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1.
基性岩高温-超高温变质作用与TTG质岩成因 总被引：10，自引：6，他引：4
变质基性岩在高温-超高温下部分熔融可以形成TTG(英云闪长质-奥长花岗质-花岗闪长质)质熔体,有关熔融反应机理、熔体地球化学特征以及太古宙TTG质岩石成因问题备受国内外学者关注。本文基于对相关实验岩石学研究的总结,结合基性岩高温-超高温相平衡的模拟计算,分析了变质基性岩(斜长角闪岩)深熔变质反应过程、P-T条件及其与TTG质岩石成因的联系。变质基性岩高温-超高温深熔作用主要受角闪石脱水熔融反应控制。在1.0GPa以下的无石榴石域,角闪石分解反应主要为:角闪石=单斜辉石+斜方辉石+斜长石+熔体(R1),该反应为多变滑动反应,以斜方辉石出现(800℃)和角闪石消失(1000~1100℃)为标志,其滑动温度范围超过200~300℃。实验岩石学确定的斜长角闪岩开始熔融或缺流体固相线大致相当于斜方辉石出现温度。实际上角闪石脱水熔融反应是从饱和水固相线开始的,反应为:角闪石+石英=单斜辉石+斜长石+熔体(R1a),开始有黑云母参与熔融反应,但该反应对熔体贡献有限。在1.0GPa以上的石榴石域,不同实验所确定的石榴角闪岩缺流体固相线温度主要介于800~900℃之间,固相线表现为正斜率、负斜率、或者为与压力无关的直线等不同结果。相平衡模拟计算表明在石榴石稳定域角闪石脱水熔融反应为较陡的负斜率,分为两部分:当有斜长石存在时,反应为角闪石+斜长石+石英=石榴石+单斜辉石+熔体(R2),低温部分有白云母、绿帘石参与反应。该反应从饱和水固相线(约630℃)开始,到角闪石消失(超过1000℃),滑动温度范围可超过400℃,跨越石榴角闪岩亚相与角闪高压麻粒岩亚相范围;在斜长石消失后角闪石脱水熔融反应为角闪石+石英=石榴石+单斜辉石+熔体(R2a),低温部分有绿帘石、白云母参与熔融反应,该反应从饱和水固相线(约650℃)开始,到角闪石消失(超过900℃),滑动温度范围可超过200~300℃。角闪石脱水熔融反应形成的无水残余物形成麻粒岩和榴辉岩,无水麻粒岩的峰期温度会超过1000℃,由于降温过程中的退变质演化,如超固相线下滞留熔体与残余物之间发生的深熔反应的逆反应,以及在亚固相线下离子交换反应,导致大多数麻粒岩只记录缺流体固相线组合与退变质温度。基性岩部分熔融的熔体成分取决于全岩成分、P-T条件及熔融程度。当熔融程度很低时(如小于5%)可形成富钾花岗质熔体,随着熔融程度增加,熔体成分可转变为奥长花岗质(如5%~20%)和英云闪长质(如大于20%),部分熔融的熔体成分受全岩成分影响很大,只有相对富钾的基性岩才能形成花岗闪长质到石英二长质熔体。太古宙TTG质岩石表现出富Sr、低Y、Yb、Nb、Ta、Ti以及稀土分馏程度高等地球化学特征,要求部分熔融压力较高,残余物中有石榴石(及金红石)存在。争论的焦点是部分熔融究竟发生在石榴角闪岩亚相(及角闪高压麻粒岩亚相),还是发生在榴辉岩相。对此,不同实验给出的不同结论应该与源岩地球化学特征不同有关。考虑到TTG质岩石的可能源岩如太古宙科马提岩和玄武岩地球化学特征的多样性,TTG质岩石本身地球化学特征上的差异也许不能完全指示熔融发生的P-T条件。综合实验岩石学和相平衡模拟结果,本文确定TTG质岩石是由基性岩在角闪石和石榴石共同稳定域由角闪石脱水熔融反应R2和R2a在角闪高压麻粒岩亚相和角闪榴辉岩亚相形成的,P-T条件为1.0~2.5GPa和800~1000/1100℃。角闪高压麻粒岩亚相相对应的地热梯度为15~25℃/km,角闪榴辉岩亚相对应的地热梯度为10~15℃/km。TTG质岩石形成的构造环境不能简单对应发生在显生宙的洋壳热俯冲带、碰撞造山带和洋底高原等。 相似文献
2.
