木兰山蓝片岩中两种文石的产出特征及其动力学意义

微米－纳米尺度显微超显微研究表明，木兰山蓝片岩中存在微米级粒间文石和亚微米级文石包裹体，它们是木兰山蓝片岩快速折返动力学机制的证据。并指出木兰山蓝片岩区硬柱石和绿纤石等Ca-Al硅酸盐矿物的缺失与本区变质流体中CO2浓度较高和（或）岩石中含方解石／文石有关。     

Retrogressive Microstructures of the Eclogites from the Northern Dabie Mountains, Central China： Evidence for Rapid Exhumation

The ultrahigh-pressure eclogites from the northern Dabie Mountains in central China occurred as tectonic lens or blocks within granitic gneisses or meta-peridotites. Petrologic studies suggest that the studied eclogites experienced strongly retrogressive metamorphism and produced a series of characteristic retrogressive microstructures. The retrograde structures mainly include: (1) oriented needle mineral exsolution, e. g. , quartz needles in Na-clinopyroxene and rotile, clinopyroxene and apatite exsolution in garnet formed under decreasing pressure conditions during exhumation; (2) symplectite, especially, two generations of symplectites developed outside the garnet grains, which are called ““double symplectite““ here; (3) compositional zoning of minerals such as garnet and clinopyroxene; (4) minerals with a reaction rim or retrograde rim, e.g. , omphacite with a diopside rim, diopside with an amphibole rim and rutile with a rim of ilmenite. These retrograde textures, especially mineral zoning and symplectite, provide important petrologic evidence for the exhumation process and uplift of high-grade metamorphic rocks such as eclogite in the northern Dabie Mountains, indicating a rapid exhumation process.     

Triassic Collisional Structures and Post—Collisional Deformation of Bixiling UHP Rock Stack： Insights for Tectonic Evolution of UHP Metamorphic Belt in Dabie Massif, Central China

Detailed three-dimensional structural studies indicate that the Bixiling area,Dabie massif,central Chian shows the deepest exposed levels of the orogenic wedge formed during the Triassic Yangtze0Sino-Korean continental collision.New1:10000 scale structural mapping,combined with detailed petrological analysis in this area,has enabled us to accurately distinguish structures related to the Trias-sic continental collision from those related to post-collisional deformation in the ultrahigh pressure (UHP) metamorphic unit.The collisional or compressional structures include the massive eclogite with a weak foliation,foliated eclogite or UHP ductile shear zones,as well as upper amphibolite facies shear zones,whereas the post-collisional deformation is characterized by a regionally,flat-lying foliation con-taining stretching lineations and common reclined folds .The former is present exclusively in the eclogite lenses and their margins,representing orogenic thickening or syn-collisional events,while the latter was best occurred on variable scales under amphibolite facies conditions,showing sub-vertical,extreme short-ening and ductile thinning of the metamorphic rock stack.The eclogite facies tectonites that have a marked fabric discordance to the penetrative amphibolite facies extension flow fabric are common.It is emphasized that an extensional tectonic setting following the collision-orogenic thickening stage was,at least partly,responsible for exhumation of the UHP metamorphic rocks in the Dabie massif.A new tec-tionic evolution model is proposed for the UHP metamorphic belt on the scale of the Dabie massif.The Bixiling area thus provides a window,from which the dynamic processes concerning the formation and exhumation of the UHP rocks can be observed.Regional studies in the Dabie Mountains have confirmed this interpretation.     

大别山高压、超高压变质岩结构构造的演化规律(PTt-D轨迹)

根据大别山高压、超高压变质岩的中尺度-显微构造分析及PTt研究,建立它们的结构和构造随变质作用（前榴辉岩相、超高压变质峰期、前角闪岩相和角闪岩相）有序演化的PTt-D轨迹。这一演化主要包括：在岩石的矿物结构方面从石榴石静态重结晶结构到柯石英假像及放射状张裂隙构造;在岩石组构方面从L>S到L-S和S>L榴辉岩;以及在中尺度构造方面发育的D1和D2变形构造。该PTt-D轨迹同时可以提供有关高压、超高压变质岩折返模式的信息。     

PTtD Path and Fluid Evolution of HighPressure Eclogites from the Dabie Mountains,Central East China

