马里亚纳海沟南部海域沉积物的工程地质特性及其成因

大洋27航次中,在马里亚纳海沟挑战者深渊南翼斜坡上获得了箱式插管和重力柱状样品,并对这些样品现场进行了含水率、湿密度、微型扭力十字板、微型贯入和无侧限抗压强度试验,获得了深海表层沉积物的物理力学性质参数,具有较高的含水率、较低的密度、较大的孔隙比、较低的抗剪强度和贯入阻力,各项参数随深度增加呈现规律性变化。归航后通过对沉积物的粒度、碎屑矿物、黏土矿物、微体古生物的鉴定,进一步从物质组成、物质来源和沉积环境等方面对此特殊工程地质性质沉积物的成因进行分析。     

马里亚纳海沟挑战者深渊南部7000m水深处发现硅藻化石软泥

在马里亚纳海沟"蛟龙号"载人深潜器海试区约7000m水深的海底,发现了硅藻化石软泥沉积物,为中国首次在此大深度船载采集到硅藻化石软泥。室内硅藻化石分析显示,重力柱状样顶部约10cm厚的软泥为大筛盘藻Ethmodiscus rex硅藻软泥。化石主要由大筛盘藻组成,呈碎片状,数量巨大,并伴生有Azpeitia等热带远洋浮游种类。硅藻化石软泥发育表明,本区曾发生过E.rex勃发事件,具有重要的古海洋学和古生物学研究意义。     

Composition and origin of lipid biomarkers in the surface sediments from the southern Challenger Deep,Mariana Trench

The surface sediments collected from the southern Mariana Trench at water depths between ca. 4900 m and 7068 m were studied using lipid biomarker analyses to reveal the origin and distribution of organic matters. For all samples, an unresolved complex mixture (UCM) was present in the hydrocarbon fractions, wherein resistant component tricyclic terpanes were detected but C₂₇–C₂₉ regular steranes and hopanes indicative of a higher molecular weight range of petroleum were almost absent. This biomarker distribution patterns suggested that the UCM and tricyclic terpanes may be introduced by contamination of diesel fuels or shipping activities and oil seepage elsewhere. The well-developed faults and strike-slip faults in the Mariana subduction zone may serve as passages for the petroleum hydrocarbons. In addition, the relative high contents of even n-alkanes and low Carbon Preference Indices indicated that the n-alkanes were mainly derived from bacteria or algae. For GDGTs, the predominance of GDGT-0 and crenarchaeol, together with low GDGT-0/Crenarchaeol ratios (ranging from 0.86 to 1.64), suggests that the GDGTs in samples from the southern Mariana Trench were mainly derived from planktic Thaumarchaeota. However, the high GDGT-0/crenarchaeol ratio (10.5) in sample BC07 suggests that the GDGTs probably were introduced by methanogens in a more anoxic environment. Furthermore, the n-alkanes C₁₉–C₂₂ and the n-fatty acids C_20:0–C_22:0 were depleted in ¹³C by 3‰ compared to n-alkanes C₁₆–C₁₈ and the n-fatty acids C_14:0–C_18:0, respectively, which was interpreted to result from the preferential reaction of fatty acid fragments with carbon “lighter” terminal carboxyl groups during carbon chain elongation from the precursors to products. The abundance of total alkanes, carboxylic acids, alcohols and total lipids were generally increased along the down-going seaward plate, suggesting the lateral organic matter inputs play an important role in organic matter accumulation in hadal trenches. The extremely high contents of biomarkers in sample BC11 were most likely related to trench topography and current dynamics, since the lower steepness caused by graben texture and proximity to the trench axis may result in higher sedimentation rate. This paper, for the first time, showed the biomarker patterns in surface sediments of the Mariana Trench and shed light on biogeochemistry of the hardly reached trench environment.     

