish evidence of the genetic relationships.These include proximity and a coeval nature in the field;all protolith magmas are subalkaline in nature following calc-alkaline series with minor tholeiitic affinities;common geochemical signature of the arc rocks and subduction-related magmatism;their similar enrichment in LREEs;and similar major element compositions with mafic melts derived from metasomatized mantle wedge.The volcano-sedimentary and the OG rocks underwent multiphase deformation events whereas the MGD complexes deformed slightly.Based on the magmatic,sedimentological,and metamorphic evolutions constrained by geochronological data as well as the progressive evolutionary trend from extensional to compressional regimes,a possible gradual decrease in the subducted slab dip angle is the most infl uential in any geodynamic model for arc assemblage in the ED of Egypt.

A preliminary analysis of arcuate structures-relationship of the island arc and deep-sea trench to the dip angle of Benioff zone

The origin of arcuate islands and deep-sea trenches has been studied for a long time and various interpretations have been proposed. In this paper, some analytical models are put forward from a geometrical viewpoint and then the theoretical dip angles of the underthrusting slabs of circum-Pacific island arcs are computed and compared with those of the Benioff zone. As a result, it is found that the dip angle of the underthrusting slab is one of the main factors determining the curvature of the arcuate structure. The authors consider that this result may contribute to the plate theory.

ACCRETION OF AN EARLY CRETACEOUS INTRA- OCEANIC ISLAND ARC TO INDIA: EVIDENCE FROM THE YARLUNG ZANGBO SUTURE ZONE

A discontinuous line of ophiolitic bodies occurs along the Yarlung Zangbo Suture Zone (YTSZ), which stretches across southern Tibet and beyond. This zone marks the locus of collision between Eurasia and India in the Early Cenozoic. Should we assume that the entire Tethyan Ocean basin that lay between these two continental blocks was oceanic or might it have been more complex? Fragments of any terranes that developed within this once extensive ocean potentially lie within the YTSZ. Detailed investigations over the past three field seasons reveal the presence of several terranes distributed along this zone. Work is currently underway to analyze the nature of individual terranes and the timing of any inter\|relationships.

Geology and Genesis of Peraluminous Granites in East Tianshan Upper Paleozoic Island Arc Belt

A peraluminous granite belt occurs along the connecting zone between the TurPan-Hami Precambrian block and the Upper Paleozoic island arc belt. Muscovite granite and two-mica granite are the essential lithological components of that belt. All the potassium feldspars inthese granites are microcline. Heavy minerals are dominated by magnetite. SiO2 contents ofthese granites are greater than 73 % with most of the A/NKC values greater than 1.1, norma-tive corundum values greater than 1. Plots of CIPW norms in the (AL-K-Na)-Ca-(Fe2++ Mg)diagram are mostly situated in the plagioclase-cordierite-muscovite region. The rocks are char-acterized by very low contents of minor elements and ΣREE with strong Eu depletion, δ18Ovalues between 6. 69‰ and 7. 0‰, Rb-Sr isochron age of 260. 2 ± 6. 2 Ma and an initial 87Sr/86Sr ratio of 0. 7052. These granites might have been produced by partial melting of moderatelyacidic volcanites and low-maturity sediments in the basement sequences and could be geneticallyconnected with the southward A-type subduction of the Turpan-Hami block following the clo-sure of the Middle Carboniferous back-arc basin.

MULTIPLE ISLAND ARC-BASIN SYSTEM AND ITS EVOLUTION IN GANGDISE TECTONIC BELT,TIBET

Gangdise tectonic belt, located in the middle part of Tibet—Qinghai plateau Tethys tectonic domain, is the most representative region in Tibet—Qinghai plateau Tethyan evolution especially in Mesozoic era. It is mainly covered by thick Jurassic—Cretaceous system layer. During the Mesozoic to Cenozoic era, strong island\|arc types volcanism and volcanic rocks and intrusive rocks belt.. Geologists had divided the Tibet Tethyan evolution into three or four stages (Huang, Jiqing, 1987; Pan Guitang, Li Xinzheng, 1993), according to the ocean\|land conversion process of Tethyan evolution .The Tethyan evolution and the nature of Gangdise tectonic belt had been well\|studied by geologists (Huang Jiqing, 1987; Deng Wanming, 1984; Xia Daixiang, 1986; Cheng Changlun 1987; ZhouXiang 1993; Pan Guitang, 1996). Studies showed that Gangdise tectonic belt, from upper Paleozoic to Mesozoic era, had been developed alternate multiple island arc\|basin system, and characterized by many basin types and strong tectonic\|magma activity. Based on the study of Gangdise multiple island arc\|basin system, I present another version of Gangdise tectonic belt tectonic units division and evolution here.

