琼中麻粒岩的成因:稀土元素地球化学制约

稀土元素地球化学分析表明,琼中麻粒岩可以分为"高Ti"麻粒岩(TiO2含量大于1.0%)和"低Ti"麻粒岩(TiO2含量低于1.0%)两种化学类型."高Ti"麻粒岩以稀土总量高,轻稀土高度富集,轻、重稀土强烈分馏为特征,稀土配分曲线呈右倾单斜型,与本区变基性火山岩的稀土分布特征相似;低"Ti"麻粒岩以稀土总量较低,轻稀土分馏强烈,但重稀土分馏不明显为特征,稀土配分曲线呈重稀土平坦的左高右低型,与许多浅成基性岩的稀土分布特征相似;认为琼中麻粒岩形成于晋宁期的可能性最大.两类麻粒岩的识别,有利于深化对琼中杂岩形成和演化过程的认识.     

汉诺坝麻粒岩捕虏体锆石U-Pb 分析初步结果及讨论

本文报道了汉诺坝玄武岩中麻粒岩捕虏体的锆石 U-Pb 初步分析结果，并讨论了其成因的两种可能性。     

Metapelitic Migmatites From Pangidi Granulite Complex,Eastern Ghats Belt,India: Petrological Constraints on Crustal Melting and Tectonic Exhumation

Metapelitic migmatites in the Pangidi Granulite Complex, Eastern Ghats belt preserve a range of high-grade mineral assemblages that vary with bulk composition. Reaction textures preserved in the migmatites indicate that the crystallized granitic melt was formed in situ by biotite dehydration-melting reactions. Decompression occurred during an episode of partial melting and melt crystallization, and was synchronous with exhumation of migmatites along shear zones. Retrograde reaction textures and the calculated positions of the mineral reactions and discrete P-T points obtained by thermobarometry reflect ∼3 kbar (11 km) of exhumation from near peak P-T conditions of ∼9 kbar and 950°C.Decompression has been traditionally ascribed to be the cause of dehydration melting in many orogens, but the bulk of melting reactions in Pangidi were ultimately driven by elevated temperatures. Simple pressure release during exhumation did not force melting reactions, instead as the present study reveals, it is more likely that the presence of melt triggered deformation in the migmatites and facilitated exhumation.     

Metapelites of the Kanskiy Granulite Complex (Eastern Siberia): Kinked P-T Paths and Geodynamic Model

The Southern Yenisey Range (Eastern Siberia) consists of thegranulite-facies Kanskiy complex bordered by the lower-gradeYeniseyskiy and Yukseevskiy complexes. Samples of metapeliteof the Kanskiy complex typically show characteristic garnet-formingreaction textures and near-isobaric cooling P–T paths.An important new result of this study concerns the differencein shape of the P–T paths from different parts of theKanskiy granulite complex: metapelites collected 8 km from theboundary with the Yeniseyskiy complex followed a linear pathwith dP/dT 0·006 kbar/°C; metapelites collected3 km from this boundary reveal a kinked P–T path withan interval of burial cooling (dP/dT –0·006 kbar/°C).The difference in the shape of the P–T paths is supportedby the chemical zoning of garnet studied in the second groupof samples. A mechanism of buoyant exhumation of granulite issuggested by comparison with the results of numerical modelling,which indicate that such a diversity of P–T paths mayresult from a transient disturbance of the thermal structureby rapid differential movement of material from different crustallevels. To arrive at a correct tectonic interpretation, thewhole assemblage of interrelated P–T paths of metamorphicrocks collected from different localities within the same complexmust be studied. KEY WORDS: crustal diapirism; exhumation; granulites; numerical modelling; P–T path     

包头—忽鸡沟一带麻粒岩相岩石的矿物学和结晶P-T条件

本文提供了77个石榴石、辉石、角闪石、黑云母和斜长石等单矿物能谱和湿化学分析资料,研究了各种矿物对的分配系数。用二辉石地质温度计估算的变质作用温度为770—860℃,用其他矿物对估算的温度多数在二辉石温度计获得的温度范围内。用Wood的石榴石—斜方辉石地质压力计和Newton—Perkins以及Wells石榴石—斜方辉石—斜长石地质压力计公式估算的变质作用压力为(8—10)×10~8Pa,地热梯度为24.6—27.5℃/km,属低—中压型麻粒岩相。     

