2013, Vol. 29
2. 中国地质科学院地质研究所，大陆构造与动力学国家重点实验室，北京 100037
2. State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
石榴橄榄岩通常产出于高压/超高压变质带中(Carswell et al., 1983; Medaris and Carswell, 1990; Yang et al., 1993; Zhang et al., 1994; Brueckner, 1998; Liou and Zhang, 1998; Medaris, 1999; Brueckner and Medaris, 2000; Liou and Carswell, 2000; Nimis and Morten, 2000; Trommsdorff et al., 2000; Yang and Jahn, 2000; Zhang et al., 2000; Menzies et al., 2001; Carswell and Cuthbert, 2003; Reverdatto and Selyatitskiy, 2005; Scambelluri et al., 2006; Vrijmoed et al., 2006；Ernst and Liou, 2008)，常与方辉橄榄岩、纯橄岩、榴辉岩和高压麻粒岩等岩石伴生(Liou et al., 1998; Carswell and Compagnoni, 2003; Chopin, 2003)。尽管石榴橄榄岩在高压/超高压变质带中所占体积很小，但却为研究俯冲带中地幔物质的演化和壳幔相互作用等提供了重要的信息(Yang et al., 1993; Zhang et al., 1994; Dobrzhinetskaya et al., 1996; van Roermund and Drury, 1998; Brueckner and Medaris, 2000)，石榴橄榄岩的成因研究对探讨高压/超高压变质带的俯冲类型和构造演化具有直接的指示意义(Zhang et al., 2005；张建新等, 2007)。此外，石榴橄榄岩还常见于碱性玄武岩和金伯利岩筒中，以地幔岩石捕虏体的形式出现。
世界上许多碰撞造山带的高压/超高压变质带中都有石榴石橄榄岩出露，如挪威加里东造山带的西部片麻岩地区(van Roermund and Drury, 1998；Brueckner et al., 2010)、阿尔卑斯造山带的不同地区(Ernst, 1978; Obata and Morten, 1987; Nimis and Morten, 2000；Nimis and Trommsdorff, 2001; Paquin and Altherr, 2001)、哈萨克斯坦的Kokchetav地块(Zhang et al., 1997; Parkinson et al., 1998)、希腊的Rhodope地体(Mposkos and Kostopoulos, 2001)、中欧华力西造山带的Bohemian地块(Medaris et al., 1990; Nakamura et al., 2004; Medaris et al., 2006; Faryad, 2009) 以及我国的大别-苏鲁造山带(杨建军, 1991; Zhang et al., 1994；Liou and Zhang, 1998；You et al., 2000；Zhang et al., 2007；Yang et al., 2009；Ye et al., 2009)、柴北缘绿梁山胜利口地区(杨建军等, 1994；Song et al., 2005a, b, 2007；Yang et al., 2008；Shi et al., 2010) 和南阿尔金巴什瓦克地区(校培喜等, 2001；刘良等, 2002; 王永和等，2004；Zhang et al., 2005；张建新等, 2007; Wang et al., 2011) 等，其岩石成因、侵位机制、形成时代及构造热演化历史因不同造山带而异。
南阿尔金巴什瓦克地区是继大别-苏鲁地区、柴北缘绿梁山地区之后，我国第三个石榴橄榄岩出露地区。与前两者一样，巴什瓦克地区的石榴橄榄岩构成了HP/UHP变质带的组成部分(校培喜等, 2001；刘良等, 2002, 2003, 2005；王永和等, 2004；Zhang et al., 2005)，但在空间分布、岩石组合及围岩关系等与其他两个地区存在差异。在南阿尔金巴什瓦克地区，石榴橄榄岩空间上呈透镜体状与高压基性麻粒岩和含石榴石长英质片麻岩(高压酸性麻粒岩) 伴生。前人已在岩相学、同位素年代学、变质演化P-T轨迹等方面对本区石榴橄榄岩作了一定程度的研究，已获得的代表原岩的岩浆锆石年龄在800Ma左右，变质锆石U-Pb年龄分别为501±16Ma和498±3Ma (Zhang et al., 2005; Wang et al., 2011)，在误差范围内一致，但所获得的峰期变质条件却存在差异：刘良等(2002)所估算的峰期变质条件为P=38~51kbar、T=880~970℃；Zhang et al.(2005)所估算的峰期变质条件为P=18.5~27.3kbar、T=870~1050℃，其压力条件明显要低得多；Wang et al.(2011)将该地区石榴橄榄岩划分为尖晶-石榴橄榄岩和含角闪石的石榴橄榄岩，其对前者所估算的峰期变质条件分别为P=23~28kbar、T=970~1020℃，后者为P=42~60kbar、T=920~990℃。另外，一些学者通过石榴橄榄岩中的一些出溶结构，认为其形成压力甚至达70kbar以上(刘良等, 2002, 2005)。
正因为这些研究结果的差异性，本文拟通过对南阿尔金巴什瓦克石榴橄榄岩的岩相学和成因矿物学研究，来确定不同变质阶段矿物共生组合特征，在此基础上，结合矿物化学分析，估算石榴橄榄岩形成的温压条件，确定石榴橄榄岩的变质演化P-T轨迹，并探讨其变质反应历史及成因机制。
2 地质背景和样品位置以阿尔金断裂为界，其西侧为阿尔金构造带(造山带) 的主体，从北到南可分为3个构造岩石单元(图 1)，最北部是北阿尔金(红柳沟-拉配泉) 俯冲增生杂岩带，主要由早古生代蛇绿混杂岩、弧岩浆杂岩及高压/低温变质岩(包括典型的蓝片岩和低温榴辉岩) 所组成(Zhang et al., 2005; 杨经绥等, 2008)。中部被称之为中阿尔金地块，主要由浅变质的陆缘碎屑岩和碳酸盐岩(金雁山群或塔什大坂群)、中高级变质杂岩(阿尔金岩群) 及不同时代的侵入岩所组成。其中碳酸盐岩中含有叠层石化石，并据此认为其时代为中新元古代(矿产局, 1993)；阿尔金群原被认为时代为古元古代，近年来一些新的研究资料显示其主要形成于中元古代-新元古代(张建新等, 2011；Wang et al., 2013)。最南部被称之为南阿尔金俯冲碰撞杂岩带，以包含超高压榴辉岩、高压麻粒岩及石榴橄榄岩等为特征。其中榴辉岩主要出露在南阿尔金西南部的江尕勒萨依-玉石矿沟一带(刘良等, 1996；张建新等, 1999, 2002; Zhang et al., 2001；Liu et al., 2012)；而石榴橄榄岩则出露在东北部的巴什瓦克地区(校培喜等, 2001; 刘良等, 2002; 王永和等, 2004; Zhang et al., 2005; Wang et al., 2011)。
|
图 1 阿尔金造山带地质简图(据Zhang et al., 2005) Fig. 1 Simplified geological map showing tectonic units of the Altyn Tagh (after Zhang et al., 2005) |
巴什瓦克地区的石榴橄榄岩与长英质高压麻粒岩、高压基性麻粒岩和不含石榴子石的超基性岩构成了一个大约5km宽的构造岩石单元，其南北分别为韧性剪切带与角闪岩相的片麻岩接触，而东西方向的野外分布关系不清楚(图 2)。石榴橄榄岩常与基性麻粒岩(或石榴辉石岩) 共生，并呈互层状产出(图 3)，并一起呈透镜状分布在长英质片麻岩中，透镜体的宽度可达200m以上。野外关系、岩性剖面及取样位置见图 3。
|
图 2 巴什瓦克石榴橄榄岩-高压麻粒岩单元地质简图(据Zhang et al., 2005) Fig. 2 Sketch Geological map of garnet peridotite-HP granulite unit in the Bashiwake area (after Zhang et al., 2005) |
|
图 3 巴什瓦克石榴橄榄岩野外岩性剖面图 Fig. 3 The cross section and field photograph of the Bashiwake garnet peridotite |
新鲜石榴橄榄岩样本呈灰黑-黑色，风化面呈黄绿色，具中-粗不等粒斑状变晶结构，致密块状构造。岩石矿物组成简单，主要由石榴子石(5%~10%)、橄榄石(30%~40%)、斜方辉石(15%~25%)、单斜辉石(10%~15%)、角闪石(5%~10%) 等矿物所组成，同时含有少量的尖晶石、磁铁矿、金云母、蛇纹石、绿泥石以及白云石等矿物( < 5%)。
橄榄石 单偏光下无色，他形-半自形粒状，不规则裂理发育，粒度约为0.05~1.50mm。根据其结构特征，可识别出两种形式的橄榄石：一种为包裹在粗粒的石榴子石和单斜辉石中的细粒浑圆状橄榄石，粒度约为0.05~0.20m (图 4a)；另一种分布在基质中，粒度约为0.15~1.50mm，与石榴子石、单斜辉石、斜方辉石平衡共生(图 4b)，局部因蛇纹石化而呈孤岛状。
|
图 4 巴什瓦克石榴橄榄岩矿物组合和典型结构显微照片 (a)-石榴子石(Grt) 变斑晶中浑圆状的橄榄石(Ol) 包裹体，单偏光；(b)-石榴子石、斜方辉石(Opx)、单斜辉石(Cpx) 和橄榄石共生，单偏光；(c)-垂直石榴子石边界生长的次生边，背散射图像；(d)-斜方辉石中针状单斜辉石出溶，背散射图像；(e)-石榴子石变斑晶中包裹体矿物金云母(Phl)+单斜辉石，单偏光；(f)-单斜辉石变斑晶中针状斜方辉石出溶，背散射图像；(g)-尖晶石-磁铁矿(Spl-Mag) 填隙于橄榄石颗粒之间, 角闪石增生其上，单偏光；(h)-细粒尖晶石+透闪石(Tr) 集合体，推测为石榴子石分解的产物，单偏光 Fig. 4 Photomicrographs and back-scattered electron image showing mineral assemblages and typical textures of the Bashiwake garnet peridotite (a)-round olivine inclusion within coronitic garnet porphyroblast (plane polarized light); (b)-mineral assemblages of garnet、clinopyroxene、orthopyroxene and olivine (plane polarized light); (c)-back-scattered electron image of part of inner and outer kelyphite rims; (d)-exsolution lamellae of clinopyroxene in orthopyroxene porphyroblast (back-scattered electron image); (e)-euhedral phlogopite and round clinopyroxene inclusions within garnet porphyroblast (plane polarized light); (f)-exsolution lamellae of orthopyroxene in clinopyroxene porphyroblast (back-scattered electron image); (g)-spinel-magnetite filling between olivine grains (plane polarized light); (h)-fine-grained assemblage consisting of spinel and tremolite, resulting from breakdown of garnet grain (plane polarized light) |
