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1.
Analysis of magnetic data between the Jan Mayen and Senja fracture zones indicates that the anomaly 24A-B sequence extends from the Lofoten Basin onto the outer Vøring Plateau. Anomaly patterns, including those on the conjugate margin, suggest that the pre-23 sea floor spreading was characterized by an unstable plate boundary between fracture zones. The pre-23 spreading rate was at least 2.5 cm yr-1 which is remarkably high compared with the post-23 rates. An evolutionary model which assumes Cenozoic oceanic crust as far landward as the Vöring Plateau and Greenland escarpments is suggested. 相似文献
2.
W. R. Roest J. J. Dañobeitia J. Verhoef B. J. Collette 《Marine Geophysical Researches》1992,14(1):1-24
The data from a recent magnetic compilation by Verhoefet al. (1991) off west Africa were used in combination with data in the western Atlantic to review the Mesozoic plate kinematic evolution of the central North Atlantic. The magnetic profile data were analyzed to identify the M-series sea floor spreading anomalies on the African plate. Oceanic fracture zones were identified from magnetic anomalies and seismic and gravity measurements. The identified sea floor spreading anomalies on the African plate were combined with those on the North American plate to calculate reconstruction poles for this part of the central Atlantic. The total separation poles derived in this paper describe a smooth curve, suggesting that the motion of the pole through time was continuous. Although the new sea floor spreading history differs only slightly from the one presented by Klitgord and Schouten (1986), it predicts smoother flowlines. On the other hand, the sea floor spreading history as depicted by the flowlines for the eastern central Atlantic deviates substantially from that of Sundvik and Larson (1988). A revised spreading history is also presented for the Cretaceous Magnetic Quiet Zone, where large changes in spreading direction occurred, that can not be resolved when fitting magnetic isochrons only, but which are evident from fracture zone traces and directions of sea floor spreading topography.Deceased 11 November 1991 相似文献
3.
Morpho-tectonic analysis of the Azores Volcanic Plateau from a new bathymetric compilation of the area 总被引：13，自引：0，他引：13
Lourenço N. Miranda J.M. Luis J.F. Ribeiro A. Victor L.A. Mendes Madeira J. Needham H.D. 《Marine Geophysical Researches》1998,20(3):141-156
The existing studies of the Azores triple junction, although based on specific geological or geophysical data, largely rely upon morphological considerations. However, there is no systematic bathymetric coverage of this area, and the quality of the available bathymetric charts does not allow consistent morpho-structural analysis.In this work we present a new bathymetric grid elaborated with all the available data sources in an area comprised between 24° W to 32° W and 36° N to 41° N. The basic data set corresponds to the merge of NGDC data with new swath profiles. This new map, included as an Appendix, combined with other results from seismology and neotectonics, is the basis for the study of the morpho-structural pattern of the Azores area, the present day stress field and its implications on the current view of the Azores geodynamics.As a major result, we conclude that the Azores region is controlled by two sets of conjugated faults with 120° and 150° strikes that establish the framework for the onset of volcanism, expressing as linear volcanic ridges or as point source volcanism. This interaction develops what can be considered as the morphological signature of the Azores Spreading axis segmentation. We argue that the Azores domain, presently in a broad transtensional regime, is acting simultaneously as a ultra slow spreading centre and as a transfer zone between the MAR and the dextral Gloria Fault, as it accommodates the differential shear movement between the Eurasian and African plates. 相似文献
4.
Natasha Stanton Gianreto Manatschal Julia Autin Daniel Sauter Marcia Maia Adriano Viana 《Marine Geophysical Researches》2016,37(3):185-205
This study investigates the magnetic and gravity signatures and associated seismic character of hyper-extended, exhumed and embryonic oceanic domains along the conjugate Iberia–Newfoundland rifted margins. As these margins have been drilled down to basement along their distal parts, it is possible to explore and test different geophysical techniques and interpretations. The aims of this work are twofold: (1) to investigate the location and nature of the two main marginal boundaries—the necking zone and the J Anomaly, which define the limits of major domains; and (2) to map the lateral variations of gravity and magnetic signatures and their detailed correlation with seismic data, from the proximal margin until the first unequivocal oceanic magnetic anomaly (e.g. C34 Anomaly). The results point out that the J Anomaly corresponds to a first-order tectono-magmatic boundary, with a basement formed by polyphase magmatism. It marks the boundary between the exhumed mantle domain, with little magmatic additions, from a domain oceanwards that reveals comparable trends, frequencies and a general magnetic pattern at both sides of the Atlantic, suggesting a coeval evolution. We propose that the domain between the J and the C34 Anomalies was formed by an embryonic spreading system, with intermittent budgets of magma, similar to those observed at very slow spreading systems. The J Anomaly may thus correspond to the location of lithospheric breakup though its origin and the nature of the domain oceanwards remains to be constrained. 相似文献
5.