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Late Mesozoic Thermotectonic Evolution of the Jueluotage Range,Eastern Xinjiang, Northwest China: Evidence from Apatite Fission Track Data

Although many authors have emphasized the Cenozoic history of deformation, exhumation and cooling in the Tiaushan area related to the India-Asia collision, very little is known about the Mesozoic history of compression and uplift within the Tianshan. In order to obtain information about the Mesozoic exhumation history and processes of cooling in eastern Tianshan, fission track methods on apatite were used. Sampling was made in the Jueluotage Range. Three samples （Z001-Z003） were taken from granite in borehole ZK6301 of Yandong pluton; the ages range from 97.0 to 87.6 Ma that are much younger than the pluton age which was dated by U-Pb zircon at 334±2 Ma. Two samples in northern piedmont of the Jueluotage Range were collected from Jurassic strata in Dikaner （DK001） and Dananhu （D001） whose ages are 91.5 and 93.4 Ma respectively. The average apparent exhumation rate is 0.039 nun/a calculated by extrapolation on the basis of Yandong samples, indicating an extremely slow exhumation in the Jueluotage Range since the Late Cretaceous. Two Jurassic samples reached the maximum depths after deposition and experienced the maximum temperatures of ca. 105 and 108℃ until the late Early Cretaceous before a period of cooling and exhumation occurred at 114 and 106 Ma.     

Emplacement Mechanism of the Akebasitao Pluton: Implications for Regional Tectonic Evolution of West Junggar, NW China

Late Carboniferous to Early Permian A-type granites are extensively distributed throughout the West Junggar region, NW China, and the Akebasitao pluton is extremely distinguished among these plutons. In this paper, we reported new anisotropy of magnetic susceptible (AMS) data combine with detailed field study and audio magnetotelluric (AMT) sounding to assess the three-dimensional shape and magmatic emplacement mechanism of the Akebasitao pluton. The geological features and the AMT sounding indicate that the pluton had a slightly oblique movement of magma from northwest to southeast, which was most likely to correspond to an asymmetrical torch with a laccolith-shaped upper part, and a lower part formed by sub-vertical “root” that was located within its northwestern part, probably controlled by the NE-trending Anqi fault. The AMS fabrics of all the specimens reveal a low Pj value (mean of 1.02) and a low T value (mean of ?0.024), suggesting that the deformation of the AMS ellipsoid is relatively weak. The specimens exhibit both oblate and prolate shapes of the AMS ellipsoid. Magnetic lineations and foliations are randomly distributed throughout the pluton without any preferred orientation. These AMS patterns indicate that the pluton formed in a relatively stable structural environment with no regional extrusion. Therefore, we propose a complex emplacement process in which the magmas reached the shallower crust levels via deep-faults and subsequently occupied the room created by doming, accompanied by stoping near the pluton roof. Additionally, the regional tectonic setting was relatively stable during the emplacement of the Akebasitao pluton, indicating the termination of compressional orogeny during the late Late Carboniferous in the West Junggar region. This conclusion perfectly coincides with the regional tectonic paleogeography, magmatic system, and paleostress field.     

扬子陆块北缘西大别地区定远组双峰式火山岩U-Pb年代学及其地质构造意义

西大别地区定远组由浅变质的酸性火山岩(流纹岩和流纹质凝灰岩)和基性火山岩组成,二者在空间上互层产出,具典型的双峰式火山岩系组合特征,为认识南秦岭-大别造山带及扬子陆块北缘前寒武纪物质组成和地质演化提供了极佳的研究对象.通过对2件变流纹岩、1件变流纹质晶屑凝灰岩和1件变基性火山岩样品进行LA-ICP-MS锆石原位U-Pb测年,获得其成岩年龄分别为737±5Ma、740±3Ma、740±5Ma和739±6Ma.结果表明,定远组双峰式火山岩系形成时代并非前人认识的古生代,而是新元古代约740Ma.定远组与红安岩群双峰式火山建造形成时间基本一致,指示了西大别地区新元古代一次重要的拉张构造-岩浆事件,可能形成于大陆边缘裂谷环境.扬子陆块北缘武当-随枣-大别地区新元古代800～720Ma岩浆活动广泛且强烈,其峰期为755～730Ma,可能是对Rodinia超大陆裂解事件的响应.     