麻粒岩相变质作用与花岗岩成因-Ⅱ:变质泥质岩高温-超高温变质相平衡与S型花岗岩成因的定量模拟 总被引：12，自引：12，他引：0
高温-超高温变质岩石的矿物组合及组构特点取决于不同的进变熔融反应,不同程度的熔体丢失以及不同程度的退变反应三种过程的综合效应。利用相平衡定量研究方法可以很好地模拟进变熔融反应的类型、P-T条件、熔体含量及其丢失行为、以及熔融过程中熔体与残余物的化学成分变化等,这对探讨高温-超高温变质作用过程以及花岗岩的成因非常重要。对平均泥质岩(APR)进行相平衡模拟表明变质泥质岩在等压(0.8GPa)升温熔融过程中可发生5种熔融反应:饱和流体固相线、白云母脱水熔融、黑云母熔融、钾长石-石榴石熔融和铝铁镁矿物熔融,后两种熔融反应主要发生在超高温条件下。减压过程中发生怎样的熔融反应受减压温度控制:在麻粒岩相(如850℃)减压可发生钾长石熔融、黑云母熔融和钾长石-石榴石熔融反应;在高角闪岩相(如750℃)减压主要发生白云母脱水熔融和钾长石熔融;在超高温麻粒岩相(如950~1000℃)减压主要发生钾长石-石榴石熔融和铝铁镁矿物熔融。熔体成分受熔融反应和P-T条件控制,如在高角闪岩相发生的饱和流体固相线和白云母脱水熔融可形成弱过铝的奥长花岗质和二长花岗质熔体;在麻粒岩相发生的黑云母熔融和钾长石熔融形成的熔体具有强过铝的二长花岗岩成分;在中压超高温发生的钾长石-石榴石熔融和铝铁镁矿物熔融形成强过铝的二长(钾长)花岗岩质熔体,可形成石榴石花岗岩;在低压超高温下发生的铝铁镁矿物熔融可形成堇青石花岗岩。除了极端超高温下的铝铁镁矿物熔融外,其它熔融反应都会使残余物的成分更贫硅,贫Na_2O和K_2O,富FeO和MgO,但Al_2O_3和Mg#基本不变。高温-超高温下发生深熔的岩石只记录降温过程形成的固相线组合,但固相线的类型与温度条件取决于熔体的丢失行为。在不丢失熔体或者获得熔体的岩石中,岩石最后只记录流体饱和固相线组合;发生熔体部分丢失的岩石会记录缺流体固相线组合,并且熔体丢失越多,缺流体固相线的温度越高;发生全部流体丢失的岩石可记录岩石所达到的最高温度。因此,在一个麻粒岩相区,甚至一个野外露头上不同部位的岩石记录不同的P-T条件。熔体丢失是导致使麻粒岩相组合在升温过程中发生超高温变质,在降温过程中得以部分保存的重要条件。发生部分熔融的高级变质岩中随着温度升高,熔体含量增加,会发生锆石分解,只有在降温过程中发生锆石结晶,因此,麻粒岩中新生锆石只记录降温过程到固相线及以后的年龄,一般不会记录麻粒岩相峰期时代。对泥质高压麻粒岩来说,如果经历ITD型变质演化,会发生递进减压熔融,变质反应易于达到平衡,但如果减压速度快并使岩石直接抬升到地壳浅部,会出现一些ITD型结构标志,如残留金红石、蓝晶石,或在石榴石周围出现堇青石的反应冠状体等,此时锆石记录的退变质年龄会与峰期变质年龄相差不大(如10~30Myr);但如果泥质高压麻粒岩减压至中、深地壳,受其中有滞留熔体影响易于发育IBC型结构特征,表现为麻粒岩组合被(中压)角闪岩相组合叠加,在泥质岩中出现黑云母+夕线石构成的暗色条带,或者出现退变白云母和含白云母的浅色体。在中、深地壳经历IBC过程的麻粒岩锆石记录的退变质年龄会与峰期年龄相差很大(如~100Myr)。高级变质岩中由于出现熔体使水流体活度降低,麻粒岩作为排除部分熔体的残余物,其水活度更低。从这一角度来说,水活度低是麻粒岩相变质作用的结果,而不是条件。某些麻粒岩区之所以出现多期麻粒岩相变质叠加受流体行为控制。在亚固相线下流体饱和岩石变质熔融作用从饱和水固相线开始,然后依次发生含水矿物的脱水熔融和无水矿物熔融,这一过程中流体是内部缓冲的,在麻粒岩相温度峰期形成一组平衡矿物组合,难以保留峰期之前的信息。而流体不饱和岩石(如已形成的麻粒岩或岩浆侵入体)变质作用受外部注入流体控制,与构造变形密切相关。如果发生两期麻粒岩相变质叠加变质,在强应变域会形成晚期麻粒岩组合;在弱应变域,会出现两期麻粒岩组合,其中晚期矿物表现为反应冠状体或细粒交生体;而在一些应变非常弱的区域,可能只保留早期矿物组合。 相似文献
3.