The Formation Mechanism of Island Arc

The shape of island arc is formed by changing the axis of back-arc basin caused by rock expansion along the long axis of back-arc basin;that is, island arc is driven to bend along the subduction zone, so that the arc-shaped island is formed.Rock expansion along the long axis of back-arc basin is attributed to lower part of continental crust melting (underplating) on the dehydration belt (along the long axis of back-arc basin) due to dehydration of subducted oceanic crust, and the arched melting plane is formed, so that rocks on the melting plane are subject to differentiated temperature rise and differentiated expansion. The length of rock expansion along the long axis of back-arc basin is in direct proportion to the radian of island arc. The arc length of island arc is equal to the sum of the length of the long axis of back-arc basin and the length of rock expansion. The displacement and the arc length of island arc can be calculated according to the length of rock expansion;on the contrary, the length of rock expansion can be calculated according to the displacement or the arc length of island arc. According to the length and the lithology of rock expansion, the value of temperature rise of rocks above the melting plane, the melting thickness (underplating) at the bottom of continental crust and the settlement depth of back-arc basin can be reckoned.

The Vertical Deformation and Horizontal Displacement Fields,Movement, and Seismicity of the Island Arc Tectonics

In this work,the vertical deformation,horizontal displacement,and stress fields of arcuate tectonics are theoretically derived from the horizontal tectonic stress; then the characteristics of tectonic movement,seismicity,and focal mechanism of arcuate tectonics of the entire world are explained.It is pointed out that the island arc and other arcuate tectonics are gradually developed under the displacement and stress fields of the arcuate tectonics and that the under-thrusting action of the ocean plate is secondary.The distance formulas between the volcanic arc and the trench are suggested and also that theoretical results are consistent with actual data.

Late Palaeogene emplacement and late Neogene-Quaternary exhumation of the Kuril island-arc root (Kunashir island) constrained by multi-method thermochronometry

The Kuril islands constitute a volcanic island arc-trench system, stretching from eastern Hokkaido （Japan） to Kamchatka （Russia） along the northwestern Pacific subduction system, The current arc consists of several volcanic islands mainly with Neogene basement and capped by several, predominantly andesitic, active subduction stratovolcanoes, Kunashir Island is the southwestern-most island of the arc, just off the Hokkaido coast and represents the study area in this paper. The island is composed of a Lower Complex of mainly late Miocene to Pliocene volcanic rocks, covered by an Upper Complex of younger （basaltic） andesitic lava flows and tuffs on which currently four active volcanic edifices are built. In the Lower Complex sub-volcanic and deeper-seated intrusives of the so-called Prasolov and Dokuchaev magmatic complexes are found, More differentiated, tonalitic-granodioritic rocks were collected from these small intrusive bodies. An early Oligocene zircon LA-ICP-MS U/Pb age of 31 Ma for the Prasolov Complex was obtained, showing that the basement of Kunashir Island is older than previously thought. Thermochronometry （apatite fission-track and U-Th-Sm/He and zircon U-ThJHe analyses） further shows that the magmatic basement of the island was rapidly exhumed in the Pleistocene to present levels in a differential pattern, with He-ages ranging from 1.9 to 0.8 Ma. It is shown that the northern section of the island was hereby exhumed more intensely.

