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1.
《Gondwana Research》2014,25(3):999-1007
Abundant data have been acquired on the lower Cambrian small shelly fossils (SSFs) of the Yangtze platform during the last three decades, demonstrating that these fossils are an important piece of evidence for the Cambrian radiation and are useful biostratigraphic tools for correlating the lower Cambrian. Here we report SSF associations from the Yanjiahe Formation in the Three Gorges area, South China. The Yanjiahe Formation is well exposed near the Yanjiahe village, and its 40-m-thick sequence can be subdivided on the basis of lithology into five stratigraphic intervals (beds). Small shelly fossils occur mainly in Beds 2 and 5, but abundant SSFs were discovered in thin sections of siliceous–phosphatic nodules from Bed 3 for the first time. No skeletal fossils were discovered in the basal siliceous rock interval (Bed 1), but the negative δ13Ccarb excursion and the occurrence of the acritarch Micrhystridium regulare indicate that it belongs to the basal Cambrian. The SSF associations are somewhat similar to those of East Yunnan, and can be differentiated into three biozones (in ascending order): the Anabarites trisulcatus–Protohertzina anabarica assemblage zone (Bed 2), the Purella antiqua assemblage zone (Bed 3), and the Aldanella yanjiaheensis assemblage zone (Bed 5). The occurrence of A. yanjiaheensis in Bed 5 probably indicates that Bed 5 belongs to Cambrian Stage 2, but the Stage 2/Stage 1 boundary is uncertain since Bed 4 lacks fossils. SSF biostratigraphy indicates that the Yanjiahe Formation is pretrilobitic Meishucunian in age (equivalent to the Nemakit–Daldynian to Tommotian of Siberia, Terreneuvian). Five SSF genera occur in Bed 2, more than six genera in Bed 3, and twenty-three genera in Bed 5. The stepwise increase in generic diversity through the Yanjiahe Formation is comparable with the global diversity increase through the Nemakit–Daldynian to early Tommotian interval. 相似文献
2.
Sections from the eastern margin of the Siberian Platform provide important reference sections for stable isotopic correlation of the newly defined Precambrian–Cambrian boundary level since they contain some of the earliest pre-Tommotian shelly fossil assemblages known, and are amenable to δ13C stratigraphy. Stable isotopes are examined from the Dvortsy and Ulakhan–Sulugur sections (River Aldan), where sparse pre-Tommotian assemblages occur, and from the Uchur River region, where the putative Anabarites trisulcatus and Purella antiqua Zones of the Nemakit–Daldynian Stage are well-developed. Diagenetic resetting of δ18O and δ13C must be taken into account when comparing such sections. Simple corrections allow for stable isotopic correlation of basal Nemakit–Daldynian and Tommotian strata across eastern Siberia. 相似文献
3.
YU Wen 《《地质学报》英文版》2014,88(4):1262-1287
Yangtzeconus priscus-Archaeospira ornata, an important earliest Cambrian benthonic Assemblage of the Yangtze micromolluscan fauna, occurs mainly in the Lower Cambrian Zhongyicun and Dahai Members of the Yuhucun Formation in E Yunnan, the Tianzhushan Member （=Huangshandong Member） of the Dengying Formation in W Hubei and the Maidiping Member of the Hungchunping Formation in C Sichuan, China. About 90% of the genera of this Assemblage are unknown from the Nemakit-Daldynian and Tommotian molluscan Assemblages of the Siberian Platform, Russia. About 90% of the Siberian molluscan genera do not occur in the Zhongyicun and Dahai Members in the Meishucun section and in the corresponding beds of the Yangtze Platform, because the Tommotian molluscan Assemblage is characterizedly abundant archaeocyathids. It is clearly indicated that the Yangtze and Siberian molluscan Assemblages represent different bio- and lithofacies and ages. The age of the pre-trilobitic Yangtzeconus priscus-Archaeospira ornata Assemblage is older than that of the Nemakit-Daldynian and Tommotian molluscan Assemblages and referable to the Earliest Cambrian. Two new genera Mcnamaraconus and Zhangwentangoconus are herein proposed. 相似文献
4.
