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1.
Geochemistry of the Lesser Antilles volcanic island arc   总被引：1，自引：0，他引：1  
New analyses of 1518 rocks for major and certain trace elements are used to examine chemical variations between the 15 larger volcanic islands of the Lesser Antilles island arc. The depth to the top of the subduction zone dipping westward at about 40° lies about 100km below all the volcanoes of the arc. Most of the sampled eruptions are post-Miocene (5-1 m.y.) although south of Martinique, the Oligocene-Miocene and the younger arc are superimposed.There is a chemical variation along the arc axis, from alkalic (southern) through calc-alkalic (central) to tholeiitic (northern) volcanic suites. Three islands are examined in detail as type examples of this variation, i.e. Grenada (south), Dominica (centre), and St. Kitts (north). The Grenada suite includes basanites, alkalic basalts, and subalkalic basalts, andesites and dacites. The subalkalic basalts, andesites and dacites each fall into three chemical groupings along the axis of the arc, distinguished especially by K, Zr, Ni and Cr abundances. The whole Lesser Antilles assemblage is characterised by low K abundances and low K/Rb ratios, compared with other island arcs.The magmas are believed to have evolved through processes of partial melting and crystal fractionation. Partial melting of garnet Iherzolite at about 100km depth in a relatively ‘fertile’ zone of upper mantle in the southern sector, above the subducted slab of basaltic ocean crust, could have produced the undersaturated alkalic magmas. In the central and northern sectors, where the crustal structures are more complex, partial melting may have occurred within more ‘barren’ upper mantle, to produce tholeiitic and calc-alkalic magmas depleted in certain trace elements. In either case, water was probably added to the melted zone from the subducted and hydrated oceanic crust, since the whole arc assemblage was erupted explosively and the rocks are rich in A12O3, plagioclase is very calcic, and amphibole is an important phase. The second process was crystal fractionation at low pressure, as evidenced by the abundance of cumulate xenoliths. Separating phases for the southern volcanoes were olivine, calcic augite and Cr-spinel, followed by hornblende, anorthite and Ti-magnetite at lower temperatures. There is little evidence of the higher-temperature fractionation controls for the central and northern volcanoes.  相似文献   

2.
Natural Hazards - The arc of the Lesser Antilles is associated with a significant tectonic activity due to the subduction of the Atlantic oceanic plate under the Caribbean plate. Earthquakes in...  相似文献   

3.
Results from recent fieldwork and the Aguadomar marine survey in the Lesser Antilles clearly indicate that the volcanic field of southern Dominica has experienced three major edifice collapse events. This led to formation of the most voluminous debris avalanches known in the Caribbean Arc. Submarine hummocky morphology with plurikilometric megablocks is characteristic of debris avalanche deposits. We propose that steep slopes on the western Caribbean side of the island and intense hydrothermal alteration lead to recurrent large-scale edifice collapses. Therefore islands in the Lesser Antilles face a non-negligible risk from generation of tsunamis associated with potential future edifice collapse. To cite this article: A. Le Friant et al., C. R. Geoscience 334 (2002) 235–243.  相似文献   