高级变质岩中深熔作用的相平衡研究 总被引：3，自引：0，他引：3
深熔作用在高级变质岩中非常普遍并受到广泛关注。自20世纪90年代以来,随着变质相平衡研究的突破性发展,利用THERMOCALC程序和视剖面图方法可以定量研究固相线以上的熔体形成、熔体分馏和退变质反应。变质沉积岩中的熔融作用主要有三种机制饱和水固相线上的熔融、白云母脱水熔融和黑云母脱水熔融。在模拟泥质岩石的KFMASH体系和NCKFMASH体系中的相平衡计算表明,NCKFMASH体系中铁镁矿物的相平衡关系受KFMASH亚体系中矿物相平衡关系的控制,但KFMASH亚体系中固相线位置要比实际的高50~60℃。因此,模拟泥质岩石的固相线以上的相平衡关系最好在NCKFMASH或组分更多的体系中进行。相平衡研究表明麻粒岩相岩石的保存与熔体丢失有关;混合岩的形成过程包括部分熔融作用、不同程度熔体分凝与汲取和不同程度的逆反应和退变反应。 相似文献
4.
变质相平衡的研究进展 总被引：18，自引：3，他引：18
变质相平衡是变质岩石学中最核心的问题之一,20世纪90年代以来,国外在这一领域取得了重要进展,即利用内洽性热力学数据库、THERMOCALC程序以及合理的矿物相活度模型定量计算模式体系中的岩石成因格子(P-T投影图)和有关的各种剖面图,如共生图解和针对特定岩石组分的p-T、p-x和T-x视剖面图等。尤其是在p-T视剖面图解上,可以定量计算矿物成分、矿物摩尔含量及岩石饱和水含量等值线,从而可以定量地阐述天然岩石在p-T-x空间内的相平衡关系、确定岩石形成的p-T条件和p-T-t轨迹。 相似文献
5.
在温度约800—1300℃和压力1.0—3.5GPa下,对加入约2％水的钾质玄武岩和榴辉岩样品的熔融实验研究结果表明,两种岩石的固相线都明显低于干体系同类成分岩石熔融实验研究获得的固相线温度;其中前者由于相对富钾其熔点总体上又低于后者,与已有的研究资料一致。不同的是榴辉岩是随着压力的增大熔点温度增高,钾质玄武岩仅在1.5—2.5GPa和大于3.0GPa压力时其熔点随着压力的增大而增高,在2.5—3.0GPa压力范围内则相反。笔者认为这是由于钾质玄武岩在压力2.5GPa以下,存在着角闪石,2.5GPa以上存在金云母所致,二者矿物特定的成分决定了角闪石具有高于(或接近于)而金云母具有低于湿体系固相线的脱水温度;而含水榴辉岩实验的连续固相线特征则是其角闪石的脱水温度低于或接近含水条件的熔点温度所致。从而造成高压条件下岩石熔点的降低。因此,岩石圈中岩石的成分及其所决定的含水矿物类型和稳定温压条件是控制岩石固相线形式的重要因素,并可以很好地解释深部岩石的部分熔融和地震波低速带的成因。 相似文献
6.
