Geochronology and origin of Paleoproterozoic charnockites with old crustal signature in the Haisyn block of the Ukrainian shield

Results of a geochemical and geochronological study of the Paleoproterozoic rock assemblage in the Haisyn block of the Ros-Tikych Domain of the Ukrainian Shield are reported.Within the block,the Haisyn Complex comprises granitoids,including pyroxene-bearing diorites,quartz diorites,granodiorites,amphibole-biotite and biotite granites,and aplite and pegmatite granites.Monazite U-Pb isotope age of charnockitic syenite belonging to the Haisyn Complex was defined at 2027±6 Ma.This age coeval with the time of granulite facies metamorphism and emplacement of numerous granitic intrusions in the area.The Sm–Nd apatite isochron yielded an age of 2100±150 Ma.TheεNd isochron value of-5 indicates a long crustal residence time of the crustal protolith.Geochemical data do not indicate any enrichment of the studied rocks in relation to the Eoarchean and Neoarchean charnockites developed in the same area.So,if the model of partial melting of the older crustal protolith is involved then the degree of melting must be quite high.However,deep negative anomalies of Sr,Eu,Zr,and Ti indicate that plagioclase,zircon,and Fe–Ti oxides probably remained unmelted in the source.The Haisyn block was buried in the lower crust at high temperature and pressure conditions in the Paleoproterozoic time.Such a situation resulted in partial melting of the existing crust and formation of melts,containing undigested zircon and bearing ancient Nd isotope signature.

Geochemical Characteristic of Charnockites in North Margin of North China Craton: Indicating the Significiant of the Neoarchean Tecnotic Event

The Neoarchean charnockites of North margain of North China Craton(NCC) has become a hot topic into understanding the Early Precambrian basement. Although there is a broad consensus that charnockite is usually related to granulite facies metamorphism, whether its petrogenesis and tectonics characteristics remains controversial. Inclusions within hypersthene and garnet in charnockite are used to identify the peak granulite facies mineral assemblage, with the formation of Magnesian-charnockite attributed to anatexis of the protolith associated with this granulite facies metamorphism. The distribution of major and trace elements in charnockite is very uneven, significant depleted in LILEs(eg. Cs, U, Th) and HFSEs(eg. Nb, Ta, P and Ti), riched in Sr. Raising to the coexistence of Eu-enrichment and Eu-depletion type of REE patterns that influenced by the content of plagioclase and the remnants minerals of zircon and apatite. Comparative the petrography, geochemistry and geochronology data of Magnesian-charnockite indicate that the ratios of mafic pellites and basalts involved in anatectic melting are different by the upwelling of mantle magma, also resulting in the Eu anormals characteristics. The formation of the Magnesian-charnockite is closely connected with the subduction of the NCC oceanic crust(About ~2.5 Ga). However, Ferroan-charnockite may be the formed by the crystallization differentiation of the upwelling of mantle-derived shoshonitic magma(About ~2.45 Ga), with the lower crust material addition.

A geochemical perspective on charnockite magmatism in Peninsular India

Large charnockite massifs occur in the high-grade Southern Granulite Terrain （SGT） and Eastern Ghats Belt （EGB） crustal provinces of Peninsular India. Available geochronological data indicate that the magmatism is episodic, associated with distinct orogenic cycles in the different crustal domains. The geochemical data also indicate a change in composition from trondhjemitic at - 3.0-2.9 Ga to domi- nantly tonalitic at - 2.6-2.5 Ga to tonalitic-granodiorite-granitic at - 2.0--1.9 Ga to dominantly tonalitic at 1.7--1.6 Ga to quartz monzonitic or tonalitic at - 1.0-0.9 Ga to granodiorite-granitic at - 0.8-0.7 Ga. The trondhjemitic and tonalitic end members are metaluminous, magnesian and calcic to calc-alkalic, characteristic of magnesian group charnockites. The granodioritic to granitic end members are metalumi- nous to slightly peraluminous, ferroan and calc-alkalic to alkali-calcic, characteristic of ferroan group charnockites. The quartz monzonitic end members are metaluminous to peraluminous, magnesian to ferro- an and calcic to calc-alkalic, neither characteristic of the magnesian group nor of the ferroan group of char- nockites. Based on the occurrence and difference in composition of the charnockite massifs, it is suggested that the charnockite magmatism registers the crustal growth of the Indian plate on its southern （SGT） and eastern （EGB） sides, along active continental margins by accretion of arcs.