石榴子石 单偏光下为浅红色，不规则粒状，粒度约为2~10mm，呈散点状分布在基质中，少量石榴子石变斑晶可见变形拉长现象。粗粒的石榴子石变斑晶中可见细粒浑圆状橄榄石、单斜辉石和金云母等矿物包裹体(图 4a, e)。围绕石榴子石变斑晶生有纤维状次生边形成的冠状体反应结构(图 4a)，次生边基本垂直于石榴子石边界生长，并且自石榴子石边部向外逐渐变粗(长度约为0.50~1.50mm)，主要由细粒尖晶石、单斜辉石和斜方辉石组成(图 4c)。
斜方辉石 单偏光下具淡粉红色多色性，他形-半自形粒状，粒度约为0.05~1.50mm。主要以粗粒变斑晶和细粒基质两种形式产出，通常与石榴子石、单斜辉石平衡共生(图 4b)，一些粗粒的斜方辉石变斑晶中可见单斜辉石出溶细条带(图 4d)。此外，斜方辉石亦存在于石榴子石边部纤维状次生边中(图 4c)。
单斜辉石 单偏光下无色，他形-半自形粒状，粒度约为0.05~2.00mm。根据其结构特征，可识别出三种单斜辉石：第一种为包裹在粗粒石榴子石变斑晶中的细粒浑圆状单斜辉石，粒度约为0.05~0.10mm (图 4e)；第二种为分布在基质中的中-粗粒单斜辉石，粒度约为1.00~2.00mm，并与石榴子石、斜方辉石、橄榄石等矿物形成粒状镶嵌变晶结构，形成平衡共生矿物组合(图 4b)。第三种单斜辉石分布于石榴子石边部纤维状的次生边中(图 4c)。此外，在粗粒的单斜辉石变斑晶中可见斜方辉石出溶现象(图 4f)，在其他HP/UHP地区石榴橄榄岩中有过类似的报道(Godard et al., 1996; Zhang et al., 2003; Carswell and van Roermund, 2005)。
尖晶石 单偏光下浅绿色-深绿色，他形-半自形粒状，粒度约为0.02~0.80mm，通常颗粒细小，无裂理。本区石榴橄榄岩中尖晶石可分为两种：第一种存在于石榴石周围纤维状次生边中(图 4c)；第二种分布在橄榄石之间，形成典型的填隙结构，与第一种相比，通常颜色较深，并且与磁铁矿伴生(图 4g)。此外，局部可见少量细粒尖晶石呈集合体产出，可能为石榴子石分解的产物(图 4h)。
角闪石 单偏光下浅褐色，半自形-自形柱状和粒状，粒度约为0.50~2.00mm，常分布在石榴子石、斜方辉石和单斜辉石边部，或增生在这些矿物之上(图 4g)。此外，在橄榄石等矿物的裂隙中可见少量的角闪石与绿泥石、蛇纹石等含水矿物共生，探针结果显示其成分为透闪石。
金云母 单偏光下浅黄色，自形柱状和片状，粒度约为0.20~1.00mm。以两种结构形式产出，一种以包裹体的形式存在于石榴子石变斑晶中(图 4e)，另一种与角闪石一起分布在石榴子石变斑晶的周围。
4 反应结构及变质演化尽管在一些石榴子石变斑晶中发现有浑圆状的橄榄石、单斜辉石和少量尖晶石，但是考虑到这些石榴子石变斑晶不具有明显的进变质生长环带，且部分所包裹的矿物有裂隙与基质相连，我们不能确定这些所包裹的矿物为进变质阶段产物。因此，石榴橄榄岩的峰期变质前的矿物组合无法确定。根据矿物共生组合关系和矿物反应结构特征, 我们将该区石榴橄榄岩的变质演化分为3个阶段：峰期变质阶段(M1)、峰后早期退变质阶段(M2) 和晚期角闪岩相-绿片岩相退变质阶段(M3)。各阶段矿物演化序列和共生组合特征见图 5。现将不同变质阶段矿物组合特征及相应的变质反应性质分述如下。
|
图 5 巴什瓦克石榴橄榄岩各阶段矿物演化序列 Fig. 5 Mineral paragenesis of the different metamorphic stages from the Bashiwake garnet peridotite |
峰期变质阶段典型的矿物组合为石榴子石(Grt)+橄榄石(Ol)+斜方辉石(Opx)+单斜辉石(Cpx)，这与世界其它地区典型石榴橄榄岩的峰期矿物组合基本一致(Carswell, 1986; Kadarusman et al., 2000; Janák et al., 2006)。
4.2 峰后早期退变质阶段(M2)峰后早期退变质阶段的矿物组合为斜方辉石(Opx)+单斜辉石(Cpx)+尖晶石(Spl)，以石榴子石周围冠状体的矿物组合为特征，与石榴子石的分解有关，其可能的变质反应为：Grt+Ol=Opx+Cpx+Spl (Becke, 1881; Mrha, 1900; Sederholm, 1916)。这种冠状体结构普遍发育于石榴橄榄岩中，被认为是峰期变质作用后降压所致(Godard et al., 1996; Godard and Martin, 2000; Kadarusman and Parkinson, 2000; Janák et al., 2006)。
4.3 晚期角闪岩相-绿片岩相退变质阶段(M3)晚期退变质阶段以形成含水矿物角闪石(Amp)、绿泥石(Chl)、磁铁矿(Mag) 及蛇纹石(Srp) 等为特征，由于无法分别识别出角闪岩相和绿片岩相矿物组合，我们统称之为角闪岩相-绿片岩相退变质阶段。在此阶段早期，以形成大的浅褐色角闪石(韭闪石) 为特征，并可见蛇纹石和磁铁矿沿橄榄石的裂隙呈网格状分布。此外，橄榄石裂隙中可见与尖晶石伴生的贫Cr磁铁矿分布，这种尖晶石-磁铁矿的相转变结构，在其他地区超镁铁质岩石中曾有类似的报道(Karipi et al., 2007; Farahat, 2008; Oh et al., 2010)，并被解释为尖晶石在角闪岩相-绿片岩相变质条件下发生的典型退变结构，其可能的相转变反应为：尖晶石→磁铁矿+流体。透闪石形成在此阶段的晚期，与绿泥石、蛇纹石等含水矿物构成绿片岩相矿物组合，这与流体的强烈活动有关。
5 矿物化学成分矿物的电子探针成分分析在中国地质科学院地质研究所完成，所用探针型号为JXA-8100, 加速电压为15kV，电流为2×10-8A，电子束斑为5μm (纤维状次生边采用1μm)。Fe3+的计算据Droop (1987)，除标注外，本文的矿物缩写据Kretz (1983)。
5.1 橄榄石石榴橄榄岩中橄榄石具有代表性的电子探针分析结果见表 1，相应的Fo与NiO (%) 相关关系如图 6所示。表 1显示，峰期变质阶段(M1) 形成的橄榄石中MgO和NiO含量分别为40.31%~45.46%和0.11%~0.24%，相应的Fo端员组分变化于79~85之间；FeO含量变化于14.23%~20.10%之间。而以包裹体形式存在的橄榄石MgO和NiO的含量分别集中于41.27%~42.81 %和0.09%~0.23%，FeO含量变化于17.21%~18.89%之间，相应的Fo端员组分变化于80~82之间。与印度尼西亚Sulawesi石榴橄榄岩(Kadarusman et al., 2000) 和挪威西部Mg-Cr型橄榄岩(Carswell et al., 1983) 相比，本区石榴橄榄岩中橄榄石的Cr2O3(~0.02%) 和TiO2(~0.03%) 含量较低。由图 6可知，包裹在石榴子石和单斜辉石中的橄榄石与基质中的橄榄石没有明显的成分差异，应为同一期变质作用的产物。
|
表 1 巴什瓦克石榴橄榄岩中橄榄石化学成分(wt%) Table 1 Chemical composition of olivine from the Bashiwake garnet peridotite (wt%) |
|
图 6 巴什瓦克石榴橄榄岩中橄榄石的Fo-NiO (%) 成分关系图解 Fig. 6 Relationship between Fo and NiO (%) of olivines from the Bashiwake garnet peridotite |
图 7为石榴橄榄岩中石榴子石背散射图像，其中A-B代表成分剖面位置。石榴子石具有代表性的电子探针分析结果和成分剖面分别见表 2和图 8，石榴子石以富含镁铝榴石和铁铝榴石端元组分为主，而钙铁榴石、钙铝榴石和锰铝榴石端元组分含量相对较少。其中MgO含量为13.17%~16.45%，相应的Prp端元组分为49.42~62.62；FeO含量为13.83%~16.84%，相应的Alm端元组分为19.26~34.19；CaO含量为5.38%~6.29%，相应的Grs端元组分为5.09~13.91，MnO含量为0.44%~0.77%，相应的Sps端元组分为0.96~1.64。石榴子石成分剖面显示核部和幔部相对平坦，边部Prp含量略有降低，Alm含量稍稍升高(图 8)，这种成分环带剖面与Alpe Arami (Brenker and Brey, 1997) 石榴橄榄岩中石榴子石成分剖面相类似，核部反映了峰期变质阶段，而边部可能与后期次生边形成有关。Grs-(Alm+Sps)-Prp图解显示从核部到边部Prp含量略有降低，Alm含量稍稍升高(图 9)。
|
图 7 石榴子石背散射图像(A-B代表成分剖面位置) Fig. 7 Back-scattered electron image of showing the location of the compositional profile (A-B) of garnet |
|
|
表 2 巴什瓦克石榴橄榄岩中石榴子石化学成分(wt%) Table 2 Chemical composition of garnet from the Bashiwake garnet peridotite (wt%) |
|
图 8 巴什瓦克石榴橄榄岩中石榴子石成分剖面 Fig. 8 Compositional profile of garnet from the Bashiwake garnet peridotite |
|
图 9 巴什瓦克石榴橄榄岩中石榴子石的Grs-(Alm+Sps)-Prp图解 Fig. 9 Grs-(Alm+Sps)-Prp compositional diagram of garnet from the Bashiwake garnet peridotite |
与其它地区石榴橄榄岩中峰期阶段的石榴子石成分相比，本区石榴橄榄岩中峰期阶段(M1) 形成的石榴子石中CaO的含量(~6.29%) 高于挪威西部片麻岩省地区(CaO=~4.37%)(van Roermund and Drury, 1998) 和印度尼西亚Sulawesi地区(CaO=~4.80%)(Kadarusman and Parkinson, 2000)。而MgO的含量(~16.45%) 明显低于挪威西部片麻岩省地区(MgO=~22.34%)(van Roermund and Drury, 1998) 和印度尼西亚Sulawesi地区(MgO=~20.71%)(Kadarusman and Parkinson, 2000)。
5.3 斜方辉石石榴橄榄岩中具有代表性的斜方辉石化学成分列入表 3中，其化学成分图解如图 10和图 11所示。不同世代斜方辉石的化学成分差异不大，峰期变质阶段(M1) 和退变早期阶段(M2) 形成的斜方辉石中MgO的含量分别为28.24%~29.37%和28.59%~29.12%，FeO含量分别为12.41%~14.07%和12.43%~15.15%，其化学成分均属于古铜辉石(图 10)。M1和M2阶段A12O3的含量分别变化于2.77%~4.84 %和3.93%~4.56%之间。同时，斜方辉石边部A12O3和MgO的含量有所升高，而CaO的含量有所降低，紧邻石榴子石斑晶的斜方辉石边部FeO的含量有所降低。斜方辉石的这种成分变化特征与其在温度降低过程中的变化规律相一致(Smith and Barron, 1991)。与区内基性麻粒岩中斜方辉石相比(Zhang et al., 2005)，石榴橄榄岩中斜方辉石MgO的含量明显偏高，而FeO含量相对较低，表明不同类型的岩石中，斜方辉石的化学成分与寄主岩石的化学成分存在着密切的成因联系。
|
|
表 3 巴什瓦克石榴橄榄岩中斜方辉石化学成分(wt%) Table 3 Chemical composition of orthopyroxene from the Bashiwake garnet peridotite (wt%) |
|
图 10 巴什瓦克石榴橄榄岩中斜方辉石Wo-Fs-En图解(据Deer et al., 1997) Fig. 10 Wo-Fs-En diagram of orthopyroxenes from the Bashiwake garnet peridotite (after Deer et al., 1997) |
|
图 11 巴什瓦克石榴橄榄岩中斜方辉石XMg-AlⅥ成分关系图解 Fig. 11 Relationship between XMg and AlⅥ of orthopyroxenes from the Bashiwake garnet peridotite |
