滇西蓝片岩中的角闪石

滇西蓝片岩的原岩为玄武质岩石和泥质岩,其矿物组合分别为Cr(或Win)+Chl±Ab+Ph+Ep±Act+Sph±Qz和Gl+Ph+Alm+Tc+Act+Chl+Qz+Do。哀牢山蓝片岩中的闪石普遍具有成分分带,核心为蓝透闪石,边缘为阳起石。澜沧江带中的蓝片岩,其碱性闪石显示了一定的成分变化,既有青铝闪石、镁钠闪石,也有蓝闪石。另外,在滇西蓝片岩中,共存的碱性闪石和钙质闪石之间存在着较大的成分间断。澜沧江带蓝片岩的变质年龄为193Ma。     

早古生代北阿尔金HP/LT混杂岩片——一个“化石”俯冲隧道

北阿尔金高压/低温(HP/LT)变质岩呈构造岩片分布在俯冲-增生杂岩中，主要由强变形的变质沉积岩(泥质片岩、钙质片岩和石英片岩)和少量呈透镜状分布在变沉积岩中的蓝片岩和榴辉岩组成，与相邻的蛇绿混杂岩呈断层接触。榴辉岩主要矿物为绿辉石、石榴子石、多硅白云母、石英、冻蓝闪石，含少量蓝闪石、绿泥石、方解石、钠长石、榍石。蓝片岩主要矿物为蓝闪石、石榴子石、碳酸盐类矿物、阳起石、绿帘石、钠云母、绿泥石、钠长石和石英，偶见多硅白云母，其中在部分蓝片岩的石榴子石中有少量硬柱石和绿辉石包体。本文对蓝片岩(样品A06-16-7)和榴辉岩(样品A03-3-5.3)开展了岩石学和相平衡模拟研究，得到它们形成的压力峰期的温压条件分别是：T=～524℃、P=～2.1GPa和T=～527℃、P=～2.2GPa,并均经历了后期蓝片岩相的退变质叠加。结合区域上已有的研究表明，北阿尔金HP/LT混杂岩片中不同类型岩石可能经历了不同的变质演化历史，反映了古俯冲隧道的不均匀性，并在俯冲隧道的较浅部混杂在一起，共同经历了蓝片岩相或蓝片岩-绿片岩过渡相条件下的透入性变形作用。     

中国蓝闪片岩相的变质作用

本文论述了中国蓝闪片岩的分布、变质条件及其构造位置。中国的蓝闪片岩从中晚元古代开始,各变质期均有出现。根据矿物组合,可分为两类:第一类蓝闪片岩常含有高压矿物,如硬柱石、硬玉和文石以及蓝闪石、绿纤石、黑硬绿泥石、多硅白云母、红帘石等,属高压亚绿片岩相,称蓝闪—硬柱石片岩相,形成温度约250—350℃,压力大于500—800MPa,甚至可达1200MPa。此类蓝闪—硬柱石片岩相多代表海洋板块古消减带。第二类蓝闪片岩的常见矿物为蓝闪石、青铝闪石或镁钠闪石、黑硬绿泥石、红帘石和绿片岩相中的绿帘石、阳起石、绿泥石、白云母、有时还有黑云母、铁铝榴石和钠质辉石。形成温度约350—450℃,压力500—800MPa。此类蓝闪绿片岩相虽处于活动带,但与板块构造没有直接关系。我国西藏南部和内蒙温都尔庙属第一类,但大部分蓝闪片岩带属第二类。     

澜沧江杂岩带小黑江-上允地区蓝片岩的成因及变质演化

通过对澜沧江杂岩带小黑江-上允地区蓝片岩的岩相学、地球化学、成因矿物学以及相平衡模拟的综合研究,阐述蓝片岩的原岩以及变质演化过程。地球化学分析结果显示,蓝片岩具有一致的稀土元素配分模式,具弱Eu正或负异常,稀土元素和微量元素特征与OIB相似,其原岩可能为OIB型玄武岩。详细矿物学研究表明,本区蓝片岩记录了俯冲峰期蓝片岩相变质和峰期后绿片岩相变质两个变质阶段,其矿物组合分别为蓝闪石+钠长石+多硅白云母+绿泥石+绿帘石和蓝闪石+钠长石±阳起石+绿泥石+绿帘石。通过Na_2O-Ca O-Fe O-MgO-Al_2O_3-SiO_2-H_2O-O体系相平衡计算,得到两个阶段的压力范围分别约为0.95 GPa和0.40 GPa。     