4.
La Désirade, a small island east of Guadeloupe, is underlain by the only exposed pre-Tertiary basement rocks in the Lesser Antilles. The basement complex comprises spilitic and keratophyric flows and pillow lavas (with interbedded and overlying radiolarian cherts), swarms of mafic to silicic dikes, and subjacent plagiogranite. These features, and the absence of carbonates, terrigenous clastic sediments, or tuffaceous sediments from the complex indicate that it developed in a deep marine environment beyond the reach of terrigenous sedimentation or emergent island arc pyroclastic deposition. Previous workers have suggested that the Désirade basement complex originated either as oceanic crust or during an early (tholeiitic) stage of island arc growth. The isotopic compositions of Sr and Pb from the complex, and previously reported rare earth data (Johnston and Schilling, 1974) do not provide a clear distinction between these two possibilities. Nor does the presence of siliceous keratophyre in the complex rule out an oceanic crustal origin-such rocks are common in well studied ophiolites that originated as oceanic crust. Hence we turn to the age relationships of the complex, the surrounding ocean floor, and adjacent island arcs in an attempt to resolve this problem. The age of the complex strongly supports an oceanic crustal (ophiolitic) origin. The ages of zircons and a previously reported K-Ar age indicate that the complex is 145±5 m.y. old. The complex predates the next oldest volcanic rocks of the Lesser Antilles arc by ca. 110 m.y., and the oldest known rocks of the Aves Ridge, a possible Mesozoic precursor of the Lesser Antilles arc, by 50–60 m.y. This makes it unlikely that the Désirade complex is related to an early phase of either of these arcs. Instead, the age of the complex falls in the range of ages expected for oceanic crust in the vicinity of the Lesser Antilles prior to the development of any subduction zone and resulting arc. Thus we interpret the Désirade complex to be an uplifted segment of oceanic crust that represents the basement on which the later island arcs grew: first the Aves Ridge, an arc that was active in middle to late Cretaceous time (but whose exact mode of origin is enigmatic, and is considered in four alternate tectonic models), then the Eocene to Recent Lesser Antilles arc.  相似文献   

5.
Bioclastic flow deposits offshore from the Soufrière Hills volcano on Montserrat in the Lesser Antilles were deposited by the largest volume sediment flows near this active volcano in the last 26 kyr. The volume of these deposits exceeds that of the largest historic volcanic dome collapse in the world, which occurred on Montserrat in 2003. These flows were most probably generated by a large submarine slope failure of the carbonate shelf comprising the south‐west flank of Antigua or the east flank of Redonda; adjacent islands that are not volcanically active. The bioclastic flow deposits are relatively coarse‐grained and either ungraded or poorly graded, and were deposited by non‐cohesive debris flow and high density turbidity currents. The bioclastic deposit often comprises multiple sub‐units that cannot be correlated between core sites; some located just 2 km apart. Multiple sub‐units in the bioclastic deposit result from either flow reflection, stacking of multiple debris flow lobes, and/or multi‐stage collapse of the initial landslide. This study provides unusually precise constraints on the age of this mass flow event that occurred at ca 14 ka. Few large submarine landslides have been well dated, but the slope failures that have been dated are commonly associated with periods of rapid sea‐level change.  相似文献   

6.
Pliocene and Pleistocene deposits from Grande‐Terre (Guadeloupe archipelago, French Lesser Antilles) provide a remarkable example of an isolated carbonate system built in an active margin setting, with sedimentation controlled by both rapid sea‐level changes and tectonic movements. Based on new field, sedimentological and palaeontological analyses, these deposits have been organized into four sedimentary sequences (S1 to S4) separated by three subaerial erosion surfaces (SB0, SB1 and SB2). Sequences S1 and S2 (‘Calcaires inférieurs à rhodolithes’) deposited during the Late Zanclean to Early Gelasian (planktonic foraminiferal Zones PL2 to PL5) in low subsidence conditions, on a distally steepened ramp dipping eastward. Red algal‐rich deposits, which dominate the western part of Grande‐Terre, change to planktonic foraminifer‐rich deposits eastward. Vertical movements of tens of metres were responsible for the formation of SB0 and SB1. Sequence S3 (‘Formation volcano‐sédimentaire’, ‘Calcaires supérieurs à rhodolithes’ and ‘Calcaires à Agaricia’) was deposited during the Late Piacenzian to Early Calabrian (Zones PL5 to PT1a) on a distally steepened, red algal‐dominated ramp that changes upward into a homoclinal, coral‐dominated ramp. Deposition of Sequence S3 occurred during a eustatic cycle in quiet tectonic conditions. Its uppermost boundary, the major erosion surface SB2, is related to the Cala1 eustatic sea‐level fall. Finally, Sequence S4 (‘Calcaires à Acropora’) probably formed during the Calabrian, developing as a coral‐dominated platform during a eustatic cycle in quiet tectonic conditions. The final emergence of the island could then have occurred in Late Calabrian times.  相似文献   