石榴橄榄岩中单斜辉石代表性的化学成分列入表 4中, 其化学成分图解如图 12和图 13所示。各阶段的单斜辉石的化学成分均落在透辉石区(图 12)。总体来看，单斜辉石的化学成分变化不大，相对于M1阶段，M2阶段的单斜辉石中Na2O和A12O3的含量略有降低，而CaO的含量略有升高，与区内基性麻粒岩中单斜辉石相比(Zhang et al., 2005)，石榴橄榄岩中单斜辉石MgO和CaO的含量相对较高，FeO和Na2O的含量相对较低，而与区内石榴辉石岩中单斜辉石化学成分相近(Zhang et al., 2005)。Cr2O3的含量仅为0.01%~0.12%，远远低于挪威西部Mg-Cr型橄榄岩中单斜辉石的Cr2O3含量(Carswell et al., 1983)。
|
|
表 4 巴什瓦克石榴橄榄岩中单斜辉石化学成分(wt%) Table 4 Chemical composition of clinopyroxene from the Bashiwake garnet peridotite (wt%) |
|
图 12 巴什瓦克石榴橄榄岩中单斜辉石Wo-Fs-En图解(据Deer et al., 1997) Fig. 12 Wo-Fs-En diagram of clinopyroxenes from the Bashiwake garnet peridotite (after Deer et al., 1997) |
|
图 13 巴什瓦克石榴橄榄岩中单斜辉石XMg-AlⅥ成分关系图解 Fig. 13 Relationship between XMg and AlⅥ of clinopyroxenes from the Bashiwake garnet peridotite |
石榴橄榄岩中代表性尖晶石的化学成分列入表 5中，其化学成分图解如图 14和图 15所示。总体来看，尖晶石的化学成分具高铝-低铬的特点。石榴子石周围次生边中尖晶石Cr2O3的含量仅为0.28%~0.76%，MgO含量为16.53%~17.49%，FeO含量为18.10%~19.97%，相应的XMg值为0.65~0.69。而基质中尖晶石Cr2O3的含量为1.18%~4.36%，MgO的含量为15.47%~17.98%，FeO含量为17.79%~22.93%，相应的XMg值为0.61~0.64。此外，次生边中尖晶石中铝的含量比基质中尖晶石铝的含量稍高。
|
|
表 5 巴什瓦克石榴橄榄岩中尖晶石化学成分(wt%) Table 5 Chemical composition of spinels from the Bashiwake garnet peridotite (wt%) |
|
图 14 巴什瓦克石榴橄榄岩中尖晶石Cr-Al-Fe3+成分图解(据Barnes and Roeder, 2001) Fig. 14 Cr-Al-Fe3+ compositional diagram of spinels from the Bashiwake garnet peridotite (after Barnes and Roeder, 2001) |
|
图 15 巴什瓦克石榴橄榄岩尖晶石XMg-Cr /(Cr+Al) 关系图解 Fig. 15 Relationship between XMg and Cr/(Cr+Al) of spinels from the Bashiwake garnet peridotite |
石榴橄榄岩中具有代表性的角闪石化学成分列入表 6中，其化学成分图解如图 16所示，本区石榴橄榄岩中角闪石均属于钙质角闪石，FeO的含量为6.84%~9.10%，Al2O3的含量为12.91%~14.70%，TiO2的含量为0.05%~1.90%，K2O和Na2O的含量分别变化于0.12%~2.95%和1.63%~2.98%之间。在钙质角闪石Mg/(Mg+Fe2+)-TSi分类图解中(Na+K>0.5, Ti < 0.5, Fe3+ < AlⅥ)，角闪石落在韭闪角闪石-韭闪石过渡区(图 16)。
|
|
表 6 巴什瓦克石榴橄榄岩中角闪石化学成分(wt%) Table 6 Chemical composition of amphibole from the Bashiwake garnet peridotite (wt%) |
|
图 16 巴什瓦克石榴橄榄岩中角闪石Mg/(Mg+Fe2+)-TSi分类图解(据Leake et al., 1997) Fig. 16 Relationship between Mg/(Mg+Fe2+) and TSi of Amphibole from the Bashiwake garnet peridotite (after Leake et al., 1997) |
石榴橄榄岩中具有代表性的金云母化学成分列入表 7中，以包裹体形式存在于石榴子石变斑晶中的金云母和存在于基质中的金云母成分差异不大，前者MgO的含量略微偏高，FeO的含量略微偏低，相应的XMg分别为0.88~0.90和0.91~0.92。
|
|
表 7 巴什瓦克石榴橄榄岩中金云母化学成分(wt%) Table 7 Chemical composition of phlogopite from the Bashiwake garnet peridotite (wt%) |
根据不同变质阶段的矿物共生组合关系和变质反应结构特征, 本文采用适宜的地质温压计对巴什瓦克地区石榴橄榄岩不同阶段的平衡温度和压力进行估算。采用的地质温压计包括：Grt-Opx压力计(Harley, 1984b; Nickel and Green, 1985; Brey and Köhler, 1990) 和Grt-Cpx温度计(Powell, 1985)、Grt-Opx温度计(Harley, 1984a; Aranovich and Berman, 1997; Brey et al., 2008)、Opx-Cpx温度计(Brey and Köhler, 1990)、Grt-Ol温度计(Wu and Zhao, 2007)。计算过程中，所有的Fe均按Fe2+计算，因为在超镁铁矿物中Fe3+的含量通常是可以忽略的(Krogh and Carswell, 1996; Zhang et al., 1994)。不同阶段代表性的P-T计算结果总结于表 8中，不同类型温压计在不同样品中计算的P-T图解如图 17所示。结果显示各个阶段所估算的温压条件与相邻的石榴辉石岩、长英质麻粒岩和基性麻粒岩的温压条件范围基本一致(Zhang et al., 2005)。
|
|
表 8 巴什瓦克石榴橄榄岩中不同阶段代表样品温压估算结果 Table 8 P-T estimates for representative garnet peridotites samples |
|
图 17 巴什瓦克石榴橄榄岩温压估算结果P-T图 Fig. 17 P-T diagrams showing the results of thermobarometric calculations Grt-Cpx (P85): Powell (1985); Grt-Opx (H84): Harley (1984a); Opx-Cpx (BK90): Brey and Köhler (1990); Grt-Ol (Wu07); Wu and Zhao (2007); Grt-Opx (BK90): Brey and Köhler (1990); Grt-Opx (NG85): Nickel and Green (1985); Grt-Opx (H84b): Harley (1984b) |
峰期变质阶段典型的矿物组合为石榴子石(Grt)+橄榄石(Ol)+斜方辉石(Opx)+单斜辉石(Cpx)。我们采用相邻矿物对Grt-Ol、Grt-Cpx、Grt-Opx、Opx-Cpx的核部和边部成分分别计算该阶段的温度条件。如表 8所示，在P=20kbar下，核部成分计算的结果分别集中于912~1025℃、903~1054℃、899~1001℃和891~981℃，代表了峰期变质阶段的温度条件，相应的边部成分计算的温度条件比用核部成分计算的温度条件低约50~73℃，可能代表了最初期退变质的温度条件。在假定T=950℃下，不同类型的Grt-Opx压力计计算结果有较大的变化(表 8)，变化于17.2~24.7kbar之间，代表了峰期变质的压力条件。值得注意的是，运用适用范围为60~100kbar的Grt-Opx温压计(Brey et al., 2008) 在T=950℃下计算的峰期压力范围为38.4~42.5kbar，远远高于其它类型Grt-Opx压力计计算的压力范围，明显不适合于巴什瓦克石榴橄榄岩的压力估算。
6.2 峰后早期退变质阶段(M2)峰后早期退变质阶段的矿物组合为斜方辉石(Opx)+单斜辉石(Cpx)+尖晶石(Spl)。我们采用石榴子石边部纤维状次生边中共生的Opx-Cpx的成分对其温度条件进行估算，在假定P=10kbar下所估算的温度条件为711~796℃(P=10kbar是参照围岩基性麻粒岩和长英质麻粒岩早期退变质阶段的压力条件，见张建新和孟繁聪, 2005；Zhang et al., 2005)，而且外冠比内冠的温度低约12~35℃，代表了峰后早期退变质阶段的温度条件。
6.3 晚期退变质阶段(M3)没有合适的温压计来估算晚期退变质阶段的温压条件，但可根据矿物组合和反应结构来定性估计其形成的变质条件。橄榄石裂隙中存在尖晶石-磁铁矿的相转变结构，这种矿物相转变的温度条件约为500~600℃ (Farahat, 2008)，而绿泥石等矿物的出现，反映在退变质晚期的温度更低，表明石榴橄榄岩折返(抬升) 到浅层次，并遭受到强烈流体(H2O) 活动参与的退变质作用改造。
7 讨论 7.1 峰期变质条件及P-T轨迹基于岩相学观察和温压条件估算结果，本文所获得的石榴橄榄岩的峰期变质阶段(M1) 的温压条件为：T=891~1054℃、P=17.2~24.7kbar，在石榴橄榄岩稳定区域(图 18)。此温压条件与Zhang et al.(2005)所估算的结果基本上一致，但与刘良等(2002)和Wang et al.(2011)获得的结果存在明显差异。刘良等(2002)通过石榴子石中出现单斜辉石、金红石出溶和单斜辉石+菱镁矿反应生成白云石+斜方辉石证明本区石榴橄榄岩经历了超高压变质作用，其所估算的峰期压力变质条件远远高于本文所估算的压力范围。Wang et al.(2011)所估算的含尖晶石石榴橄榄岩峰期变质条件为T=970~1020℃和P=23~28kbar，略高于本文所估算的峰期变质条件，而其所估算的含角闪石石榴橄榄岩样品的最高压力条件达到42~60kbar (在T=920~990℃条件下)(Wang et al., 2011)。我们知道，温压估算中所采用的斜方辉石Al压力计与Al的含量具有负相关关系(Wu and Zhao, 2011)，Al2O3含量越小，其估算的压力越大。通过比较矿物成分结果发现，Wang et al.(2011)文中含尖晶石石榴橄榄岩的斜方辉石成分中Al2O3的含量在1.81%~3.84%之间，与本文所获得的石榴橄榄岩中峰期变质组合的斜方辉石成分近一致或略低；而其中的含角闪石石榴橄榄岩峰期组合中斜方辉石的Al2O3含量明显低于前者(0.36%~0.72%)。在我们所获得的石榴橄榄岩样品中，峰期变质组合斜方辉石Al2O3含量均大于2.77%(2.77%~3.59%)，也与我们早期所获得石榴橄榄岩峰期组合斜方辉石Al2O3含量近一致(Zhang et al., 2005)，没有获得Al2O3含量明显低的斜方辉石。一种可能是采样位置的差异；另外一种可能是我们样品中的斜方辉石并不代表峰期压力条件下的组合，而与降压过程中的再平衡有关。因此，我们不排除巴什瓦克石榴橄榄岩可能经历了更高压力条件下的变质作用，但本文所估算的石榴橄榄岩的峰期变质条件与围岩长英质片麻岩(高压酸性麻粒岩，T=930~980℃、P=22~24kbar) 及高压基性麻粒岩的峰期变质条件(T=940~1010℃、P=18.5~24kbar) 近一致(张建新和孟繁聪, 2005；Zhang et al., 2005; 于胜尧等, 2011)，反映石榴橄榄岩与围岩一起经历高压(超高压?)/高温条件的变质作用。
|