Tectonic setting of the Azores Plateau deduced from a OBS survey 总被引：1，自引：0，他引：1
Miranda J.M. Mendes Victor L.A. Simões J.Z. Luis J.F. Matias L. Shimamura H. Shiobara H. Nemoto H Mochizuki H. Hirn A. Lépine J.C. 《Marine Geophysical Researches》1998,20(3):171-182
The studies of Azores seismicity generally show shocks with either normal faulting or right-lateral strike-slip along the ESE direction, compatible with a eastward relative motion of the Eurasian (EU) relative to the African (AF) plate. However, the 1 January 1980 earthquake was interpreted as a clear left-lateral strike-slip shock along the N150E direction. This pattern is difficult to explain in terms of the relative motion between the EU, AF and North American (NA) plates: all available models for the present day movement of this triple junction fail to explain the regional variability in the stress conditions of the area. Here we present data from a 34-day long Ocean Bottom Seismograph array deployment. We show that the seismicity is distributed along a band aligned with the island chain itself, and is concentrated along several faults with an approximate N150E strike, cutting the Azores plateau in all the area covered by the OBS network. The combination of these new results with other geophysical data permits us to conclude that the tectonic setting of the Azores plateau is characterised by the existence of two sets of faults, in the N120E and N150E directions, defining several crustal blocks, whose relative motion accommodates the interaction of the three megaplates. The deformation of these tectonic blocks is probably driven by the shear between the EU and AF plates. This model explains well the spatial variability of the stress conditions in the Azores domain, the combination of dextral and sinistral strike slip mechanisms and the observed seismotectonics of the Azores islands. 相似文献
6.
The Tamayo transform fault is located at the north end of the East Pacific Rise where it enters the Gulf of California. This paper presents bathymetric, seismic reflection, magnetic, and gravity data from a detailed survey of the transform fault. The dominant feature of the offset region is a bathymetric ridge trending 120°, parallel to the predicted transform plate boundary. This transform ridge is associated with a large (600 ) positive magnetic anomaly, and a very small positive free-air gravity anomaly. Magnetic and gravity models indicate either a basalt or serpentinite composition for the ridge, but cannot distinguish between these possibilities. At its eastern end, the modern zone of strike-slip motion is in a narrow valley south of the transform ridge. The transform plate margin appears to pass through a saddle in the transform ridge and meet the western spreading center segment in the trough north of the transform ridge. On the basis of this survey and previous work, the history of the Tamayo from continental breakup to the present has been reconstructed. Initial rifting occurred along a trend of 130° at approximately 3.5 m.y.b.p. Once the transform fault was free of the constraints imposed by continent-continent and continent-oceanic lithospheric interaction, the trend of the transform fault rotated counter-clockwise. This rotation resulted in a leaky transform fault and intrusion of a large continuous transform ridge. Further adjustments in the spreading center/transform fault plate boundary configuration have given rise to an incipient zone of rifting cutting across the transform ridge and emplacement of diapiric structures.Contribution of the Scripps Institution of Oceanography, new series. 相似文献
7.
S.C. MohapatraT. Sahoo 《Applied Ocean Research》2011,33(1):31-40
In the present paper, a hydroelastic model is developed to deal with surface gravity wave interaction with an elastic bed based on the small amplitude water wave theory and plate deflection in finite water depth. The elastic bottom bed is modelled as a thin elastic plate and is based on the Euler-Bernoulli beam equation. The wave characteristics in the presence of the elastic bed is analyzed in both the cases of deep and shallow water waves. Further, the linearized long wave equation is generalized to include bottom flexibility. A generalized expansion formula for the velocity potential is derived to deal with the boundary value problems associated with surface gravity waves having an elastic bed. The utility of the expansion formula is illustrated by demonstrating specific physical problems which will play significant role in the analysis of wave structure interaction problems. Behavior of the wave spectra are discussed in the case of closed basin having a free surface and an elastic bottom topography. 相似文献
8.