7.
The island of St Martin lies inthe inactive part of the northernLesser Antilles island arc. The island consists of volcaniclasticsediments overlain and intruded by volcanic and plutonic rocks,which are in turn overlain by Miocene limestones. The extrusiveand intrusive rock suites are closely spaced in time (around27 Ma) although field relations suggest that the volcanic rockswere intruded by the plutons. Pluton emplacement gave rise tothermal metamorphism of the volcanic and volcaniclastic carapace,and to widespread hydrothermal alteration throughout the island. Geochemically, the igneous rocks of St Martin form a mildlytholeiitic to calc-alkaline typical subduction-related suite.The extrusive rocks are basalts to andesites, and the magmasappear to have differentiated largely through fractional crystallizationof plagioclase, clinopyroxene, and olivine. The REE displayflat chondrite-normalized patterns, with no significant Eu anomalydespite convincing evidence for plagioclase fractionation. Theplutonic rocks are more silica-rich diorites to granites, containingplagioclase, amphibole, and, less commonly, K-feldspar, sphene,zircon, and pyroxene. REE patterns are slightly LREE enrichedbut display distinct negative Eu anomalies. The fractionationof amphibole and accessory phases may have been important inthe evolution of the plutonic suite, as REE contents do notincrease overall with differentiation. Sr and Nd isotopic ratios of the St Martin suite form restrictedranges which vary little with differentiation, or between theextrusive and intrusive suiteSi 87Sr/86Sr ratios are slightlyhigher and 143Nd/l44Nd slightly lower than for volcanic rocksuites from the currently active northern Lesser Antilles volcanicarc. Some of the high 87Sr/86Sr ratios are explained in termsof hydrothermal alteration involving a high 87Sr/86Sr fluid,associated with pluton emplacement. Pb isotope ratios are similarto those of the currently active northern Lesser Antilles arc,and correlate with SiO2. Such correlations, together with largeranges of incompatible (and immobile) trace element ratios suggestthat open-system differentiation occurred during the evolutionof the St Martin suite. The composition of magma sources in the northern Lesser Antillesarc apparently has not changed significantly over the last 30Ma, despite a westward shift in the locus of arc magmatism.Addition of a slab-derived fluid to the mantle wedge is responsiblefor the high relative abundances of large ion lithophile elements(LILE) and enrichment in radiogenic Pb and Sr relative to mid-oceanridge basalt (MORB). Subsequent differentiation may involveassimilation of the arc basement in St Martin, which is believedto consist of Cretaceous to early Tertiary arc material, similarto that encountered in the Greater Antilles. *Present address: Department of Geosciences, University of Arizona, Tucson, Arizona 85721  相似文献   