Magnetostratigraphic evidence for deep-sea erosion on the Pacific Plate,south of Mariana Trench,since the middle Pleistocene: potential constraints for Antarctic bottom water circulation

Abstract

The Antarctic Bottom Water (AABW) current plays a crucial role in storing and transporting heat, water, and nutrients around the world. However, it is impossible to monitor AABW in the Plio-Pleistocene by direct measurement. Hence, abyssal erosion was usually chosen as an effective indicator of the presence of the AABW in the Indian and Eastern Pacific Oceans during that period. Here, we report a high-resolution magnetostratigraphy of a gravity core, the JL7KGC-01A from the south of the Mariana Trench, northwest Pacific Ocean. The main results are as follows: (1) polarity data suggest that the sequence recorded the late Gauss chron to the early Brunhes chron, including the Jaramillo, Cobb Mountain, and Olduvai normal subchrons; (2) the sedimentary processes in the study area since 2.9 Ma show three stages of sedimentation: 83 cm/Ma during 2.9–1.2 Ma, 183 cm/Ma during 1.2–0.7 Ma, and no sedimentation since ~0.7 Ma; (3) the area south of the Mariana Trench experienced a significant change in the deposition rate at 1.2 Ma, which could be correlated with the intensified desertification in inland Asia, and experienced a prominent depositional hiatus since the early middle Pleistocene, which likely resulted from the enhanced/expanded AABW. Based on these new polarity data and comparisons with previous studies around the Pacific Ocean, we therefore propose that the AABW experienced a notable change during the early–mid Pleistocene transition.     

The solubility of TiO2 in olivine: implications for the mantle wedge environment

One characteristic of many subduction-zone garnet peridotites is that they contain titanium-bearing phases not otherwise found in mantle rocks. In particular, titanoclinohumite and/or its breakdown assemblage consisting of symplectic intergrowths of olivine and ilmenite is common in many of these bodies. The Alpe Arami garnet lherzolite of the Swiss Alps, while lacking titanoclinohumite, displays instead large numbers of FeTiO₃ rod-shaped precipitates in the oldest generation of olivine, amounting to approximately 1% by volume, indicating that at some time in its past, the peridotite experienced conditions under which the solubility of TiO₂ in olivine was >0.6 wt.%. In order to test the hypothesis that the environment of very high solubility of TiO₂ in olivine is to be found at very high pressures, we have conducted experiments on lherzolite compositions with added ilmenite at pressures between 5 and 12 GPa and temperatures of 1350–1700 K. Our results on anhydrous compositions show that whereas solubility of TiO₂ was not detected in olivine at 5 GPa, 1400 K where it coexists with rutile, when rutile disappeared from the paragenesis, the solubility climbed to 0.4 wt.% at 8 GPa, 0.5 wt.% at 10 GPa and to >1.0 wt.% at 12 GPa, 1700 K. These results support our previous interpretations from titanate morphology and abundance that the Alpe Arami massif has surfaced from P=10 GPa but remove the need to suggest a deeper origin and possible precursor phase such as wadsleyite. They also support the hypothesis that garnet peridotites with unusual Ti-bearing phases reflect a unique mantle environment occurring in the mantle wedge overlying subduction zones.     

Structural characteristics controlling the seismicity crustal structure of southern Japan Trench fore-arc region, revealed by ocean bottom seismographic data

The Japan Trench is a plate convergent zone where the Pacific Plate is subducting below the Japanese islands. Many earthquakes occur associated with plate convergence, and the hypocenter distribution is variable along the Japan Trench. In order to investigate the detailed structure in the southern Japan Trench and to understand the variation of seismicity around the Japan Trench, a wide-angle seismic survey was conducted in the southern Japan Trench fore-arc region in 1998. Ocean bottom seismometers (15) were deployed on two seismic lines: one parallel to the trench axis and one perpendicular. Velocity structures along two seismic lines were determined by velocity modeling of travel time ray-tracing method. Results from the experiment show that the island arc Moho is 18–20 km in depth and consists of four layers: Tertiary and Cretaceous sedimentary rocks, island arc upper and lower crust. The uppermost mantle of the island arc (mantle wedge) extends to 110 km landward of the trench axis. The P-wave velocity of the mantle wedge is laterally heterogeneous: 7.4 km/s at the tip of the mantle wedge and 7.9 km/s below the coastline. An interplate layer is constrained in the subducting oceanic crust. The thickness of the interplate layer is about 1 km for a velocity of 4 km/s. Interplate layer at the plate boundary may cause weak interplate coupling and low seismicity near the trench axis. Low P-wave velocity mantle wedge is also consistent with weak interplate coupling. Thick interplate layer and heterogeneous P-wave velocity of mantle wedge may be associated with the variation of seismic activity.     