《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(5):875-899
The region of the North Atlantic between the Azores, the Canary Islands and the Gibraltar Strait is the subject of the multidisciplinary CANIGO project. A fine resolution primitive equation level model, called the CANIGO regional model, has been constructed to help with the integration of the observations. The model has open boundaries on three sides and at the Strait of Gibraltar.The output from the regional model gives a good representation of the Azores Current, the variability around Madeira, the Canary Current and the associated upwelling, the Cape Ghir and other cool filaments, and the spreading of Mediterranean Water. After passing south of the Azores, the Azores Current splits into two branches. The northern branch meanders towards the Gulf of Cadiz and the Gibraltar Strait, and the southern branch passes south of Madeira and through the Canary Archipelago. 相似文献
9.
Ulrich Fleischer 《Marine Geophysical Researches》1971,1(3):314-327
A regional survey of the southern Reykjanes Ridge (52°N to 57°N) shows an irregular topography: a rift valley which is only partly recognizable as such, with varying azimuth and some fracturezone-like interruptions. The survey also comprised gravity and magnetic measurements.The course of the axis as well as the perpendicular fractures show up well in the free air anomalies as relative troughs within an area of positive free air gravity (Figure 5). There is no indication of density variations within the topographic masses.The anomaly pattern of total magnetic intensity indicates the exact position of the rift axis and a bifurcation at about 55°N. From the parallel magnetic anomalies south of 55°N (Figure 2) a spreading rate can be deduced of 1.10 cm/yr perpendicular to the rift axis (Figure 3). This spreading rate is at the same time the plate movement involved.A survey of the Iceland-Faeroe Ridge with a 3–5 miles grid shows large gravity and magnetic anomalies over a smooth topography, indicating large pockets of light material, probably of volcanic origin. These areas have normal magnetization. Positive gravity anomalies forming a ring structure along the 200 m isobath are characterized by reversed magnetization.The dissimilarity in morphology, seismicity and inner structure between the two ridges that intersect in Iceland suggest that there is no relation between the two phenomena.Paper presented at the meeting of the International Gravity Commission, Paris, on September 8, 1970. 相似文献
10.
冲绳海槽海底地形的补偿模式初步研究 总被引：1，自引：1，他引：1
从区域补偿模式和实验均衡理论出发,利用重力和地形资料计算了冲绳海槽的均衡响应函数,结果表明：冲绳海槽南段弹性板有效厚度和补偿深度明显大于中段,结合其它地质地球物理资料解释认为,产生这种差异的原因主要是南,中两段岩石圈温度和补偿机制的不同所致。 相似文献
11.
The Kerguelen Province, consisting of two oceanic plateaus (Kerguelen, Broken Ridge) and three basins (Enderby, Labuan and
Diamantina), covers a large area of ocean floor in the southeast Indian Ocean. As very few magnetic anomalies have been identified
in this area and only a few basement ages from the Kerguelen Plateau are known, reconstruction models of the Kerguelen Province
are not well constrained. In an effort to gain more understanding about the evolution of this area, we have used satellite
gravity to identify additional fracture zones. As they are likely to be associated with high frequency and low amplitude gravity
anomalies, we have computed the vertical derivative map instead of the regular satellite gravity map. Using this approach,
we have identified a series of fracture zones in the Enderby Basin, which are aligned with the Mesozoic fracture zones in
the Perth Basin and converge to the Kerguelen Fracture Zone. In the conjugate Bay of Bengal, we traced an equivalent pattern
of fracture zones which, together, better constrain the early evolution of this part of the Indian Ocean. Synthesis of these
images and the other available data from the Kerguelen Province, suggests that the spreading of India from both Australia
and Antarctica is closely related. Spreading between the three continents appears to have begun about the same time, in the
early Cretaceous and thus, the accretion of some parts of the Kerguelen Province must have occurred before the onset of the
quiet magnetic period at 118 Ma. At about 96–99 Ma, when the spreading direction in the Indian Ocean had changed into a N-S
direction, it also took place throughout the Kerguelen Province. We find that previously proposed slow spreading in the Diamantina
Zone and Labuan Basins, between 96–99 Ma and the initiation of the Southeast Indian Ridge at 43 Ma, could not have taken place.