8.
The Solonker suture zone has long been considered to mark the location of the final disappearance of the PaleoAsian Ocean in the eastern Central Asian Orogenic Belt(CAOB). However, the time of final suturing is still controversial with two main different proposals of late Permian to early Triassic, and late Devonian. This study reports integrated wholerock geochemistry and LA-ICP-MS zircon U-Pb ages of sedimentary rocks from the Silurian Xuniwusu Formation, the Devonian Xilingol Complex and the Permian Zhesi Formation in the Hegenshan-Xilinhot-Linxi area in central Inner Mongolia, China. The depositional environment, provenance and tectonic setting of the Silurian-Devonian and the Permian sediments are compared to constrain the tectonic evolution of the Solonker suture zone and its neighboring zones. The protoliths of the silty slates from the Xuniwusu Formation in the Baolidao zone belong to wacke and were derived from felsic igneous rocks with steady-state weathering, poor sorting and compositional immaturity. The protoliths of metasedimentary rocks from the Xilingol Complex were wackes and litharenites and were sourced from predominantly felsic igneous rocks with variable weathering conditions and moderate sorting. The Xuniwusu Formation and Xilingol Complex samples both have two groups of detrital zircon that peak at ca. 0.9–1.0 Ga and ca. 420–440 Ma, with maximum deposition ages of late Silurian and middle Devonian age, respectively. Considering the ca. 484–383 Ma volcanic arc in the Baolidao zone, the Xuxiniwu Formation represents an oceanic trench sediment and is covered by the sedimentary rocks in the Xilingol Complex that represents a continental slope sediment in front of the arc. The middle Permian Zhesi Formation metasandstones were derived from predominantly felsic igneous rocks and are texturally immature with very low degrees of rounding and sorting, indicating short transport and rapid burial. The Zhesi Formation in the Hegenshan zone has a main zircon age peak of 302 Ma and a subordinate peak of 423 Ma and was deposited in a back-arc basin with an early marine transgression during extension and a late marine regression during contraction. The formation also crops out locally in the Baolidao zone with a main zircon age peak of 467 Ma and a minor peak of 359 Ma, and suggests it formed as a marine transgression sedimentary sequence in a restricted extensional basin and followed by a marine regressive event. Two obvious zircon age peaks of 444 Ma and 280 Ma in the Solonker zone and 435 Ma and 274 Ma in Ondor Sum are retrieved from the Zhesi Formation. This suggests as a result of the gradual closure of the Paleo-Asian Ocean a narrow ocean sedimentary environment with marine regressive sedimentary sequences occupied the Solonker and Ondor Sum zones during the middle Permian. A restricted ocean is suggested by the Permian strata in the Bainaimiao zone. Early Paleozoic subduction until ca. 381 Ma and renewed subduction during ca. 310–254 Ma accompanied by the opening and closure of a back-arc basin during ca. 298–269 Ma occurred in the northern accretionary zone. In contrast, the southern accretionary zone documented early Paleozoic subduction until ca. 400 Ma and a renewed subduction during ca. 298–246 Ma. The final closure of the Paleo-Asian ocean therefore lasted at least until the early Triassic and ended with the formation of the Solonker suture zone.  相似文献   

9.
In the Lesser Caucasus and NE Anatolia, three domains are distinguished from south to north: (1) Gondwanian-derived continental terranes represented by the South Armenian Block (SAB) and the Tauride–Anatolide Platform (TAP), (2) scattered outcrops of Mesozoic ophiolites, obducted during the Upper Cretaceous times, marking the northern Neotethys suture, and (3) the Eurasian plate, represented by the Eastern Pontides and the Somkheto-Karabagh Arc. At several locations along the northern Neotethyan suture, slivers of preserved unmetamorphozed relics of now-disappeared Northern Neotethys oceanic domain (ophiolite bodies) are obducted over the northern edge of the passive SAB and TAP margins to the south. There is evidence for thrusting of the suture zone ophiolites towards the north; however, we ascribe this to retro-thrusting and accretion onto the active Eurasian margin during the latter stages of obduction. Geodynamic reconstructions of the Lesser Caucasus feature two north dipping subduction zones: (1) one under the Eurasian margin and (2) farther south, an intra-oceanic subduction leading to ophiolite emplacement above the northern margin of SAB. We extend our model for the Lesser Caucasus to NE Anatolia by proposing that the ophiolites of these zones originate from the same oceanic domain, emplaced during a common obduction event. This would correspond to the obduction of non-metamorphic oceanic domain along a lateral distance of more than 500?km and overthrust up to 80?km of passive continental margin. We infer that the missing volcanic arc, formed above the intra-oceanic subduction, was dragged under the obducting ophiolite through scaling by faulting and tectonic erosion. In this scenario part of the blueschists of Stepanavan, the garnet amphibolites of Amasia and the metamorphic arc complex of Erzincan correspond to this missing volcanic arc. Distal outcrops of this exceptional object were preserved from latter collision, concentrated along the suture zones.  相似文献   

