The Kuiqi Peralkaline Granitic Complex (SE China): Petrology and Geochemistry   总被引：44，自引：1，他引：43  

MARTIN  H.; BONIN  B.; CAPDEVILA  R.; JAHN  B. M.; LAMEYRE  J.; WANG  Y. 《Journal of Petrology》1994,35(4):983-1015

The Mesozoic volcano-plutonic belt of SE China is characterized,in the Kuiqi area, by acid volcanics followed by the Yanshangranites. The Kuiqi granitic complex, which belongs to the latterunit, is made up of a calc-alkaline and a peralkaline group.The calc-alkaline group consists of two intrusions, the Danyangmonzogranite and the Fuzhou syenogranite, emplaced 10310 Maand 104 5 Ma ago, respectively (Rb-Sr whole-rock isochrons).Formation of the Danyang monzogranite can be explained by athree-stage model: (1) partial melting of a metasomatized mantlegenerated a dioritic magma known in the area as the Nanyu diorite;(2) the magma was contaminated (25%) by lower continental crust;(3) large amounts (70–80%) of fractional crystallizationof hornblende and plagioclase at depth gave rise to the magmaticsuite. The Fuzhou syenogranite is more fractionated and itsformation involved crystallization of plagioclase + biotite+ K-feldspar + apatite. Intrusion of the peralkaline group isdated at 93 1 Ma (Kuiqi peralkaline granite) and at 91.80.9(Bijiashan peralkaline granite). These units are homogeneousand their petrogenesis is less constrained than for the calc-alkalinesuite. Nevertheless, a multistage process can be proposed: (1)partial melting of a metasomatized mantle produced a dioriticmagma; (2) fractional crystallization began with segregationof hornblende + plagioclase ilmenite and/or magnetite; subsequently,hornblende no longer crystallized; (3) the last stage of fractionationcorresponded to the crystallization of K-feldspar + plagioclase+ REE-rich accessory phases. Mineralogical study indicates thatduring the last stage, fluids played a prominent role and controlledthe nature of the crystallizing minerals. The magma evolvedfrom F- and S-rich, and water-undersaturated to water-oversaturated,leading to the exsolution and dissociation of an H₂O vapourphase and to the loss of H₂. The change from calc-alkaline toperalkaline magmatism is related to inferred changes in thetectonic environment. The calc-alkaline granites were generatedin a subduction setting in which water was supplied by dehydrationof the downgoing slab. The peralkaline granites were producedin a crustal thinning environment where little water was available,thus necessitating high temperatures to initiate partial melting.On the other hand, petrogenetic modelling shows that both calc-alkalineand peralkaline granites could have been derived from the samesource which is metasomatized mantle. This possibly indicatesthat the volcanic are source, active during subduction, persistedbeneath the continent and was reactivated during the post-orogenicmagmatism. The reactivation was caused by a deep crustal fault.  相似文献   

Active ice-sheet deglaciation and ice-dammed lakes in the northern Cairngorm Mountains, Scotland   总被引：1，自引：0，他引：1  

VANESSA BRAZIER  MARTIN P. KIRKBRIDE  JOHN E. GORDON 《Boreas: An International Journal of Quaternary Research》1998,27(4):297-310

Mapping of ice-marginal and glaciolacustrine deposits in the northern Cairngorm Mountains allows the nature of deglaciation following the Last Glacial Maximum (c.18 000 BP) to be reinterpreted. Two ice-dammed lakes were ponded between the Glenmore lobe of the Scottish ice sheet and local glaciers draining northwards from the Cairngorm Mountains. Delta progradation from the southern end of each lake reflects dominant meltwater sources and glacio-hydrological gradients. Sediment facies representing subaqueous mass-flow deposits, lakebottom rhythmites, lower and upper foresets and topsets are associated with prograding delta fronts. Moraines show that the lakes were ice dammed at both ends, evidence that active glaciers existed in the Cairngorm Mountains while ice was retreating from Strath Spey, and that deglaciation was punctuated by readvances of the ice margin. These results indicate that an ice-stagnation model of deglaciation is invalid for most of the duration of ice wastage, but instead support an active-retreat hypothesis with multiple, climatically forced readvances.  相似文献   

A coarse-grained turbidite system with morphotectonic control (Middle Albian, Ondarroa, northern Iberia)     

THOMAS PLETSCH  MARTIN MESCHEDE 《Sedimentology》1995,42(3):523-523

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Characterization of pebble fabrics in modern terrestrial glacigenic sediments   总被引：1，自引：0，他引：1  