Late Triassic bivalves associated with a hydrothermal vent system in the Yidun Island Arc (SW China) of the eastern Tethys

The Yidun Island Arc in the Three Rivers (Jinsha River, Lancang River, Nujiang River) region of southwestern China is one of the most important Kuroko-type volcanogenic massive sulfide deposits (VMS) in China. Intra-arc rifting of Yidun Island occurred during the Late Carnian-Norian when VMS deposits such as the Gacun Pb-Zn-Cu deposit were formed. A bivalve fauna was found in fine-grained tuffaceous slate and in mineralized tuffaceous siltstone containing very high contents of Pb (45.01-103.37 ppm) and Zn (135.78-300.03 ppm) of the upper Tumugou Formation in the Changtai-Gacun volcanic-sedimentary rift basin. Stratigraphically, the bivalve-bearing beds are equivalents of the Gacun Pb-Zn-Cu deposits. The diversity of this bivalve fauna is very low. It consists mainly of the thin-shelled, epibyssate suspension-feeding bivalves Pergamidia eumenea and Parapergamidia changtaiensis, the burrowing large, elongated, suspension-feeding Trigonodus keuperinus and Unionites? sp., and occasional specimens of the endobyssate suspension-feeding Trigonodus? sp. and the deep burrowing suspension-feeding Pleuromya markiamensis. Individuals of the first four taxa are so abundant that the specimens are sometimes concentrated in shell beds, probably indicating a gregarious habit. This bivalve fauna is associated with internal moulds of cylindrical, slightly conical tubes most likely produced by a worm-shaped organism. Composition, morphology, diversity, and high abundance of this fauna, chemical features of the surrounding sediment, and the tectonic setting all suggest that this bivalve fauna lived in a deep-water environment in or around a hydrothermal vent system.

Huanggang Intrusive Complexin Northern Tongbai Area:Island-Arc Tectonic Environment and Its Geological Significance

The Huanggang intrusive complex in northern Tongbai area was formed in Early Paleozoic. It mainly consists of ultra basic, basic, intermediate and acid rocks, dominated by intermediate and basic rocks. The complex belongs to calc alkaline series. Geochemical characteristics of major and trace elements show that the complex was derived from the fractional crystallization of co source magma. It is suggested that the complex was formed in island arc tectonic environment and was closely related to the northward subduction of the Erlangping back arc basin. Thus, the subduction of the back arc basin can induce the island arc type magmatism similar to the one formed in the setting of ocean plate subduction.

Zircon LA-ICP-MS U-Pb Age and Island-Arc Origin of the Bayanhua Gabbro in the Hegenshan Suture Zone, Inner Mongolia

Objective The Bayanhua Nb-enriched gabbro is newly discovered in the Diyanmiao-Meilaotewula SSZ-type ophiolitic m61ange belt of the Hegenshan suture zone, Inner Mongolia. Nb-enriched arc gabbros are usually believed to result from partial melting of the mantle wedge peridotites metasomatized by slab melts derived from the subducting oceanic slab, which represent arc magmatic markers of the oceanic subduction zone. However, whether the Hegenshan ocean basin of the Paleo-Asian Ocean was in its subduction stage in the Early Permian requires further study for a final conclusion, and what is the evolution process of the oceanic subduction and lithospheric mantle of the Hegenshan suture zone remains speculative for the lack of further definitely petrological and chronological evidence and constraints. Therefore, this study carried out zircon LA-ICP-MS U-Pb geochronology and geochemistry on the Bayanhua Nb-enriched gabbro to discuss its origin, in order to provide new evidence for the tectonic evolution of the Hegenshan suture zone of the eastern Central Asian Orogenic Belt.

Constraints on early Paleozoic magmatic processes and tectonic setting of Inexpressible Island, Northern Victoria Land, Antarctica

During the Cambrian and Ordovician, widespread magmatic activity occurred in the Ross Orogen of central Antarctica, forming the Granite Harbor Intrusives and Terra Nova Intrusive Complex. In the Terra Nova Intrusive Complex, the latest magmatic activity comprised the emplacement of the Abbott Unit(508 Ma) and the Vegetation Unit(～475 Ma), which were formed in different tectonic settings. Owing to their similar lithological features, the tectonic transformation that occurred between the formation of these two units has not been well studied. Through a detailed geological field investigation and geochemical and geochronological analyses, four types of magmatic rock—basalt, syenite, mafic veins, and granite veins—were identified on Inexpressible Island, Northern Victoria Land. Our SHRIMP(Sensitive High Resolution Ion Micro Probe) zircon U–Pb ages of the basalt and the granite veins are 504.7 ± 3.1 and 495.5 ± 4.9 Ma, respectively. Major-and trace-element data indicate a continental-margin island-arc setting for the formation of these two rock types. The zircon U–Pb ages of the syenite and the monzodiorite veins are 485.8 ± 5.7 and 478.5 ± 4.0 Ma, respectively. Major-and trace-element compositions suggest a collisional setting for the former and an intracontinental extensional setting for the latter. These results elucidate the evolution from subduction to collision and intracontinental extension in Northern Victoria Land during the 20 Ma spanning the late Cambrian–Early Ordovician and improve our understanding of the tectonics and evolution of the Ross Orogen in the Transantarctic Mountains.