大别造山带北麓苏家河地区两种不同基性岩浆作用的识别

详细的岩石学和地球化学研究表明，产于大别造山带北麓苏家河地区的基性岩性不同是同一套岩浆演化系列的产物，它们在岩相分带，岩石结构，矿物组合，主元素和微量元素特征及成岩机制等方面存在较大的空间差异。东部岩石为部分熔融作用形成，且受结晶分异影响微弱，其化学成分可近似代表原生玄武岩浆的性质，西部岩石则经历了较强的结晶分异作用，研究揭示，整个基性岩带可能由不同时代基性岩浆沿桐柏－商城断裂带侵位形成；其中，西部基性岩体年龄有待于进一步研究确定。     

大别造山带构造归属：海西期以来地幔化学成分特征证据

通过对海西湘以来幔源岩石化学成分（特别是高度不相容元素对比值和具有相似性质的元素对比值）研究并与相邻构造单元（扬子板块北缘，华北板块南缘，北秦岭带，南秦岭带）地幔特征对比表明，大别造山带中海西期春秋庙－王母观辉长岩，碰撞后晚燕山早期镁铁－超镁铁质岩体（包括南，北大别造山带）以及产于大别造山带南部和扬子地块北缘的晚燕山晚期碱性玄武岩源区地，均具有富Sc,Cu,贫MgO，低Zr/Hf和高Rb/Sr,Ba/Sr,Ba/La,Nb/Ta,Yb/Hf等特征，源区地幔的这些特点与元古宙以来扬子地幔特征相似，而与华北地幔特征存在显著区别，反映大别造山带发育在扬子地幔上，根据大量的地质学，构造地质学，岩石学，地球物理及地球化学等研究结果，指出桐柏－商城－磨子潭－晓天断裂带是秦岭造山带中商丹断裂带的东延，综合研究证实大别造山带主体属南秦岭的组成部分。     

东昆仑东段哈拉郭勒-哈图一带中生代的岩石隆升剥露--锆石和磷灰石裂变径迹年代学证据

根据对东昆仑地区东段哈拉郭勒—哈图一带不同高度基岩的系列锆石裂变径迹年龄分析，结合磷灰石裂变径迹年龄分析和中酸性侵入岩角闪石压力计分析揭示了东昆仑东段中生代的岩石隆升剥露冷却历史．巴隆哈图一带中酸性侵入岩角闪石压力计分析结果反映晚海西—印支期以来的总体剥露幅度约8～9km，早二叠世至晚三叠世初剥蚀作用极为缓慢，大约为20～40m／Ma．不同高程样品的锆石裂变径迹年龄分析结果揭示了东昆仑地区东段在中晚侏罗世处于缓慢的岩石隆升剥露阶段，其中中侏罗世相对较快，抬升速率77～88m／Ma，晚侏罗世相对较慢，抬升速率小于37m／Ma，且呈减慢趋势，这种减慢趋势反映了早中侏罗世之交强构造抬升期后的逐渐衰退．锆石裂变径迹—磷灰石裂变径迹年龄分析结果反映了中侏罗世以来的剥蚀速率一般不超过55m／Ma，岩石的剥蚀速率与岩石的抬升速率基本为同一量级，中侏罗世—白垩纪剥蚀作用与岩石抬升作用基本处于平衡状态。     

Early Paleozoic Ocean Plate Stratigraphy of the Beishan Orogenic Zone,NW China: Implications for Regional Tectonic Evolution

The Beishan orogenic zone is a key area to understand evolution of the Central Asian Orogenic Belt that is an accretionary factory well-enough preserved in the Paleozoic. In early Paleozoic, the tectonic mélange zone containing the coherent unit and mélange unit is triggered by the complicated accretionary process of the Beishan area. The early Paleozoic tectonic evolution of the Beishan orogenic zone is investigated in this study using sedimentology and stratigraphic correlations of the lowe Pa...     