Charnockite microstructures:From magmatic to metamorphic

Charnockites sensu lato （charnockite-enderbite series） are lower crustal felsic rocks typically characterised by the presence of anhydrous minerals including orthopyroxene and garnet. They either represent dry （H2O-poor） felsic magmas that are emplaced in the lower crust or granitic intrusions that have been dehydrated during a subsequent granulite facies metamorphic event. In the first case, post- magmatic high-temperature recrystallisation may result in widespread metamorphic granulite microstruc- tures, superimposed or replacing the magmatic microstructures. Despite recrystallisation, magmatic remnants may still be found, notably in the form of melt-related microstructures such as melt inclusions. For both magmatic charnockites and dehydrated granites, subsequent fluid-mineral interaction at inter- grain boundaries during retrogradation are documented by microstructures including K-feldspar micro- veins and myrmekites. They indicate that a large quantity of low-H2O activity salt-rich brines, were present （together with CO2 under immiscible conditions） in the lower crust.

Phase equilibrium modeling of incipient charnockite formation in NCKFMASHTO and MnNCKFMASHTO systems:A case study from Rajapalaiyam,Madurai Block,southern India

Incipient charnockites represent granulite formation on a mesoscopic scale and have received considerable attention in understanding fluid processes in the deep crust. Here we report new petrological data from an incipient charuockite locality at Rajapalaiyam in the Madurai Block, southern India, and discuss the petrogenesis based on mineral phase equilibrium modeling and pseudosection analysis. Rajapalaiyam is a key locality in southern India from where diagnostic mineral assemblages for ultrahigh-temperature （UHT） metamorphism have been reported. Proximal to the UHT rocks are patches and lenses of charnockite （Kfs＋Qtz ＋Pl＋ Bt ＋ Opx＋ Grt ＋Ilm） occurring within Opx-free Grt-Bt gneiss （Kfs ＋Pl ＋ Qtz ＋ Bt ＋ Grt ＋ Ilm ＋ Mt） which we report in this study. The application of mineral equilibrium modeling on the charnockitic assemblage in NCKFMASHTO system yields a p-T range of 820 ℃ and -9 kbar. Modeling of the charnockite assemblage in the MnNCKFMASHTO system indicates a slight shift of the equilibrium condition toward lower p and T （- 760 ℃ and - 7.5 kbar）, which is consistent with the results obtained fiom geothermobarometry （710--760 ℃, 6.7-7.5 kbar）, but significantly lower than the peak temperatures （〉1000 ℃） recorded from the UHT rocks in this locality, suggesting that charnockitization is a post-peak event. The modeling of 7 versus molar H2O content in the rock （M（H2O）） demonstrates that the Opx-bearing assemblage in charnockite and Opx- free assemblage in Grt-Bt gneiss are both stable at M（H2O） = 0.3 mol%--0.6 mol%, and there is no significant difference in water activity between the two domains. Our finding is in contrast to the previous petrogenetic model of incipient charnockite formation which envisages lowering of water activity and stabilization of orthopyroxene through breakdown of biotite by dehydration caused by the infiltration of CO2-rich fluid. T-XFe3＋ （= Fe2O3/（FeO ＋ Fe2O3） in mole） pseudosections suggest that the oxidation condition of the rocks played a major role on the stability of orthopyroxene; Opx is stable at XFe3＋〈0.03 in charnockite, while Opx-free assemblage in Grt-Bt gneiss is stabilized at XFe3＋ 〉0.12. Such low oxygen fugacity conditions of XFe3＋ 〈0.03 in the charnockite compared to Ort-Bt gneiss might be related to the infiltration of a reduced fluid （e.g., H2O ＋ CH4） during the retrograde stage.

Multiple origins of charnockite in the Mesoproterozoic Natal belt,Kwazulu-Natal,South Africa