The Fluid-absent Partial Melting of a Zoisite-bearing Quartz Eclogite from 1{middle dot}0 to 3{middle dot}2 GPa; Implications for Melting in Thickened Continental Crust and for Subduction-zone Processes

Fluid-absent melting experiments on a zoisite- and phengite-bearingeclogite (omphacite, garnet, quartz, kyanite, zoisite, phengiteand rutile) were performed to constrain the melting relationsof these hydrous phases in natural assemblages, as well as themelt and mineral compositions produced by their breakdown. From1·0 to 3·2 GPa the solidus slopes positively from1·5 GPa at 850°C to 2·7 GPa at 1025°C,but bends back at higher pressures to 975°C at 3·2GPa. The melt fraction is always low and the melt compositionsalways felsic and become increasingly so with increasing pressure.The normative Ab–An–Or compositions of the initialmelts vary from tonalites at 1·0 GPa to tonalite–trondhjemitesat 1·5 GPa, adamellites at 2·1 and 2·7GPa, and to true granites at 3·2 GPa. At pressures <     

Fluid inclusions in Adirondack granulites: Implications for the retrograde P-T path

Investigation of fluid inclusions in granitic and cale-silicate gneisses from the Adirondack Mountains, New York, has revealed the presence of various types, including: (1) CO₂-rich, (2) mixed H₂O–CO₂±salt and (3) aqueous inclusions with no visible CO₂. Many, if not all, of these inclusions were trapped or modified after the peak of granulite facies metamorphism, as shown by textural relations or by the lack of agreement between the composition of the fluids found in some inclusions and the composition of the peak-metamorphic fluid as estimated from mineral equilibria. Many fluid inclusions record conditions attained during retrograde cooling and uplift, with minimum pressures and temperatures of 2 to 3 kbar and 200 to 300°C. The temperatures and pressures derived from the investigation of these inclusions constrain the retrograde P-T path, and the results indicate that a period of cooling with little or no decompression.     

The Influence of Retrograde Cation Exchange on Granulite P-T Estimates and a Convergence Technique for the Recovery of Peak Metamorphic Conditions

Chemical relationships in garnet-orthopyroxene-plagioclase-quartzrocks are governed principally by three equilibria: the Fe-Mgexchange reaction between garnet and orthopyroxene, the solubilityof alumina in orthopyroxene coexisting with garnet, and thereaction of garnet and quartz to form orthopyroxene and plagioclase.Various thermobarometric calibrations of these equilibria havebeen applied to granulite-facies gneisses from two areas ofthe Proterozoic Complex of East Antarctica, and a wide rangeof P-T estimates is obtained for each area. Some of this P-Tvariation reflects the different thermodynamic data and mineralmixing models used by each calibration, but other differencesare attributed to the effects of retrograde Fe-Mg exchange.An inter-specimen spread of temperatures in each area, obtainedfor mineral core compositions with a single calibration of thegarnet-orthopyroxene exchange reaction, is attributed to a variableextent of Fe-Mg exchange on cooling from peak metamorphic conditions.A similar spread of pressures from the garnet-orthopyroxenealumina solubility barometer indicates that this calibrationis also reset by retrograde Fe-Mg exchange. In contrast, pressuresfrom the garnet-orthopyroxene-plagioclase-quartz barometer formineral cores show little variation between specimens from thesame area, indicating that this equilibrium is relatively insensitiveto changes in the Fe-Mg distribution coefficient and that derivedpressures are more likely to reflect peak metamorphic conditionsthan those from the alumina solubility barometer. Temperaturescan be corrected for Fe-Mg exchange using the Fe-Mg distributioncoefficient required to bring pressures from the exchange-sensitivealumina solubility barometer into agreement with reference pressurescalculated from the exchange-insensitive garnet-orthopyroxene-plagioclase-quartzbarometer. These corrected temperatures are closure temperaturesfor Al diffusion, which in many cases are likely to be goodestimates for the peak metamorphic temperature. The extent oftemperature correction in these specimens is 0–140C,and can be qualitatively related to textural features such asgrain size and mutual proximity of garnet and orthopyroxenegrains. Retrograde Fe-Mg exchange has clearly been significantin these rocks, with major consequences for thermobarometry.It is likely that Fe-Mg exchange during cooling is more widespreadthan currently recognized, and that the suggested convergencemethod for retrieving peak metamorphic conditions is applicableto other granulite terrains.     

