岩石学报
巖石學報
암석학보
ACTA PETROLOGICA SINICA
2009年
8期
1937-1946
,共10页
任留东%杨崇辉%王彦斌%刘晓春%赵越
任留東%楊崇輝%王彥斌%劉曉春%趙越
임류동%양숭휘%왕언빈%류효춘%조월
夕线石%变形%深熔作用%组分迁移%南极拉斯曼丘陵
夕線石%變形%深鎔作用%組分遷移%南極拉斯曼丘陵
석선석%변형%심용작용%조분천이%남겁랍사만구릉
Sillimanite%Deformation%Anatexis%Component migration%Larsemann Hills
南极拉斯曼丘陵高级长英质片麻岩的夕线片麻岩中可有两类结构和变质矿物组合均有所不同的两种域,一种含夕线石部分对应于片理组合,另一种对应无夕线石的非片理化组合.岩石的变形尤其是破裂性裂隙的率先出现对于富夕线石部分的形成是必要的.在非破裂性片麻理岩石域中,中-低压/高温条件下黑云斜长片麻岩进变质发展的结果往往是形成Grt+Qtz±Opx组合.这两种不同的变质域的组合与应变分解造成的强应变带和弱应变域相一致.而且,夕线石的形成不是简单的变质早期矿物固相反应的结果,而是反应链上的一部分.其出现是由开放体系中组分的差异迁移造成的,这种差异迁移实际上是碱土金属迁出(淋滤)的过程,与变形相伴的流体活动使得SiO_2发生强烈淋滤,残留组分中SiO_2活度大为降低,并使长英质组分和镁铁质组分分凝,主要组分大都可以单独富集(集中)、形成复杂的矿物演化和分布.这种演化还可从MgO等碱(土)金属组分的外迁程度差异来理解.随着碱(土)金属丢失程度的减小,依次出现夕线石、石榴子石、斜方辉石和堇青石,或者说,不同的变质或分异阶段形成不同的矿物(组合):变形-变质起始阶段,碱(土)金属组分迁移初期残留形成夕线石,之后为镁(铁)质组分迁移,初期残留不透明钛铁氧化物,晚期残留组分形成堇青石.石榴子石-长英质组合为体系基本封闭情况下的结晶.此外,夕线石的形成往往标志着深熔作用的开始,一旦深熔作用发展完善,夕线石呈准稳定状态或趋于消失.拉斯曼丘陵与夕线石有关的长英质岩石经历了复杂的变形、变质和流体活动变化.
南極拉斯曼丘陵高級長英質片痳巖的夕線片痳巖中可有兩類結構和變質礦物組閤均有所不同的兩種域,一種含夕線石部分對應于片理組閤,另一種對應無夕線石的非片理化組閤.巖石的變形尤其是破裂性裂隙的率先齣現對于富夕線石部分的形成是必要的.在非破裂性片痳理巖石域中,中-低壓/高溫條件下黑雲斜長片痳巖進變質髮展的結果往往是形成Grt+Qtz±Opx組閤.這兩種不同的變質域的組閤與應變分解造成的彊應變帶和弱應變域相一緻.而且,夕線石的形成不是簡單的變質早期礦物固相反應的結果,而是反應鏈上的一部分.其齣現是由開放體繫中組分的差異遷移造成的,這種差異遷移實際上是堿土金屬遷齣(淋濾)的過程,與變形相伴的流體活動使得SiO_2髮生彊烈淋濾,殘留組分中SiO_2活度大為降低,併使長英質組分和鎂鐵質組分分凝,主要組分大都可以單獨富集(集中)、形成複雜的礦物縯化和分佈.這種縯化還可從MgO等堿(土)金屬組分的外遷程度差異來理解.隨著堿(土)金屬丟失程度的減小,依次齣現夕線石、石榴子石、斜方輝石和堇青石,或者說,不同的變質或分異階段形成不同的礦物(組閤):變形-變質起始階段,堿(土)金屬組分遷移初期殘留形成夕線石,之後為鎂(鐵)質組分遷移,初期殘留不透明鈦鐵氧化物,晚期殘留組分形成堇青石.石榴子石-長英質組閤為體繫基本封閉情況下的結晶.此外,夕線石的形成往往標誌著深鎔作用的開始,一旦深鎔作用髮展完善,夕線石呈準穩定狀態或趨于消失.拉斯曼丘陵與夕線石有關的長英質巖石經歷瞭複雜的變形、變質和流體活動變化.