《Gondwana Research》2016,29(4):1543-1565
Early Cambrian small skeletal fossils (SSFs) are studied and revised from the Zhenba–Fangxian Block of the transitional zone between the Yangtze Block and the South Qinling Terrane. The study reveals a diverse fauna with 47 species of various biological affinities, including the new species Gapparodus gapparites sp. nov. The SSFs are assigned to the newly defined Cambroclavus fangxianensis–Rhombocorniculum cancellatum Assemblage Zone. Based on the investigated SSF fauna from Zhenba County, Southeast Shaanxi of China and published data, a palaeobiogeographic study is carried out for the Cambrian Stage 3 (equivalent to the Atdabanian–Botoman of Siberia). A hierarchical Pearson similarity cluster analysis of 295 species from 32 regions of the world indicates a distinct palaeobiogeographic pattern with seven faunal provinces. The result is mostly consistent with existing palaeogeographic reconstructions for the early Cambrian. However, it is also shown that the SSF assemblages of the Zhenba–Fangxian Block have low similarity with those of the Yangtze Block. Instead, they share high similarity with those from Armorica, Tarim and the Karatau–Naryn terranes (South Kazakhstan/North Kyrgyzstan). The Yangtze Block has a unique SSF assemblage dissimilar to most of other regions. The Terreneuvian–Cambrian Stage 3 sedimentary sequence of the Zhenba–Fangxian Block is more consistent with that of the South Qinling Terrane. Besides, sedimentary Ediacaran manganese ore deposits and Cambrian barite/witherite deposits have unique distribution pattern on the Zhenba–Fangxian Block. Derived from the profound dissimilarities in faunal composition, sedimentary sequence and distribution of sedimentary ore deposits, we hypothesize that during the Neoproterozoic–Cambrian transition, the Zhenba–Fangxian Block might have been an independent terrane and more distant from the Yangtze Block. The palaeobiogeographic analysis of SSFs also indicates a closer alliance between Avalonia and Siberia. It corroborates the palaeogeographic reconstruction of North China at the margin of Gondwana, in the vicinity of Australia, Antarctica, and Armorica. 相似文献
5.
V. V. Khomentovsky 《Stratigraphy and Geological Correlation》2008,16(6):581-598
In Russia, the terminal Neoproterozoic formally includes the Vendian of western part of the East European platform and the concurrent Yudoma Group of Siberia. As is shown in this work, the designated subdivisions correspond in the stratotypes only to the upper, Yudomian Series of the Vendian. In the Siberian platform, the Ust-Yudoma and Aim horizons of the Yudomian are tightly interrelated. The lower of them, bearing remains of Ediacaran Fauna, represents the Ediacarian Stage, whereas the upper one containing small-shelled fossils (SSF) corresponds to the Nemakit-Daldynian Stage divided into the trisulcatus and antiqua superregional zones. In more complete sections of the platform periphery, sediments of these subdivisions conformably rest on siliciclastic succession that should be ranked as basal subdivision of the Yudomian. The succession is concurrent to the Laplandian Stage of the East European platform. According to geochronological dates obtained recently, the Yudomian Series spans interval of 600–540 Ma. In the East European platform, the Upper Vendian (Yudomian) begins with the Laplandian basal tillites of synonymous stage. In the west of the platform, tillites are dated at 600 Ma like the Upper Vendian base in Siberia. The next Ediacarian Stage of the East European platform is stratigraphic equivalent of the Redkino Horizon, while summary range of the Kotlin and Rovno horizons is concurrent to that of the Nemakit-Daldynian Stage. The Vendian of Russia is conformably overlain by the Tommotian Stage of the Lower Cambrian. Intense pre-Vendian events constrained distribution areas of the Lower Vendian sediments in Russia. The Lower Vendian deposits of the East European platform are most