Four different varieties of charnockitic rocks, with different modes of formation, from the Mesoproterozoic Natal belt are described and new C isotope data presented. Excellent coastal exposures in a number of quarries and river sections make this part of the Natal belt a good location for observing charnockitic field relationships. Whereas there has been much debate on genesis of charnockites and the use of the term charnockite, it is generally recognized that the stabilization of orthopyroxene relative to biotite in granitoid rocks is a function of low aH2O （-- high CO2）, high temperature, and composition （especially Fe/（Fe ＋Mg））. From the Natal belt exposures, it is evident that syn-emplacement, magmatic crystallization of charnockite can arise from mantle-derived differentiated melts that are inherently hot and dry （as in the Oribi Gorge granites and Munster enderbite）, as well as from wet granitic melts that have been affected through interaction with dry country rock to produce localized charnockitic marginal facies in plutons （as in the Portobello Granite）. Two varieties of post-emplacement sub-solidus charnock- ites are also evident. These include charnockitic aureoles developed in leucocratic, biotite, garnet granite adjacent to cross-cutting enderbitic veins that are attributed to metamorphic-metasomatic processes （as in the Nicholson＇s Point granite, a part of the Margate Granite Suite）, as well as nebulous, patchy charnocki- tic veins in the Margate Granite that are attributed to anatectic metamorphic processes under low-aH2O fluid conditions during a metamorphic event. These varieties of charnockite show that the required physical conditions of their genesis can be achieved through a number of geological processes, providing some important implications for the classification of charnockites, and for the interpretation of charnock- ite genesis in areas where poor exposure obscures field relationships.

Incipient charnockites from southern India:The role of brines

Southern India and Sri-Lanka are the places where “incipient charnockites”,i.e.the local transformation of amphibolite-facies gneisses into orthopyroxene-bearing,igneous looking charnockites,have been discovered in the early sixties.The fact that some incipient charnockites occur along a network of brittle fractures,together with CO2 remnants preserved in mineral inclusions,had called for the role of fluids during charnockite alteration.The present work presents new observations on fluid inclusions and microtextures of incipient charnockites from type localities in southern India.In addition to CO2-rich fluid inclusions in quartz and feldspar,all of the occurrences have disrupted remnants of concentrated aqueous alkali chloride solutions.CO2 inclusions are more abundant in paragneiss (Kerala) than in orthogneiss (Karnataka/Tamil Nadu).The finding of disrupted brine inclusions in the Kabbal charnockite is a key link between closely associated massive charnockites and Closepet Granite,both of which also share the brine remnants.All of the occurrences studied here have feldspar or feldspar-quartz microvein networks along grain boundaries of recrystallized quartz,feldspar and orthopyroxene.These metasomatic veins again indicate the action of alkali-exchanging fluids (i.e.,saline solutions).Feldspar microveins,which have been found in most “massive” charnockites,along with the CO2-rich fluid inclusions,suggest a commonality of incipient charnockite and massive charnockite,both types differing in intensity of interaction with metasomatizing pore fluids.

Charnockites and charnockites

1. Introduction The continental crust, covering nearly a third of the Earth＇s surface, is dominantly made up of granites and granodiorites （Rudnick and Gao, 2003）. Although the vast majority of these granitoids are amphibole- and/or biotite-bearing, orthopyroxene-bearing granitoids form a minor but important component of the lower continental crust in many high-grade terrains （e.g., Bohlender et al., 1992; Kilpatrick and Ellis, 1992; Sheraton et al., 1992; Berger et al., 1995; Zhou et al.,

New experimental constraints: implications for pe-trogenesis of charnockite of dioritic composition

Hornblende-dehydration melting experiments at high temperatures (> 950oC) indicate change of melt composition from tonalite/granodiorite to quartz-diorite;clinopyroxene instead of hornbl- ende as the residual phase and change in melting reaction from peritectic hornblende-dehydr- ation to eutectic clinopyroxene-orthopyroxene- plagioclase. In the light of these experimental results, petrogenesis of a charnockite pluton of homogeneous dioritic composition in the Eastern Ghats Belt, India, can be explained as melting at high-temperatures (> 950oC). Negative Sr and Eu anomalies further indicate plagioclase as a major residual phase, consistent with melt- ing at high-temperatures (> 950oC).