10.
Carriacou is one of the small islands in the Grenadine chain in the southern Lesser Antilles. It preserves two Miocene successions, that on the south coast shallowing upwards and separated by a probable fault from the extensively exposed turbidite sequence, called the Grand Bay Formation, on the east coast. These formations show a range of features beautifully exposed in coastal sections, including unconformities, turbidites and a starfish bed.  相似文献   

11.
We present here the first available estimations of chemical weathering and associated atmospheric CO2 consumption rates as well as mechanical erosion rate for the Lesser Antilles. The chemical weathering (100–120 t/km2/year) and CO2 consumption (1.1–1.4 × 106 mol/km2/year) rates are calculated after subtraction of the atmospheric and hydrothermal inputs in the chemical composition of the river dissolved loads. These rates thus reflect only the low-temperature basalt weathering. Mechanical erosion rates (approx. 800–4000 t/km2/year) are estimated by a geochemical mass balance between the dissolved and solid loads and mean unaltered rock. The calculated chemical weathering rates and associated atmospheric CO2 consumption rates are among the highest values worldwide but are still lower than those of other tropical volcanic islands and do not fit with the HCO3− concentration vs. 1/T correlation proposed by Dessert et al. (2001). The thick soils and explosive volcanism context of the Lesser Antilles are the two possible keys to this different weathering behaviour; the development of thick soils limits the chemical weathering and the presence of very porous pyroclastic flows allows an important water infiltration and thus subsurface weathering mechanisms, which are less effective for atmospheric CO2 consumption.  相似文献   

12.
Basanitoid, alkal basalt, andesite and dacite compositions fromGrenada, Lesser Antilles, show a differentation trend from nepheline-normative,through hypersthene-normative to quartz-normative. This unusualsequence, in which the liquids migrate through the low pressurethermal divide of olivine-clinopyroxene-plagioclase from criticallyundersaturated compositions, is interpreted from experimentaland chemical data as the result of crystallization of amphiboleunder a hydrous pressure of several kilobars.  相似文献   

13.
To reveal the causes of differences in the hydrocarbon accumulation in continental marginal basins in the centralsouthern South China Sea,we used gravity-magnetic,seismic,drilling,and outcrop data to investigate the tectonic histories of the basins and explore how these tectonic events controlled the hydrocarbon accumulation conditions in these basins.During the subduction of the Cenozoic proto-South China Sea and the expansion of the new South China Sea,the continental margin basins in the central-southern South China Sea could be classified as one of three types of epicontinental basins:southern extensional-foreland basins,western extensional-strike slip basins,and central extensional-drift basins.Because these basins have different tectonic and sedimentary histories,they also differ in their accumulated hydrocarbon resources.During the Cenozoic,the basin groups in the southern South China Sea generally progressed through three stages:faulting and subsidence from the late Eocene to the early Miocene,inversion and uplift in the middle Miocene,and subsidence since the late Miocene.Hydrocarbon source rocks with marine-continental transitional facies dominated byⅡ-Ⅲkerogen largely developed in extremely thick Miocene sedimentary series with the filling characteristics being mainly deep-water deposits in the early stage and shallow water deposits in the late stage.With well-developed sandstone and carbonate reservoirs,this stratum has a strong hydrocarbon generation potential.During the Cenozoic,the basin groups in the western South China Sea also progressed through the three developmental stages discussed previously.Hydrocarbon source rocks with lacustrine facies,marine-continental transitional facies,and terrigenous marine facies dominated byⅡ2-Ⅲkerogen largely developed in the relatively thick stratum with the filling characteristics being mainly lacustrine deposits in the early stage and marine deposits in the late stage.As a reservoir comprised of self-generated and self-stored sandstone,this unit also has a high hydrocarbon generation potential.Throughout those same three developmental stages,the basin groups in the central South China Sea generated hydrocarbon source rocks with terrigenous marine facies dominated byⅢkerogen that have developed in a stratum with medium thicknesses with the filling characteristics being mainly sandstone in the early stage and carbonate in the late stage.This reservoir,which is dominated by lower-generation and upper-storage carbonate rocks,also has a high hydrocarbon generation potential.  相似文献   

