江苏青龙山磷灰石中出溶体的初步研究   总被引：5，自引：4，他引：5  

陈晶  曾令森陈方远梁凤华 《岩石学报》2006,22(7):1921-1926

最近的研究证实，在大别-苏鲁超高压变质带的多硅白云母榴辉岩和超基性岩中的磷灰石矿物内普遍发育有针柱状出溶晶体，初步研究证明这些出溶晶体多为各种硫化物：如黄铁矿、黄铜矿等。本文重点研究苏鲁青龙山地区的多硅白云母榴辉岩和退变榴辉岩中磷灰石内的出溶晶体，通过扫描电镜、电子探针和X-光能谱的线扫描分析，确认这些出溶晶体是铜的硫化物，并根据无标样定量的分析结果初步推测有可能是CuS2晶体。目前已知的CuS2晶体都是在高温高压（T=700-1000℃和P=4．5-5．0GPa）条件下人工合成的。这样的温压条件与青龙山榴辉岩的超高压变质条件是吻合的。在磷灰石中能保存超高压的硫化物，可能是由于磷灰石自身的稳定性和化学惰性。因此推测在超高压变质作用中，磷灰石晶体中易于保存硫化物出溶体与石榴石和绿辉石中易于保存柯石英和金刚石的作用相类似。  相似文献   

青龙山超高压变质榴辉岩绿帘石化学成分与流体包裹体特征     

翟伟孙晓明  梁金龙徐莉汤倩梁业恒苏丽薇 《岩石学报》2006,22(7):2029-2038

青龙山超高压变质榴辉岩中的绿帘石经历了四个演化阶段：早期绿帘角闪岩相进变质阶段形成的绿帘石，其化学成分以含铁高为特征，Fe2O3为14．796～17．84％，XFe=0．413～0．486，而CaO和Al2O3含量较低；柯石英榴辉岩相变质阶段和石英榴辉岩相变质阶段形成的绿帘石，其化学成分呈现连续变化，核部相对富Fe2O3，为11．933～12．993％，XFe=0．322-0．358，而CaO和Al2O3含量低，主要形成于柯石英榴辉岩相变质阶段；边部Fe2O3的含量低，为9．628-10．138％，XFe=0．275～0．286，而CaO和Al2O3的含量高，主要形成于石英榴辉岩相退变质阶段；晚期退变质角闪岩相阶段形成的绿帘石，其化学成分与绿帘角闪岩相变质阶段相似，也以富含Fe2O3为特征，XFe=0．433。绿帘石化学成分的变化反映了苏鲁超高压变质带快速俯冲快速折返的过程。绿帘石中存在三种不同盐度的含Mg^2＋、Fe^2＋等金属阳离子的NaCl水溶液包裹体，高盐度（22．5wt％NaCl至略大于23．2wt％NaCl）的水溶液包裹体形成于柯石英榴辉岩相变质阶段，中高盐度（12．6-16．0wt％NaCl）的水溶液包裹体形成于石英榴辉岩相变质阶段，而中等盐度（6．4-11．7wt％NaCl）的溶液包裹体形成于角闪岩相退变质阶段。绿帘石中流体包裹体的研究证实超高压变质作用及后期的折返过程中并不存在大规模的流体作用，变质流体的活动限于矿物晶体颗粒范围。  相似文献   

东亚大陆边缘的构造格架及其中-新生代演化   总被引：10，自引：0，他引：10  

吴根耀  矢野孝雄 《地质通报》2007,26(7):87-800

燕山运动在亚洲大陆雏形东缘形成2条北东向的剪切带:郯庐断裂带和长乐-南澳-中央构造线断裂带,晚侏罗世—古近纪早期沿之发生地体/地块的拼贴。系统叙述了各移置地体/地块的主要岩石记录和拼贴时代,据起源分为3类:异地的(包括源自冈瓦纳的和源自盘古大洋的)、半异地的和准原地的;据拼贴位置分为2组:拼贴后基本位于原地的(日本海张开以前) 和发生过向北东错移的。新生代内东亚大陆边缘发生解体,可以台湾岛以北的菲律宾海盆断裂为界将东亚大陆边缘弧分为2段,北段仍处于剪切-拉张中,南段已进入剪切挤压-造山阶段。强调该地区中—新生代演化经历了2个里丁旋回, 形成早白垩世的北东向和新近纪的北东东向2期新生构造。  相似文献   