利用石榴橄榄岩重建大陆俯冲带的古动力学环境及其演化过程

本文提出一种对于造山带石榴橄榄岩的简单概念分类模型。该模型将造山带石榴橄榄岩划分为地幔楔型和俯冲带型两种类型,根据所记录温压条件及P-T轨迹的差异,地幔楔型石榴橄榄岩进而被划分为A-D四个亚类,分别对应不同厚度的克拉通型岩石圈地幔及普通大陆岩石圈地幔环境中冷的/古老的/稳定的地幔环境及与之对应的相对热的/年轻的/活动地幔环境。我们选择研究程度较高的斯堪的纳维亚加里东期造山带及我国柴北缘造山带中出露的石榴橄榄岩来检验该模型的适用性。出露于挪威西片麻岩地区的Mg-Cr型及Fe-Ti型石榴橄榄岩分别属于地幔楔型的A亚类(来自于古老的/冷的/厚的/亏损的克拉通岩石圈地幔)及壳源俯冲带石榴橄榄岩,而来自Seve,Troms和Linds地体的石榴橄榄岩则属于地幔楔型的C亚类(来自于古老的/冷的/薄的/亏损的大陆岩石圈地幔)后经历俯冲过程变为俯冲带石榴橄榄岩。对我国柴北缘超高压带绿梁山石榴橄榄岩的检验结果相对复杂。前人的研究表明绿梁山石榴橄榄岩存在三种不同的成因方式,对应分类模型中的:1)D亚类橄榄岩(阿拉斯加型岩浆岩堆晶体);2)壳源俯冲带型石榴橄榄岩;3)A亚类来自克拉通岩石圈地幔的太古代石榴橄榄岩。检验结果表明,该分类模型能较好的解释斯堪的纳维亚加里东期造山带中的石榴橄榄岩的出露规律,岩石学及矿物学特征及不同期次矿物之间的年代学关系,但对于我国绿梁山石榴橄榄岩的成因分类仍需进一步研究。假设该分类模型能适用于大多研究程度较高的造山带石榴橄榄岩,起到决定性作用的两个分类参数为地幔楔形成初期的平均温度(T)及造山带岩石圈地幔的厚度(P)。熔融作用发生的时间及深度同样是区分不同类型石榴橄榄岩的重要因素。     

华北克拉通西北部显生宙岩石圈地幔属性与演化特征: 橄榄岩捕虏体证据

众所周知,华北克拉通东部岩石圈地幔的组成和性质在显生宙发生了显著变化,但由于西部出露含有捕虏体的火山岩较少,这在一定程度上限制了人们对该区岩石圈地幔属性与演化特征的认识。本文将华北克拉通西北部晚白垩世-新生代玄武岩中橄榄岩捕虏体的研究成果归纳总结,旨在进一步揭示该区岩石圈地幔的属性与演化特征。研究表明,华北克拉通西北部岩石圈地幔主要由低Mg^#的二辉橄榄岩和少量高Mg^#的方辉橄榄岩组成。高Mg^#橄榄岩代表该区受轻微再富集作用影响的古老岩石圈地幔残余,低Mg^#橄榄岩是软流圈来源熔体与高Mg^#橄榄岩反应的产物,代表地幔再富集作用对古老岩石圈地幔改造的结果。该区岩石圈地幔经历了多期地幔交代作用的改造,早期交代事件与古亚洲洋俯冲有关,近期与软流圈来源的玄武质熔体有关。这种广泛的地幔再富集作用对华北克拉通古老岩石圈地幔的转变做出了重要贡献。

     

西藏马攸木地区雅江南带方辉橄榄岩的显微构造特征及其矿物结构水的初步研究

青藏高原地区广泛出露地幔橄榄岩体,但对其显微构造特征和矿物结构水的研究仍很缺乏。本文以马攸木地区雅江南带方辉橄榄岩为研究对象,采用光学显微镜、电子背散射衍射(EBSD)及傅里叶变换红外光谱(FTIR)对其进行系统分析。研究结果表明:(1)马攸木地区雅江南带方辉橄榄岩中橄榄石发育扭折带和波状消光,并具有显著的结晶学优选方位(A型组构),指示其主导变形机制为位错蠕变;(2)红外光谱测试表明,马攸木方辉橄榄岩中橄榄石几乎没有明显的结构水吸收峰,推断其经历了明显的H丢失。斜方辉石含水量处于85wt ppm~209wt ppm之间,代表地幔源区含水量或其下限值;(3)该区橄榄岩中橄榄石含水量低于包体和造山带橄榄岩中橄榄石含水量,斜方辉石结构水含量则与包体和造山带橄榄岩中斜方辉石的可以比较。我们的研究结果为了解青藏高原地幔橄榄岩中橄榄石的结构水和变形机制提供了初步资料。     