西藏羌塘中部才多茶卡蓝闪石40Ar/39Ar年代学及地质意义

本文报道了藏北羌塘中部才多茶卡地区晚三叠世蓝闪石片岩及蓝闪石矿物的新发现及地质意义。通过对才多茶卡构造混杂岩地质剖面的实测,在剖面第6层灰绿色变基性火山岩(绿片岩)中新发现以产蓝闪石类矿物为特征的中—高压变质岩系——蓝闪石片岩。对蓝闪石片岩的岩石学和矿物学特征进行了详细室内研究。从蓝闪石片岩中挑选出蓝闪石单矿物进行了40Ar/39Ar同位素年龄测定,结果表明,蓝闪石单矿物的坪年龄值为209±4Ma,等时线年龄值为216±4Ma,坪年龄与等时线年龄基本一致,属于晚三叠世诺利期,这与区域上羌塘中部发育的红脊山—双湖蓝闪石片岩的中—高压变质事件相吻合。由于蓝闪石类矿物的产出具有特殊的构造机制和地质意义,因此双湖以东的才多茶卡地区蓝闪石片岩的新发现及蓝闪石矿物的40Ar/39Ar同位素年代学研究进一步补充和丰富了青藏高原腹地羌塘中部龙木错-双湖构造混杂岩带的物质组成和同位素年代学信息,同时也为解决羌塘地区"龙木错-双湖构造混杂岩带是否向东延伸"等重大基础性地质问题,提供了新的重要资料。研究资料表明,羌塘中部自西向东从冈玛错、红脊山、绒马,经嘎尔错到才多茶卡地区,沿构造线方向断续分布的长达600km的含蓝闪石片岩的中—高压变质岩系,都是龙木错-双湖构造混杂岩带印支期构造活动事件的产物。     

阿拉斯加Seward半岛区域前进高压变质作用

在Seward半岛蓝片岩相岩石构成了一个构造上连贯的岩带,其出露面积至少有15000km~2。放射性年龄数据表明,高压变质作用多伴发生在侏罗纪,而不象以前推测的古生代或前寒武纪。原岩属内陆盆地或大陆边缘类型的沉积物(Nome Group),并具有早古生代或许是晚前寒武纪的年龄。这样在年龄上就早于高压变质作用的年龄200Ma之多。蓝闪石片岩相矿物组合几乎在Nome Group的所有岩性中都有发育,在富含Fe、Ti的变质基性岩(篮闪石+铁铝榴石+绿帘石)和泥质岩(蓝闪石+硬绿泥石+多硅白云母)中,硬柱石—青铝闪石亚相在Darby山东侧发育,可能在Nome Group岩石中有所发育,半岛西南部钠长石—绿帘岩—角闪岩相组合代表Nome Group岩石的特征。岩带中部地区的变质作用从早期的硬柱石,到后来的绿帘石—铁铝榴石—篮闪石片岩亚相,局部发育有榴辉岩组合(Nome河以东)。高压变质矿物是同构造期的,并拥有中等规模的层内等斜褶皱和方向一致的压扁的叶理,隆起的开始很可能相当于在较早的钠质和阳起石质角闪石环边上有冻蓝闪石的生长,部分构造后绿片岩相的各种交代作用记录了后来的减压阶段,蛇绿岩及混杂岩不与Seward半岛的蓝片岩伴生,高压变质作用是由一个不定成因的外来体所引起的大陆板块的构造负荷所引起的,高压变质作用的P—T 条件大约是 9～11Kb,400～450℃,介于Shuksan和Franciscan岩区的P—T轨逆之间。     

内蒙古头道桥地区蓝闪石片岩和相关变质岩石岩石学特征及其构造意义

内蒙古头道桥地区出露了一套经高压变质形成的岩石组合。本次研究通过岩相学和矿物化学分析,根据矿物组合的不同,识别出蓝片岩、绿片岩两种不同类型的岩石类型。其中,蓝片岩的矿物组合为角闪石（蓝闪石、蓝透闪石）+绿帘石+钠长石+绿泥石+石英+赤铁矿±多硅白云母±方解石±榍石;绿片岩的矿物组合为绿泥石+钠长石+石英±绿帘石±角闪石（阳起石、镁角闪石、蓝透闪石、冻蓝闪石等）±多硅白云母±赤铁矿。确定了蓝片岩的峰期变质级别为绿帘-蓝闪片岩相,峰期变质温度为400~600℃,压力为1.2~1.4 GPa。绿片岩的峰期变质级别为绿帘-角闪岩相。结合前人研究成果,认为蓝片岩和绿片岩的形成与额尔古纳地块和兴安地块的碰撞拼合有关。     