Genesis and Tectonic Implications of the Kabr El-BonayaUltramafic Rocks,Sinai Peninsula,Egypt: Constraints fromMineralogical and Geochemical Characteristics

The Kabr El-Bonaya mafic–ultramafic intrusion is exposed along the southeastern border of the Sinai Peninsula and the northernmost segment of the Arabian-Nubian Shield(ANS). It occurs as an elliptical intrusive body that is located along the major NE–SW trending fracture zones that prevail in the Kid metamorphic complex. The ultramafic rocks in the complex comprise ultramafic cumulates of peridotites(dunite, harzburgite and wehrlite) and pyroxenite. These rocks are generally unmetamorphosed and have intrusive contacts with the country rock. Mineral chemistry and whole-rock chemical compositions of these ultramafic rocks are mostly consistent with those of residual mantle peridotites from refractory suprasubduction tectonic settings. Based on the variations of the major elements, the studied ultramafic rocks are consistent with those of a supra-subduction zone mantle, as it seems to have melted at 1–2 GPa and 1300–1450°C. Linear variations of Al2 O3, CaO, V and Ni with MgO, coupled with incompatible and rare-earth-element depletion and mineral compositions,suggest prior events of partial melting in both wehrlites and harzburgites. The LREE enrichment in the harzburgite, as well as the development of Cr-rich spinel, is consistent with a history of melt–peridotite interaction. The calculated(Sm/Yb)N variations for the studied peridotites indicate a general increase in the addition of fluids with an increasing degree of melting from the wehrlite(～13–15 wt% of fluid) in the source, after initial spinel peridotite melting to the harzburgite(～20–25 wt% of fluid) in the same source, which is contrary to normal abyssal peridotites. The estimated equilibration temperature ranges from 1214 to 1321°C for the studied wehrlites and from 1297 to 1374°C for harzburgites. The Mg-rich nature of the analysed olivines from the studied ultramafic rocks(Fo = 81.41 to 91.77) reflect their primary composition and are similar to olivines in Alaskan-type ultramafic rocks. The Fo content of the analyzed olivines decrease slightly from the dunite to the harzburgite to the wehrlite and to pyroxenite, reflecting a fractional crystallization trend. The high Cr# and very low TiO2 contents(0.03–0.12 wt%) of the Cr-spinels from the studied peridotites are mostly consistent with modern highly refractory fore-arc peridotites, indicating that these peridotites developed in a supra-subduction zone environment.     

冀东秦家峪中元古界高于庄组锰矿成因: 来自矿物学和地球化学的制约

冀东秦家峪锰矿赋存于中元古界蓟县系高于庄组二段底部含锰岩系内,其成因尚不明确.以秦家峪锰矿ZK58-2钻孔样品为研究对象,通过显微薄片观察、电子探针分析及全岩地球化学分析等方法,探讨了高于庄组锰矿的锰质来源和沉积环境对成矿的贡献.显微薄片观察、电子探针分析表明,原生矿带中含锰矿物主要为菱锰矿、铁镁菱锰矿、钙菱锰矿、锰方...     

Southern Granulite Terrain, South of the Palghat-Cauvery Shear Zone: Implications for India-Madagascar Connection