14.
Quantifying mercury (Hg) emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element. Here we report on the abundance of total gaseous (TGM = Hg0(g) + HgII(g)) and particulate (Hg(p)) mercury in the summit gas emissions of La Soufrière andesitic volcano (Guadeloupe island, Lesser Antilles), where enhanced degassing of mixed hydrothermal-magmatic volatiles has been occurring since 1992 from the Southern summit crater. We demonstrate that Hg in volcanic plume occurs predominantly as gaseous mercury, with a mean TGM/Hg(p) mass ratio of ~ 63. Combining the mean TGM/H2S mass ratio of the volcanic plume (~ 3.2 × 10− 6), measured close to the source vent, with the H2S plume flux (~ 0.7 t d− 1), determined simultaneously, allows us to estimate a gaseous mercury emission rate of 0.8 kg yr− 1 from La Soufrière summit dome. Somewhat lower TGM/Stot mass ratio in fumarolic gases from the source vent (4.4 × 10− 7) suggests that plume chemical composition is not well represented by the emission source (fumaroles) due to chemical processes prior to (or upon) discharge. Current mercury emission from La Soufrìere volcano represents a very small contribution to the estimated global volcanic budget for this element.  相似文献   

15.
We report an extensive helium isotope survey of basaltic toandesitic lavas from the Lesser Antilles island arc—anarc system with well-documented evidence of crustal contamination.Given the sensitivity of helium isotopes as a tracer of theeffects of crustal additions, our aim is to evaluate the relationshipof 3He/4He ratios to other indices of contamination processessuch as oxygen and strontium isotopes. To this end, we havecarried out 53 3He/4He analyses on separated minerals (olivinesand pyroxenes) from throughout the arc, which we compare withwhole-rock strontium and phenocryst oxygen isotope measurements.We show that the three isotopic tracers show coherent patternsthroughout the Lesser Antilles, indicating a regional controlon crustal contamination. The southern section of the arc (Grenadato Martinique) shows clear evidence for major crustal contaminationin all three isotopic systems with results for our samples inthe range 3He/4He(olivine) 3·6–7·6RA,  相似文献   

16.
Large variations are reported in the B concentrations and isotopic ratios of river and thermal spring waters in Guadeloupe, Lesser Antilles. Rivers have δ11B values around 40‰ and B concentrations lower than 30 μg/L, while thermal springs have δ11B of 8–15‰ and B concentrations of 250–1000 μg/L. River samples strongly impacted by hydrothermal inputs have intermediate δ11B and B contents. None of these surface water samples have δ11B comparable to the local unweathered volcanic rocks (around 0‰), implying that a huge isotopic fractionation of 40‰ takes place during rock weathering, which could be explained by preferential incorporation of 10B during secondary mineral formation and adsorption on clays, during rock weathering or in the soils. The soil-vegetation B cycle could also be a cause for such a fractionation. Atmospheric B with δ11B of 45‰ represents 25–95% of the river B content. The variety of the thermal spring chemical composition renders the understanding of B behavior in Guadeloupe hydrothermal system quite difficult. Complementary geochemical tracers would be helpful.  相似文献   

17.
试论内蒙古狼山式（型）铅锌矿床成矿地质分析   总被引：1，自引：0，他引：1  
热水喷流-沉积型铅锌矿床多产于古大陆边缘或陆间裂陷槽中;巨厚沉积物堆积与强烈还原环境是该类型矿床形成的前提。泥岩-细碎屑岩型（SEDEX型）及海相火山岩型（VMS型）铅-锌矿床虽具块状硫化物矿石,硫化铁矿物含量都很高,但二者产出的地质背景有明显不同。前者是冒地槽或陆相浅海环境,大量泥砂堆积;后者则是优地槽环境,伴随钙碱系列或拉斑玄武的海底火山活动。文章通过对狼山成矿带上各典型矿床成矿特征的研究和总结后认为：狼山多金属成矿带的各赋矿次级盆地是华北古陆边缘拉张条件下具有还原性质的海相裂谷盆地,矿床具有明显的层控与岩控特征,并且同生断裂活动及其对成矿的控制作用,喷流成矿过程中的同沉积期火山活动特点都比较明显,说明狼山成矿带上典型矿床成矿作用与成矿动力来源的多样性、复杂性和独特性,对在该区找矿具有一定指导意义。  相似文献   