图 18 巴什瓦克石榴橄榄岩变质演化P-T轨迹 图中附加了Zhang et al.(2005)(深灰色实线) 和Wang et al.(2011)(浅灰色虚线) 的P-T轨迹，其中成岩格子据Maruyama et al. (1996)，石墨-金刚石的转化界限据Bundy (1980)，柯石英-石英和石榴石-尖晶石二辉橄榄岩的平衡转化分别据Bohlen and Boettcher (1982)和Webb and Wood (1986).普通角闪石、绿泥石和蛇纹石的稳定界限分别据Niida and Green (1999)和Ulmer and Trommsdorff (1999) Fig. 18 P-T path showing the metamorphic evolution of the Bashiwake garnet peridotite Additional P-T data is from Zhang et al.(2005)and Wang et al. (2011). The petrogenetic grid is based on that of Maruyama et al. (1996), graphite-diamond transition curve is after Bundy (1980), coesite-quartz equilibrium from Bohlen and Boettcher (1982) and the garnet-spinel lherzolite transition from Webb and Wood (1986). Stability limits of pargasitic amphibole, and chlorite and serpentine in ultramafic rocks are from Niida and Green (1999) and Ulmer and Trommsdorff (1999), respectively |
峰后早期退变质阶段(M2) 在P=10kbar记录的温度条件为：T=711~796℃，显示石榴橄榄岩经历了中压麻粒岩相的叠加，并在晚期发生广泛流体参与条件下的角闪岩相-绿片岩相退变质作用(M3)。类似的变质叠加在围岩长英质片麻岩和高压基性麻粒岩中也有记录(张建新和孟繁聪, 2005; Zhang et al., 2005)，反映石榴橄榄岩和围岩一起反生折返和抬升到相对浅层次(图 18)。
7.2 成因机制近年来，国内外许多学者对碰撞造山带中出露的石榴橄榄岩成因机制提出了很多模式，归纳起来主要有以下三种：(1) 来源于深部地幔，没有经历深俯冲过程而是直接被折返到地壳浅部(Dobrzhinetskaya et al., 1996; van Roermund and Drury, 1998; Song et al., 2007；Scambelluri et al., 2008)；(2) 俯冲陆壳在俯冲过程中将上部板片中的地幔楔橄榄岩卷入，一起经历深俯冲作用，而后折返到地壳浅部(Brueckner, 1998; Brueckner and Medaris, 2000)；(3) 侵位到陆壳中的镁铁质-超镁铁质岩石与陆壳一起发生深俯冲作用和折返作用(Carswell et al., 1983; Zhang et al., 2000)。
本区石榴橄榄岩与石榴辉石岩、含假蓝宝石的基性麻粒岩和含蓝晶石的长英质麻粒岩“伴生”，它们共同组成了一个长度约为5km的HP/HT (UHT) 变质岩片，岩片与周围不含高压变质组合的片麻岩为韧性剪切带接触(张建新和孟繁聪, 2005；Zhang et al., 2005)。正如上面提到的那样，高压基性麻粒岩和长英质麻粒岩的峰期温压变质条件大都落在T=930~1010℃、P=18.5~24kbar之间(Zhang et al., 2005)，与本文所估算的石榴橄榄岩的峰期变质条件基本一致。它们的锆石U-Pb变质年龄也均在500Ma左右(Zhang et al., 2005)。
刘良等(2002)和Wang et al.(2011)认为本区石榴橄榄岩经历了从尖晶石橄榄岩到石榴橄榄岩的进变质阶段，并根据石榴子石等变斑晶中包裹的尖晶石、单斜辉石、斜方辉石和橄榄石等矿物的存在，认为其代表了新元古代侵位到地壳层次的尖晶石橄榄岩的残留组合。本文中，我们虽然在石榴子石变斑晶中也观察到橄榄石、单斜辉石等矿物包裹体，但考虑到石榴子石变斑晶并没有显示出明显的进变质成分环带，且这些矿物与基质中相同矿物并没有明显的成分差异，我们认为其不代表原岩残留的矿物。因此，本文没有明确识别出其原岩形成条件及进变质历史。然而，我们初步的地球化学数据显示，与阿尔卑斯等碰撞造山带典型的地幔橄榄岩相比，巴什瓦克石榴橄榄岩中FeO、TiO2含量较高，MgO、Cr2O3的含量较低；而且本区石榴橄榄岩稀土元素Eu正异常，微量元素Cs、Rb、Ba、Th、U、Sr高于原始地幔(Wang et al., 2011)，这些特征表明其可能为“壳源”橄榄岩(Carswell et al., 1983; Zhang et al., 2000; Reverdatto and Selyatitskiy, 2005)。因此，我们倾向认为本区石榴橄榄岩原岩可能为新元古代侵位于地壳的镁铁质-超镁铁质杂岩，并在早古生代与长英质地壳物质一起俯冲经历高压/超高压变质作用, 峰期变质作用之后, 它们折返到下地壳层次, 经历中压麻粒岩相变质作用的改造，然后岩石抬升到中上地壳环境遭受角闪岩-绿片岩相变质作用的叠加。
8 结论(1) 南阿尔金巴什瓦克石榴橄榄岩经历了至少三个阶段的变质反应历史：峰期变质阶段(M1)，标志性矿物组合为：石榴子石+橄榄石+单斜辉石+斜方辉石，所估算的温压条件为：T=846~1054℃、P=17.2~24.7kbar；峰后早期退变质阶段(M2)，标志性矿物组合为：单斜辉石+斜方辉石+尖晶石，在P=10kbar记录的温度条件为：T=711~796℃；晚期角闪岩-绿片岩相退变质阶段(M3)，其矿物组合为角闪石、蛇纹石、金云母、磁铁矿、绿泥石等矿物。
(2) 巴什瓦克石榴橄榄岩具有与相邻的长英质麻粒岩和高压基性麻粒岩类似的变质演化历史。结合其成因矿物学和初步的地球化学特征，我们认为本区石榴橄榄岩原岩可能为新元古代侵位于地壳的镁铁质-超镁铁质杂岩，并在早古生代与长英质地壳物质一起俯冲经历高压/超高压变质作用, 峰期变质作用之后, 它们折返到中下地壳层次, 经历中压麻粒岩相变质作用的改造，然后岩石抬升到中上地壳环境遭受角闪岩-绿片岩相变质作用的叠加。
致谢 中国地质科学院地质研究所戎合老师协助完成了电子探针矿物成分分析；审稿人吴春明教授和孟繁聪研究员提出了宝贵的修改意见；中国地质大学(北京) 冀磊、颜琛同学协助完成数据处理和图件绘制工作；在此一并表示感谢。| [] | Aranovich LY, Berman RG. 1997. A new garnet-orthopyroxene thermometer based on reversed Al2O3 solubility in FeO-Al2O3-SiO2 orthopyroxene. American Mineralogist, 82: 345–353. DOI:10.2138/am-1997-3-413 |
| [] | Barnes SJ, Roeder PL. 2001. The range of spinel compositions in terrestrial mafic and ultramafic rocks. Journal of Petrology, 42(12): 2279–2232. DOI:10.1093/petrology/42.12.2279 |
| [] | Becke F. 1881. XI. Die gneissformation des niederösterreichischen Waldviertels. Mineralogische und petrographische Mitteilungen, 4(3): 189–264. |
| [] | Bohlen SR, Boettcher AL. 1982. The quartz-coesite transformation: A pressure determination and the effects of other components. Journal of Geophysical Research, 87(B8): 7073–7078. DOI:10.1029/JB087iB08p07073 |
| [] | Brey GP, Köhler T. 1990. Geothermobarometry in four-phase lherzolite Ⅱ. New thermobarometers and practical assessment of existing thermobarometers. Journal of Petrology, 31(6): 1353–1378. DOI:10.1093/petrology/31.6.1353 |
| [] | Brey GP, Bulatov VK, Girnis AV. 2008. Geobarometry for peridotites: Experiments in simple and natural systems from 6 to 10 GPa. Journal of Petrology, 49(1): 3–4. |
| [] | Brenker FE, Brey GP. 1997. Reconstruction of the exhumation path of the Alpe Arami garnet-peridotite body from depths exceeding 160km. Journal of Metamorphic Geology, 15(5): 581–592. DOI:10.1111/jmg.1997.15.issue-5 |
| [] | Brueckner HK. 1998. Sinking intrusion model for the emplacement of garnet-bearing peridotites into continent collision orogens. Geology, 26: 631–634. DOI:10.1130/0091-7613(1998)026<0631:SIMFTE>2.3.CO;2 |
| [] | Brueckner HK, Medaris LG. 2000. A general model for the intrusion and evolution of mantle garnet peridotites in high-pressure and ultrahigh pressure metamorphic terranes. Journal of Metamorphic Geology, 18(2): 123–134. DOI:10.1046/j.1525-1314.2000.00250.x |
| [] | Brueckner HK, Carswell DA, Griffin WL, Medaris LG, van Roermund HLM, Cuthbert SJ. 2010. The mantle and crustal evolution of two garnet peridotite suites from the Western Gneiss Region, Norwegian Caledonides: An isotopic investigation. Lithos, 117(1-4): 1–19. DOI:10.1016/j.lithos.2010.01.011 |
| [] | Bundy FR. 1980. The P-T phase and reaction diagram for elemental carbon. Journal of Geophysical Research: Solid Earth (1978~2012), 85(B12): 6930–6936. DOI:10.1029/JB085iB12p06930 |
| [] | Bureau of Geological and Mineral Resourses of Xinjiang Uygur Autonomous Region. 1993. Regional Geology of Xinjiang Uygur Autonomous Region. Beijing: Geological Publishing House. |
| [] | Carswell DA, Harvey MA, Azzam Al-Samman A. 1983. The petrogenesis of contrasting Fe-Ti and Mg-Cr garnet peridotite types in the high grade gneiss complex of Western Norway. Bulletin de Minéralogie, 106(6): 727–750. |