The present paper correlates the southern Madgascar terrain, south of the Ranotsara shear with the granulite terrain of southern India, occurring south of the Palghat-Cauvery (P-C) shear zone. Both the terrains have witnessed high temperature to ultra high temperature granulite metamorphism at 550 Ma and are traversed by shear zones and deep crustal faults. The 550 Ma old granulite terrains of Madagascar and southern India have similar lithologies, in particular, sapphirine bearing pelitic assemblages. Graphite deposits and gem occurrences are common to both these terrains. The 550 Ma old southern granulite terrain of southern India comprises of different blocks, the Madurai and the Kerala Khondalite belt, but all the blocks have similar lithologies with pelite—calc silicate rocks inter-banded with two pyroxene granulite bodies. These lithologies occur amidst an essentially charnockitic terrain. The protolith ages of the southern granulite terrain, south of the P-C shear zone ranges between 2400–2100 Ma. The terrain as a whole has witnessed the 550 Ma old granulite event. The granulite metamorphism took place under temperatures of 800–1000°C and at pressures of 9.5 to 5 Kbar.The source of heat for the high temperature granulite event of the southern Madagascar terrain has been linked to advective heat transfer along mantle deep faults. The source for the high temperature granulite metamorphism for the southern granulite terrain may be attributed to high temperature carbonatite and alkaline intrusives in an extensional setting which followed an initial crustal thickening.Many workers have linked Madagascar to southern India by connecting the Ranotsara shear either to the P-C shear zone or to the Achankovil shear zone, further south. The important factor is the lithologies of the Madagascar terrain, south of Ranotsara shear zone and the 550 Ma. old southern Indian granulite terrain are similar in many aspects. It will be more appropriate to link the Ranotsara shear to the curvilinear lineament bounding the Anaimalai-Kodaikanal ranges and which merges with the southern margin of the P-C shear zone.However, north of the Ranotsara shear/fault, the northern Madagascar terrain comprises of a dominant Itremo sequence (< 1850 Ma) and 780 Ma old calc-alkaline intrusives. The latter have similarities with that of Aravallis and the Sirohi, Malani sequences occurring further north east. The Rajasthan terrain has witnessed igneous intrusive activity at 1000–800 Ma. If we can broaden the area of investigations and include the above areas, the Madagascar-India connection can be better understood.     

古特提斯洋的闭合时代的古地磁分析:松潘复理石杂岩形成的构造背景

对华南地块、塔里木地块和基墨里大陆(包括保山、缅泰和羌塘地块)进行了古纬度和纬度运移量的对比分析,以确定古特提斯洋盆的闭合时代。结果表明：①保山与华南地块于晚二叠世碰撞,然后继续和华南地块、缅泰地块一起向北漂移,直到晚三叠世,并导致华南地块与华北地块碰撞和秦岭—大别造山带的形成;②羌塘地块与塔里木地块碰撞发生在晚三叠世;古特提斯洋沿着保山地块东缘和羌塘地块北缘的闭合是不同时的,东早西晚;③华南地块向北漂移,可能引起了华南地块西部和东昆仑—柴达木地块南部的古特提斯洋北岸的凹入,这为松潘—甘孜海底扇的发育提供了空间;古特提斯洋闭合引起的俯冲造成了华南地块西部大陆边缘的裂离,也共同为海底扇的发育提供了空间。包括塔里木地块、华南地块、东昆仑—柴达木地块和羌塘地块在内的几个地块的合围,导致了松潘—甘孜地块三角形的构造形状。支持以前的假设：松潘—甘孜三叠纪复理石杂岩的物源来自华北地块南缘或秦岭—大别造山带。     

Geochemical characteristics of Proterozoic granite magmatism from Southern Granulite Terrain,India: Implications for Gondwana

Granitoid intrusions occur widely in the Southern Granulite Terrain (SGT) of India, particularly within the Cauvery Suture Zone (CSZ), which is considered as the trace of the Neoproterozoic Mozambique ocean closure. Here we present the petrological and geochemical features of 19 granite plutons across the three major tectonic blocks of the terrain. Our data show a wide variation in the compositions of these intrusions from alkali feldspathic syenite to granite. The whole rock geochemistry of these intrusions displays higher concentrations of \(\hbox {SiO}_{2}\), FeO*, \(\hbox {K}_{2}\hbox {O}\), Ba, Zr, Th, LREE and low MgO, \(\hbox {Na}_{2}\hbox {O}\), Ti, P, Nb, Y and HREE’s. The granitoids are metaluminous to slightly peraluminous in nature revealing both I-type and A-type origin. In tectonic discrimination plots, the plutons dominantly show volcanic arc and syn-collisional as well as post-collisional affinity. Based on the available age data together with geochemical constrains, we demonstrate that the granitic magmatism in the centre and south of the terrain is mostly associated with the Neoproterozoic subduction–collision–accretion–orogeny, followed by extensional mechanism of Gondwana tectonics events. Similar widespread granitic activity has also been documented in the Arabian Nubian shield, Madagascar, Sri Lanka and Antarctica, providing similarities for the reconstruction of the crustal fragments of Gondwana supercontinent followed by Pan-African orogeny.     