Sheared peridotite xenolith from the V. Grib kimberlite pipe,Arkhangelsk Diamond Province,Russia: Texture,composition, and origin

The petrography and mineral composition of a mantle-derived garnet peridotite xenolith from the V. Grib kimberlite pipe (Arkhangelsk Diamond Province, Russia) was studied. Based on petrographic characteristics, the peridotite xenolith reflects a sheared peridotite. The sheared peridotite experienced a complex evolution with formation of three main mineral assemblages: (1) a relict harzburgite assemblage consist of olivine and orthopyroxene porphyroclasts and cores of garnet grains (Gar1) with sinusoidal rare earth elements (REE) chondrite C1 normalized patterns; (2) a neoblastic olivine and orthopyroxene assemblage; (3) the last assemblage associated with the formation of clinopyroxene and garnet marginal zones (Gar2). Major and trace element compositions of olivine, orthopyroxene, clinopyroxene and garnet indicate that both the neoblast and clinopyroxene-Gar2 mineral assemblages were in equilibrium with a high Fe-Ti carbonate-silicate metasomatic agent. The nature of the metasomatic agent was estimated based on high field strength elements (HFSE) composition of olivine neoblasts, the garnet-clinopyroxene equilibrium condition and calculated by REE-composition of Gar2 and clinopyroxene. All these evidences indicate that the agent was a high temperature carbonate-silicate melt that is geochemically linked to the formation of the protokimberlite melt.     

Geochemistry of peridotites from the Yap Trench,Western Pacific: implications for subduction zone mantle evolution

ABSTRACT

This study examines the major and trace elements of peridotites from the Yap Trench in the western Pacific to investigate mantle evolution beneath a subduction zone. Major element results show that the peridotites are low in Al₂O₃ (0.31–0.65 wt.%) and CaO (0.04–0.07 wt.%) contents and high in Mg# (Mg/(Mg+Fe)) (0.91–0.92) and have spinels with Cr# (Cr/(Cr+Al)) higher than 0.6 (0.61–0.73). Trace element results show that the peridotites have extremely low heavy rare earth element (HREE) contents compared with abyssal peridotites but have U-shaped chondrite-normalized rare earth element (REE) patterns. The degree of mantle melting estimated based on the major elements, HREEs, and spinel Cr# range from 19% to 25%, indicating that the Yap Trench peridotites may be residues of melting associated with the presence of water in the mantle source. In addition to light rare earth element (LREE) enrichment, the peridotites are characterized by high contents of highly incompatible elements, positive U and Sr anomalies, negative Ti anomalies, and high Zr/Hf ratios. The correlations between these elements and both the degree of serpentinization and high field strength element (HFSE) contents suggest that fluid alteration alone cannot account for the enrichment of the peridotites and that at least the enrichment of LREEs was likely caused by melt–mantle interaction. Comparison between the peridotites and the depletion trend defined by the primitive mantle (PM) and the depleted mantle (DM) suggests that the Yap Trench mantle was modified by subduction-related melt characterized by high contents of incompatible elements, high Zr/Hf ratios, and low HFSE contents. Hydrous melting may have been enhanced by tectonic erosion of the subducting Caroline Plate with complex tectonic morphostructures at the earliest stages of subduction initiation.     