Heavy clastic minerals from the Far East island-arc complexes     

A. I. Malinovsky  P. V. Markevich 《Russian Journal of Pacific Geology》2007,1(1):71-81

The results of the study of heavy clastic minerals from the Cretaceous-Paleogene terrigenous complexes of Sikhote-Alin and Kamchatka, as well as from the Cenozoic sediments of the deepwater Vanuatu Trench, are summarized. The data obtained have been interpreted on the basis of their comparison with heavy mineral assemblages of recent sediments deposited in known geodynamic settings. It is shown that the heavy clastic minerals of sedimentary rocks, their relative quantities, and chemical compositions may serve as reliable indicators of different island-arc settings and magmatic processes; these indicators may also be used for identification of such settings in paleobasins of orogenic regions.  相似文献   

深俯冲和折返动力学:来自中国大陆科学钻探主孔及苏鲁超高压变质带的制约   总被引：2，自引：0，他引：2  

许志琴 《岩石学报》2007,23(12):3041-3053

中国大陆科学钻探工程和苏鲁高压-超高压变质带为大陆岩石圈的深俯冲与折返动力学的研究提供了以下制约:(1)苏鲁高压/超高压变质地体迭置于南、北苏鲁两个不同时代及属性的基底之上;(2)苏鲁巨量表壳岩石深俯冲至200km以下的上地幔深度,并经历超高压变质作用;(3)根据不同类型超高压变质岩石锆石的SHRIMP-U/Pb原位精确定年,获得超高压变质岩石的深俯冲-折返全过程(240～252Ma→230～237Ma→207～218Ma)时限.并建立了新的深俯冲-折返全过程的P-T-t轨迹;(4)富钛铁的辉长岩在大陆地壳的深俯冲过程中,经历了超高压变质作用并转变成了富含金红石的榴辉岩,形成了超高压变质的钛矿床;(5)通过榴辉岩和石榴石橄榄岩的显微构造分析及石榴石、绿辉石和橄榄石EBSD测量,确定深俯冲过程中绿辉石和橄榄石的组构运动学和流变学特征;(6)在大陆的深俯冲过程中,强烈水化的陆壳岩石经历了进变质脱水过程,巨量的地表水带入到＞100～200Km的地幔深处,在超高压变质峰期的极端条件下,通过含水超高压变质矿物的分解形成超临界的含水熔体,导致有效的壳-幔物质交换和岩石圈物质分异;(7)苏鲁超高压变质地体在折返阶段形成挤出纳布构造,与岩石圈深俯冲管道流的折返挤出机制有关;(8)提出新的深俯冲-折返动力学模式:陆.陆碰撞的深俯冲剥蚀模式及大陆地壳多重性、分层型和穿时性的俯冲和折返模式.  相似文献   

Sapphirine-bearing granulites and related high-temperature metamorphic rocks from the Higo metamorphic terrane, west-central Kyushu, Japan   总被引：7，自引：0，他引：7  

Y. OSANAI  T. HAMAMOTO  O. MAISHIMA  & H. KAGAMI 《Journal of Metamorphic Geology》1998,16(1):53-66

The Higo metamorphic unit in west-central Kyushu island, southwest Japan is an imbricated crustal section in which a sequence of units with increasing metamorphic grade from high (northern part) to low (southern part) structural levels is exposed. The basal part of the metamorphic sequence representing an original depth of 23–24  km consists mainly of garnet–cordierite–biotite gneiss, garnet–orthopyroxene gneiss, orthopyroxene-bearing amphibolite and orthopyroxene-bearing S-type tonalite. These metamorphic rocks underwent high amphibolite-facies up to granulite facies metamorphism with peak P – T  conditions of 720  MPa, 870  °C. In addition sapphirine-bearing granulites and related high-temperature metamorphic rocks also occur as tectonic blocks in a metamorphosed peridotite intrusion. The sapphirine-bearing granulites and their related high-temperature metamorphic rocks can be subdivided into five types of mineral assemblages reflecting their bulk chemical compositions as follows: (1) sapphirine–corundum–spinel–cordierite (2) corundum–spinel–cordierite (3) garnet–corundum–spinel–cordierite (4) garnet–spinel–gedrite–corundum, and (5) orthopyroxene–spinel–gedrite. These metamorphic rocks are characterized by unusually high Al₂O₃ and low SiO₂ contents, which could represent a restitic nature remaining after partial melting of pelitic granulite under the ultra high-temperature contact metamorphism at the peak metamorphic event of the Higo metamorphic unit. The metamorphic conditions are estimated to be about 800  MPa and above 950  °C which took place at about 250  Ma as a result of the thermal effect of the regional gabbroic rock intrusions.  相似文献   