| [] | Carswell DA. 1986. The metamorphic evolution of Mg-Cr type Norwegian garnet peridotites. In: Griffin WL (ed.). Second International Eclogite Conference. Lithos, 19(3-4): 279-297 |
| [] | Carswell DA and Cuthbert SJ. 2003. Ultrahigh pressure metamorphism in the western Gneiss Region of Norway. In: Carswell DA and Compagnoni R (eds.). Ultrahigh Pressure Metamorphism, 5. EMU Notes in Mineralogy, 51-53 |
| [] | Carswell DA, van Roermund HLM. 2005. On multiphase mineral inclusions associated with microdiamond formation in mantle-derived peridotite lens at Bardane on Fjortoft, western Norway. European Journal of Mineralogy, 17(1): 31–42. DOI:10.1127/0935-1221/2005/0017-0031 |
| [] | Chopin C. 2003. Ultrahigh-pressure metamorphism: Tracing continental crust into the mantle. Earth and Planetary Science Letters, 212(1-2): 1–14. DOI:10.1016/S0012-821X(03)00261-9 |
| [] | Deer WA, Howie RA, Zussman J. 1997. The Rock-forming Minerals Vol.2B, Double-Chain Silicates. 2nd Edition. Longman: 1–764. |
| [] | Dobrzhinetskaya LF, Green HW, Wang S. 1996. Alpe Arami: A Peridotite Massif from depths of more than 300km. Science, 271(5257): 1841–1845. DOI:10.1126/science.271.5257.1841 |
| [] | Droop GTR. 1987. A general equation for Fe3+ concentrations in ferromagnesian silicates and oxides from microprobe analyses, using stoichiometric criteria. Mineralogical Magazine, 51(361): 431–435. DOI:10.1180/minmag |
| [] | Ernst WG. 1978. Petrochemical study of lherzolitic rocks from the Western Alps. Journal of Petrology, 19(3): 341–392. DOI:10.1093/petrology/19.3.341 |
| [] | Ernst WG, Liou JG. 2008. High and ultrahigh-pressure metamorphism: Past results and future prospects. American Mineralogist, 93(11-12): 1771–1786. DOI:10.2138/am.2008.2940 |
| [] | Farahat ES. 2008. Chrome-spinels in serpentinites and talc carbonates of the El Ideid-El Sodmein District, central Eastern Desert, Egypt: Their metamorphism and petrogenetic implications. Chemie der Erde-Geochemistry, 68(2): 193–205. DOI:10.1016/j.chemer.2006.01.003 |
| [] | Faryad SW. 2009. The Kutná Hora Complex (Moldanubian zone, Bohemian Massif): Acomposite of crustal and mantle rocks subducted to HP/UHP conditions. Lithos, 109(3-4): 193–208. DOI:10.1016/j.lithos.2008.03.005 |
| [] | Godard G, Martin S, Prosser G, Kienast JR, Morten L. 1996. Variscan migmatites, eclogites and garnet-peridotites of the Ulten zone, Eastern Austroalpine system. Tectonophysics, 259(4): 313–341. DOI:10.1016/0040-1951(95)00145-X |
| [] | Godard G, Martin S. 2000. Petrogenesis of kelyphites in garnet peridotites: A case study from the Ulten zone, Italian Alps. Journal of Geodynamics, 30(1-2): 117–145. DOI:10.1016/S0264-3707(99)00030-7 |
| [] | Harley SL. 1984a. An experimental study of the partitioning of Fe and Mg between garnet and orthopyroxene. Contributions to Mineralogy and Petrology, 86(4): 359–373. DOI:10.1007/BF01187140 |
| [] | Harley SL. 1984b. The solubility of alumina in orthopyroxene coexisting with garnet in FeO-Al2O3-SiO2 and CaO-FeO-MgO-Al2O3-SiO2. Journal of Petrology, 25(3): 665–696. DOI:10.1093/petrology/25.3.665 |
| [] | Janák M, Froitzheim N, Vrabec M, Kroch Ravna EJ, de Hood JCM. 2006. Ultrahigh-pressure metamorphism and exhumation of garnet peridotite in Pohorje, Eastern Alps. Journal of Petrology, 24(1): 19–31. |
| [] | Kadarusman A, Parkinson CD. 2000. Petrology and P-T evolution of garnet peridotites from central Sulawesi, Indonesia. Journal of Metamorphic Geology, 18(2): 193–209. DOI:10.1046/j.1525-1314.2000.00238.x |
| [] | Karipi S, Tsikouras B, Hatzipanagiotou K, Grammatikopoulos TA. 2007. Petrogenetic significance of spinel-group minerals from the ultramafic rocks of the Iti and Kallidromon ophiolites (Central Greece). Lithos, 99(1-2): 136–149. DOI:10.1016/j.lithos.2007.06.005 |
| [] | Kretz R. 1983. Symbols for rock-forming minerals. American Mineralogist, 68(1-2): 277–279. |
| [] | Krogh EJ and Carswell DA. 1996. HP and UHP eclogites and garnet peridotites in the Scandinavian Caledonides. In: Coleman RG and Wang X (eds.). Ultra-High Pressure Metamorphism. Cambridge: Cambridge University Press, 244-298 |
| [] | Leake B, Woolley A, Arps CS. 1997. Nomenclature of amphiboles: Report of the Subcommittee on Amphiboles of the International Mineralogical Association, comments on new minerals and mineral names. The Canadian Mineralogist, 35(9-10): 219–246. |
| [] | Liou JG, Zhang RY. 1998. Petrogenesis of an ultrahigh-pressure garnet-bearing ultramafic body from Maowu, Dabie Mountains, east-central China. The Island Arc, 7(1-2): 115–134. DOI:10.1046/j.1440-1738.1998.00188.x |
| [] | Liou JG, Carswell DA. 2000. Preface: Garnet peridotites and ultrahigh-pressure minerals. Journal of Metamorphic Geology, 18(2): 121–122. DOI:10.1046/j.1525-1314.2000.00246.x |
| [] | Liu L, Che ZC, Luo JH, Wang Y, Gao ZJ. 1996. Identification of the eclogite at the west part of Altyn Tagh Mountains and its geological implications. Chinese Science Bulletin, 41(16): 1485–1488. |
| [] | Liu L, Sun Y, Xiao PX, Che ZC, Luo JH, Chen DL, Wang Y, Zhang AD, Chen L, Wang YH. 2002. Discovery of ultrahigh pressure magnesite-bearing garnet lherzolite (>3.8Gpa) in the Altyn Tagh, Northwest China. Chinese Science Bulletin, 47(11): 881–885. DOI:10.1360/02tb9197 |
| [] | Liu L, Sun Y, Luo JH, Wang Y, Chen DL, Zhang AD. 2004. Ultra-high pressure metamorphism of granitic gneiss in the Yinggelisayi area, Altun Monutains, NW China. Science in China (Series D), 47(4): 338–346. DOI:10.1360/02YD0466 |