representative and well studied in the central Urals, where they are attributed to the Serebryanka Group. In Siberia, separate subdivisions representing the Lower Vendian are the Maastakh Formation of the Olenek Uplift, two lower members of the Ushakovka Formation in the Baikal region, and the Taseeva Group of the Yenisei Range. Chronological interval of the Lower Vendian corresponds to 650–600 Ma. The Marinoan Glaciation dated in Australia at 650–635 Ma is concurrent to basal part of the pre-Yudomian interval of the Vendian in Russia, whereas the Laplandian Tillite and Gaskiers Glaciation (600–580 Ma) correspond to onset of the Yudomian Epoch. The new Ediacaran System (Knoll et al., 2004) legalized in the International Neoproterozoic scale is close in range to the entire Vendian (635–544 Ma), although without basal beds (Marinoan Tillite) it deprives the terminal Neoproterozoic of its original sense. Inferiority of the system consists also in its indivisibility into stages. Hence, it is clear that the Vendian System subdivided in detail in Russia should be retained in the rank of terminal system of the Precambrian, one of the basic in general scale of the Neoproterozoic. 相似文献
6.
Luo Huilin Jiang Zhiwen Wu Xiche Ouyang Lin Song Xueliang Xue Xiaofeng 《《地质学报》英文版》1992,66(2):197-207
This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the studyof the microtexture of Lapworthella and some new materials of trace fossils. Phycodes pendum Seilacher, animportant index for correlation, was also discovered in the Zhongyicun Member. In the Yu' anshan Membermany worms, medusas and arthropods of the Chengjiang fauna have been found by other workers. Asupplemental study was made on the fossil zones of the Meishucunian stage. Based on new isotopic data, theage of the Precambrian-Cambrian boundary should now be 597 Ma. It is further suggested that point "B" re-mains as an optimum selection for defining the Precambrian-Cambrian boundary. 相似文献
7.
Sedimentary rocks in the western Anabar region, northwestern Siberia, preserve an exceptional record of evolution and biogeochemical events near the Proterozoic-Cambrian boundary. Carbon isotopic data on petrographically and geochemically screened samples collected at 1 to 2 m intervals support correlation of the lower Anabar succession (Staraya Reckha and lower Manykai Formations) with sub-Tommotian carbonates of the Ust'-Yu-doma Formation in southeastern Siberia. In contrast, the upper Manykai and most of the overlying Medvezhya Formation appear to preserve a sedimentary and paleontological record of an evolutionary important time interval represented in southeastern Siberia only by the sub-Tommotian unconformity. Correlation of the Anabar section with other northern Siberian successions that contain well-dated volcanic rocks permits the estimate that the sub-Tommotian unconformity in southeastern Siberia spans approximately 3 to 6 m.y. Diverse small shelly fossils (but not archaeocyathans) previously thought to mark the base of the Tommotian Stage evolved sequentially throughout this earlier interval. 相似文献
8.
E. M. Bugrova 《Stratigraphy and Geological Correlation》2008,16(1):81-91
Benthic foraminifers from borehole sections recovered by drilling in the Yamal Peninsula, West Siberia, characterize the Ceratobulimina cretacea Beds (the upper Campanian-lower Maastrichtian) and the Spiroplectammina variabilis-Gaudryina rugosa spinulosa and Spiroplectammina kasanzevi-Bulimina rosenkrantzi regional zones of the lower and upper Maastrichtian, respectively. The Danian Stage is missing from the sections, which include marine deposits of the Selandian Stage attributed to the Ceratolamarckina tuberculata Beds. Foraminiferal assemblages of the beds include the Siberian endemic species associated with Paleocene foraminifers of the Midway-type fauna of subglobal distribution range. Occurrence of the latter suggests that warm-water surface currents from the North Atlantic reached southern areas of the Kara Sea. 相似文献
9.