Implications of ε_(Nd) -La/ Nb, Ba/Nb, Nb/Th Diagrams to Mantle Heterogeneity─Classification of Island-arc Basalts and Decomposition of EMII Component

A group of εNd-La/Nb, Ba/Nb, Nb/Th diagrams are used to study mantleheterogeneity. Island-arc basalts (IAB) are distributed in a triangle of these diagrams.Three end-member components (the MORB-type depleted mantle, the fiuid released fromsubducted oceanic crust and the sediments from the continental crust) of the source ofIAB may be displayed in these diagrams. Two types of IAB are identified. They areof the two-component type (with little continental sediments), such as the basalts fromAleutians and New Britain, and the three-component type, such as those from Sunda,Lesser Antilles and Andes. In addition, the EMII type mantle-derived rocks may alsobe divided into two groups. One is exemplifled by continental flood basalts and someperidotite xenoliths, similar to IAB, with high La/Nb and Ba/Nb and low Nb/Th ratios.The other includes the Samoa-type oceanic island basalts, with low La/Nb and Ba/Nband high Nb/Th ratios. The corresponding two sub-components of EMII are EMIIM,which is related to the metasomatism of lithosphere mantle by fluids released from thesubducted oceanic crust, and EMIISR, related to the intervention of recycling continentalsediments into the convective mantle.

Newly developed evidence for the original Tethysan island-arc volcanic rocks in the southern segment of the South Lancangjiang Belt

This paper re-describes the characteristics of pre-Ordovician (Pt3) metamorphic volcanic rocks in the Huimin-Manlai region of Yunnan Province from the aspects of petrographic characteristics, rock assemblage, petrochemistry, REE, trace elements, lead isotopes and geotectonic setting. The metamorphic volcanic rocks maintain blasto-intergranular and blasto-andesitic textures; the volcanic rocks are characterized by a basalt-andesite-dacite assemblage; the volcanic rocks are basic-intermediate-intermediate-acid in chemical composition, belonging to semi-alkaline rocks, with calc-alkaline series and tholeiite series coexisting, and they are characterized by low TiO2 contents; their REE distribution patterns are of the LREE-enrichment right-inclined type; the volcanic rocks are enriched in large cation elements and commonly enriched in Th and partly depleted in Ti, Cr and P, belonging to the Gondwana type as viewed from their Pb isotopic composition; petrochemically the data points fall mostly within the field of island-arc volcanic rocks. All these characteristics provided new evidence for the existence of original Tethysan island-arc volcanic rocks in the region studied.

大地幔楔的两个深部碳循环圈:差异及宜居效应

本文总结评述了西太平洋板块深俯冲及在东亚地幔过渡带滞留和与之相关的晚白垩世和新生代东亚板内玄武岩共同构成的大地幔楔板内深部碳循环圈存在的证据;探讨了大地幔楔板内碳循环圈与岛弧系统碳循环圈在地幔碳酸盐化交代介质、碳酸盐种属、氧化还原反应及碳酸盐化地幔部分熔融发生机制等方面的差异和对显生宙大气氧含量保持稳定及温室效应周期性变化的影响;并指出了定量估计深俯冲碳酸盐歧化反应还原成金刚石而留在地幔过渡带和通过板内玄武质火山返还大气的碳各自所占有比例应是未来需研究的重要课题。