Furthermore, we suggest that there is growing evidence that the same is true for spreading in the eastward continuation of
the Diamantina Zone and Labuan Basin, between Australia and Antarctica. Initiation of spreading in this area is likely to
be contemporaneous with the spreading in the Kerguelen Province and, thus, older than 96–99 Ma.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
12.
《Marine and Petroleum Geology》2012,38(1):184-194
Brun and Fort (2011) use mechanical analysis, experimental models, and geologic data to suggest that deformation in passive-margin salt basins is dominantly a result of gravity gliding rather than gravity spreading. They claim that only seaward tilt of the salt layer is effective in driving basinward translation of the salt and overburden and that differential loading alone requires extreme conditions that do not occur in nature. In this Discussion, we refute many of their arguments and conclusions. We show that: i) a more thorough mechanical analysis indicates that gravity spreading is effective if the proximal overburden is at least three times thicker than the distal overburden, a common occurrence on passive margins; ii) more realistic analogue models also demonstrate that extreme thickness variations are not necessary for gravity spreading; iii) their analysis of structures or structure associations is sometimes misleading; and iv) there is abundant evidence that gravity spreading is dominant on some margins. In particular, modern data from the northern Gulf of Mexico confirm traditional interpretations that Cenozoic failure was mainly due to downslope movement driven by sedimentary loading, not SW-directed gliding driven by tilt of the deep salt as claimed by Brun and Fort (2011). We conclude that both gravity gliding and gravity spreading are common processes which may vary spatially and temporally in any one salt basin. 相似文献
13.
Edwin L. Hamilton 《Marine Geology》1973,14(5):295-325
Five expeditions (1965–1970) across parts of the Aleutian Abyssal Plain and adjacent areas in the Gulf of Alaska, and results of the Deep Sea Drilling Project, provide new information for the geologic history of the region which forms restrictive limits on models of plate tectonics. In general: (1) the Eocene-Oligocene, turbidite Aleutian Abyssal Plain was deposited from channelized turbidity currents from the north or northeast; (2) the plain is bounded on the south by the northern ridges of the Surveyor Fracture Zone, and is isolated from the Tufts Abyssal Plain; (3) turbidites were deposited from many buried channels and smaller surficial channels, but mainly from four great channels: Seamap, Sagittarius, Aquarius, and Taurus.The channels are depositional features; accumulation of sediments causes the channels to lie, topographically, along low ridges, with channels above distal portions of their levees. Western levees are higher and broader than eastern levees. Levee heights decrease from 30–100 m in the north to 15–25 m in the south.Rates of deposition and thicknesses of pelagic sediments in the northwest are 3 to 4 times greater than in the southeast. The data indicate the pelagics were deposited near the margin of the Pacific, at or near present locations. Thus, little or no northward plate motion is indicated.Turbidite thicknesses decrease from about 400–800 m in the north to about 200 m in the south. Turbidite thicknesses in the east-central plain are greater than in the Alaskan Abyssal Plain (formed since the Miocene), the northern Tufts Abyssal Plain, or the Sohm Abyssal Plain in the North Atlantic.Faulting and flexure of the oceanic crust seaward of the Aleutian Trench have strongly affected the channels. Seamap Channel has its high point midway along its course. The other three major channels are uplifted and faulted in the north.Required volumes of off-scraped sediments, undisturbed turbidites in the Aleutian Trench floor, and paleoclimatology also argue for little northward plate movement.The total evidence indicates that the turbidite Aleutian Abyssal Plain was formed in the Eocene-Oliogocene at, or near, its present position, and that the sediment source was probably Alaska. Cretaceous flysch of the Alaska Peninsula continental terrace was a possible source.The evidence does not require, but does not exclude, plate tectonics hypotheses. The evidence apparently excludes those continuous spreading models which cannot explain deposition of an Eocene-Oligocene turbidite plain over the magnetic bight, or which require an active, subducting, paleogene Aleutian Trench. Plate movements to the north over small distances cannot be excluded. The evidence is consistent with concepts of discontinuous sea-floor spreading with episodic subduction, or discontinuous, relative plate motion in this area. Two models are outlined which are consistent with the regional evidence: (1) a model with discontinuous relative plate motion and episodic subduction (a variation of one published by Hayes and Pitman, 1970); or (2) a no-plate-motion, or very-little-motion, model with long periods of inter-plate inactivity without subduction. 相似文献
14.