| [] | Liu L, Chen DL, Zhang AD, Sun Y, Wang Y, Yang JX, Luo JH. 2005. UHP (>7GPa) gneissic K-feldspar pyroxenite evidence from clinopyroxene exsolutions in garnet. Science in China (Series D), 35(2): 105–114. |
| [] | Liu L, Wang C, Cao YT, Chen DL, Kang L, Yang WQ, Zhu XH. 2012. Geochronology of multi-stage metamorphic events: Constraints on episodic zircon growth from the UHP eclogite in the South Altyn, NW China. Lithos, 136-139: 10–26. DOI:10.1016/j.lithos.2011.09.014 |
| [] | Maruyama S, Liou JG, Terabayashi M. 1996. Blueschists and eclogites of the world and their exhumation. International Geological Review, 38(6): 485–594. DOI:10.1080/00206819709465347 |
| [] | Medaris LG Jr and Carswell DA. 1990. Petrogenesis of Mg-Cr garnet peridotites in European metamorphic belts. In: Carswell DA (ed.). Eclogite Facies Rocks. New York: Chapman and Hall, 260-290 |
| [] | Medaris LG Jr, Wang HF, Mísař Z, Jelínek E. 1990. Thermobarometry, diffusion modelling and cooling rates of crustal garnet peridotites: Two examples from the Moldanubian zone of the Bohemian Massif. Lithos, 25(1-3): 189–202. DOI:10.1016/0024-4937(90)90014-R |
| [] | Medaris LG. 1999. Garnet peridotites in Eurasian high-pressure and ultrahigh-pressure terranes: A diversity of origins and thermal histories. International Geology Review, 41(9): 799–815. DOI:10.1080/00206819909465170 |
| [] | Medaris LG, Beard BL, Jelínek E. 2006. Mantle-derived, UHP garnet pyroxenite and eclogite in the Moldanubian Gföhl Nappe, Bohemian Massif: A geochemical review, new P-T determinations and tectonic interpretation. International Geology Review, 48(9): 765–777. DOI:10.2747/0020-6814.48.9.765 |
| [] | Menzies MA, Vannucci R, Bodinier JL, Frey FA, Shimizu N, Kelemen PB, Rampone E, Rivalenti G, Hoffman AW. 2001. Orogenic lherzolites and mantle processes: Editorial. Journal of Petrology, 42(1): 3–4. DOI:10.1093/petrology/42.1.3 |
| [] | Mposkos ED, Kostopoulos DK. 2001. Diamond, former coesite and supersilic garnet in metasedimentary rocks from the Greek Rhodope: A new ulteahigh-pressure metamorphic province established. Earth and Planetary Science Letters, 192(4): 497–506. DOI:10.1016/S0012-821X(01)00478-2 |
| [] | Mrha J. 1900. Beiträge zur Kenntnis des Kelyphit. Zeitschrift für Kristallographie, Mineralogie und Petrographie, 19(1): 111–143. |
| [] | Nakamura D, Svojtka M, Naemura K. 2004. Very-high-pressure (>4GPa) eclogite associated with the Moldanubian Zone garnet peridotite (Nové Dvory, Czech Republic). Journal of Metamorphic Geology, 22(6): 593–603. DOI:10.1111/jmg.2004.22.issue-6 |
| [] | Nickel KG, Green DH. 1985. Empirical geothermobarometry for garnet peridotites and implications for the nature of the lithosphere, kimberlites and diamonds. Earth and Planetary Sciences Letters, 73(1): 158–170. DOI:10.1016/0012-821X(85)90043-3 |
| [] | Niida K, Green DH. 1999. Stability and chemical composition of pargasitic amphibole in MORB pyrolite under upper mantle conditions. Contributions to Mineralogy and Petrology, 135(1): 18–40. DOI:10.1007/s004100050495 |
| [] | Nimis P, Morten L. 2000. P-T evolution of "crustal" garnet peridotites and included pyroxenites from Nonsberg area (upper Austroalpine), NE Italy: From the wedge to the slab. Journal of Geodynamics, 30(1): 93–115. |
| [] | Nimis P, Taylor WR. 2000. Single clinopyroxene thermobarometry for garnet peridotites. Part Ⅰ. Calibration and testing of a Cr-in-Cpx barometer and an enstatite-in-Cpx thermometer. Contributions to Mineralogy and Petrology, 139(5): 541–554. DOI:10.1007/s004100000156 |
| [] | Nimis P, Trommsdorff V. 2001. Revised thermobarometry of Alpe Arami and other garnet peridotites from the Central Alps. Journal of Petrology, 42(1): 103–115. DOI:10.1093/petrology/42.1.103 |
| [] | Obata M, Morten L. 1987. Transformation of spinel lherzolite to garnet lherzolite in ultramafic lenses of the austridic crystalline complex, northern Italy. Journal of Petrology, 28(3): 599–623. DOI:10.1093/petrology/28.3.599 |
| [] | Oh CW, Rajesh VJ, Seo J, Choi SG, Lee JH. 2010. Spinel compositions and tectonic relevance of the Bibong ultramafic bodies in the Hongseong collision belt, South Korea. Lithos, 117(1-4): 198–208. DOI:10.1016/j.lithos.2010.02.015 |
| [] | Parkinson CD, Katayama I, Liou JG, Maragama S. 1998. The Diamond-bearing Kokchetav Massif, Kazakhstam. Tokyo: Universal Academy Press: 1-527. |
| [] | Paquin J, Altherr R. 2001. New constraints on the P-T evolution of the Alpe Arami garnet peridotite body (Central Alps, Switzerland). Journal of Petrology, 42(6): 1119–1140. DOI:10.1093/petrology/42.6.1119 |
| [] | Powell R. 1985. Regression diagnostic and robust regression in geothermometer/geobarometer calibration: The garnet-clinopyroxene geothermobarometer revisited. Journal of Metamorphic Geology, 3(3): 231–243. DOI:10.1111/jmg.1985.3.issue-3 |
| [] | Reverdatto VV, Selyatitskiy AY. 2005. Olivine garnet, olivine spinel and orthopyroxene metamorphic rocks of the Kokchetav Massif, Northern Kazakhstan. Petrology, 14(1): 115. |
| [] | Scambelluri M, Hermann J, Morten L, Rampone E. 2006. Melt-versus fluid-induced metasomatism in spinel to garnet wedge peridotites (Ulten Zone, Eastern Italian Alps): Clues from trace element and Li abundances. Contributions to Mineralogy and Petrology, 151(4): 372–394. DOI:10.1007/s00410-006-0064-9 |