Apatite Fission Track Thermochronology of Granite from the Xiazhuang Uranium Ore Field, South China: Implications for Exhumation History and Ore Preservation

Xiazhuang uranium ore field, located in the southern part of the Nanling Metallogenic Belt, is considered one of the largest granite-related U regions in South China. In this paper, we contribute new apatite fission track data and thermal history modeling to constrain the exhumation history and evaluate preservation potential of the Xiazhuang Uranium ore field. Nine Triassic outcrop granite samples collected from different locations of Xiazhuang Uranium ore field yield AFT ages ranging from 43 to 24 Ma with similar mean confined fission track lengths ranging from 11.8 ± 2.0 to 12.9 ± 1.9 μm and Dpar values between 1.01 and 1.51 μm. The robustness time-temperature reconstructions of samples from the hanging wall of Huangpi fault show that the Xiazhuang Uranium ore field experienced a time of monotonous and slow cooling starting from middle Paleocene to middle Miocene (~60–10 Ma), followed by relatively rapid exhumation in the late Miocene (~10–5 Ma) and nearly thermal stability in the Pliocene–Quaternary (~5–0 Ma). The amount of exhumation after U mineralization since the Middle Paleogene was estimated as ~4.3 ± 1.8 km according to the integrated thermal history model. Previous studies indicate that the ore-forming ages of U deposits in the Xiazhuang ore field are mainly before Middle Paleocene and the mineralization depths are more than 4.4 ± 1.2 km. Therefore, the exhumation history since middle Paleocene plays important roles in the preservation of the Xiazhuang Uranium ore field.     

The Grenvillian Songshugou ophiolite in the Qinling Mountains, Central China: Implications for the tectonic evolution of the Qinling orogenic belt

The Qinling Mountains in Central China mark a gigantic composite orogenic belt with a complex tectonic evolution involving multiple phases of rifting and convergence. This belt separates the North China and South China Blocks and consists of the South and North Qinling terranes separated by the Shangdan suture. The suture is marked by the Grenvillian Songshugou ophiolite along the southern margin of the North Qinling terrane, which is key to understanding the Proterozoic tectonic evolution of the belt. The ophiolite consists of highly metamorphosed ultramafic and mafic rocks. Three groups of meta-basalts are present: group 1 rocks are LREE depleted and have a MORB compositional affinity. Their low Ta/Yb ratios (<0.1) are consistent with high degrees of partial melting of a depleted asthenospheric mantle. Rocks of group 2 have higher TiO₂ (1.63–2.08 wt%) and Ta/Yb ratios (>0.12), and display slight enrichment of LREE, suggesting that the original magmas were derived from a depleted mantle source mixed with some enriched material. Samples from group 3 are enriched in LREE and other incompatible elements (Ti, Zr, Ta, Nb), suggesting derivation from an enriched mantle source, possibly a plume. All the basalts have high εNd(t) (+4.2 to +6.9), variable εSr(t) and high ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios for given ²⁰⁶Pb/²⁰⁴Pb ratios. These characteristics are compatible with formation at a mid-ocean ridge system above an anomalous Dupal mantle region. The mafic rocks have a Sm–Nd whole-rock isochron age of 1030 ± 46 Ma.The Songshugou ophiolite was emplaced onto the southern margin of the North Qinling terrane, an active continental margin from the Meso-Proterozoic to Neo-Proterozoic.     

Unusual Hf contents in metamorphic zircon from coesite-bearing eclogites of the Dabie Mountains, east-central China: implications for the dating of ultrahigh-pressure metamorphism

Metamorphic zircon from coesite‐bearing eclogites in the Dabie Mountains encloses high‐P phases, and may have formed at the peak of ultrahigh‐pressure (UHP) metamorphism. Morphologically, the metamorphic zircon typically occurs as small, multi‐faceted, near‐spherical grains with homogeneous internal structure and weak backscattered electron (BSE) luminescence. Geochemically, it is characterized by extremely high and relatively constant contents of hafnium (Hf) and very low contents of Y, U and Th, reflecting the contraction of the zircon lattice under the UHP conditions. High contents of Hf may be characteristic of zircon formed during UHP metamorphism, which has important consequences for interpretation of geochronological results. We propose that the metamorphic zircon extremely enriched in Hf may be used to date the peak of UHP metamorphism that produced the coesite‐bearing eclogites in the Dabie Mountains, and potentially in other UHP terranes.     