10.
华南寒武系年代地层系统的修订及相关问题 总被引：10，自引：3，他引：7
将早先提出的华南寒武系4统9阶的年代地层系统,修订成4统10阶,除王村阶的底界略高于全球鼓山阶(Drumian Stage)的底界外,其余界线都与目前的全球4统10阶的年代地层界线一致。新系统采纳了在我国华南建立的全球芙蓉统、排碧阶和古丈阶,在原桃源阶的上部另建"牛车河阶"。原王村阶和桃源阶的时限因这一修订有所缩减。全球鼓山阶的底界与台江阶上部的Ptychagnostus atavus带底界可以精确对比。滇东统包含晋宁阶和梅树村阶(狭义)两个年代地层单位,晋宁阶的底界采用全球寒武系的底界,梅树村阶的底界采用罗惠麟等1994年正式修订后的定义,即位于梅树村剖面的"B"点。梅树村阶的原始定义仅指梅树村剖面的磷块岩层(即现今的中谊村段),它的底界高于现在的以Tricophycus pedum首现定义的全球寒武系底界。 相似文献
11.
Sections and fusulinids of the Bolorian (presumably) and Kubergandian (lower part) stages in the Sanandaj-Sirjan tectonic zone are described. Two fusulinid assemblages are distinguished in a most complete section near Sirjan. The lower one is represented by Skinnerella, Paraleeina, and relatively primitive Misellina forms, whereas Armenina, Kubergandella, and Yangchienia species appear in the upper assemblage and suggest its early Kubergandian age. Accordingly, the lower assemblage is attributed to the Bolorian Stage, although it is lacking fusulinids typical of this stage except for the primitive Misellina morphotypes. Fusulinids from the Tange-Darchaleh section near Qomsheh (Shahreza) are typical of the Kubergandian Stage. The described three new species of the genus Skinnerella are close to morphotypes known from younger (Murgabian) deposits and represent their ancestral forms most likely. 相似文献
12.
Qian Jiaju 《《地质学报》英文版》1987,61(2):1-13
The Late Ordovician Wufengian sediments in western Zhejiang include three facies: 1) graptolite shale facies, composed of two parts--the upper part the Yankou Formation, with the Diplograplus bohemicus(graptolite) zone and Dalmanitina sp.(trilobite), and the lower part the yuqian Formation with four graptolite zones:(4) the Paraorthograptus yuqianensis zone,(3) the Climacograptus venustus zone,(2) the Dicellograptus szechuanensis zone and(1) the Pseudoclimacograptus anhuiensis zone; 2) mixed facies, consisting of the Wenchang Formation in its upper part and the Changwu Formation in its lower; and 3) shelly limestone facies, whose upper and lower parts are separately the Wenchang Formation and Sanjushan Formation, containing Taeniolites, Proheliolites, etc. In this region the Dalmanitina-Hirnantia bed is well exposed,and Da. and H. are associated with Diplograptus bohemicus, belonging to the late Late Ordovician.The Ordovician-Silurian boundary is drawn as follows:(1) for the graptolite facies, it lies between the Diplograptus bohemicus zone and Glyptograptus persculptus zone;(2) for the graptolite-sheny limestone facies(brachiopod fauna), it is placed between the top of the Diplograptus bohemicus zone and the base of the horizon with the Eospirifer fauna; and 3) for the shelly facies(brachiopod fauna), it is drawn between the top of the horizon with the Dalmanitina-Hirnantia fauna and thebase of the horizon with the Eospirifer fauna. 相似文献
13.