Constraining peak P–T conditions in UHP eclogites: calculated phase equilibria in kyanite‐ and phengite‐bearing eclogite of the Tromsø Nappe,Norway     

M. JANÁK  E. J. K. RAVNA  K. KULLERUD 《Journal of Metamorphic Geology》2012,30(4):377-396

Kyanite‐ and phengite‐bearing eclogites have better potential to constrain the peak metamorphic P–T conditions from phase equilibria between garnet + omphacite + kyanite + phengite + quartz/coesite than common, mostly bimineralic (garnet + omphacite) eclogites, as exemplified by this study. Textural relationships, conventional geothermobarometry and thermodynamic modelling have been used to constrain the metamorphic evolution of the Tromsdalstind eclogite from the Tromsø Nappe, one of the biggest exposures of eclogite in the Scandinavian Caledonides. The phase relationships demonstrate that the rock progressively dehydrated, resulting in breakdown of amphibole and zoisite at increasing pressure. The peak‐pressure mineral assemblage was garnet + omphacite + kyanite + phengite + coesite, inferred from polycrystalline quartz included in radially fractured omphacite. This omphacite, with up to 37 mol.% of jadeite and 3% of the Ca‐Eskola component, contains oriented rods of silica composition. Garnet shows higher grossular (X_Grs = 0.25–0.29), but lower pyrope‐content (X_Prp = 0. 37–0.39) in the core than the rim, while phengite contains up to 3.5 Si pfu. The compositional isopleths for garnet core, phengite and omphacite constrain the P–T conditions to 3.2–3.5 GPa and 720–800 °C, in good agreement with the results obtained from conventional geothermobarometry (3.2–3.5 GPa & 730–780 °C). Peak‐pressure assemblage is variably overprinted by symplectites of diopside + plagioclase after omphacite, biotite and plagioclase after phengite, and sapphirine + spinel + corundum + plagioclase after kyanite. Exhumation from ultrahigh‐pressure (UHP) conditions to 1.3–1.5 GPa at 740–770 °C is constrained by the garnet rim (X_Ca^Grt = 0.18–0.21) and symplectite clinopyroxene (X_Na^Cpx = 0.13–0.21), and to 0.5–0.7 GPa at 700–800 °C by sapphirine (X_Mg = 0.86–0.87) and spinel (X_Mg = 0.60–0.62) compositional isopleths. UHP metamorphism in the Tromsø Nappe is more widespread than previously known. Available data suggest that UHP eclogites were uplifted to lower crustal levels rapidly, within a short time interval (452–449 Ma) prior to the Scandian collision between Laurentia and Baltica. The Tromsø Nappe as the highest tectonic unit of the North Norwegian Caledonides is considered to be of Laurentian origin and UHP metamorphism could have resulted from subduction along the Laurentian continental margin. An alternative is that the Tromsø Nappe belonged to a continental margin of Baltica, which had already been subducted before the terminal Scandian collision, and was emplaced as an out‐of‐sequence thrust during the Scandian lateral transport of nappes.  相似文献   

Unpairing metamorphic belts: P–T paths and a tectonic model for the Ryoke Belt, southwest Japan     

