地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据

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	地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据; Metamorphic evolution during subduction and exhumation of crust:Evidence from phase equilibria modelling for high-and ultrahigh-pressure eclogites
	魏春景 ; 崔莹
刊名	岩石学报
	2011
关键词	相平衡变质流体高压-超高压榴辉岩地壳的俯冲与折返 Phase equilibrium Metamorphic fluid HP-UHP eclogite Crustal subduction and exhumation
英文摘要	本文以大别山双河柯石英榴辉岩为基础,在NCKMnFMASHO体系中计算了P-T、T-M(H2O)和P-M(H2O)一系列相图.这些相图表明在地壳冷俯冲(地热梯度约为6℃·km-1)过程中饱和水的变质基性岩通过脱水反应导致矿物组合演化,随着P-T条件增加,约在2.2GPa(80ktn)处,绿泥石被滑石取代,在2.4GPa处,蓝闪石消失,在2.5GPa处,滑石消失,在2.9GPa(105km)处,硬柱石消失.相应地可出现硬柱石蓝片岩、蓝闪石-硬柱石榴辉岩、硬柱石榴辉岩和多硅白云母榴辉岩等高压-超高压组合.俯冲基性岩中即使含有很少量的水(如0.3%-0.5%),都会在超高压硬柱石榴辉岩相条件下达到饱和.因此硬柱石会广泛出现于经历冷俯冲地壳的变质基性岩中.高压-超高压榴辉岩的折返过程受折返温度及峰期矿物组合的控制.当峰期矿物组合中含有硬柱石(±蓝闪石±滑石,T = 540-600℃)时,其早期折返发生在硬柱石稳定城,受脱水反应控制,难以保存峰期矿物组合;晚期折返发生在绿帘石稳定域,岩石处于流体缺失状态,有利于保存硬柱石消失后的高压矿物组合.当峰期矿物组合中含有绿泥石、硬柱石和蓝闪石时(T < 540℃),其折返过程中的脱水作用仅发生在硬柱石与绿帘石共生的狭窄区城,在硬柱石稳定域的早期折返与绿帘石稳定域的晚期折返阶段,都不发生脱水作用,岩石处于流体缺失状态,因此,虽然峰期形成的硬柱石难以保存,但峰期形成的其他矿物可能仅受轻微改造.当硬柱石消失(T>600℃)后,多硅白云母高压-超高压榴辉岩中含有很少量水,在早期折返过程中的很大压力范围内,岩石保持水含量不变,更容易保留峰期矿物组合.高压-超高压榴辉岩在减压至1.5GPa以下时,由于外来流体注入,发生部分水化,形成含有钠钙质、钙质角闪石榴辉岩,它们一般不是平衡矿物组合.榴辉岩中名义上的无水矿物在减压过程中释放的水有助于榴辉岩部分水化,但不足以形成水饱和的斜长角闪岩.; Based on coesite-bearing eclogites from Shuanghe of Dabieshan terrane, pseudosections including P-T,T-M (H2O) and P-M (H2O) were calculated in the NCKMnFMASHO system. Phase equilibria modeling predicts that the mineral assemblages in water-saturated metabasic rocks evolve via dehydration in cold crustal subduction zones ( geothermal gradient of about 6 degrees C km (-1)). With increasing P-T conditions, chlorite is replaced by talc at about 2. 2GPa (80km), and then glaucophane, talc and lawsonite disappear at 2. 4GPa, 2. 5GPa and 2. 9CPa (105km), respectively. Accordingly, high-ultrahigh pressure ( HP-UHP) mineral assemblages such as lawsonite-bearing blueschist, glaucophane-lawsonite eclogite, lawsonite eclogite and phengite eclogite are modeled to be presented. Phase equal:ilia modeling also suggests that even the subducted basic rocks contain quite small quantities of water ( such as 0. 3% similar to 0. 5%), they can also be water-saturated under UHP lawsonite eclogite fades. Thus, lawsonite will be widely present in the metabasic rocks which have experienced the cold subduction. The exhumation of HP-UHP eclogites is controlled by the temperature and the peak mineral assemblage. When the peak eclogitic assemblage contains lawsonite ( +/- glaucophane +/- talc) at T = 540 similar to 600 degrees C), it will involve two stages of exhumation; The early-stage exhumation is modeled to proceed in the lawsonite stability field, controlled by dehydration reactions, and thus, it will be difficult to preserve the peak mineral assemblage. The late-stage exhumation proceeds in the epidote stability field where the rock is fluid-absent and the HP eclogitic assemblage after the lawsonite disappearance is prone to be preserved. When the peak mineral assemblage includes chlorite, lawsonite and glaucophane at T <540 degrees C, the decompression-driven dehydration reactions only occur in the narrow area with the coexistence of lawsonite and epidote, and will not be happened either in the early exhumation with lawsonite stability and the late exhumation with epidote stability, where the rocks are fluid-absent. Under such conditions, although lawsonite formed in the peak stage is hard to be preserved during decompression, the other peak minerals may only suffer slight modification. After the disappearance of lawsonite at T > 600 degrees C, the HP-UHP phengite eclogites contain very small amounts of water, which is modeled to be unchanged in a large range of pressure during the early exhumation stage. This favors the preservation of peak mineral assemblage. When HP-UHP eclogites are decompressed to pressures below 1. 5GPa, they will be partially hydrated duo to external fluid-infiltration, producing sodic-calc or calc amphibole-bearing eclogites, which are generally not in an equilibrium state. The amount of fluid released by the namely anhydrous minerals during eclogite decompression can cause the partial hydration of eclogite, but is not enough to form water-saturated amphibolite.; 国家自然科学基金资助项目; 科技部973项目; SCI(E); 中文核心期刊要目总览(PKU); 中国科技核心期刊(ISTIC); 中国科学引文数据库(CSCD); 4; 4; 1067-1074; 27
语种	中文
内容类型	期刊论文
源URL	[http://ir.pku.edu.cn/handle/20.500.11897/49941]
专题	地球与空间科学学院
推荐引用方式 GB/T 7714	魏春景,崔莹. 地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据, Metamorphic evolution during subduction and exhumation of crust:Evidence from phase equilibria modelling for high-and ultrahigh-pressure eclogites[J]. 岩石学报,2011.
APA	魏春景,&崔莹.(2011).地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据.岩石学报.
MLA	魏春景,et al."地壳俯冲与折返过程的变质作用演化:来自高压-超高压榴辉岩相平衡模拟的证据".岩石学报 (2011).