The Early Evolution of the Acanthomorphic Acritarchs in China and Their Biostratigraphical Implication 总被引：1，自引：0，他引：1
Yin Chongyu Gao Linzhi Institute of Geology Chinese Academy of Geological Sciences Beijing 《《地质学报》英文版》1996,70(2):193-206
On the basis of a study of the acanthomorphic acritarchs discovered in the Late Proterozoicto Early Cambrian Meishucunian Stage in different regions of China, especially in southernShaanxi and the Yangtze Platform, coupled with a study of the assemblages, morphological cor-relation, microstructure, and evolutional relations of the acanthorphic acritarchs, as well as awide correlation with those found in different regions of the world, the authors discuss the earlyevolutionary stages of the acanthomorphs, features of their assemblages in various stages, theirbiostratigraphical significance, and their evolutionary trend in China. 相似文献
14.
Cambrian explosion: Birth of tree of animals 总被引：5，自引：5，他引：0
Excluding the sponges the Kingdom Animalia is usually divided into three subkingdoms: Diploblasta, Protostomia and Deuterostomia. The Cambrian Explosion consists of three major episodes, two of which were in the early Early Cambrian (one represented by the small skeletal fossils “SSFs” at the base of the Cambrian and the other represented by the succeeding Chengjiang faunas “CFs”), and the other episode as their prelude took place in the “Eocambrian” (i.e. the latest Precambrian), represented by the Ediacaran faunas. This unique Big Bang of life has been recognized as giving birth to the entire morphological Tree Of Animals (or metazoans), in short the TOA. Its “seed” in the deep Precambrian, represented by some sort of protist from which the complete TOA must have grown, remains unknown paleontologically. However, the fossil evidence suggests that the three major episodes of the Cambrian Explosion are responsible for the earliest radiations of the three subkingdoms of animals respectively. While the observed Ediacaran fauna might constitute only a small part of the whole Ediacaran biota, our evidence supports that it was dominated by diploblasts (the “trunk” of the TOA) with only a few possible stem-group triploblasts. The Early Cambrian in turn in two phases explosively yielded almost all the major triploblastic crown-branches (Bilateria: the huge “crown” of the TOA), which include the other two subkingdoms: first the extremely diverse protostomes in the Meishucunian Age and then followed by a nearly entire lineage of early deuterostomes from the Chengjiang, including even its most derived member – the earliest true vertebrates. Among the four most significant milestones of morphological origins and radiations in animal history, the first one (i.e. appearance of metazoans) took place in the Ediacaran Period or earlier times, and the other three can be seen in the windows available from the Chengjiang and the Meishucunian fossil assemblages. The newly discovered extinct Phylum Vetulicolia, which has primitively segmented body with simple gill slits in its anterior division, most probably represents one of the roots of the deuterostome subkingdom. Showing a mosaic of basic features possessed in both the bilateral vetulicolians and some primitive echinoderms, the soft-bodied vetulocystids are best regarded as one of the roots of the extant pentamerous echinoderms. Standing on the “top” of the deuterostome super-branch in the early Cambrian TOA are the “the first fish” Myllokunmingia and Haikouichthys, which bear paired eyes and salient proto-vertebrae. These animals represent the real root of the remainder of the vertebrates or craniates. On the contrary, yunnanozoans, including Yunnanozoon and Haikouella, possess neither eyes nor unequivocal vertebrae, and may have nothing to do with the craniates, let alone the vertebrates. Those enigmatic creatures share a similar body-plan with vetulicolians and should be treated as a side-branch within the lower deuterostomes. 相似文献
15.
16.