我们利用Holland和Powell(1990)的内部一致的热动力学数集,在0～18kb,460～720℃温压范围内计算出了KFMASH(K_2O—FeO—MgO—Al_2O3—SiO_2—H_2O)体系和KFASH、KMASH亚体系中的单变平衡线和不变平衡点,这些体系中含有十字石、硬绿泥石、绿泥石、黑云母、堇青石、石榴石、红柱石、矽线石和蓝晶石组合及过剩的白云母、石英和水。我们不仅获得了这些平衡的温压位置,而且还确定了涉及到MgFe—1和MgSiAl—2置换的矿物成分。除了在我们的KFMASH体系格子中由于没有Fe~(+3)而无硬绿泥石+黑云母或红柱石+黑云母组合的稳定范围以外,Harte和Hudson(1979)所确立的岩石一致格子是特别出色的。但考虑到格子中反应位置的不确定性以及黑云母和硬绿泥石可能富集了更多的那部分Fe,这些组合在格子中即是稳定的。我们检验了一个内部一致的数集是否象我们合理预测的与那些天然泥质岩石一样复杂的相关系,尽管结果与岩石学观察是有惊人的一致性,但仍需进一步的实验工作,特别是含堇青石和十字石的反应,在进一步改进以前,可以得出这种推算出的格 相似文献
7.
《岩石学报》2016,(6)
麻粒岩相岩石作为洞察下地壳的窗口一直备受重视。二十世纪九十年代以来麻粒岩研究的一个重要进展是利用变质相平衡的定量研究方法模拟岩石中所发生的深熔变质反应、熔体成分变化、及熔体丢失对变质矿物组合的影响等。本文利用KASH、NKASH和KFMASH等简单体系的相平衡关系,做出P-T投影图、组分共生图解和基于固定全岩成分的P-T视剖面图解,并结合有关实验岩石学结果,讨论了高温和超高温条件下变质泥质岩和杂砂岩中的变质熔融反应、矿物组合、全岩成分与P-T条件之间的相互关系。多数变质泥质岩和杂砂岩中饱和流体固相线熔融反应可利用NKASH体系中有水流体参与的熔融反应模拟,在没有外来流体注入时,这些反应可形成3mol%熔体。在不同体系中白云母脱水熔融反应型式及其P-T条件不同,如在NKASH和KFMASH体系中模拟计算的白云母脱水熔融反应与相应的实验结果相似,分别控制了白云母分解熔融的温度下限和上限;白云母的分解温度会随着其中Fe、Mg和Ti含量的增加而升高,也随着共生斜长石中钙长石组分增加而升高,泥质岩中白云母脱水熔融可以形成~10mol%熔体。在KFMASH体系中黑云母脱水熔融反应表现为4条单变反应,其理论计算的温度比实验模拟的结果低一些。在NCKFMASH体系或实际岩石中黑云母脱水熔融反应为滑动反应,如NCKFMASH体系中黑云母从其开始熔融到最后消失在泥质岩中可跨越~100℃,在杂砂岩中可跨越30~50℃。黑云母的稳定温度随着镁值升高而升高,其稳定上限受钛影响更大,黑云母脱水熔融可以形成超过30mol%~40mol%熔体。KFMASH体系中的相平衡模拟表明以出现斜方辉石+夕线石和假蓝宝石为特征的超高温组合易于出现于富镁泥质岩中,而对正常成分泥质岩在达到1000℃的超高温条件下,主要出现石榴石+夕线石(即夕线榴),该组合在更高温度反应形成假蓝宝石+尖晶石。利用饱和水固相线反应和白云母与黑云母分解反应可以更好地限定不同的变质相。如中压和低压条件下低角闪岩相和高角闪岩相的界限可利用NKASH体系中有水流体和白云母参与的熔融反应和亚固相线条件下的白云母分解反应限定;实验确定的泥质岩中黑云母开始熔融与消失的反应可分别用于限定高角闪岩相与(正常)麻粒岩相的界限,以及(正常)麻粒岩相和超高温麻粒岩相的界限。因此,从矿物组合角度,正常麻粒岩相可限定在黑云母开始熔融到完全消失的温度范围,超高温麻粒岩相可限定在黑云母消失(有石英存在)之后的温度范围。 相似文献
8.