班公湖-怒江缝合带东段丁青地幔橄榄岩成因: 来自钻孔ZK02地幔橄榄岩矿物学及地球化学特征约束

丁青蛇绿岩位于班公湖-怒江缝合带东段,是该缝合带出露面积最大的蛇绿岩。为查明岩体成因,在丁青东岩体中实施了一口165.19m的钻孔。除最顶部有约0.5m厚的第四系残坡积物外,其余均为地幔橄榄岩。结合显微镜鉴定将岩心划分出17个岩性单元层,岩性主要以方辉橄榄岩为主,夹少量纯橄岩和含铬铁矿纯橄岩。地幔橄榄岩中橄榄石的Fo变化于88.79~93.73,铬尖晶石的Cr^#变化于44.33~81.66,揭示丁青地幔橄榄岩可能经历过约20%~40%的中高度部分熔融作用;全岩地球化学分析表明其具有富镁（MgO=45.98%~49.45%）、贫铝（Al₂O₃=0.19%~1.37%）和贫钙（CaO=0.28%~0.70%）的特点,属于熔融程度较高的地幔残余物质。岩石具有明显不同于阿尔卑斯蛇绿岩的轻稀土元素富集特征,指示区内地幔橄榄岩先经历了较强程度的部分熔融,后经历了俯冲消减过程中的流体交代。利用地幔橄榄岩中的铬尖晶石成分计算母熔体Al₂O₃含量对应的FeO/MgO值,与不同构造环境原始岩浆成分相比较,发现丁青地幔橄榄岩母熔体大多处于玻安岩中。纯橄岩氧逸度估算FMQ=-3.05~-0.71,方辉橄榄岩氧逸度FMQ=-3.89~+1.47,显示丁青地幔橄榄岩有俯冲作用的参与。通过丁青钻孔岩心的研究,提出丁青东岩体可能形成于俯冲带之上的弧前环境这一观点。

     

南苏鲁芝麻房石榴石橄榄岩中橄榄石的“C”类组构及其形成条件探讨

上地幔地震的各向异性主要归因于橄榄石的优选方位,不同的橄榄石优选方位模式可以作为上地幔不同动力学作用的指示剂。不同应力和含水量条件下的高温变形实验已经确定出五类橄榄石组构模式(“A”型、“B”型、“C”型、“D”型和“E”型)。本文运用电子背散射(EBSD)技术对来自苏鲁超高压变质带南部的芝麻房石榴石橄榄岩的橄榄石进行了优选方位测定,不同变形程度的橄榄石均显示了[100]轴近垂直于面理和[001]轴近平行于线理的特征,为“C”类组构模式,可见组构类型与变形程度没有关系,并且橄榄石组构所显示的NW向SE的剪切指向,与围岩-正、副片麻岩中形成于折返过程的石英优选方位所显示的SE向NW的剪切指向完全不同,说明芝麻房石榴石橄榄岩中橄榄石的“C”类组构是折返前形成的。结合橄榄石结构水的测量和已有的芝麻房石榴石橄榄岩形成的温压条件,推测该组构形成于含水俯冲带中,认为芝麻房石榴石橄榄岩的原岩来自于高含水的上部地幔楔碎块,与俯冲的陆壳物质一起经历了超高压变质作用并最终折返至地表。     

Refertilization of ancient lithospheric mantle beneath the central North China Craton: Evidence from petrology and geochemistry of peridotite xenoliths

The petrology and geochemistry of peridotite xenoliths in the Cenozoic basalts from Fanshi, the central North China Craton (NCC), provide constraints on the evolution of sub-continental lithospheric mantle. These peridotite xenoliths are mainly spinel-facies lherzolites with minor harzburgites. The lherzolites are characterized by low forsterite contents in olivines (Fo < 91) and light rare earth element (LREE) enrichments in clinopyroxenes. In contrast, the harzburgites are typified by high-Fo olivines (> 91), high-Cr# spinels and clinopyroxenes with low abundances of heavy REE (HREE). These features are similar to those from old refractory lithospheric mantle around the world, and thus interpreted to be relics of old lithospheric mantle. The old lithospheric mantle has been chemically modified by the influx of melts, as evidenced by the Sr–Nd isotopic compositions of clinopyroxenes and relatively lower Fo contents than typical Archean lithospheric mantle (Fo > 92.5). The Sr–Nd isotopic compositions of harzburgites are close to EM1-type mantle, and of the lherzolites are similar to bulk silicate earth. The latter could be the result of recent modification of old harzburgites by asthenospheric melt, which is strengthened by fertile compositions of minerals in the lherzolites. Therefore, the isotopic and chemical heterogeneities of the Fanshi peridotite xenoliths reflect the refertilization of ancient refractory lithospheric mantle by massive addition of asthenospheric melts. This may be an important mechanism for the lithospheric evolution beneath the Central NCC.     