JULIAN A. DOWDESWELL  MARTIN J. SHARP 《Sedimentology》1986,33(5):699-710

ABSTRACT Pebble fabric data are available from several facies of glacigenic sediments deposited by modern glaciers, where sedimentary processes can be observed or inferred with relatively little ambiguity. Over 100 samples from contemporary environments illustrate fabrics characterizing melt-out till, deformed and undeformed lodgement till, sediment flow deposits and ice slope colluvium. Lodgement till fabric variability is related to the two-layer structure of these sediments; a structureless, friable upper layer with low shear strength and high consolidation coefficient, overlying a very compact material of horizontal platy structure. Fabric strength (assessed by eigenvalue analysis) is weaker and pebble dip is more dispersed in the upper structureless horizon. Stronger fabrics in the lower platy horizon may be primary depositional fabrics which are destroyed by subglacial shearing to give weaker fabrics in the upper horizon. Alternatively, upper horizon fabrics may be characteristic of all recently-deposited lodgement tills, with stronger fabrics developing at depth by dewatering and consolidation. There is a general reduction in fabric strength and an increase in particle dip associated with the transition from melt-out tills, through undeformed and deformed lodgement tills, to sediment flow deposits and ice slope colluvium. There is, however, considerable overlap in the fabric strengths characteristic of sediment flow deposits and deformed lodgement tills. Fabric data from modern glacial sedimentary facies are used to assist in interpreting the mode of deposition of some Quaternary glacial sediments. Relatively strong fabrics characteristic of melt-out tills and undeformed lodgement tills are more likely to be diagnostic of genesis than weaker fabrics associated with deformed sediments.  相似文献   

Characteristics of two Pleistocene channel-fill deposits and their implication on the interpretation of megasequences in ancient sediments     

JEAN LAJOIE  DENIS A. ST-ONGE 《Sedimentology》1985,32(1):59-67

Two Pleistocene channel fills located in two different geological settings, on Guadeloupe in the lesser Antilles and along the Coppermine River in the Northwest Territories of Canada, have different clast compositions, scale, and origin of fragmentation but have similar depositional characteristics. Massive bedding or absence of structures caused by traction, sharp non-erosive contacts, reverse coarse-tail grading, matrix-supported clasts together indicate a debris-flow mechanism in which mixtures of fine and coarse sediments moved downslope by laminar flow. Field evidence suggests subaqueous deposition for both deposits. Both bed thickness (BTh)/maximum grain size (MGS) ratios and correlations appear characteristic of subaqueous masses capable of flowing on slopes less than 1°. The two channel fills have random BTh and MGS variations, they do not thin and fine up-section. It is suggested that fills originating from laminar mass transport could normally have random BTh and MGS up-section variations. In flysch and volcaniclastic sequences, where coarse sediments interpreted as laminar flow deposits are common, up-section BTh and MGS variations may result from processes related to source, slope, and flow characteristics rather than from the environment in which the sediments accumulate (channel).  相似文献   

Lunar Pyroxene-Phyric Basalts: Crystallization Under Supercooled Conditions   总被引：1，自引：2，他引：1  

DOWTY  ERIC; KEIL  KLAUS; PRINZ  MARTIN 《Journal of Petrology》1974,15(3):419-453

Pyroxene-phyric basalts constitute a distinct petrologic groupin samples from lunar maria at both Apollo 12 and Apollo 15sites. Textures of pyroxene-phyric basalts from both sites aresimilar, but bulk compositions and mineralogy are somewhat different.Pyroxene-phyric basalts are characterized by large pyroxenephenocrysts with cores of magnesian pigeonite and mantles ofaugite grading to ferroaugite, usually set in a distinctly finergroundmass of iron-rich pyroxene, plagioclase, ilmenite, andother minor minerals. Olivine is scarce or absent modally andnormatively. Controversy has arisen over whether the porphyritictexture is a result of (1) a two-stage cooling history, e.g.phenocrysts formed at depth, and groundmass formed on extrusion;or (2) single stage, rapid cooling under supercooled conditions(cooling history here refers to cooling conditions imposed byexternal factors, and is not to be equated with ‘crystallizationhistory’). A study of six rocks belonging to this groupfrom Apollo 15 rake samples is reported here. A considerablerange of textures is present in these rocks, and they may beranked in order of decreasing late-stage cooling rate (15125,15666, 15682, 15118, 15684, 15116) on the basis of groundmasscrystal size. The same ranking is obtained from delta-beta (measuredin X-ray precession photos) of pigeonite and augite exsolvedfrom once homogeneous crystals, or of epitaxially overgrownaugite and pigeonite. The size of the phenocrysts in these rocks tends to be positivelycorrelated with the coarseness of the groundmass. Furthermorethe same correlation is evidently present in almost all otherApollo 12 and Apollo 15 pyroxene-phyric rocks. This constitutesa strong argument in favor of a single-stage cooling historyfor all pyroxene-phyric rocks, because the correlation wouldbe fortuitous for a two-stage cooling history. On the basisof this and many other arguments advanced previously and inthis paper, it is concluded that all the pyroxene-phyric rocksoriginated in a single-stage cooling process. A crystallization model for pyroxene-phyric rocks accounts forthe bimodal distribution of crystal size by two episodes ofsupercooling and nucleation during the continuous cooling process,the first of pyroxene, which nucleates homogeneously, the secondof plagioclase, which nucleates heterogeneously on the pyroxenephenocrysts. The more rapidly cooled rocks attained greaterdegrees of supercooling in both stages, hence greater nucleationrates and smaller crystals.  相似文献   