黑龙江杂岩蓝片岩—云母片岩矿物成分及变质作用P-T条件

黑龙江构造混杂岩中保留着一套曾遭受过中高压变质作用的岩石,其代表性岩石为:蓝片岩-云母片岩;蓝闪石、铁蓝闪石和多硅白云母(单位结构中Si=3.37～3.46>3.30)等具有中高压性质的典型变质矿物在岩石中平衡共生.蓝片岩-云母片岩组合至少经历了早期和晚期两阶段变质,早期为绿帘蓝片岩相,变质温压条件为T=320～460℃,P=7.8×108～11×108Pa.晚期为高绿片岩相,出现富镁绿泥石(XMg=0.565～0.646)交代早期钠质角闪石和多硅白云母等高压变质矿物现象,变质温度升高而压力有所降低,由石榴石云母片岩所限定的高绿片岩相变质条件为T=536～598℃,P=6.8×108～9.5×108Pa,属中温和中高压变质.     

陕甘川交界区碧口群的变质作用及其地质意义

碧口群由一套中晚元古代的变质双峰式火山岩及复理石型深积岩组成，其变质作用分为蓝片岩相和绿片岩相。据其野外分布及白云母ｂ０值的变化可分成Ａ、Ｂ、Ｃ三个变质带。蓝片岩相以钠质闪石＋绿帘石共生为特征，在Ａ带的大面积绿片岩中呈条带或残片状分布。对区内的角闪石、绿泥石、绿帘石及白云母等矿物及其间的交代关系研究表明蓝片岩和绿片岩并非同一物理化学条件下的产物。蓝片岩相的温度为３００－４００℃，压力为０．５－０．     

甘肃玉门昌马地区的蓝闪片岩

蓝闪片岩产于一套含放射虫硅质岩、硅质大理岩、板岩、变质基性火山岩中,与此相伴的超基性岩块,以一系列向南逆冲的断片产出。蓝闪片岩中的蓝闪石往往和黑硬绿泥石、钠长石、绿泥石以及钠钙闪石(蓝透闪石、冻蓝闪石等)、钙闪石(阳起石等)共存。据钠角闪石、绿泥石计算的生成压力是0.65GPa至0.8GPa,略大于美国佛兰西斯科的瓦尔德溪蓝片岩中该矿物对生成的压力。稀土元素分析证明蓝片岩的原岩是典型洋底(中脊)玄武岩和岛弧玄武岩,这是蓝片岩沟-弧俯冲-碰撞的证据之一。     

Triassic blueschists and eclogites from northwest Turkey: vestiges of the Paleo-Tethyan subduction

Triassic eclogite and blueschist facies rocks occur as a thrust sheet, 25-km long and over 2-km thick, in an Eocene fold-and-thrust belt in northwest Turkey along the zmir–Ankara suture. The thrust sheet consists mainly of metabasites with minor marble, phyllite and metachert, and rare lenses of serpentinite. The common blueschist facies mineral assemblage in the metabasites is sodic amphibole+epidote+albite+chlorite+phengite±garnet. Sodic amphibole commonly shows replacement by barroisite, and there is continuous petrographic transition from blueschist–metabasites to barroisite-bearing epidote–amphibolites. Eclogite with the mineral assemblage of garnet+sodic pyroxene+sodic–calcic amphibole+epidote is found only in one locality. P–T conditions of the epidote–blueschist facies metamorphism are estimated as 450±50 °C and 11±2 kbar. The blueschist formation was followed by a decrease in pressure and increase in temperature, leading to the development of barroisite-bearing epidote–amphibolites. Phengite, sodic amphibole and barroisite Ar/Ar ages from three metabasic rocks range between 215 and 205 Ma, and indicate Late Triassic high-pressure metamorphism. The Triassic blueschists in northwest Turkey constitute part of a much larger allochthonous tectonic unit of Triassic mafic volcanic rocks. They probably represent the upper layers of a Triassic oceanic plateau, which was accreted to the Laurasian margin during the latest Triassic. The close spatial association of the Triassic and Cretaceous blueschists along the zmir–Ankara suture suggests that the suture represents a long-lived plate boundary of Late Palaeozoic to early Tertiary age.     