西南天山东德沟橄榄岩的岩相学、矿物学演化特征及其地质意义

中国西南天山东德橄榄岩出露于天山伊犁-中天山板块和塔里木板块碰撞造山带北缘,普遍经历了复杂多期的含水流体(熔体)交代作用.主要矿物为橄榄石、斜方辉石、尖晶石、角闪石、金云母和单斜辉石,研究发现,橄榄石和斜方辉石与地幔楔橄榄岩中橄榄石和斜方辉石成份相近,原生铬尖晶石具有SSZ环境橄榄岩的特征,次生绿色尖晶石形成于麻粒岩相-角闪相环境.岩相学、矿物转变结构分析和矿物组合及矿物成分变化表明,东德沟橄榄岩记录了复杂的演化历史,先后经历了地幔交代、麻粒岩相-角闪相退变质作用和蛇纹石化等阶段的演化.研究认为东德沟橄榄岩最初可能形成于915～961℃的地幔环境,而发生地幔交代时的温压条件约为770 ～ 900℃,10～18kbar.该橄榄岩全岩较低的TiO2含量和尖晶石中较低TiO2含量,以及矿物组合显示出因俯冲板块脱水而造成的快速冷却特征,表明东德沟橄榄岩极有可能是SSZ环境俯冲板片上地幔楔橄榄岩残片.     

Geochemical cycling during subduction initiation: Evidence from serpentinized mantle wedge peridotite in the south Andaman ophiolite suite

The ophiolite suite from south Andaman Islands forms part of the Tethyan Ophiolite Belt and preserves the remnants of an ideal ophiolite sequence comprising a basal serpentinized and tectonised mantle peridotite followed by ultramafic and mafic cumulate units, basaltic dykes and spilitic pillow basalts interlayered with arkosic wacke. Here, we present new major, trace, rare earth(REE) and platinum group(PGE) element data for serpentinized and metasomatized peridotites(dunites) exposed in south Andaman representing the tectonized mantle section of the ophiolite suite. Geochemical features of the studied rocks, marked by Al_2 O_3/TiO_2 23, LILE-LREE enrichment, HFSE depletion, and U-shaped chondrite-normalized REE patterns with(La/Sm)N 1 and(Gd/Yb)N 1, suggest contributions from boninitic mantle melts. These observations substantiate a subduction initiation process ensued by rapid slab roll-back with extension and seafloor spreading in an intraoceanic fore-arc regime. The boninitic composition of the serpentinized peridotites corroborate fluid and melt interaction with mantle manifested in terms of(i) hydration, metasomatism and serpentinization of depleted, MORB-type, sub-arc wedge mantle residual after repeated melt extraction; and(ii) refertilization of refractory mantle peridotite by boninitic melts derived at the initial stage of intraoceanic subduction. Serpentinized and metasomatized mantle dunites in this study record both MOR and intraoceanic arc signatures collectively suggesting suprasubduction zone affinity. The elevated abundances of Pd(4.4-12.2 ppb) with highΣPPGE/∑IPGE(2-3) and Pd/Ir(2-5.5) ratios are in accordance with extensive melt-rock interaction through percolation of boninitic melts enriched in fluid-fluxed LILE-LREE into the depleted mantle after multiple episodes of melt extraction. The high Pd contents with relatively lower Ir concentrations of the samples are analogous to characteristic PGE signatures of boninitic magmas and might have resulted by the infiltration of boninitic melts into the depleted and residual mantle wedge peridotite during fore-arc extension at the initial stage of intraoceanic subduction. The PGE patterns with high Os + Ir(2-8.6 ppb)and Ru(2.8-8.4 ppb) also suggest mantle rejuvenation by infiltration of melts derived by high degree of mantle melting. The trace, REE and PGE data presented in our study collectively reflect heterogeneous mantle compositions and provide insights into ocean-crust-mantle interaction and associated geochemical cycling within a suprasubduction zone regime.     