本文采用石英和人工合成长石的混合物配制成的原料在P_(H2O)=2～15千巴的压力范围内进行了Qz-Or-Ab-H_2O体系初熔的反演。在无钙长石的碱性长石花岗岩体系Qz-Or-Ab-H_2O中,其熔融温度随着增压,从2千巴时的690℃降低到17千巴时的630℃。在花岗岩体系Qz-Or-Ab-An-H_2O中,随着钙长石含量的增加其固相线温度的升高是非常小的。与碱性长石花岗岩体系相比较,如果钠长石被斜长石An20(An40)代替,其固相线温度升高3℃(7°D)。碱性长石花岗岩体系和石英—钙长石—透长石组合(Qz-Or-An-H_2O体系)的固相线温度间的差别接近50℃。随着水压增高,斜长石及斜长石—碱性长石组合就变得不稳定,并分别被黝帘石+蓝晶石+石英和黝帘石+白云母-钠云母_(固溶体)+石英代替。并发现这些组合的压力稳定范围在600℃时介于6和16千巴之间。在高水压条件下(10～18千巴)。黝帘石-白云母-石英组合稳定到700和720℃。这个组合的固相线在透长石-黝帘石-白云母-石英混合物开始熔融温度以上10～20℃。为产生足够量的熔体,把变质岩变成岩浆岩状的岩石所需要水量只是非常少的。在层状混合岩的情况下证明,1％的水(或甚至更少)就足以使片麻岩局部转变为(岩浆状的)浅色部分,高级变质岩石或许是比较干的,而花岗岩质和花岗闪长岩质成分的重熔岩浆通常处于水不饱和状态。 相似文献
9.
在已知的P-T条件下,5组分-5相体系的共生关系能定量地表示在二维或三维的固溶体成分图解上(Korzhinskii,1958;Mixashiro和Shido,1985;Hosotani和Banno,1986;Shibakusa,1989),根据SiO_2-Al_2O_3-Fe_2O_3-FeO-MgO-CaO-H_2O已经描述了许多低级变质岩石的共生,假如不是全部,该共生组合的主体也可描述为有过量石英,钠长石和以水为主的流体体系,而绿泥石是一常见的组分。有绿纤石或钠质角闪石这样一个 相似文献
10.
基于岩石相平衡，对富铝泥质岩K2O-Al2O3-SiO2一H2O(KASH)和K2O-FeO—MgO—A12O3-SiO2-H2O(KFMASH)体系的混合岩化深熔作用相关系进行了模拟计算，得到泥质岩深熔作用的成岩格子、熔体成分变化特征、熔体含水量及其温压条件、石榴石变斑晶成分演化趋势和泥质岩进变质、退变质矿物组合特征、各种压力条件下S型花岗质熔体特征等，并进一步将模拟结果应用于内蒙古固阳等地的泥质岩，根据相关岩石的矿物组合及结构特征，获得了变质反应历史和P—T轨迹。 相似文献
11.
Behavior and effects of phosphorus in the system Na2O−K2O−Al2O3−SiO2−P2O5−H2O at 200 MPa(H2O) 总被引：1，自引：1，他引：1
David London George B. Morgan VI Harold A. Babb Jennifer L. Loomis 《Contributions to Mineralogy and Petrology》1993,113(4):450-465
The addition of phosphorus to H2O-saturated and initially subaluminous haplogranitic (Qz–Ab–Or) compositions at 200 MPa(H2O) promotes expansion of the liquidus field of quartz, a marked decrease of the solidus temperature, increased solubility limits of H2O in melt at low phosphorus concentrations, and fractionation of melt out of the haplogranite plane (projected along an Or28 isopleth) toward a peralkaline, silica-poor but quartz-saturated minimum composition. The partition coefficient for P2O5 between aqueous vapor and melt with an ASI (aluminum saturation index, mol Al/[mol Na+K])=1 is negligible (0.06), and consequently so are the effects of phosphorus on other melt-vapor relations involving major components. Phosphorus becomes more soluble in vapor, however, as the concentration of a NaPO3 component increases via the fractionation of melt by crystallization of quartz and feldspar. The experimental results here corroborate existing concepts regarding the interaction of phosphorus with alkali aluminosilicate melt: phosphorus has an affinity for alkalis and Al, but not Si. Phosphorus is incorporated into alkali feldspars by the exchange component AlPSi-2. For subaluminous compositions (ASI=1), the distribution coefficient of phosphorus between alkali feldspar and melt, D[P]Af/m, is 0.3. This value increases to D[P]Af/m=1.0 at a melt ASI value of 1.3. The increase in D[P]Af/m with ASI is expected from the fact that excess Al promotes the AlPSi-2 exchange. With this experimental data, the P2O5 content of feldspars and whole rocks can reveal important facets of crystallization and phosphorus geochemistry in subaluminous to peraluminous granitic systems. 相似文献
12.