Clay mineral distribution patterns as influenced by depositional processes in the Southeastern Levantine Sea   总被引：1，自引：0，他引：1  

ANDRÉS MALDONADO  DANIEL JEAN STANLEY 《Sedimentology》1981,28(1):21-32

Analysis of the clay minerals in stratigraphically defined cores (23,000 years BP to the present) in the southeastern Levantine-Nile Cone sector of the eastern Mediterranean indicates that depositional processes are very significant in determining the distribution of clay assemblages. The interplay of long-distance transport by water mass circulation, downslope mass gravity transport and wind dispersal is recorded by the clay assemblages in each of the stratigraphic layers. The temporal variations and spatial distribution of smectite, the dominant clay mineral of the River Nile, can be related closely to downslope gravity-related processes and to deposition from water mass flow. Increased kaolinite, in part of wind-blown origin from North Africa, correlates with areas receiving low terrigenous input but influenced by enhanced suspended sediment transport. Illite and chlorite distributions are most closely associated with a northern Levantine provenance and dispersal by the circulation of eastern Mediterranean water masses. Climatically induced changes may have altered the clay minerals in the region and minor diagenetic changes may have occurred, but these factors do not fully explain observed vertical clay mineral changes in the Late Quaternary. We conclude that palaeoclimatic interpretations based on vertical clay mineralogical changes at single core localities should be approached cautiously in small ocean basins such as the Mediterranean.  相似文献   

Depositional models for fine-grained sediment in the western Hellenic Trench, Eastern Mediterranean     

DANIEL JEAN STANLEY  RÉS MALDONADO 《Sedimentology》1981,28(2):273-290

Sediment in tectonically active, topographically restricted settings of the western Hellenic Arc, eastern Mediterranean, consists primarily of clayey silt and silty clay. Failure of metastable sediment temporarily stored on relatively steep slopes is triggered by earthquake tremors and eustatic oscillations. Redeposition of these materials by gravitative transport has resulted in markedly different lithofacies from site to site. Most piston cores include three Late Quaternary stratigraphic units that can be correlated with sections in other parts of the eastern Mediterranean; numerous radiocarbon-age determinations enhance the correlation. Seven fine-grained sediment types are identified in cores from eight distinct depositional environments. Some muds are closely related to specific environments (slump and debris flow deposits on slope and high-relief environments), or to time (well laminated mud during the latest Pleistocene-mid-Holocene), or to both (uniform and faintly laminated muds restricted to trench basins). Turbiditic and hemipelagic muds are common throughout the study area. Mud distribution patterns correlate closely with calculated sedimentation rates. We propose two depositional models for these sediments. The first emphasizes downslope transformations resulting in progressively reduced flow concentration during transport: from slump and debris flow–>turbidity current–>low density turbidity current or turbid layer mechanisms. The distal end-member deposits settling from low concentration flows are thick, rapidly emplaced, fine-grained uniform muds closely associated with faintly laminated muds. These were ponded in flat trench basin-plains. Planktonic and terrigenous fractions in the turbiditic, finely laminated and uniform muds record mixing of materials of gravitative and suspension origin during redeposition. This sequence prevails under conditions of minimal stratification of water masses, as characterized by the present Mediterranean. In the second model developed for conditions of well-developed water mass stratification, well laminated rather than uniform mud prevails as the end product of low concentration flows. These very finely laminated and graded muds record particle-by-particle settling from detached turbid layers concentrated along density interfaces; they include material from turbid layers complemented by the normal ‘rain’ of pelagic material. Stratification barriers resulted in region-wide distribution of such deposits, in both slope and trench environments.  相似文献   

Experimentally Determined Conditions in the Fish Canyon Tuff, Colorado, Magma Chamber   总被引：8，自引：7，他引：8  

JOHNSON  MARIE C.; RUTHERFORD  MALCOLM J. 《Journal of Petrology》1989,30(3):711-737