New data on biostratigraphy of the Vendian Nemakit-Daldynian stage in the southern Siberian platform
New paleontological finds in sediments of the Upper Vendian Nemakit-Dadynian Stage from different areas of the southern Siberian
Platforms (Yenisei Range, Sayany region, central areas, Patom Highland) are discussed. The base of the Lower Cambrian Tommotian
Stage (∼540 Ma) is established at the first appearance level of characteristic small-shelled fossils in the western part of
the Patom Highland. This boundary coincides with the episode of a brief sea-level fall and enhanced terrigenous sedimentation
in the basin with dominant carbonate sediment deposition. The base of the Purella antiqua Zone (544 Ma), which is registered by paleontological data in the Yenisei Range sections, is marked by the replacement of
terrigenous sedimentation by the carbonate one. In the northwestern Yenisei Range, this boundary coincides, in addition, with
a major hiatus and subsequent paleobasin extension. The base of the Nemakit-Daldynian Stage (base of the Anabarites trisulcatus Zone, ∼550 Ma) in most sections corresponds to the onset of sea transgression. In addition to small-shelled remains, sediments
of this zone contain characteristic ichnofossils and Vendotaenia flora. It is shown that defined boundaries are traceable through the entire southern part of the Siberian Platform. This
makes them useful for wider stratigraphic interpretations. 相似文献
17.
The Albany–Fraser Orogen in southwestern Australia preserves an important thermo‐tectonic record of Australo‐Antarctic cratonic assembly during the Mesoproterozoic. New petrologic and thermobarometric data from the Coramup Gneiss (a 10 km wide zone of high strain rocks within the NE‐trending eastern Albany–Fraser Orogen) indicate at least two high‐grade metamorphic events during 1345–1140 Ma convergence and amalgamation of the West Australian and Mawson cratons. The first event (M1) involved c. 1300 Ma granulite facies metamorphism of the Coramup Gneiss (M1a: 800–850 °C, 5–7 kbar), followed by burial and recrystallization under high‐P conditions (M1b: 800–850 °C, c. 10 kbar) prior to high‐T decompression (M1c: 700–800 °C, 7–8 kbar) and the 1290–1280 Ma emplacement of Recherche Granite sills. The second event (M2) entailed high‐T, low‐P metamorphism within dextral D2 shear zones (M2a: 750–800 °C, 5–6 kbar), followed by fluid‐present amphibolite facies M2b retrogression. Subsequent sinistral D3 mylonites and pseudotachylites are considered contemporaneous with similar structures in the adjacent Nornalup Complex that postdate the c. 1140 Ma Esperance Granite. Our petrological and thermobarometric data permit two end‐member P–T‐time relationships between M1 and M2: (1) a single post‐M1b event involving continuous M1b–M1c–M2a–M2b cooling and decompression, and (2) a two‐stage post‐M1b evolution involving M1c metamorphism during the waning stages of an event unrelated causally or temporally to subsequent M2a metamorphism and D2 deformation. In a companion paper, new structural and U–Pb SHRIMP zircon data are presented to support a two‐stage P–T evolution for the Coramup Gneiss, with M1 and M2, respectively, reflecting thermo‐tectonic activity during Stage I (1345–1260 Ma) and Stage II (1215–1140 Ma) of the Albany–Fraser Orogeny. 相似文献
18.
Within the Albany–Fraser Orogen of southwestern Australia, the Coramup Gneiss is a NE–SW trending zone of high‐strain rocks that preserves a detailed record of orogenesis related to Mesoproterozoic convergence of the West Australian and Mawson cratons. New structural, metamorphic and U–Pb SHRIMP zircon age data establish that the Coramup Gneiss underwent high‐grade tectonism during both Stage I (c. 1290 Ma) and Stage II (c. 1170 Ma) of the Albany–Fraser Orogeny. Stage I commenced with c. 1300 Ma high‐T, low‐P M1a metamorphism during extension, and the formation of small‐scale ptygmatic folds within a subhorizontal S1a gneissosity. High‐P M1b metamorphism at c. 1290 Ma was accompanied by the transposition and shearing of S1a into a composite, shallow SE‐dipping S1b foliation, and the development of tight recumbent F1b folds with S1‐parallel axial surfaces and asymmetries indicating NW‐directed thrusting. The preservation of a similar P–T–time record in the Fraser Complex (NE of the Coramup Gneiss) is consistent with large‐scale, NW‐directed Stage I thrusting of the Mawson Craton margin over the south‐eastern edge of the West Australian Craton. Stage II tectonism in the western Coramup Gneiss involved high‐T, low‐P M2a metamorphism and the formation of subvertical SE‐dipping D2 shear zones, shallow SW‐plunging L2 mineral stretching lineations, and NW‐verging F2 folds with S2‐parallel axial surfaces. A synkinematic pegmatite dyke emplaced into a D2 shear zone yielded a U–Pb SHRIMP zircon age of 1168 ± 12 Ma. Kinematic indicators suggest a combination of pure shear flattening perpendicular to S2, and dextral simple shear. However, contemporaneous structures elsewhere in the Albany–Fraser Orogen are consistent with continued NW–SE convergence at craton‐scale during Stage II, and oblique compression in the Coramup Gneiss is attributed to the arcuate geometry of the orogen‐scale deformation front. 相似文献
19.