西准噶尔南部晚石炭世中-酸性火山岩成因机制及其对准噶尔洋闭合时限的约束

西准噶尔地区广泛分布石炭纪岩浆岩类,了解它们的成因和形成机制可为揭示准噶尔洋盆晚古生代构造格局和发展演化以及约束古大洋闭合时限提供重要依据。本文报道了西准噶尔南部哈拉阿拉特山地区晚石炭世中酸性火山岩的岩石学、锆石U-Pb年代学以及地球化学特征。岩石学研究表明其岩性主要为安山岩、英安质安山岩、流纹英安斑岩和流纹岩。LA-ICP-MS锆石U-Pb定年结果表明哈拉阿拉特山地区中酸性火山岩年龄为308~305 Ma,为晚石炭世中晚期。中酸性火山岩均相对富集轻稀土和大离子亲石元素,亏损Nb、Ta等高场强元素,富钠贫钾,属于低钾拉斑中钾钙碱性系列岛弧火山岩。其中安山岩和英安质安山岩具有较高SiO_(2)(56.15%~66.13%)、Al_(2)O_(3)(16.03%~17.94%)、Na_(2)O(3.44%~5.59%)、Sr((364~576)×10^(-6))含量和Na_(2)O/K_(2)O(3.20~6.40)、Sr/Y(33.5~55.6)比值,贫MgO(1.59%~2.68%)、Y((10.0~16.0)×10^(-6))和Yb((1.08~1.83)×10^(-6))的特征,并且具有Eu正异常(δEu=1.09~1.22),属于典型的埃达克岩,是经俯冲的洋壳板片在石榴角闪岩相发生部分熔融而成,且熔融产生的埃达克质熔体在上升过程中未与上覆地幔橄榄岩发生明显交代作用;流纹岩和流纹英安斑岩具有高的SiO_(2)(69.59%~75.03%)和全碱(w(Na_(2)O+K_(2)O)=7.81%~8.89%)、极低的TFe 2O 3(0.94%~1.57%)和MgO(0.12%~0.97%)含量以及弱负Eu异常(δEu=0.63~1.00)等特征,为准铝质I型流纹岩,是下地壳镁铁质岩石部分熔融的产物,很可能有少量幔源岩浆混入。综合本文数据并结合研究区大量前人已发表的岩浆岩类研究成果,认为西准噶尔南部地区在晚石炭世中晚期仍处于岛弧弧后盆地演化体系,准噶尔洋的闭合时限可能至少推迟至早二叠世早期之后。

北秦岭饭铺闪长岩的岩石成因及其构造意义

饭铺闪长岩的岩石成因模型可为深入认识北秦岭古生代中性岩浆作用的活动规律及深部过程提供进一步的限定。饭铺岩体两件样品的锆石U-Pb同位素年龄值分别为422.1±5.5 Ma和424.2±5.2 Ma,表明其形成于晚志留世。其锆石的^(176)Hf/^(177)Hf比值介于0.282560~0.282676,ε_(Hf)(t)值介于-8.48~14.45,T_(DM2)为1938~488 Ma。地球化学分析结果显示,饭铺岩体属钙碱性系列,均具有富硅、碱、钙和镁,Mg^(#)值介于41.7~57.4。在微量元素蛛网图中,饭铺岩体具有Nb、Ta、Ti异常。饭铺岩体的稀土总量为117×10^(-6)~171×10^(-6),(La/Yb)_(N)比值范围是6.71~18.1,δEu值介于0.82~0.95,表现为轻稀土元素富集、重稀土元素亏损的配分特征,未显示明显的负Eu异常。饭铺岩体形成于岛弧构造环境,岩浆起源于下地壳,可能受到少量幔源物质的混合,推测是商丹洋向北深俯冲作用的产物。