The youngest blueschist belt in SW Japan: implication for the exhumation of the Cretaceous Sanbagawa high-P/T metamorphic belt

The tectonic evolution of the Northern Shimanto belt, central Shikoku, Japan, was examined based on petrological and geochronological studies in the Oboke area, where mafic schists of the Kawaguchi Formation contain sodic amphibole (magnesioriebeckite). The peak P–T conditions of metamorphism are estimated as 4–4.5 kbar (15–17 km depth), and 240–270 °C based on available phase equilibria and sodic amphibole compositions. These metamorphic conditions are transitional between blueschist, greenschist and pumpellyite–actinolite facies. Phengite K–Ar ages of 64.8 ± 1.4 and 64.4 ± 1.4 Ma were determined for the mafic schists, and 65.0 ± 1.4, 61.4 ± 1.3 and 63.6 ± 1.4 Ma for the pelitic schists. The metamorphic temperatures in the Oboke area are below the closure temperature of the K–Ar phengite system, so the K–Ar ages date the metamorphic peak in the Northern Shimanto belt. In the broad sense of the definition of blueschist facies, the highest‐grade part of the Northern Shimanto belt belongs to the blueschist facies. Our study and those of others identify the following constraints on the possible mechanism that led to the exhumation of the overlying Sanbagawa belt: (i) the Sanbagawa belt is a thin tectonic slice with a structural thickness of 3–4 km; (ii) within the belt, metamorphic conditions varied from 5 to 25 kbar, and 300 to 800 °C, with the grade of metamorphism decreasing symmetrically upward and downward from a structurally intermediate position; and (iii) the Sanbagawa metamorphic rocks were exhumed from ～60 km depth and emplaced onto the Northern Shimanto metamorphic rocks at 15–17 km depth and 240–270 °C. Integration of these results with those of previous geological studies for the Sanbagawa belt suggests that the most probable exhumation mechanism is wedge extrusion.     

Palaeoproterozoic arc magmatism and collision in Liaodong Peninsula (north-east China)

In the north‐eastern part of the North China Block, a mafic magmatic belt consisting of mafic–ultramafic rocks and marine sedimentary rocks crops out between the northern Archean Anshan Block and a southern Palaeoproterozoic Block. ⁴⁰Ar/³⁹Ar amphibole ages around 1.9 Ga from gabbros, and trace element analyses of gabbros, pyroxenite and shale show that these rocks formed along a Palaeoproterozoic active continental margin. The mafic magmatic belt is interpreted as an arc developed above a south‐directed subduction zone, which was subsequently overthrust to the north upon the Anshan Archean Block. This study provides a new example agreeing with increasing evidence supporting plate mobility and thrust tectonics during the Palaeoproterozoic. These new insights must be considered with regard to the formation of the North China Block by magmatic accretion and tectonic collision.     

Tectonic setting, petrology and geochronology of jadeite + glaucophane and chloritoid + glaucophane schists from north-west Turkey

The north-west Turkish blueschists represent a subducted passive continental margin sequence dominated by metaclastic rocks and marble. The depositional age of the blueschist protoliths are probably Palaeozoic to Mesozoic, while the age of the high-pressure/low-temperature metamorphism is Late Cretaceous. Blueschists are tectonically overlain by a volcanosedimentary sequence made up of accreted oceanic crustal material that locally shows incipient blueschist metamorphism and by spinel peridotite slices. The metaclastic rocks with regional jadeite and glaucophane, which comprise the lower part of the blueschist unit, make up an over 1000-m-thick coherent sequence in the Kocasu region of north-west Turkey. Rare metabasic horizons in the upper parts of the metaclastic sequence with sodic amphibole + Iawsonite but no garnet indicate lawsonite blueschist facies metamorphism. The blueschist metaclastics in the Kocasu region are practically free of calcium and ferric iron and closely approximate the NFMASH system in bulk composition. Two low-variance mineral assemblages (with quartz and phengite) are jadeite + glaucophane + chlorite + paragonite and chloritoid + glaucophane + paragonite. The metaclastics comprise up to several-metres-thick layers of jadeite schist with quartz, phengite and nearly 100 mol% jadeite. Phase relations in the metaclastics show that the chloritoid + glaucophane assemblage, even in Fe²⁺-rich compositions, is stable in the jadeite stability field. In the NFASH system the above assemblage without the accompanying garnet has a narrow thermal stability field. Mineral equilibria in the metaclastics involving chloritoid, glaucophane, jadeite, paragonite and chlorite indicate metamorphic P-T conditions of 20 ± 2 kbar and 430 ± 30 d? C, yielding geothermal gradients close to 5d? C km^-1, one of the lowest geotherms recorded. Blueschists in the Kocasu region, which have been buried to 70 km depth, are tectonically overlain by the volcanosedimentary sequence and by peridotite buried not deeper than 30 km. Phengites from two jadeite schists were dated by Ar/Ar laser probe; they give an age of 88.5 ± 0.5 Ma, interpreted as the age of metamorphism. Blueschists and the overlying peridotite bodies are intruded by 48-53-Ma-old granodiorite bodies that were emplaced at 10 km depth. This suggests that the exhumation of blueschists by underplating of cold continental crust, and normal faulting at the blueschist-peridotite, interface occurred during the Late Cretaceous to Palaeocene (88-53 Ma).     