Review: the charnockite problem, a twenty first century perspective

Beginning of the twentieth century was marked by coinage of a new rock name, Charnockite, first described as a hypersthene-bearing granite from Southern India. Since then charnockites have been described from most of the conti-nents and mostly restricted to high-grade belts. Later half of the last century saw a lively debate over an igneous versus metamorphic origin. However, two factors acted as deterrents for the resolution of the debate. First, charnockites and associated rocks occur in a variety of different structural setting and display diverse field rela-tions, attesting to possible different mode of origin. Second and possibly more important is the lack of consensus on the nomenclature of charnockites and associated rocks and this is commonly linked with the metamorphic versus magmatic perspective. Scanning the literature of this period makes one believe that both metamorphic and magmatic hypotheses are valid, but applicable to different field setting only. Before critically evaluating individual cases, it is imperative that a uniform approach in nomenclature should be agreed upon. It is proposed that name charnockite be adopted for any quartzofeldspathic rock with orthopyroxene, irrespective of its mode of occurrence, struc-tural setting and mode of origin. The associated more mafic varieties, be better described as mafic granulite, rather than basic charnockite. For the patchy charnockites of east Gondwana (including parts of Peninsular India, Sri Lanka and Antarctica), metamorphic transformation from amphibolite facies gneiss, by two different mechanisms: CO2 ingress from deep level, and drop in fluid pressure, has been proposed. However, all such patchy occurrence is not amenable to explanation by metamorphic trans- formation. In some instances, migmatisation of older charnockitic rocks is evident. Also pro- gressive charnockitisation relating patchy char-nockite to banded variety could be argued against on two counts: grain-size relation and time-relation. Larger bodies or bands have been explained as magmatic, but in many instances, from geochemical consideration alone. The compositional variation, commonly encoun-tered in many high-grade belts, if not described in terms of field relation, may lead to wrong no-tions of magmatic differentiation of mantle-de- rived melts. Crustal melting of dry granulite fa-cies source rocks has been proposed from geochemical and isotopic data of charnockitic intrusions. This model proposes high-tempera-ture melting of previously dehydrated and dry granulite source rocks. However, tectonic per-turbation subsequent to granulite facies meta-morphism that might have been responsible for such high temperatures, is not well constrained in this model. Finally, with advent of high- pressure dehydration-melting experiments in the nineties, dehydration-melting of mafic to intermediate composition, syn-kinematic with granulite facies metamorphism has been pro-posed.

High Ba-Sr adakitic charnockite suite from the Nagercoil Block,southern India:Vestiges of Paleoproterozoic arc and implications for Columbia to Gondwana

The Nagercoil block is the southernmost crustal segment of the Southern Granulite Terrane(SGT)in India and is mainly composed of charnockitic rocks and felsic gneisses(charnockite suite).In this study,we present petrologic,geochemical,zircon U-Pb,REE,and Hf isotopic studies on the charnockites and leucogneiss from the Nagercoil block.Based on field investigations and petrologic studies,the charnockites can be divided into garnet-bearing and garnet-absent anhydrous granulite facies rocks with orthopyroxene.The charnockites and leucogneiss show transition from adakites to non-adakitic magmatic rocks,with enrichment in LREEs(light rare earth elements)and LILEs(large ion lithophile elements),and depletion in HREEs(heavy rare earth elements)and HFSEs(high field strength elements).Some of the charnockites and the leucogneiss show typical HSA(high silica adakite)characters,(high SiO_(2),Al_(2)O_(3),Ba-Sr,La/Yb,and Sr/Y).The HSA is considered to have formed from the interaction of slab derived melts and peridotitic mantle wedge.The high Ba-Sr features were possibly inherited from subducted oceanic crust melting under high thermal gradient during Precambrian.The magmas were underplated and subjected to fractional crystallization.Zircon grains from the charnockite and leucogneiss show zoned magmatic cores surrounded by structureless metamorphic rims.Magmatic zircon grains from the charnockites show ages ranging from 1983±8.8 Ma to 2046±14 Ma,and the metamorphic domains show an age range of 502±14 Ma to 547±8.7 Ma.Zircon from the leucogneiss yielded magmatic and metamorphic ages of 1860±20 Ma and 575.6±8.8 Ma.Both charnockites and leucogneiss show two prominent age peaks at 1987 Ma and 568 Ma.The REE data of the zircon grains show LREE depletion and HREE enrichment,with the metamorphic grains showing more depletion in HREE.Zircon Hf isotopic data of the magmatic cores of zircon grains from the charnockite yieldedε_(Hf)(t)values from-1.17 to 0.46 with T_(DM)and T_(DM)~C and age peaks at 2392 Ma and 2638 Ma,suggesting Neoarchean to Paleoproterozoic juvenile sources.We suggest that the high Ba-Sr adakitic charnockite suite from the Nagercoil block formed in a Paleoproterozoic magmatic arc setting during the assembly of the Columbia supercontinent,and underwent high-grade metamorphism associated with the amalgamation of the Gondwana supercontinent during the late Neoproterozoic-Cambrian.Our study provides new insights into the vestiges of Columbia fragments within the Gondwana assembly with two distinct cycles of crustal evolution.