MICHAEL BROWN 《Journal of Metamorphic Geology》1998,16(1):3-22

Southwest Japan is divided into Outer and Inner Zones by the Median Tectonic Line (MTL), a major transcurrent fault. The Outer Zone is composed of the Sambagawa (high-pressure intermediate or high P/T type metamorphism), Chichibu and Shimanto Belts. In the Inner Zone, the Ryoke Belt (andalusite– sillimanite or low P/T type metamorphism) was developed mainly within a Jurassic accretionary complex. This spatial relationship between high P/T type and low P/T type metamorphic belts led Miyashiro to the idea that metamorphic belts were developed as ‘paired’ systems. Textural relationships and petrogenetically significant mineral assemblages in pelites from the Ryoke Belt imply peak P–T conditions of ≈5 kbar and up to 850 °C in migmatitic garnet–cordierite rocks from the highest-grade metamorphic zone. It is likely that the thermal anomaly responsible for metamorphism of the Ryoke Belt was related to a segment of the Farallon–Izanagi Ridge as it subducted under the eastern margin of the Asian continent during the Cretaceous. The sequence of mineral assemblages developed in pelites implies a metamorphic field gradient with shallow dP/dT slope, inferred to have been generated by a nested set of hairpin-like ‘clockwise’P–T paths. These P–T paths are characterized by limited prograde thickening, minor decompression at peak-T , and near-isobaric cooling, features that may be typical of P–T paths in low P/T type metamorphic belts caused by ridge subduction. A ridge subduction model for the Ryoke Belt implies that juxtaposition of the high-P/T metamorphic rocks of the Sambagawa Belt against it was a result of terrane amalgamation. Belt-parallel ductile stretching, recorded as syn-metamorphic, predominantly constrictional strain in both Ryoke and Sambagawa Belt rocks, and substantial sinistral displacement on the MTL are consistent with left-lateral oblique convergence. Diachroneity in fast cooling of the Ryoke Belt is implied by extant thermochronological data, and is inferred to relate to progressive SW to NE docking of the Sambagawa Belt. Thus, an alternative interpretation of ‘paired’ metamorphic belts in Japan is that they represent laterally contemporaneous terranes, rather than outboard and inboard components of a trench/arc ‘paired’ system. Amalgamation of laterally contemporaneous terranes during large translations of forearcs along continental margins may explain other examples of ‘paired’ metamorphic belts in the geological record.  相似文献   

Tracing the 850-Ma continental flood basalts from a piece of subducted continental crust in the North Qaidam UHPM belt,NW China   总被引：10，自引：0，他引：10  

Shuguang Song  Li Su  Xian-hua Li  Guibing Zhang  Yaoling Niu  Lifei Zhang 《Precambrian Research》2010

A Paleozoic ultrahigh-pressure metamorphic (UHPM) belt extends along the northern margin of the Qaidam Basin, North Tibetan Plateau. Eclogites in the Yuka eclogite terrane, northwest part of this UHPM belt, occur as blocks or layers of varying size intercalated with granitic and pelitic gneisses. These eclogites have protoliths geochemically similar to enriched-type mid-ocean ridge basalts (E-MORB) and oceanic island basalts (OIB). On the basis of Ti/Y ratios, they can be divided into low-Ti and high-Ti groups. The low-Ti group (LTG) eclogites exhibit relatively low TiO₂ (most <2.5 wt%) and Ti/Y (<500) but comparatively high Mg# (48–55), whereas the high-Ti group (HTG) eclogites have high TiO₂ (most >2.5 wt%) and Ti/Y (>500) but lower Mg# (46–52). Zircons from two eclogite samples gave a magmatic crystallization (protolith) age of ∼850 Ma and a UHPM age of ∼433 Ma. The occurrence, geochemical features and age data of the Yuka eclogites suggest that their protoliths are segments of continental flood basalts (CFBs) with a mantle plume origin, similar to most typical CFBs. Our observation, together with the tectonic history and regional geologic context, lend support for the large scale onset of mantle plume within the Rodinia supercontinent at ∼850 Ma. The Qaidam block is probably one of the fragments of the Rodinia supercontinent with a volcanic-rifted passive margin. The latter may have been dragged to mantle depths by its subducting leading edge of the oceanic lithosphere in the Early Paleozoic.  相似文献   

鄂东北麻城两路口地区新元古代变质岩锆石U-Pb年龄及其地质意义   总被引：1，自引：0，他引：1  

刘锐  吴昌雄  陈觅  鄢华  赵新福 《矿物岩石地球化学通报》2014,33(6)

鄂东北麻城两路口地区位于北大别杂岩带南部,对该区变质岩的研究有重要的古构造和古气候环境意义。本文对该地区6个变质岩样品进行了LA-ICP-MS锆石U-Pb定年。结果显示,3个花岗质片麻岩和1个变质浅色花岗岩样品得到742±38~805±7 Ma的年龄,而2个斜长角闪岩样品则得到793±11~843±72Ma的年龄。其中1个斜长角闪岩样品的年龄值(793 11 Ma)与花岗质片麻岩和变质花岗岩样品的年龄值(792~805 Ma)在误差范围内一致,表明该区存在新元古代双峰式岩浆活动。秦岭(北秦岭、武当地区)–桐柏、大别和苏鲁造山带几近同时的新元古代岩浆作用表明它们在新元古代时可能是统一整体,且属于扬子陆块的组成部分;大别-苏鲁造山带新元古代岩浆岩的形成可能与Rodinia超大陆裂解、雪球地球事件和裂谷作用相关。  相似文献