Granulite Genesis and Tectonic Evolution in Tongbai Area: Single Zircon Evaporation Ages and Nd Isotopic Geochemistry

ＩＮＴＲＯＤＵＣＴＩＯＮＴｏｎｇｂａｉａｒｅａｉｎＣｅｎｔｒａｌＣｈｉｎａｉｓａｎｉｍｐｏｒｔａｎｔｒｅｇｉｏｎｆｏｒｓｔｕｄｙｉｎｇｇｅｎｅｓｉｓｒｅｌａｔｉｏｎｂｅｔｗｅｅｎＱｉｎｌｉｎｇｏｒｏｇｅｎｉｃｂｅｌｔａｎｄＤａｂｉｅｏｒｏｇｅｎｉｃｂ...     

扬子地块西缘灯影组层控铅锌矿床成因的地球化学论证

扬子地块西缘灯影组层控铅锌矿床成因的地球化学论证邵世才（有色总公司北京矿产地质研究所，北京１０００１２）李朝阳（中国科学院地球化学研究所，贵阳５５０００２）关键词层控铅锌矿床地球化学矿床成因扬子地块西缘１矿床地质特征扬子地块西缘灯影组铅锌矿床呈南北向...     

扬子台地西南部奥陶系宝塔组底部含鲕绿泥石灰岩成因意义

对四川省兴文县上奥陶统宝塔组底部含鲕绿泥石灰岩开展成因研究,有助于了解扬子台地西南部同时期的沉积环境演化过程.通过沉积学分析,并辅助以电子探针和扫描电镜等矿物学研究方法,发现富鲕绿泥石鲕粒及球粒为同生期沉积物,共生的生物碎屑组合指示海水为氧化性水体.丰富的微生物相关组构表明同期微生物席发育,且其代谢活动可致使水岩界面附...     

Granulite facies xenoliths from Prindle volcano, Alaska: Implications for the northern Cordilleran crustal lithosphere

Xenoliths collected from Prindle volcano, Alaska (Lat. 63.72°N; Long. 141.82°W) provide a unique opportunity to examine the lower crust of the northern Canadian Cordillera. The cone's pyroclastic deposits contain crustal and mantle-derived xenoliths. The crustal xenoliths include granulite facies metamorphic rocks and charnockites, comprising orthopyroxene (opx)–plagioclase (pl)–quartz (qtz) ± mesoperthite (msp) and clinopyroxene (cpx). Opx–cpx geothermometry yields equilibrium temperatures (T) from 770 to 1015 °C at 10 kbar. Pl–cpx–qtz geobarometry yields pressures (P) of  6.6–8.0 kbar. Integrated mesoperthite compositions suggest minimum temperatures of 1020–1140 °C at 10 kbar using solvus geothermometry. The absence of garnet in these rocks indicates a range of maximum pressure of 5–11.3 kbar, and calculated solidi constrain upper temperature limits. We conclude that the granulite facies assemblages represent relatively dry metamorphism at pressures indicative of crustal thicknesses similar to present day ( 36 km). Zircon separates from a single crustal xenolith yield mainly Early Tertiary (48–63 Ma) U–Pb ages which are considerably younger than the cooling ages of the high-pressure amphibolites exposed at the surface. The distribution of zircon ages is interpreted as indicating zircon growth coincident with at least two different thermal events as expressed at surface: (i) the eruption of the Late Cretaceous Carmacks Group volcanic rocks in western Yukon and adjacent parts of Alaska, and (ii) emplacement of strongly bimodal high level intrusions across much of western Yukon and eastern Alaska possibly in an extensional tectonic regime. The distributions of zircon growth ages and the preservation of higher-than-present-day (> 25 ± 3 °C km^− 1) geothermal gradients in the granulite facies rocks demonstrate the use of crustal xenoliths for recovering records of past, lithospheric-scale thermal–tectonic events.