Charnockite Formation and Early Precambrian Crust Evolution in Yishui Area, Shandong Province, China

Charnockite and granulite in Yishui area, Shandong Province are located in the middle part of the Tancheng Lujiang fault zone, eastern China. Field studies have shown that the charnockites, derived from the adjacent granulites, are classified as three types: enderbite, garnet enderbite and hypersthene trondhjemite. In addition, two generations of minerals are present in the charnockites: the relic minerals such as garnet, hypersthene and clinopyroxene, and the neocrystallized minerals such as plagioclase and K feldspar. The relic minerals occurring in the granulite facies stage were affected by the later partial melting. The relic minerals, irregular and usually ragged in shape, occupy the interstitial positions in the neocrystalline minerals. The neocrystalline minerals are usually euhedral subhedral crystals. The study of petrology, mineralogy and geochemistry of charnokites concludes that the enderbite was formed by the anatexis of the two pyroxene plagioclase granulite, that the garnet enderbite was formed by the anatexis of sillimanite garnet gneiss, and that the hypersthene trondhjemite was formed by the anatexis of the leucocratic two pyroxene plagioclase granulite. The U Pb dating of the zircon indicates that the formation of the charnockite and granulite was related to the Archean Proterozoic upwelling of a mantle plume (hot spot) around 2 500 Ma, in Yishui area, Shandong Province.

Secular evolution of continental crust: recorded from massif-type charnockites of Eastern Ghats belt, India

It is reasonably well established that the Earth has substantially cooled from the Archean to the pre-sent and hence the sites, rates and pro- cesses of crust formation must have changed through geo-logic time. Archean and Proterozoic granitic rocks are the principal record of such changes. Massif-type charnockites in the Eastern Ghats granulite belt, India, of Archean and Proterozoic ages mirror the changing conditions and/or processes of continental crust for- mation. Though both can be explained by dehydration melting of mafic rocks, the conditions differ. Potasium and rubidium rich Proterozoic charnockites have significant negative Eu ano- maly indicating melting at shallow depths in the stability field of plagioclase. In contrast, sodium and strontium rich Archean charnockites with less LREE enrichment and less depletion in Eu indicate melting at greater depths in the stability field of garnet or amphibole.

大青山地区2.5 Ga紫苏花岗岩——对深熔石榴花岗岩成因模式的启示

华北克拉通北缘西部陆块早前寒武纪基底分布广泛,现有的研究普遍认为经历2.5 Ga,2.45~2.37 Ga,1.95 Ga和1.85 Ga变质热事件影响。华北克拉通北缘阴山陆块中2.5 Ga的紫苏花岗岩研究已经成为了揭示华北克拉通北缘早前寒武纪构造演化的一个热点,但孔兹岩带中却鲜少有新太古代晚期构造热事件的相关报道。近年来,相继从大青山地区的孔兹岩带石榴黑云母片麻岩中分辨出一期具有2.45~2.37 Ga变质锆石年龄的大青山表壳岩,同时出露与其成因关系密切的深熔石榴花岗岩,但其深熔成因的模式存在争议。本文对大青山地区新发现的新太古代晚期紫苏花岗岩、石榴花岗岩及其围岩的野外空间产出关系和锆石年代学进行对比分析,为探究深熔石榴花岗岩成因模式提供重要的启示。

内蒙古半沟地区紫苏碱长花岗岩的年代学、同位素地球化学及构造意义

为进一步探讨华北克拉通古-中元古代构造演化过程,本文对位于华北克拉通北缘孔兹岩系与怀安片麻岩接触界限附近、侵入TTG片麻岩的紫苏碱长花岗岩进行了地质年代学及地球化学研究。锆石U-Pb测年结果表明,该紫苏碱长花岗岩的结晶年龄为1792±19Ma;此外,分析样品的主量元素显示高硅、贫镁铁、准过铝质-弱过铝质特征,属高钾钙碱性I型花岗岩;同时,微量元素具有右倾式稀土配分模式、Eu呈正异常、富集大离子亲石元素、亏损高场强元素的特征。锆石εHf(t)呈负值(-12.1~-6.2),εNd(t)=-4.5~-9.4,具有相对富集的同位素组成。锆石Hf和Nd同位素单阶段模式年龄分别为2.41~2.62Ga、2.40~2.61Ga,与年龄为~2.5Ga的TTG片麻岩对应值一致。岩石地球化学及Nd-Hf同位素证据指示紫苏碱长花岗岩源自碰撞后伸展抬升阶段TTG片麻岩的重熔,标志着华北克拉通古元古代造山运动结束。