SOME TRENDS IN THE STUDY OF CARBONATE SEDIMENTS IN THE FEDERAL REPUBLIC OF GERMANY

A stratigraphically coherent blueschist terrane near Aksu in northwestern China is unconformably overlain by unmetamorphosed sedimentary rocks of Sinian age (～600 to 800 Ma). The pre-Sinian metamorphic rocks, termed the Aksu Group, were derived from shales, sandstones, basaltic volcanic rocks, and minor cherty sediments. They have undergone multi-stage deformation and transitional blueschist/greenschist-facies metamorphism, and consist of strongly foliated chlorite-stilpnomelane-graphite schist, stilpnomelane-phengite psammitic schist, greenschist, blueschist, and minor quartzite, metachert, and meta-ironstone. Metamorphic minerals of basaltic blueschists include crossitic amphibole, epidote, chlorite, albite, quartz, and actinolite. Mineral parageneses and compositions of sodic amphibole suggest blueschist facies recrystallization at about 4 to 6 kbar and 300 to 400° C. Many thin diabasic dikes cut the Aksu Group; they are characterized by high alkali, TiO₂, and P₂O₅ contents and possess geochemical characteristics of within-plate basalts; some of these diabasic rocks contain sodic clinopyroxene and amphibole as primary phases and have minor pumpellyite, albite, epidote, chlorite, and calcite as the prehnite/pumpellyite-facies metamorphic assemblage. This prehnite/pumpellyite-facies overprint did not affect the host rocks of the blueschist-facies lithologies.

K-Ar and Rb-Sr ages of phengite and whole rocks from pelitic schists are ～690 to 728 Ma, and a ⁴⁰Ar/³⁹Ar age of crossite from the blueschist is 754 Ma. The basal conglomerate of the overlying Sinian to Eocambrian sedimentary succession contains clasts of both the blueschist and cross-cutting dike rocks, clearly demonstrating that conditions required for blueschist-facies metamorphism were attained and ceased at least 700 Ma. The northward-increasing metamorphic grade of the small blueschist terrane may reflect northward subduction of an accretionary complex beyond the northern edge of the Tarim craton. Abundant subparallel diabasic dikes indicate a subsequent period of Pre-Sinian rifting and diabasic intrusion along the northern margin of Tarim; a Sinian siliciclastic and carbonate sequence was deposited unconformably atop the Aksu Group and associated diabase dikes.     

Blueschist ophiolites in the melange zone,northern New Caledonia

A regional melange zone, 150 km long and 30 km wide, forms the southern boundary and structural capping to a high-pressure blueschist belt in northern New Caledonia. The disrupted country rocks in the melange zone are Mesozoic metagrey-wackes and Eocene chert-limestone sequences which have been penetrated from below by tectonically-injected ophiolite slivers containing metamorphosed serpentinite, gabbro, dolerite, basalt, tuff, chert and shale. An ocean crust origin for these rocks is indicated by chemical, mineralogical and radiometric data from coastal outcrops at Anse Ponandou on the northeast coast. The age (41 m.y.), metamorphic environment (350 ° C at 7 kb), and mineral association (acmitic jadeite-riebeckite-pyropic spessartine-pistacitic epidote-lawsonite-high Si phengite) are significantly different from those of the adjacent regional high-pressure schist belt, indicating a separate structural site for blueschist metamorphism of buried ophiolitic ocean crust during early Tertiary orogenesis.     