Volkhart Rudert 《Contributions to Mineralogy and Petrology》1972,35(4):313-329
The system albite-celsian-water was investigated at isothermal sections of 670, 760, 800, 900, 1000 and 1100° C at 1 Kbar. At temperatures above about 950° C the existence of a solid solution series could be shown. In the condensed part of the 930° C/1 Kbar section the partition of barium between melt and coexisting crystals was measured using an electron probe microanalyzer. The barium content of crystals grown in equilibrium with a melt is always higher than the barium content of the starting composition, so albite-celsian shows an ascending type solid solution series at low total water pressures. In the subsolidus region two types of solvi are existent, which show different ways of phase unmixing. The relatively low barium contents of natural albites are interpreted as being due to geochemical reasons rather than crystalchemical reasons.
Meinem hochverehrten Lehrer, Herrn Prof. Dr. K. Jasmund, danke ich für sein lebhaftes Interesse während der Durchführung dieser Arbeit und für die kritische Durchsicht des Manuskripts. Mein Dank gilt ferner Herrn Dr. H. A. Seck für die Einarbeitung in die experimentellen Methoden der Hydrothermalsynthese und für kritische Anmerkungen zum Manuskript. Fräulein Dr. M. Corlett danke ich für wertvolle Informationen zur Messung mit der Elektronenstrahl-Mikrosonde.
Die Untersuchung wurde mit Hilfe von Personal- und Sachmitteln durchgeführt, die Herrn Professor Dr. K. Jasmund von der Deutschen Forschungsgemeinschaft zur Verfügung gestellt worden waren. 相似文献
Meinem hochverehrten Lehrer, Herrn Prof. Dr. K. Jasmund, danke ich für sein lebhaftes Interesse während der Durchführung dieser Arbeit und für die kritische Durchsicht des Manuskripts. Mein Dank gilt ferner Herrn Dr. H. A. Seck für die Einarbeitung in die experimentellen Methoden der Hydrothermalsynthese und für kritische Anmerkungen zum Manuskript. Fräulein Dr. M. Corlett danke ich für wertvolle Informationen zur Messung mit der Elektronenstrahl-Mikrosonde.
Die Untersuchung wurde mit Hilfe von Personal- und Sachmitteln durchgeführt, die Herrn Professor Dr. K. Jasmund von der Deutschen Forschungsgemeinschaft zur Verfügung gestellt worden waren. 相似文献
13.
The stability of coexisting orthopyroxene, sillimanite and quartz and the composition of orthopyroxene in this assemblage has been determined in the system MgO-FeO-Fe2O3-Al2O3-SiO2-H2O as a function of pressure, mainly at 1,000° C, and at oxygen fugacities defined mostly by the hematite-magnetite buffer. The upper stability of the assemblage is terminated at 17 kbars, 1,000° C, by the reaction opx+Al-silicate gar+qz, proceeding toward lower pressures with increasing Fe/(Fe+Mg) ratio in the system. The lower stability is controlled by the reaction opx+sill+qz cord, which occurs at 11 kbars in the iron-free system but is lowered to 9 kbars with increasing Fe/(Fe+Mg). Spinel solid solutions are stabilized, besides quartz, up to 14 kbars in favour of garnet in the iron-rich part of the system (Fe/(Fe+Mg)0.30). Ferric-ferrous ratios in orthopyroxene are increasing with increasing ferro-magnesian ratio. At least part of the generally observed increase in Al content with Fe2+ in orthopyroxene is not due to an increased solubility of the MgAlAlSiO6 component but rather of a MgFe3+AlSiO6 component. The data permit an estimate of oxygen fugacity from the composition of orthopyroxene in coexistence with sillimanite and quartz. 相似文献
14.