Ferroan dolomites in Miocene sediments of the Xisha Islands and their genetic model

Carbonate rocks are important reservoirs for global petroleum exploration.The largest oilfield in the South China Sea,Liuhua 11-1,is distributed in the massive carbonate reef area of the Zhujiang(Pearl)River Mouth Basin.Previous studies showed that one 802.17-m-long core from well Xichen-1 in the South China Sea mainly consisted of white and light gray-white organic reefs.Recently,a Miocene whole core(161.9 m long)of well Xiyong-2,near well Xichen-1,was found to contain six layers of yellowish brown,light yellowish gray,iron black,or light yellowish gray-white organic reefs.Scanning electron microscope images of these layers reveal a typical ferroan dolomite rich in Fe(up to 29%),with the high concentrations of Mn,Cu,W,Zn,Cr,Ni,and Co.Systematic X-ray powder diffraction analysis yields a 1.9–6.1 match in phase ratio with ankerite,5.4–26.9 with dolomite,and zero with calcite,which indicate that the samples can be classified as ferroan dolomite.The iron and heavy metals are inferred to be originated from multiple volcanic eruptions of Gaojianshi Island in the Dongdao Atoll during the middle-late Miocene.These elements were dissolved in seawater,likely as a sol,and carried to Yongxing Island in the Xuande Atoll by sea currents and tides enhanced by prevailing winds,and deposited as a part of the sedimentation process in the study area.The ferroan dolomite has Sr content of (125–285)×10^(-6),which is lower than the accepted Sr boundary value of dolomite.This finding suggests that dolomitization occurred during large-scale global glacial regression in the late Miocene.The isolated Xisha carbonate platform,exposed to air,underwent freshwater leaching and dolomitization induced by mixed water,and caused the extensive Fe-Mg exchange along the organic reef profile to form ankerite and ferroan dolomite.These results may help to understand paleoceanographic environmental changes in the South China Sea during the Miocene.

Geochemistry and Genesis of the Sodium-Charnockitic Gneisses, Eastern Hebei Province, China

High in sodium and low in potassium (Na_2O/ K_2O>1), the charnockitic gneiss series in theSantunying- Taipingzhai area, eastern Hebei province, consists of hypersthene- quartz- diorite,hypersthene-granodiorite and hypersthene-plagioclase-granite. Geological, petrological and large ion lithophileelement(LILE), high field strength element (HFSE) and REE geochemical studies suggest that themedium-coarse-grained hypersthene-granodiorite is the product of crystallization of anatectic magmas of thesame composition. Under granulite facies conditions, the equilibrium crystallization differentiation of themagmas yielded the early crystallization phase-high-SiO_2, LILE-depleted, low-∑REE, positive Eu anomalyand REE- saturated hypersthene- plagioclase- granite. The residual phase, coarse- grained to pegmatitichypersthene- granodiorite, is marked by low SiO_2, LILE-enrichment, high ∑REE and REE-undersaturation.These rocks and hypersthene-quartz-diorite enclaves constitute the sodium-charnockitic gneiss series in easternHebei province. Model calculation for trace elements in the granitoids was applied. On the basis of a systematicgeological study, the equation for calculation was chosen, the source magma was determined and the partitioncoefficients were obtained. The resulting curves are entirely consistent with those observed in the patterns of ac-tual rocks. The study indicates that whole-rock REE patterns can not be used directly in the comparison of thesources and genesis of granitoids.

The origin of ferroan and magnesian anorthosites in the lunar crust

1 Introduction The widely accepted standard model for the lunar feldspathic crust is:the early Moon was wholly or mostly molten,forming Lunar Magma Ocean(LMO).Olivine and pyroxene crystallized first from that magma ocean and sank

再论A型花岗岩的实质——与张旗先生等商榷

A型花岗岩最实质的特征是富铁贫镁,是形成于相对还原条件的一大类长英质火成岩的集合。"A型花岗岩"这一术语本身是描述性的,没有岩石成因含义。对于常见的准铝质、过铝质A型花岗岩而言,其形成需要高的地温梯度,低压不是形成这些A型花岗岩的必要条件。

山东沂水紫苏花岗岩特征、形成时代及成因探讨

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