Polyphase and anticlockwise P-T evolution for Franciscan eclogites and blueschists from Jenner, California, USA 总被引：1，自引：0，他引：1
High-grade exotic blocks in the Franciscan Complex at Jenner, California, show evidence for polydeformation/metamorphism, with eight distinct stages. Two parallel sets of mineral assemblages [(E) eclogite, and (BS) laminated blueschist] representing different bulk chemistry were identified. Stage 1, recorded by parallel aligned inclusions (S1) of crossite + omphacite + epidote + ilmenite + titanite + quartz (E), and glaucophane + actinolite + epidote + titanite (BS) in the central parts of zoned garnets, represents the epidote blueschist facies. The onset of a second stage (stage 2) is represented by a weak crenulation of S1 and growth of garnet. This stage develops a well-defined S2 foliation of orientated barroisite + epidote + titanite (E), or subcalcic actinolite + epidote + titanite (BS) at c. 90d? to S1, with syntectonic growth of garnet, defining the (albite-)epidote-amphibolite facies. A third stage, with aligned inclusions of glaucophane + (subcalcic) actinolite + phengite parallel to S2 in the outermost rims of large garnet grains, is assigned to the transitional (albite-)epidote-amphibolite/(garnet-bearing) epidote blueschist facies. The fourth stage represents the peak metamorphism, and was identified by unorientated matrix minerals in the least retrograded samples. In this stage the mineral assemblages garnet + omphacite + glaucophane + phengite (E) and garnet + winchite + phengite + epidote (BS) both represent the eclogite facies. Stage 5 is represented by the retrogression of eclogite facies assemblages to the epidote blueschist facies assemblages crossite/glaucophane + garnet + omphacite + epidote + phengite (E), and glaucophane + actinolite + epidote + phengite (BS), with the development of an S5 foliation subparallel to S2. Stage 6 represents a crenulation of S5, with the development of a well-defined S6 crenulation cleavage wrapping around relics of the eclogite facies assemblages. This crenulation cleavage is further weakly crenulated during a D7 event. Post-D7 (stage 8) is recorded by the growth of lawsonite + chlorite ± actinolite replacing garnet, and by veins of lawsonite + pumpellyite + aragonite and phengite + apatite. The different, yet coeval, mineral parageneses observed in rock types (E) and (BS) are probably due to differences in bulk chemistry. The metamorphic evolution from stage 1 to stage 8 seems to have been broadly continuous, following an anticlockwise P-Tpath: (1) epidote blueschist (garnet-free) to (2) (albite-)epidote-amphibolite to (3) transitional epidote blueschist (garnet-bearing)/(albite-)epidote-amphibolite to (4) eclogite to (5) epidote blueschist (garnet-bearing) to (6-7) epidote blueschist (garnet-free) facies to (8) lawsonite + pumpellyite + aragonite-bearing assemblages. This anticlockwise P-T path may have resulted from a decreasing geothermal gradient with time in the Mesozoic subduction zone of California at early or pre-Franciscan metamorphism. 相似文献