This study concerns the determination of a regional geoid model in the North Atlantic area surrounding the Azores islands by combining multi-mission altimetry from the ERS (European Remote Sensing) satellites and surface gravity data. A high resolution mean sea surface, named AZOMSS99, has been derived using altimeter data from ERS-1 and ERS-2 35-day cycles, spanning a period of about four years, and from ERS-1 geodetic mission. Special attention has been paid to data processing of points around the islands due to land contamination on some of the geophysical corrections. A gravimetric geoid has been computed from all available surface gravity, including land and sea observations acquired during an observation campaign that took place in the Azores in October 1997 in the scope of a European and a Portuguese project. Free air gravity anomalies were derived by altimetric inversion of the mean sea surface heights. These were used to fill the large gaps in the surface gravity and combined solutions were computed using both types of data. The gravimetric and combined solutions have been compared with the mean sea surface and GPS (Global Positioning System)-levelling derived geoid undulations in five islands. It is shown that the inclusion of altimeter data improves geoid accuracy by about one order of magnitude. Combined geoid solutions have been obtained with an accuracy of better than one decimetre. 相似文献
15.
This study concerns the determination of a regional geoid model in the North Atlantic area surrounding the Azores islands by combining multi-mission altimetry from the ERS (European Remote Sensing) satellites and surface gravity data. A high resolution mean sea surface, named AZOMSS99, has been derived using altimeter data from ERS-1 and ERS-2 35-day cycles, spanning a period of about four years, and from ERS-1 geodetic mission. Special attention has been paid to data processing of points around the islands due to land contamination on some of the geophysical corrections. A gravimetric geoid has been computed from all available surface gravity, including land and sea observations acquired during an observation campaign that took place in the Azores in October 1997 in the scope of a European and a Portuguese project. Free air gravity anomalies were derived by altimetric inversion of the mean sea surface heights. These were used to fill the large gaps in the surface gravity and combined solutions were computed using both types of data. The gravimetric and combined solutions have been compared with the mean sea surface and GPS (Global Positioning System)-levelling derived geoid undulations in five islands. It is shown that the inclusion of altimeter data improves geoid accuracy by about one order of magnitude. Combined geoid solutions have been obtained with an accuracy of better than one decimetre. 相似文献
16.
The application of advanced enhancement techniques for geophysical anomalies to global gravity (WGM2012) and magnetic (EMAG2) models sheds light on the complex tectonic evolution of the Rio Grande Rise (RGR) in the southern South Atlantic. Long wavelength Bouguer gravity lows indicate a thicker crust beneath of the ridge, whose nature can be related to a microcontinent or an excess of volcanism within the oceanic realm. Recently dredged continental rocks reinforce the hypothesis of a microcontinent or, at least, slivers of continental crust. However, the reserval magnetic pattern of the processed magnetic anomalies provide no evidence of aborted spreading center similar to the well-studied Jan Mayen microcontinent and the surrounding (inactive) Aegir and (active) Kolbeinsey ridges in the North Atlantic Ocean. The reversal magnetic anomalies show a series N-S trending parallel stripes roughly follow the current South American coastline and segmented by E-W oriented oceanic fracture zones (FZs). The magnetic stripes are bended eastwards at the RGR, showing a more complex magnetic pattern similar to that in the Iceland. The aborted Cruzeiro do Sul Rift (CSR) and the Jean Charcot Chain (JCC) are structures that cross the RGR and contribute to the understanding of the tectonic evolution of the South Atlantic Ocean. NW-SE oriented extensive gravity lows and bathymetric valleys, which mark the CSR, are segmented by E-W trending magnetic lineaments related to FZs. This structural configuration suggests that the extensional event, which formed the rift and the seamounts chain, was replaced by strike-slip movements along the FZs. In addition, we constructed a plate kinematic model for the evolution of the RGR based on bathymetric, free-air and Bouguer gravity and magnetic data. Our model comprises five main stages of the RGR formation and evolution between late Cretaceous and Paleocene (ca. 95 - 60 Ma), separated by published seafloor isochrones. The proposed model suggests that the RGR was built at the mid-Atlantic ridge by increased magmatism probably related to the Tristan da Cunha hotspot. 相似文献
17.