남겁랍사만구릉고급장영질편마암적석선편마암중가유량류결구화변질광물조합균유소불동적량충역,일충함석선석부분대응우편리조합,령일충대응무석선석적비편이화조합.암석적변형우기시파렬성렬극적솔선출현대우부석선석부분적형성시필요적.재비파렬성편마리암석역중,중-저압/고온조건하흑운사장편마암진변질발전적결과왕왕시형성Grt+Qtz±Opx조합.저량충불동적변질역적조합여응변분해조성적강응변대화약응변역상일치.이차,석선석적형성불시간단적변질조기광물고상반응적결과,이시반응련상적일부분.기출현시유개방체계중조분적차이천이조성적,저충차이천이실제상시감토금속천출(림려)적과정,여변형상반적류체활동사득SiO_2발생강렬림려,잔류조분중SiO_2활도대위강저,병사장영질조분화미철질조분분응,주요조분대도가이단독부집(집중)、형성복잡적광물연화화분포.저충연화환가종MgO등감(토)금속조분적외천정도차이래리해.수착감(토)금속주실정도적감소,의차출현석선석、석류자석、사방휘석화근청석,혹자설,불동적변질혹분이계단형성불동적광물(조합):변형-변질기시계단,감(토)금속조분천이초기잔류형성석선석,지후위미(철)질조분천이,초기잔류불투명태철양화물,만기잔류조분형성근청석.석류자석-장영질조합위체계기본봉폐정황하적결정.차외,석선석적형성왕왕표지착심용작용적개시,일단심용작용발전완선,석선석정준은정상태혹추우소실.랍사만구릉여석선석유관적장영질암석경력료복잡적변형、변질화류체활동변화.
In the high-grade quartzofeldspathic gneisses in the Larsemann Hills, East Antarctica, two domains of distinct mineral assemblages and textures have been discerned. One is the sillimanite-bearing assemblage aligned along the foliation, while the other is the sillimanite scarce or absent assemblage domain. Deformation, especially the occurrence of the fracture is essential to the formation of sillimanite, tn the weakly foliated gneiss domains, the biotite-plagiogneiss tend to be prograded to form the assemblage of Grt+Qtz± Opx under medium-low pressure granulite facies conditions. The two domains may correspond to the high and low strain zones, respectively, of strain decomposition. In addition, sillimanite is actually stage outcome of the reaction chain in prograding metamorphism, not simply resulted from the early solid reactions. The occurrence of sillimanite is derived from the differential migration of components in the open system. The migration is substantially the leaching of the alkaline and alkaline-earth metals. The fluids accompanying deformation made the severe leaching of SiO_2 and dramatically decrease the mobility of SiO_2 in the residues. Meanwhile the leaching is responsible for the segregation of the fetsic and mafic components and the separate aggregation of some minerals of major components, forming the complex patterns in distribution and evolution of the metamorphic minerals. The evolution also can be illuminated by the differential migration of the oxides of alkaline-earth metals, like MgO. That is to say, as the degree of leaching of the component decreases, sillimanite, garnet, orthopyroxene and cordierite may occur sequentially. In other words, the major mineral or mineral assemblages may vary with the developing metamorphism or differentiation stages. In the beginning of deformation-metamorphism, the initial residues of alkaline metals leaching were responsible for the formation of sillimanite, then migration of the mafic components successively resulted in the residues of opaque iron-titanium oxides and cordierite. Garnet and related quartzofeldspathic assemblages generally crystallize in the closed system. Furthermore, the occurrence of sillimanite usually indicates the beginning of anatexis. Once anatexis is well developed, sillimanite is metastable and tends to be decomposed. The sillimanite-bearing quartzofeldspathic gneisses in the Larsemann Hills have undergone complicated evolution in deformation, metamorphism and fluid activity.