Boron-bearing kornerupine was synthesized in the simplest possible model system at fluid pressures and temperatures both within and outside the stability field of boron-free kornerupine. Best conditions for synthesis of single-phase products are 7 kb and 830 °C. Microprobe and wet chemical analyses as well as X-ray studies indicate compositional variations of kornerupines regarding all five constituent components: Increasing B-contents (from 0.37 to 3.32 wt% B2O3) are correlated with decreasing OH? values largely according to the Eq. B3+?3 H+; the ratio MgO∶Al2O3∶SiO2 varies from 4∶3∶4 in the direction towards 1∶1∶1. Thus kornerupine exhibits an at least ternary range of solid solution in the system studied. Crystallochemically speaking it is significant that, although the Mg∶Al∶Si ratio of kornerupine may remain constant with increasing boron contents, the total number of cations per formula unit increases beyond the ideal number of 14.0 as given by Moore and Bennett (1968). Considering the presence of an additional structural site at (000) it is suggested that the introduction of boron initiates a sequence of substitutions such as $$B^{[4]} \to Si^{[4] } \to A1^{[4]} \to Mg^{[6]} \to \square$$ . The filling of this site, empty in boron-free kornerupine, by Mg is connected with a loss of hydrogen located near this site. Petrologically speaking an exchange reaction relation exists between kornerupine and its coexisting fluid according to the equation Boron-free kornerupine+B2O3=boron-kornerupine+H2O. The molar fractions $$X_{B_2 O_3 } = B_2 O_3 /\left( {B_2 O_3 + H_2 O} \right)$$ of kornerupines exceed those of their coexisting fluids by about one order of magnitude. Fluids with relatively low XB 2 O 3 lead to the coexistence of kornerupine with boron-free minerals such as enstatite and sapphirine, fluids with relatively high XB 2 O 3 produce the boron-minerals grandidierite, sinhalite, and tourmaline (in the present system without Na!) in addition to kornerupine. 相似文献
15.
According to the compositions of the underground gasfield brines in the west of Sichuan Basin,the phase equilibria in the ternary systems KBr-K2B4O7-H2O and KCl-K2B4O7-H2O at 373 K were studied using the isothermal dissolution equilibrium method.The solubilities of salts and the densities of saturated solutions in these ternary systems were determined.Using the experimental data,phase diagrams and density-composition diagrams were constructed.The two phase diagrams were simple co-saturation type,each having an invariant point,two univariant curves and two crystallization regions.The equilibrium solid phases in the ternary system KBr-K2B4O7-H2O are potassium bromide （KBr） and potassium tetraborate tetrahydrate （K2B4O7·4H2O）,and those in the ternary system KCl-K2B4O7-H2O are potassium chloride （KCl） and potassium tetraborate tetrahydrate （K2B4O7·4H2O）.Comparisons of the phase diagrams of the two systems at different temperatures show that there is no change in the crystallization phases,but there are changes in the size of the crystallization regions.As temperature increases,the solubility of K2B4O7·4H2O increases rapidly,so the crystallization field of K2B4O7·4H2O becomes smaller. 相似文献
16.
Synthetic dumortierite: its PTX-dependent compositional variations in the system Al2O3-B2O3-SiO2-H2O
Dumortierite, generally simplified as Al7BSi3O18, was synthesized in the pure system Al2O3–B2O3–SiO2–H2O (ABSH) using gels with variable Al/Si ratios mixed with H3BO3 and H2O in known proportions as starting materials. Synthesis conditions ranged from 3 to 5 and 15 to 20 kbar fluid pressure at 650° to 880°C. On the basis of analyses, synthetic dumortierite shows relatively narrow homogeneity ranges with regard to Al/Si which, however, vary as a function of pressure: at low pressures (3–5 kbar) Al/Si is 2.77–2.94 versus 2.33–2.55 at high pressures (15–20 kbar). Outside of these homogeneity limits, dumortierite was found to coexist with quartz or corundum, depending on the starting composition. Whereas synthetic dumortierite invaribly contains 1.0 boron atom per formula unit (p.f.u.) based on 18 oxygens, the water contents vary drastically as a function of pressure and temperature (1.32–2.30 wt.