A detailed survey of a 1°×1°-square of seafloor 100 miles south-east of the Azores shows a strong correlation between directions of regional topographic and magnetic lineations. The area is dissected by the East Azores Fracture Zone at 36°55N, identified as the active Eurasian-African plate boundary, and by another large, non-active fracture zone at 36°10N. Both fracture zones strike 265° and are accompanied by large amplitude magnetic anomalies. The general strike in the area in between is 000°–015°. The skewing effect at this magnetic latitude is very sensitive to variations in strike of the magnetic contrasts. This effect was eliminated by a non-linear transformation which also gives the positions of magnetic contrasts. Some N-S contrasts were identified as sea floor spreading polarity contrasts (anomalies 31 and 32). Weak contrasts could be identified as topographic effects and gave a magnetization intensity of 5 A m-1. The identified sea floor spreading anomalies to both sides of the fracture zone at 36°10N agree very well, also quantatively, with a three-dimensional model for the fracture zone anomalies. This model describes the non-linear anomalies as end effects of the magnetic layer which is divided in blocks of alternating polarity. 相似文献
18.
The Solomon arc lacks subduction-associated volcanism in its eastern part. This anomalous absence arose from the collision
of the submarine Ontong Java Plateau with the Solomon arc about 8 m.y. ago and a consequent flip in subduction. Collision
was most forceful over the eastern half, so that the new, north-plunging slab of Indo-Australian plate remained in collisional
contact with the thick oceanic crust (>40 km) and lithosphere of the Ontong Java Plateau along a face of cooled depleted refractory
mantle; there is no intervening asthenospheric wedge, and therefore no magma production. 相似文献
19.
Bathymetry, satellite-derived gravity, and interpreted seismic reflection data across the northern Falkland/Malvinas Plateau
fossil continent–ocean transform rim may record the degree of mechanical coupling across the boundary after ridge–transform
intersection time. The rim comprises a broad microcontinental block in the east and a continental marginal fracture ridge
50–100 km wide elsewhere. Free-air gravity anomalies tentatively suggest that the fracture ridge is locked against oceanic
elastic lithosphere both to the north (Argentine Basin) and south (Central Falkland Basin).
Received: 18 January 1996 / Revision received: 25 March 1995 相似文献
20.
Three-dimensional SeaMARC II,gravity, and magnetics study of large-offset rift propagation at the Pito Rift,Easter microplate 总被引：1，自引：0，他引：1
Fernando Martinez David F. Naar Thomas B. Reed IV Richard N. Hey 《Marine Geophysical Researches》1991,13(4):255-285
We present results from a SeaMARC II bathymetry, gravity, and magnetics survey of the northern end of the large-offset propagating East Rift of the Easter microplate. The East Rift is offset by more than 300 km from the East Pacific Rise and its northern end has rifted into approximately 3 Ma lithosphere of the Nazca Plate forming a broad (70–100 km) zone of high (up to 4 km) relief referred to as the Pito Rift. This region appears to have undergone distributed and asymmetric extension that has been primarily accommodated tectonically, by block faulting and tilting, and to a lesser degree by seafloor spreading on a more recently developed magmatic accretionary axis. The larger fault blocks have dimensions of 10–15 km and have up to several km of throw between adjacent blocks suggesting that isostatic adjustments occur on the scale of the individual blocks. Three-dimensional terrain corrected Bouguer anomalies, a three-dimensional magnetic inversion, and SeaMARC II backscatter data locate the recently developed magmatic axis in an asymmetric position in the western part of the rift. The zone of magmatic accretion is characterized by an axis of negative Bouguer gravity anomalies, a band of positive magnetizations, and a high amplitude magnetization zone locating its tip approximately 10 km south of the Pito Deep, the deepest point in the rift area. Positive Bouguer gravity anomalies and negative magnetizations characterize the faulted area to the east of the spreading axis supporting the interpretation that this area consists primarily of pre-existing Nazca plate that has been block faulted and stretched, and that no substantial new accretion has occurred there. The wide zone of deformation in the Pito Rift area and the changing trend of the fault blocks from nearly N-S in the east to NW-SE in the west may be a result of the rapidly changing kinematics of the Easter microplate and/or may result from ridge-transform like shear stresses developed at the termination of the East Rift against the Nazca plate. The broad zone of deformation developed at the Pito Rift and its apparent continuation some distance south along the East Rift has important implications for microplate mechanics and kinematic reconstructions since it suggests that initial microplate boundaries may consist in part of broad zones of deformation characterized by the formation of lithospheric scale fault blocks, and that what appear to be pseudofaults may actually be the outer boundaries of tectonized zones enclosing significant amounts of stretched pre-existing lithosphere. 相似文献