中天山巴仑台地区花岗质岩石的Hf同位素研究：对构造演化及大陆生长的约束

中国中天山地块位于天山造山带的核心部位,对研究中亚造山带西南段构造演化、块体起源和陆壳生长等科学问题具有重要意义。本次研究围绕中天山地块西段巴仑台一带出露的古生代花岗质岩石展开,报道了部分代表性岩体的LA-ICP-MS锆石U-Pb年龄和MC-ICP-MS锆石Lu-Hf同位素特征。同时还系统总结前人发表的研究区内花岗质岩石的锆石U-Pb年龄和Lu-Hf同位素资料。本次研究的7个花岗质侵入体的锆石LA-ICPMS年龄分别为435±5 Ma、432±4 Ma、359±4 Ma、312±4 Ma、346±2 Ma、306±5 Ma和362±5 Ma。它们在成因类型上均属于I型花岗岩,起源于深部不同性质地壳物质的部分熔融,部分岩体具有壳幔混合成因。研究表明,巴仑台一带的岩浆事件主要发生在早志留世—早泥盆世(435~408 Ma)、晚泥盆世—早石炭世(370~339 Ma)和晚石炭世—中二叠世(313~263 Ma)三个阶段,第一期岩浆事件是古天山洋闭合形成的后碰撞体制以及古南天山洋俯冲导致的大陆岛弧环境共同作用的结果。而古南天山洋俯冲活动的暂停和新一轮的洋盆扩张是导致区内中、晚泥盆世岩浆活动暂停的原因。第二期花岗质侵入体是古南天山洋第二期北向俯冲所导致的大陆岛弧岩浆作用的产物,而第三期花岗质侵入体形成于古南天山洋最终闭合之后的后碰撞环境中。通过总结区内古生代花岗质岩体的锆石的Hf同位素特征,我们认为巴伦台地区前寒武基底主要形成于三个阶段:1~2.47Ga至~2.26Ga,为研究区对全球陆核生长事件的响应;2~1.47Ga至~1.25Ga,对应于哥伦比亚超大陆的裂解;3~1.20Ga至~0.90Ga,很可能是研究区对导致罗迪尼亚超大陆聚合的"Grenville运动"的响应。     

Evolution of high-Mg–Al granulites from Sunkarametta, Eastern Ghats, India: evidence for a lower crustal heating–cooling trajectory

A suite of high-Mg–Al granulites from Sunkarametta, Eastern Ghats Belt, India, shows contrasting prograde assemblages of extremely aluminous orthopyroxene+cordierite+sapphirine and similarly aluminous orthopyroxene+Ti-rich spinel in closely associated domains. Textural and compositional characteristics indicate that both were derived from prograde dehydration–melting of biotite–plagioclase–quartz-bearing protoliths. The former assemblage was stabilized at relatively more magnesian bulk composition. Geothermobarometric data and petrogenetic grid considerations place 'peak' metamorphic conditions at c. 950 °C and 9 kbar. Subsequent to peak metamorphism, the rocks cooled to c . 700–750 °C, with slight lowering of pressure, and the retrograde reactions also involved melt–solid interaction. The inferred P – T  trajectory is one of heating–cooling at lower crustal (25–30 km) depths.     

Determination of the early Paleozoic accretionary complex in Southwestern Yunnan,China: Implications for the tectonic evolution of the Proto-Tethys Ocean

Accretionary complex study provides important knowledge on the subduction and the geodynamic processes of the oceanic plate, which represents the ancient ocean basin extinction location. Nevertheless, there exist many disputes on the age, material source, and tectonic attribute of the Lancang Group, located in Southwest Yunnan, China. In this paper, the LA-ICP-MS detrital zircon U–Pb chronology of nine metamorphic rocks in the Lancang Group was carried out. The U–Pb ages of the three detrital zircons mainly range from 590–550 Ma, 980–910 Ma, and 1150–1490 Ma, with the youngest detrital zircons having a peak age of about 560 Ma. The U–Pb ages of the six detrital zircons mainly range from 440–460 Ma and 980–910 Ma, and the youngest detrital zircon has a peak age of about 445 Ma. In the Lancang Group, metamorphic acidic volcanic rocks, basic volcanic rocks, intermediate-acid intrusive rocks, and high-pressure metamorphic rocks are exposed in the form of tectonic lens in schist, rendering typical melange structural characteristics of “block + matrix”. Considering regional deformation and chronology, material composition characteristics, and the previous data, this study thinks the Lancang Group may be an early Paleozoic tectonic accretionary complex formed by the eastward subduction of the Changning-Menglian Proto-Tethys Ocean, which provides an important constraint for the Tethys evolution.©2023 China Geology Editorial Office.     