Petrofabrics and seismic properties of garnet peridotite from the UHP Sulu terrane (China): Implications for olivine deformation mechanism in a cold and dry subducting continental slab

Lattice-preferred orientations (LPO) of olivine, diopside, enstatite and garnet from the Zhimafang garnet peridotite body in the Sulu ultrahigh-pressure (UHP) metamorphic terrane (China) were measured using the electron backscatter diffraction (EBSD) technique. The peridotite was captured from a mantle wedge immediately adjacent the subducted Yangtze slab and then experienced the UHP metamorphism at 750–950 °C and 4–7 GPa. The olivine LPO is characterized by the [001] axis close to the stretching lineation and the (100) plane subparallel to the foliation, indicating the prevailing of (100) [001] slip. Enstatite LPO displays the dominance of (100) [001] slip. Diopside developed complex LPO patterns that are difficult to explain using a single slip system of (100) [001]. Garnet is almost randomly oriented due to its low volume fractions, cubic symmetry and the presence of numerous slip systems. Calculated seismic properties of the peridotite yield a maximum P-wave velocity normal to the foliation and a minimum along the foliation, with anisotropy up to 8% in strongly sheared samples. The S-wave velocity pattern is complex but the fast polarization plane generally normal to the foliation. The inferred shear sense from the olivine LPO is top-to-SE, in contrary to exhumation-induced top-to-NW thrusting recorded in the quartz LPO, implying that the olivine LPO formed at early UHP metamorphic conditions. The olivine crystals have relatively low water contents (141–475 H/10⁶ Si), indicating a fluid-deficient environment for the LPO formation. The present study suggests that a combination of low temperature and UHP plays a much more important role than the water content to promote the activation of (100) [001] slip in olivine.     

松辽盆地南部岩石圈地幔变形特征及各向异性分析——来自橄榄岩包体的约束

SKS测量结果显示松辽盆地快波方向分布较为复杂, 由于缺乏深部岩石变形资料约束, 制约了地震波各向异性成因解释。本文通过对松辽盆地南部双辽地区橄榄岩包体进行详细的岩石学、地球化学、显微结构、各向异性研究, 结果显示双辽地区橄榄岩包体的平衡温度为893~1152℃, 来源于岩石圈地幔。橄榄岩中橄榄石的晶格优选方位(CPO)类型主要为A型、D型和AG型, 其中, AG型和D型CPO可能形成于西太平洋板块向欧亚大陆俯冲回撤导致的岩石圈变形, AG型橄榄石CPO也可能形成于熔体存在下的橄榄石变形。基于CPO计算获得的橄榄岩包体全岩V_P各向异性(AV_P)为4.79%~11.80%, 最大剪切波各向异性(AV_Smax)为3.13%~7.93%。结合地球物理测量结果, 推断松辽盆地南部复杂的SKS各向异性的主要贡献可能来源于面理陡倾或直立的岩石圈地幔。

     

大别山中生代构造演化:来自盆地充填记录的启示

通过对大别山周缘盆地的对比分析,研究了大别山中生代构造演化格局。盆地充填序列分析表明,尽管中生代大别山南、北盆山耦合关系不同,但构造体制均经历了前白垩纪挠曲向白垩纪伸展的转化;砂岩物源再造反映中生代南大别山源区剥露尚未大规模触及岩浆弧“根”,剥露深度浅于北大别单元。大别山邻区晚中生代巨厚磨拉石是陆内造山强烈阶段的沉积记录,它们的产出及相关的造山带隆升与该区超高压变质岩快速折返没有直接关系。进一步讨论了恢复大别山物源结构、建立盆地类磨拉石精细地层年代学格架等在造山带构造研究中的重要性及其现存的关键问题。     

大别山中生代构造演化：来自盆地充填记录的启示

通过对大别山周缘盆地的对比分析,研究了大别山中生代构造演化格局。盆地充填序列分析表明,尽管中生代大别山南、北盆山耦合关系不同,但构造体制均经历了前白垩纪挠曲向白垩纪伸展的转化;砂岩物源再造反映中生代南大别山源区剥露尚未大规模触及岩浆弧“根”,剥露深度浅于北大别单元。大别山邻区晚中生代巨厚磨拉石是陆内造山强烈阶段的沉积记录,它们的产出及相关的造山带隆升与该区超高压变质岩快速折返没有直接关系。进一步讨论了恢复大别山物源结构、建立盆地类磨拉石精细地层年代学格架等在造山带构造研究中的重要性及其现存的关键问题。