| [] | Scambelluri M, Pettke T, Roermund HLM. 2008. Majoritic garnets monitor deep subduction fluid flow and mantle dynamics. Geology, 36(1): 59–62. DOI:10.1130/G24056A.1 |
| [] | Sederholm JJ. 1916. On synantetic minerals and related phenomena (reaction rims, corona minerals, kelyphite, myrmekite, etc.). Bulletin dela Commission GeÂologique de Finlande, 9(48): 47–59. |
| [] | Shi RD, Griffin WL, O'Reilly SY, Zhao GC, Huang QS, Li J, Xu JF. 2010. Evolution of the Lüliangshan garnet peridotites in the North Qaidam UHP belt, Northern Tibetan Plateau: Constraints from Re-Os isotopes. Lithos, 117(1-4): 307–321. DOI:10.1016/j.lithos.2010.03.006 |
| [] | Smith D, Barron BR. 1991. Pyroxene-garnet equilibration during cooling in the mantle. American Mineralogist, 76: 1950–1963. |
| [] | Song SG, Zhang LF, Chen J. 2005a. Sodic amphibole exsolutions in garnet from garnet-peridotite, North Qaidam UHPM belt, NW China: Implications for ultradeep-origin and hydroxyl defects in mantle garnets. American Mineralogist, 90(5-6): 814–820. DOI:10.2138/am.2005.1684 |
| [] | Song SG, Zhang LF, Niu YL, Su L, Jian P, Liu DY. 2005b. Geochronology of diamondbearing zircons from garnet peridotite in the North Qaidam UHPM belt, Northern Tibetan Plateau: A record of complex histories from oceanic lithosphere subduction to contine. Earth and Planetary Science Letters, 234(1-2): 99–118. DOI:10.1016/j.epsl.2005.02.036 |
| [] | Song SG, Su L, Niu YL, Zhang LF, Zhang GB. 2007. Petrological and geochemical constraints on the origin of garnet peridotite in the North Qaidam ultrahigh-pressure metamorphic belt, northwestern China. Lithos, 96(1-2): 243–265. DOI:10.1016/j.lithos.2006.09.017 |
| [] | Trommsdorff V, Hermann J, Muntener O, Pfiffner M, Risold AC. 2000. Geodynamic cycles of subcontinental lithosphere in the Central Alps and the Arami enigma. Journal of Geodynamics, 30(1-2): 77–92. DOI:10.1016/S0264-3707(99)00028-9 |
| [] | Ulmer P and Trommsdorff V. 1999. Phase relations of hydrous mantle subducting to 300 km. In: Fei Y, Bertka CM and Mysen BO (eds.). Field Observations and High Pressure Experimentation: A Tribute to Francis R. Boyd. Geochemical Society Special Publication, 6: 259-281 |
| [] | van Roermund HLM, Drury MR. 1998. Ultra-high pressure (P>6GPa) garnet peridotites in Western Norway: Exhumation of mantle rocks from >185km depth. Terra Nova, 10(6): 295–301. DOI:10.1046/j.1365-3121.1998.00213.x |
| [] | Vrijmoed JC, Van Roermund HLM, Davies GR. 2006. Evidence for diamond-grade ultrahigh pressure metamorphism and fluid interaction in the Svartberget Fe-Ti garnet peridotite/ websterite body, Western Gneiss Region, Norway. Contributions to Mineralogy and Petrology, 88(1-2): 381–405. DOI:10.1007/s00710-006-0160-6 |
| [] | Wang C, Liu L, Chen DL, Cao YT. 2011. Petrology, geochemistry, geochronology and metamorphic evolution of garnet peridotites from South Altyn Tagh UHP terrane, Northwestern China: Records related to crustal slab subduction and exhumation history. Ultrahigh Pressure Metamorphism, 17: 541–577. |
| [] | Wang C, Liu L, Yang WQ, Zhu XH, Cao YT, Kang L, Chen SF, Li RS, He SP. 2013. Provenance and ages of the Altyn Complex in Altyn Tagh: Implications for the Early Neoproterozoic evolution of northwestern China. Precambrian Research, 230: 193–208. DOI:10.1016/j.precamres.2013.02.003 |
| [] | Wang YH, Xiao PX, Zhang HW, Sun NY, Li JX. 2004. New results and major progress in regional geological survey of the Suwushijie Sheet. Geological Bulletin of China, 23(5): 560–563. |
| [] | Webb SAC, Wood BJ. 1986. Spinel-pyroxene-garnet relationships and their dependence on Cr/Al ratio. Contributions to Mineralogy and Petrology, 92(4): 471–480. DOI:10.1007/BF00374429 |
| [] | Wu CM, Zhao GC. 2007. A recalibration of the garnet-olivine geothermometer and a new geobarometer for garnet peridotites and garnet-olivine-plagioclase-bearing granulites. Journal of Metamorphic Geology, 25(5): 497–505. DOI:10.1111/jmg.2007.25.issue-5 |
| [] | Wu CM, Zhao GC. 2011. The applicability of garnet-orthopyroxene geobarometry in mantle xenoliths. Lithos, 125(1-2): 1–9. DOI:10.1016/j.lithos.2011.02.018 |
| [] | Xiao PX, Wang YH, Zhang HW. 2001. The discovery of magnesite-bearing garnet lherzolite of high-ultrahigh pressure belt and its geological significance in the middle section of Altgn Tagh. Northwestern Geology, 34(4): 67–74. |
| [] | Yang JJ. 1991. Eclogite and Ultramafic Rocks in Sulu Area. Beijing: Geological Publishing House. |
| [] | Yang JJ, Godard G, Kienast JR, Lu Y, Sun J. 1993. Ultrahigh pressure (60kbar) magnesite-bearing garnet peridotites from northeastern Jiangsu, China. Journal of Metamorphic Geology, 101(5): 541–554. |
| [] | Yang JJ, Zhu H, Deng JF, Zhou TZ, Lai SC. 1994. The discovery of garnet peridotite in northern Qaidam Mountains, and its significance. Acta Petrologica et Mineralogica, 13(2): 97–105. |
| [] | Yang JJ, Jahn BM. 2000. Deep subduction of mantle-derived garnet peridotites from the Su-Lu UHP metamorphic terrane in China. Journal of Metamorphic Geology, 18(2): 167–180. DOI:10.1046/j.1525-1314.2000.00249.x |
| [] | Yang JJ, Powell R. 2008. Ultrahigh-pressure garnet peridotites from the devolatilization of sea-floor hydrated ultramafic rocks. Journal of Metamorphic Geology, 26(6): 695–716. DOI:10.1111/jmg.2008.26.issue-6 |
| [] | Yang JS, Shi RD, Wu CL, Su DC, Chen SY, Wang XB, Wooden J. 2008. Petrology and SHRIMP age of the Hongliugou ophiolite at Milan, North Altun, at the northern margin of the Tibetan Plateau. Acta Petrologica Sinica, 24(7): 1567–1584. |