% H2O or 0.85–1.47 H p.f.u.). H2O is an essential component in dumortierite. Structural formulae based on complete chemical analyses of the dumortierites synthesized reveal that there is invariably an Si-deficiency against the ideal number of 3.0 p.f.u. In the calculation procedure used here, this deficiency is balanced by assuming tetrahedral Al. The remaining Al, taken to occupy the octahedral sites, is always below the ideal number of 7.0 p.f.u. Charge-balancing the structure with the hydrogen found analytically leads to two different mechanisms of H incorporation: (1) 3H+ + octahedral vacancy for Al[6]; (2) H+ + tetrahedral Al for Si[4]. Dumortierite synthesized at high fluid pressure contains little Al[4] and, thus, little H+ of type 2; its hydrogen is predominantly present as type 1. Conversely, dumortierite formed at low fluid pressures is high in Al[4] and hydrogen type 2. The amounts of hydrogen type 1 in low-pressure dumortierites decrease with rising temperatures of synthesis. Typical structural formulae are: (Al6.670.33)[Al0.49Si2.51–O13.53(OH)1.47](BO3) for a low-pressure product, and (Al6.680.32)[Al0.09Si2.91O13.94(OH)1.06](BO3) for a high-pressure product. Independently of the synthesis conditions, dumortierite was found always to be orthorhombic, with b0/a0 deviating slightly, but significantly from the
valid for hexagonal lattice geometry. As a function of increasing Al/Si in the synthetic crystals, their a0, c0, and V0 rise, whereas b0 decreases. Thus b0/a0 decreases most sensitively with rising Al/Si and also with growing Al[4]. More experimentation is required before the compositional variations of dumortierite found here can be applied successfully to geothermobarometry of natural rocks. 相似文献
17.
18.
The effect of composition and temperature on the relaxed adiabatic bulk modulus of melts in the P2O5-Al2O 3-Na2SiO3 system have been investigated in the temperature range of 1140 to 1450 °C using ultrasonic interferometric methods at frequencies of 3, 5 and 7 MHz. The density of these melts was determined using Pt-double-bob Archimedean densitometry techiques. P2O5 is known to dramatically affect the structure and the chemical and physical properties of granitic and pegmatitic melts as a function of the peralkalinity of the melt. The physical results of the structural changes occurring in Na2O-Al2O3-SiO2 melt upon the addition of P2O5 are observed by variations in the properties such as density and compressibility. For the present peralkaline melts, the bulk modulus and density decrease with addition of 15 mol% P2O5, and increase with the addition of 15 mol% Al2O3. The addition of P2O5 to the present melts results in a larger increase in melt compressibility than that observed with increasing polymerization between Na2SiO3 and Na2Si2O5 melts. This would suggest that not only is the polymerization of the melt increasing with the addition of P2O5 (Mysen et al. 1981; Nelson and Tallant 1984; Gan and Hess 1992), but that the tetrahedrally co-ordinated phosphorus complexes are influencing the bond lengths and energies within the melt structure; resulting in the structure becoming more compressible than expected, although incompressible (Vaughan and Weidner 1987) tetrahedral P2O5 polyhedra (Mysen et al. 1981; Gan and Hess 1992; Toplis et al. 1994) are being added to the melt structure. 相似文献
19.
20.
Various members of the KAlSi3O8-BaAl2Si2O8 feldspar series are hydrothermally synthesized. Cellparameters of these are calculated from diffractometer patterns and found to be similar to those of Gay and Roy. A variation diagram is constructed correlating Cn-content and values of ΔFeKα(2θ(111)CaF2—2θ(004)Fsss), which gives $${\text{Mol}}\% {\text{ Cn = 229}}{\text{.83}}\Delta {\text{2}}\theta ---{\text{190}}{\text{.81}}$$ by a least square regression fitting. Phase equilibria relation in the solidus-liquidus-region for the KAlSi3O8-BaAl2Si2O8-H2O system at 1000 kg/cm2 are investigated. It is found to be a case of simple solid solution in a binary system, with reservations at the potassium-rich side of the system. Goranson (1938) gives a temperature of about 1000°C at 1000 kg/cm2 \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) for the incongruent melting of sanidine, but the authors prefer a value around 930°C at the same \(P_{{\text{H}}_{\text{2}} {\text{O}}} \) . Reaction products of starting materials on the join KAlSi2O6-BaAl2Si2O8 and KAlSiO4-BaAl2Si2O8 gave no experimental hint for replacement of K+ by Ba++. 相似文献