Blue amphiboles and their significance for the metamorphic history of the Pan-African Gariep belt, Namibia

The metamorphic history of mafic exotic blocks from a tectonic melange zone within an allochthonous ophiolitic terrane (Marmora Terrane) of the Pan-African Gariep orogenic belt in south-western Namibia was studied, based on mineral parageneses and amphibole composition. Glaucophane described previously from these rocks could not be verified. Instead, two types of blue amphiboles were distinguished: (i) rims of (ferro-) edenitic to pargasitic to barroisitic hornblende composition around brownish amphibole phenocrysts replacing magmatic clinopyroxene, and (ii) deep blue porphyroblasts of magnesio-riebeckite with little ferro-glaucophane component in a highly metasomatized albite-rich rock. Textural and mineralogical evidence, particularly the existence of up to three different amphibole generations in metagabbro samples, supports a multiphase metamorphic history experienced by these exotic blocks. The first metamorphic event, M1, is interpreted as very low- P hydrothermal oceanic metamorphism that affected the igneous protoliths at up to amphibolite facies temperatures. Subsequent M2 metamorphism was syntectonic and is characterized by temperatures similar to those attained during M1 but higher pressures indicating burial to 15–20 km. This event is related to a subduction process. The third metamorphic event, M3, was low grade and of regional nature. It is the only one recorded in the sedimentary envelope of the exotic blocks. The formation of magnesio-riebeckite is considered a retrograde reaction at greenschist facies during M2. The results indicate that in the Gariep belt subduction and subsequent obduction have occurred, although blueschist facies metamorphism has not been reached.     

羌塘中部高压变质带的退变质作用及其构造侵位

羌塘中部的高压变质带主要由榴辉岩、石榴石白云母片岩和蓝片岩等组成,它们在遭受高压变质作用之后折返,构造侵位于晚古生代展金组地层中,二者以韧性变形带为接触边界.本文以高压变质带中的榴辉岩和韧性变形带为研究对象,讨论了高压变质带折返过程中的退变质作用特征及折返时代.研究表明,榴辉岩在高峰期变质作用之后的折返过程中经历了由榴辉岩相→蓝片岩相→绿帘角闪岩相的退变质作用演化过程;在高压变质带构造侵位过程形成的韧性变形带中,白云母石英片岩的白云母40Ar-39Ar坪年龄为219±2Ma.高压变质带在219Ma左右构造侵位于展金组地层中,并于214Ma之前最终抬升出露地表.     

中国的蓝片岩

<正> 蓝片岩作为板块构造的岩石学证据,近十多年来,随着对其成因解释的日趋明朗,已成为当前地学研究中的一个重要课题。 1983年9月,美国地质学会在华盛顿贝林哈姆和西雅图举行国际性蓝片岩和有关榴辉岩研究讨论会。会议期间除了讨论当前对遭受蓝片岩变质作用的造山带的认识现状之外,还从七个专题方面分别讨论:蓝片岩的相变实验,蓝片岩地体的温度压力测定,重结晶作用与构造的关系,高压变质作用后的减压、侵位和推覆构造模式,蓝片岩岩石及矿物年龄随时间演化的关系等问题。     

Oscillatory zoning in eclogitic garnet and amphibole,Northern Serpentinite Melange,Cuba: a record of tectonic instability during subduction?

Exotic blocks of eclogite from distant localities along the Northern Serpentinite Melange of Cuba have comparable P–T histories that include high‐pressure prograde sections (450–600 °C, >15 kbar) associated with subduction of oceanic lithosphere, and retrograde sections within the albite–epidote amphibolite facies (<500 °C, <10 kbar) related to melange uplift. ⁴⁰Ar/³⁹Ar and Rb/Sr cooling ages (118–103 Ma) of one of the blocks indicate pre‐Aptian subduction and Aptian–Albian uplift. Detailed X‐ray imaging and profiling further reveals that minerals in these eclogite blocks (notably garnet and amphibole) display subtle but well defined oscillatory zoning that developed along the prograde trajectory of the rocks, previous to attainment of peak eclogitic conditions. The chemistry (e.g. coupled changes of Mg# and Mn in garnet, and of Si, Ti, Al and Na in amphibole) and geometry (euhedral to anhedral shapes) of the oscillations can be interpreted in terms of subtle fluctuations in P–T during the general prograde subduction‐related metamorphic path. A (near‐) equilibrium model is presented for the formation of oscillations at near peak conditions by means of recurrent dissolution‐growth reaction processes. This model for near‐peak conditions, and the chemical signatures of earlier oscillations (notably in amphibole), suggest that episodes of retrogression (upward movement?) affected parts of the subducting slab. It is proposed that these retrograde episodes record the tectonic rupture of the subducting slab and, probably, of the upper plate mantle, either due to the intrinsic dynamic behaviour of subduction systems or to the effects of the plate‐tectonic rearrangement of the Caribbean region during the Early Cretaceous.