~(207)Pb/~(206)Pb Zircon Dating of the Huangtuling Hypersthene-Garnet-Biotite Gneiss from the Dabie Mountains, Luotian County, Hubei Province, China: New Evidence for Early Precambrian Evolution

The Huangtuling hypersthene-garnet-biotite gneiss at Luotian County, Hubei Provine, is a typicalgranulite-facies rock of the Dabie Group Complex in the Dabie orogenic belt. Investigations on the morphology andoccurrence of zircons and their internal structures shown in the thin sections lead to the recognition of three types ofzircons, which are in good agreement with the types identified on the basis of morphology, colour and external fea-tures from the related zircon concentrates. The observation of zircons in the rock reveals that part of type 1 zirconsshow signs of a double-layered structure. The interval part existed in the protolith prior to the granulite-facies meta-morphism. Type 2, the prismatic zircons which mainly occur in garnet and hypersthene are metamorphic minerals ofthe granulite-facies metamorphism. Type 3, the round multifaceted zircons in felsic minerals and biotite, are proba-bly attributed to a later geological event related to migmatization. The ~(207)Pb/~(206)Pb zircon dating by direct evaporationon (thermal evaporation ion mass spectrometer) yields ages ranging from 2814 Ma to 1992 Ma. The age discrepancyamong these different zircon types is conspicuous. The yellow-brown(type 1) zircons give ages of 2814±29 Ma to2527±6 Ma, the prismatic euhedral zircons (type 2), 2456±7 Ma to 2254±4 Ma, and the round multifaceted zircons(type 3), 1992±10 Ma. The results are geologically interpreted in consideration of the complicated behaviours of zir-cons during Precambrian geological evolution of the Dabie area. (1) If the protolith of the gneiss is a sedimentaryrock, then type 1 zircons are clastic ones and the ages 2814±29 Ma and 2811±27 Ma may reflect the minimum age ofthe rocks of its source region. also the first geological event in the area. Sedimentation of the protolith occurred be-tween 2814 Ma and 2527 Ma, probably close to 2814 Ma. If the protolith is a volcanic rock, then the formation age ofthe supracrustal rocks of the Dabie Group Complex is around 2814 Ma. The age 2456±7 Ma reflects the time whenthe granulite-facies metamorphism took place. The later migmatization event is dated at aboat 1992±10 Ma, and isprobably the latest early Precambrian event in the area. The present work provides geochronological evidence for the existence of the Dabie Archaean craton, whichhad probably experienced 3 or 4 geological events during its early Precambrian evolution.     

Reactions and textures in grossular–wollastonite–scapolite calc–silicate granulites from Maligawila, Sri Lanka: evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex

Grossular–wollastonite–scapolite calc–silicate granulites from Maligawila in the Buttala klippe, which form part of the overthrusted rocks of the Highland Complex of Sri Lanka, preserve a number of spectacular coronas and replacement textures that could be effectively used to infer their P–T–fluid history. These textures include coronas of garnet, garnet–quartz, and garnet–quartz–calcite at the grain boundaries of wollastonite, scapolite, and calcite as well as calcite–plagioclase and calcite–quartz symplectites or finer grains after scapolite and wollastonite respectively. Other textures include a double rind of coronal scapolite and coronal garnet between matrix garnet and calcite. The reactions that produced these coronas and replacement textures, except those involving clinopyroxene, are modelled in the CaO–Al₂O₃–SiO₂–CO₂ system using the reduced activities. Calculated examples of T–X_CO2 and P–X_CO2 projections indicate that the peak metamorphic temperature of about 900–875 °C at a pressure of 9 kbar and the peak metamorphic fluid composition is constrained to be low in X_CO2 (0.1<X_CO2<0.30). Interpretation of the textural features on the basis of the partial grids revealed that the calc–silicate granulites underwent high-temperature isobaric cooling, from about 900–875 °C to a temperature below 675 °C, following the peak metamorphism. The late-stage cooling was accompanied by an influx of hydrous fluids. The calc–silicate granulites provide evidence for high-temperature isobaric cooling in the meta-sediments of the Highland Complex, earlier considered by some workers to be confined exclusively to the meta-igneous rocks. The coronal scapolite may have formed under open-system metasomatism.