川东地区下侏罗统自流井组东岳庙段泥页岩沉积特征及物质来源

川东地区下侏罗统自流井组东岳庙段发育一套深色泥页岩,具有较大的页岩气资源勘探开发潜力。将宏观大地构造背景与微观岩石学特征分析相结合,利用微量元素(包括稀土元素)数据,对川东地区下侏罗统自流井组东岳庙段泥页岩的沉积环境和物质来源进行了分析与讨论。研究结果表明:(1)川东地区下侏罗统东岳庙段自下而上依次沉积灰色介壳灰岩、灰色粉砂质泥岩、深灰色介壳泥岩、灰黑色页岩、灰—深灰色泥岩。(2)研究区东岳庙段泥页岩稀土元素总体具有轻稀土元素富集、重稀土元素亏损的特征,δCe为负异常,Ce_(anom)平均值为-0.015,V/(V+Ni)平均值为0.70,Sr/Cu平均值为2.43,Sr/Ba平均值为0.16,(La/Yb)N平均值为1.32,泥页岩沉积环境为相对贫氧的弱还原环境,整体为温暖湿润气候下的淡水沉积,且沉积速率较快,有利于有机质的富集和保存。(3)Zr/Sc-Th/Sc图和La/Sc-Co/Th图显示研究区沉积物母岩为花岗岩;Th/Sc值为0.78、Th/Co值为0.65、Th/Cr值为0.14、La/Sc值为2.14,均接近上地壳的相应元素比值,表明母岩主要为来自上地壳;La,Ce元素校正后平均质量分数分别为34.5×10^(-6)、70.71×10^(-6),La/Yb,LREE/HREE,(La/Yb)_(N)校正后的平均值分别为11.32,8.13,7.67,δEu校正后的平均值为0.82,表明其与大陆岛弧相近,且La-Th-Sc,Th-Sc-Zr/10和Th-Co-Zr/10等3个三角图显示其构造背景为大陆岛弧。因此,研究区东岳庙段物质来源于北东侧大巴山和东南侧江南古陆(雪峰古陆)。

新疆北部卡拉麦里地区石炭纪火山岩成因及其构造意义

新疆北部卡拉麦里地区石炭系广泛发育安山岩、凝灰岩等火山岩,关于其形成的构造背景仍存在争议。选取卡拉麦里山2条典型的石炭系剖面,针对下石炭统姜巴斯套组、上石炭统巴山组和弧形梁组的安山岩、凝灰岩等岩石样品开展了镜下观察和主微量元素等测试分析。结果表明,样品具有较低-中等的MgO含量(0.5%~2.35%)和低-中等的Mg#(15.7%~42.5%),说明岩石样品在形成过程中发生了结晶分异作用。岩石样品的微量元素分布曲线与N-MORB、E-MORB和OIB存在明显差异,在Ta/Yb-Th/Yb图和La-Y-Nb图中岩石样品几乎全投在钙碱性系列区域中,在Nb/Yb-La/Yb图中全部落入俯冲组分范围并靠近地幔区。在Nb/Y-Rb/Y和Ba/La-Ba/Nb图中,表明样品受到过流体富集和熔体富集的影响。样品的Nb/U和Ce/Pb值分别为1.6~11.1和0.47~12.2,很接近大陆地壳的范围,指示物质来源可能有大陆地壳物质的混染。Th-Hf/3-Nb/16图投点指示所有样品均属于岛弧玄武岩范畴。综合分析表明,卡拉麦里地区从早石炭世到晚石炭世均处于活动大陆边缘的大陆岛弧环境,且这种环境至少从早石炭世一直延续到了晚石炭世。

内蒙古北山地区小黄山一带片麻状花岗岩形成时代、成因及构造环境

通过1∶5万区域地质调查,在内蒙古北山地区小黄山一带早石炭世侵入岩中新解体出片麻状中细粒花岗闪长岩、片麻状细粒二长花岗岩和片麻状似斑状细中粒黑云母二长花岗岩,其中片麻状中细粒花岗闪长岩和片麻状细粒二长花岗岩在空间上紧密伴生。本文研究小黄山一带片麻状花岗岩的形成时代、成因及构造环境。采用锆石LA-ICP-MS U-Pb法在片麻状中细粒花岗闪长岩、片麻状细粒二长花岗岩中分别获得了443.0±1.2 Ma和441.9±1.6 Ma的岩浆结晶年龄,时代为早志留世早期。岩石地球化学分析表明,片麻状中细粒花岗闪长岩和片麻状细粒二长花岗岩均为钙碱性系列岩石,碱度率AR为1.82~2.86,较低,且变化范围小,戈蒂尼指数τ为21.22~64.24(τ>10);岩石富集轻稀土元素及K、Rb、Ba等大离子亲石元素,亏损高场强元素Nb、P、Ti,具有岛弧岩浆岩或造山带岩浆岩的特征。结合前人研究成果综合分析,片麻状中细粒花岗闪长岩和片麻状细粒二长花岗岩形成于岛弧构造环境,是东七一山—公婆泉岛弧带的重要组成部分。