18.
Abstract

The Guerrero suspect terrane composed of Late Jurassic-Early Cretaceous sequences, extends from Baja California up to Acapulco and is considered to be coeval with the Late Mesozoic igneous and sedimentary arc sequences of the Greater Antilles, Venezuela and Western Cordillera of Colombia. New geological, petrological and geochemical data from central and southern Mexico, led us to propose a new model for the building of the Alisitos-Teloloapan arc. This arc, partly built on the Pacific oceanic lithosphere and partly on continental fragments, could be related to the subduction of an oceanic basin - the Arperos basin - under the Paleo-Pacific plate. This subduction was dipping southwest.

At the beginning of the magmatic activity of the oceanic segment of this arc, depleted tholeiitic basalts were emitted in a submarine environnement below the CCD. While subduction was going on, the arc magmas evolved from LREE depleted tholeiites to slightly LREE enriched tholeiites and then, to calc-alkaline basalts and andesites enriched in LREE and HFSE. Concurrently, the arc sedimentary environment changed from deep oceanic to neritic with the deposition of Aptian-Albian reefal limestones, at the end of the arc building. In the continent-based segment, the arc magmas are exclusively differentiated calc-alkaline suites depleted in HREE and Y, formed of predominantly siliceous lavas and pyroclastic rocks, emitted in a sub-aerial or shallow marine environment.

Thus, taking into account this above mentioned model, the Cretaceous volcanic series, accreted to the margins of cratonal America, in Colombia, Venezuela, Greater Antilles and Mexico, could be related to the same west-south-west dipping subduction of oceanic basins, fringing the North and South American continental cratons and connected directly with the inter-American Tethys. While the subduction was proceeding, this magmatic arc drifted towards the North and South American cratons and finally, collided with the continental margins at different periods during the Cretaceous.  相似文献   

19.
This study uses zircon and apatite fission‐track (FT) analyses to reveal the exhumation history of the granitoid samples collected from the Lesser Hinggan Mountains, northeast China. A southeast to northwest transect across the Lesser Hinggan Mountains yielded zircon FT ages between 89.8 ± 5.7 and 100.4 ± 8.6 Ma, and apatite FT ages between 50.6 ± 13.8 and 74.3 ± 4.5 Ma with mean track lengths between 11.7 ± 2.0 and 12.8 ± 1.7 µm. FT results and modelling identify three stages in sample cooling history spanning the late Mesozoic and Cenozoic eras. Stage one records rapid cooling from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110 °C) during ca. 95 to 65 Ma. Stage two records a period of relative slow cooling (∼110–60 °C) taking place between ca. 65 and 20 Ma, suggesting that the granitoids had been exhumed to the depth of ∼1−2 km. Final stage cooling (60–20 °C) occurred since the Miocene at an accelerated rate bringing the sampled rocks to the Earth's surface. The maximum exhumation is more than 5 km under a steady‐state geothermal gradient of 35 °C/km. Integrated with the tectonic setting, this exhumation is possibly led by the Pacific Plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

20.
Measurements of orientations of joints that have been made on the Leeward and Windward Islands (Lesser Antilles) from St. Martin to St. Vincent are reported. The preferred orientations of the joints have been determined by a statistical analysis. Assuming the joints to be shearing phenomena, the principal directions of the stress field that caused them, can be calculated. The latter are in very good agreement with the principal stress directions obtained by a statistical analysis of fault plane solutions of earthquakes in the area; the inferred maximum compression direction being NW-SE (ca. N 130°E). This corresponds to a model which assumes that the American plate is subducted in that direction beneath the Caribbean plate.  相似文献   

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