The Fish Canyon Tuff, Colorado, forms one of the largest (3000km³ known silicic eruptions in Earth history. The tuff is ahomogeneous quartz latite consisting of 40% phenocrysts (plagioclase,sanidine, biotite, hornblende, quartz, magnetite, apatite, sphene,and ilmenite) in equilibrium with a highly evolved rhyoliticmelt now represented by the matrix glass. Melt inclusions trappedin hornblende and quartz phenocrysts are identical to the newlyanalyzed matrix glass composition indicating that hornblendeand quartz crystallized from a highly evolved magma that subsequentlyexperienced little change. This study presents experimentalphase equilibrium data which are used to deduce the conditions(P, T, f_O2, f_H2O, etc.) in the Fish Canyon magma chamber priorto eruption. These new data indicate that sanidine and quartzare not liquidus phases until 780?C temperatures are achieved,consistent with Fe-Ti oxide geothermometry which implies thatthe magmatic temperature prior to eruption was 760?30?C. NaturalFe-Ti oxide pairs also suggest that log f_O2 was -12.4 (intermediatebetween the Ni-NiO and MnO-Mn₃O₄ oxygen buffers) in the magmachamber. This f_O2.102 is supported by the experimentally determinedvariations in hornblende and melt Mg-numbers as functions off_O2 A new geobarometer based on the aluminum content of hornblendesin equilibrium with the magmatic assemblage hornblende, biotite,plagioclase, quartz, sanidine, sphene, ilmenite or magnetite,and melt is calibrated experimentally, and yields pressuresaccurate to ?0.5 kb. Total pressure in the Fish Canyon magmachamber is inferred to have been 2.4 kb (equivalent to a depthof 7.9 km) based on the Al-content of natural Fish Canyon hornblendesand this new calibration. This depth is much shallower thanhas been proposed previously for the Fish Canyon Tuff. Variationsin experimental glass (melt) composition indicate that the magmawas water-undersaturated prior to eruption. X_H2O in the fluidphase that may have coexisted with the Fish Canyon magma isestimated to have been 0.5 by comparing the An-content of naturalplagioclases to experimental plagioclases synthesized at differentX_H2O and P_totals. This ratio corresponds to about 5 wt.% waterin the melt at depth. The matrix glass chemistry is reproducedexperimentally under these conditions: 760?C, 2.4 kb, X_H2O=0.5,and log f_o2=NNO+2 log units. The fugacity of SO₂ (91 b) is calculatedfrom the coexistence of pyrrhotite and magnetite. Maximum CO₂fugacity (2520 b) is inferred assuming the magma was volatilesaturated at 2.4 kb.  相似文献   

Emplacement of the Cleveland Dyke: Evidence from Geochemistry, Mineralogy, and Physical Modelling   总被引：2，自引：0，他引：2  

MACDONALD  R.; WILSON  L.; THORPE  R. S.; MARTIN  A. 《Journal of Petrology》1988,29(3):559-583

The igneous rocks of the British Tertiary Volcanic Province(BTVP) comprise intrusive central complexes and associated lavafields in northwest Scotland and northern Ireland. These centresare associated with linear dyke swarms which are radial aroundthe major central complexes. The most extensive dyke swarm isrelated to the Mull intrusive complex and includes the Clevelanddyke, which appears to extend some 430 km from Mull throughthe Scottish Midland Valley (SMV) to the coast of northeastEngland. The dyke may have been emplaced by lateral magma migrationfrom Mull, by vertical magma migration, or by a combinationof these processes associated with the emplacement of the Mullcentre and the presence of a regional stress field in northernBritain. Petrographic, mineralogical, and geochemical data for samplescollected across and along the Cleveland dyke have been usedto evaluate its petrogenesis and emplacement mechanism. Thesegment of the dyke north of, and along, the Southern UplandsFault, the southern boundary of the SMV, is not comagmatic withthat to the south, which is now defined as the Cleveland dykesensu stricto. The Cleveland dyke is an olivine-free, plagioclase-and pyroxene-phyric basaltic andesite. Plagioclase mineralogyand bulk composition indicate that it experienced a complexmagmatic history involving polybaric fractional crystallizationand minor crustal contamination. Despite this complex evolution,the dyke magma is relatively homogeneous and shows chemicalcharacteristics closely similar to tholeiitic rocks from Mull.The data substantiate lateral emplacement from this BVTP centre,rather than by vertical emplacement through heterogeneous lithosphere. Numerical modelling of dyke dynamics is consistent with emplacementof the Cleveland dyke as a single pulse of magma from the Mullcentre, flowing in a manner transitional between laminar andturbulent conditions. According to this model, the dyke (volumec. 85 km³ was initiated in a large magma chamber below Mullsubject to a small excess magmatic pressure. Lateral migrationat relatively high velocity (1–5 ms^–1) caused emplacementof the dyke in 1–5 days. Following emplacement, minorvertical ascent of magma may have contributed to the local enechelon distribution of dyke segments.  相似文献