| [] | Yang JS, Li TF, Chen SZ, Wu CL, Robinson PT, Liu DY, Wooden JL. 2009. Genesis of garnet peridotites in the Sulu UHP belt: Examples from the Chinese Continental Scientific Drilling Project-main Hole, PP1 and PP3 drill holes. Tectonophysics, 475(2): 359–382. DOI:10.1016/j.tecto.2009.02.032 |
| [] | Ye K, Song YR, Chen Y, Xu HJ, Liu JB, Sun M. 2009. Multistage metamorphism of orogenic garnet-lherzolite from Zhimafang, Sulu UHP terrane, E. China: Implications for mantle wedge convection during progressive oceanic and continental subduction. Lithos, 109(3-4): 155–175. |
| [] | You ZD, Zhong ZQ, Suo ST, Zheng S. 2000. A petrogenetic study of the garnet pyroxenite enclaves in spinel peridotite, North Dabieshan, China. Science in China (Series D), 43(Suppl.1): 189–199. |
| [] | Yu SY, Zhang JX, Gong JH. 2011. Zr-in-rutile thermometry in HP/UHT granulite in the Bashiwake area of the South Altun and its geological implications. Earth Science Frontiers, 18(2): 140–150. |
| [] | Zhang JX, Zhang ZM, Xu ZQ, Yang JS, Cui JW. 1999. The ages of U-Pb and Sm-Nd for eclogite from the western segment of Altyn Tagh tectonic belt. Chinese Science Bulletin, 44(24): 2256–2259. DOI:10.1007/BF02885933 |
| [] | Zhang JX, Zhang ZM, Xu ZQ, Yang JS, Cui JW. 2001. Petrology and geochronology of eclogites from the western segment of the Altyn Tagh, northwestern China. Lithos, 56(2-3): 187–206. DOI:10.1016/S0024-4937(00)00052-9 |
| [] | Zhang JX, Yang JS, Xu ZQ, Meng FC, Song SG, Li HB, Shi RD. 2002. Evidence for UHP metamorphism of eclogite from the Altun Mountains. Chinese Science Bulletin, 47(9): 751–755. DOI:10.1360/02tb9170 |
| [] | Zhang JX, Meng FC. 2005. Sapphirine-bearing high pressure mafic granulite and its implications in the South Altyn Tagh. Chinese Science Bulletin, 50(3): 265–269. DOI:10.1007/BF02897537 |
| [] | Zhang JX, Mattinson CG, Meng FC, Wan YS. 2005. An Early Palaeozoic HP/HT granulite-garnet peridotite association in the south Altyn Tagh, NW China: P-T history and U-Pb geochronology. Journal of Metamorphic Geology, 23(7): 491–510. DOI:10.1111/j.1525-1314.2005.00585.x |
| [] | Zhang JX, Meng FC, Mattinson CG. 2007. Progress, controversies and challenge of studies on South Altyn Tagh-North Qaidam HP/UHP metamorphic belt. Geological Journal of China Universities, 13(3): 526–545. |
| [] | Zhang JX, Li HK, Meng FC, Xiang ZQ, Yu SY, Li JP. 2011. Polyphase tectonothermal eventsrecorded in "metamorphic basement" from the Altyn Tagh, the southern margin of the Tarim basin, western China: Constraint from U-Pb zircon gochronology. Acta Petrologica Sinica, 27(1): 23–46. |
| [] | Zhang RY, Liou JG, Cong B. 1994. Petrogenesis of garnet-bearing ultramafic rocks and their associated eclogites in the Su-Lu ultrahigh-P metamorphic terrane. Journal of Metamorphic Geology, 12(2): 169–186. DOI:10.1111/jmg.1994.12.issue-2 |
| [] | Zhang RY, Liou JG, Ernst WG, Coleman RG, Sobolev NV, Shatsky VS. 1997. Metamorphic evolution of diamond-bearing and associated rocks from the Kokchetav Massif, northern Kazakhstan. Journal of Metamorphic Geology, 15(4): 479–496. DOI:10.1111/j.1525-1314.1997.00035.x |
| [] | Zhang RY, Liou JG, Yang JS, Yui TF. 2000. Petrochemical constraints for dual origin of garnet peridotites from the Dabie-Sulu UHP terrane, eastern-central China. Journal of Metamorphic Geology, 18(2): 149–166. DOI:10.1046/j.1525-1314.2000.00248.x |
| [] | Zhang RY, Liou JG, Yang JS, Ye K. 2003. Ultrahigh pressure metamorphism in the forbidden zone: The Xugou garnet peridotite, Sulu terrane, eastern China. Journal of Metamorphic Geology, 21(6): 539–550. DOI:10.1046/j.1525-1314.2003.00462.x |
| [] | Zhang RY, Li T, Rumble D, Yui TF, Li L, Yang JS, Pan Y, Liou JG. 2007. Multiple metasomatism in Sulu ultrahigh-P garnet peridotite constrained by petrological and geochemical investigations. Journal of Metamorphic Geology, 25(2): 149–164. DOI:10.1111/jmg.2007.25.issue-2 |
| [] | 刘良, 车自成, 罗金海, 王焰, 高章鉴. 1996. 阿尔金山西段榴辉岩的确定及其地质意义. 科学通报, 41(16): 1485–1488. |
| [] | 刘良, 孙勇, 肖培喜, 车自成, 罗金海, 陈丹玲, 王焰, 张安达, 陈亮, 王永合. 2002. 阿尔金发现超高压(>3.8GPa) 石榴二辉橄榄岩. 科学通报, 47(9): 657–662. |
| [] | 刘良, 孙勇, 罗金海, 王焰, 陈丹玲, 张安达. 2003. 阿尔金英格利萨依花岗质片麻岩超高压变质. 中国科学(D辑), 33(12): 1184–1192. |
| [] | 刘良, 陈丹玲, 张安达, 孙勇, 王焰, 杨家喜, 罗金海. 2005. 阿尔金超高压(>7GPa) 片麻状(含) 钾长石辉石岩-石榴子石出熔单斜辉石的证据. 中国科学(D缉), 35(2): 105–114. |
| [] | 王永和, 校培喜, 张汉文, 孙南一, 李建星. 2004. 苏吾什杰幅地质调查新成果及主要进展. 地质通报, 23(5): 560–563. |
| [] | 校培喜, 王永和, 张汉文. 2001. 阿尔金山中段高压-超高压带(含菱镁矿) 石榴子石二辉橄榄岩的发现及其地质意义. 西北地质, 34(4): 67–74. |
| [] | 新疆维吾尔自治区地质矿产局. 1993. 新疆维吾尔自治区区域地质志. 北京: 地质出版社. |
| [] | 杨建军. 1991. 苏鲁榴辉岩及有关超基性岩. 北京: 地质出版社. |
| [] | 杨建军, 朱红, 邓晋福, 周天祯, 赖绍聪. 1994. 柴达木北缘石榴石橄榄岩的发现及其意义. 岩石矿物学杂志, 13(2): 97–105. |
| [] | 杨经绥, 史仁灯, 吴才来, 苏德辰, 陈松永, 王希斌, WoodenJ. 2008. 北阿尔金地区米兰红柳沟蛇绿岩的岩石学特征和SHRIMP定年. 岩石学报, 24(7): 1567–1584. |
| [] | 于胜尧, 张建新, 宫江华. 2011. 南阿尔金巴什瓦克高压/超高温麻粒岩中金红石Zr温度计及其地质意义. 地学前缘, 18(2): 140–150. |
| [] | 张建新, 张泽明, 许志琴, 杨经绥, 崔军文. 1999. 阿尔金构造带西段榴辉岩的Sm-Nd及U-Pb年龄-阿尔金中加里东期山根存在的证据. 科学通报, 44: 1109–1112. |
| [] | 张建新, 杨经绥, 许志琴, 孟繁聪, 宋述光, 李海兵, 史仁灯. 2002. 阿尔金榴辉岩中超高压变质作用证据. 科学通报, 47(3): 231–234. |
| [] | 张建新, 孟繁聪. 2005. 南阿尔金含假蓝宝石高压基性麻粒岩及其意义. 科学通报, 50(2): 167–171. |
| [] | 张建新, 孟繁聪, MattinsonCG. 2007. 南阿尔金-柴北缘高压-超高压变质带研究进展、问题及挑战. 高校地质学报, 13(3): 526–545. |
| [] | 张建新, 李怀坤, 孟繁聪, 相振群, 于胜尧, 李金平. 2011. 塔里木盆地东南缘(阿尔金山)"变质基底"记录的多期构造热事件:锆石U-Pb年代学的制约. 岩石学报, 27(1): 23–46. |