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1.
本文根据以裂变径迹测年为主的低温热年代学方法，认为燕山及邻区在晚白垩世进入区域性伸展构造环境以来经历了造山带伸展裂解引发的6次强烈差异升降运动，分别发生在120～105Ma、95～85Ma、60～50Ma、38Ma左右、25～20Ma和10～5Ma，造成燕山及邻区约7～8km的剥蚀量。而在相邻两次强烈差异升降运动期之间的相对构造稳定期，则形成了燕山—太行山地5期夷平面以及周缘盆地多期沉积间断。燕山与邻区盆地之间晚中新世以来的快速差异升降运动导致燕山及邻区现今盆—山构造—地貌格局。 相似文献
2.
C.W. Rapela R.J. Pankhurst C. Casquet E. Baldo C. Galindo C.M. Fanning J.M. Dahlquist 《Journal of South American Earth Sciences》2010,29(1):105-127
New U–Pb SHRIMP zircon ages combined with geochemical and isotope investigation in the Sierra de Maz and Sierra de Pie de Palo and a xenolith of the Precordillera basement (Ullún), provides insight into the identification of major Grenville-age tectonomagmatic events and their timing in the Western Sierras Pampeanas. The study reveals two contrasting scenarios that evolved separately during the 300 Ma long history: Sierra de Maz, which was always part of a continental crust, and the juvenile oceanic arc and back-arc sector of Sierra de Pie de Palo and Ullún. The oldest rocks are the Andino-type granitic orthogneisses of Sierra de Maz (1330–1260 Ma) and associated subalkaline basic rocks, that were part of an active continental margin developed in a Paleoproterozoic crust. Amphibolite facies metamorphism affected the orthogneisses at ca. 1175 Ma, while granulite facies was attained in neighbouring meta-sediments and basic granulites. Interruption of continental-edge magmatism and high-grade metamorphism is interpreted as related to an arc–continental collision dated by zircon overgrowths at 1170–1230 Ma. The next event consisted of massif-type anorthosites and related meta-jotunites, meta-mangerites (1092 ± 6 Ma) and meta-granites (1086 ± 10 Ma) that define an AMCG complex in Sierra de Maz. The emplacement of these mantle-derived magmas during an extensional episode produced a widespread thermal overprint at ca. 1095 Ma in neighbouring country rocks. In constrast, juvenile oceanic arc and back-arc complexes dominated the Sierra de Pie de Palo–Ullún sector, that was fully developed ca. 1200 Ma (1196 ± 8 Ma metagabbro). A new episode of oceanic arc magmatism at ～1165 Ma was roughly coeval with the amphibolite high-grade metamorphism of Sierra de Maz, indicating that these two sectors underwent independent geodynamic scenarios at this age. Two more episodes of arc subduction are registered in the Pie de Palo–Ullún sector: (i) 1110 ± 10 Ma orthogneisses and basic amphibolites with geochemical fingerprints of emplacement in a more mature crust, and (ii) a 1027 ± 17 Ma TTG juvenile suite, which is the youngest Grenville-age magmatic event registered in the Western Sierras Pampeanas. The geodynamic history in both study areas reveals a complex orogenic evolution, dominated by convergent tectonics and accretion of juvenile oceanic arcs to the continent. 相似文献
3.
The Sierra de Pie de Palo located between 67°30′–68°30′ W and 31°00′–32°00′ S in the Argentine Western Sierras Pampeanas in Argentina is a distinct basement range, which lacks thermochronological data deciphering its exhumation and uplift history below 200 °C. Integrated cooling histories constrained by apatite fission-track data as well as (U–Th)/He measurements of zircon and apatite reveal that the structural evolution of this mountain range commenced during the Late Paleozoic and was mainly controlled by tectonically triggered erosion. Following further erosional controlled exhumation in a more or less extensional regime during the Mesozoic, the modern topography was generated by denudation in the Paleogene during the early stage of the Andean deformation, whereupon deformation propagated towards the west since the Late Mesozoic to Paleogene. This evolution is characterised by a total of 3.7–4.2 km vertical rock uplift and by 1.7–2.2 km exhumation with a rate of 0.03–0.04 mm/a within the Sierra de Pie de Palo since ca. 60 Ma. Onset of uplift of peak level is also referred to that time resulting in a less Pliocene amount of uplift than previously assumed. 相似文献
4.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(6-7):555-563
Apatite fission track analysis is used as a tectonic tool to unravel the evolution of the Sierra de Guadarrama, an mountain range in central Spain, and the far-field effects of the Alpine plate tectonics, expressed by reactivation of NE-SW trending lineaments in the Hercynian basement. 18 basement samples were analysed, and 4 sediments of Mesozoic and Tertiary age. Thermal histories were modelled for most samples and conversion to resultant amounts of denudation and rock uplift was possible for the Tertiary history, because of constraints on the paleo-topography and -elevation in Upper Cretaceous to Paleocene times. Accelerated cooling (up to 100 °C in 5 Ma) occurred around 100 Ma in the entire Sierra de Guadarrama. In the northern part, this cooling was preceded by reheating of Lower Triassic sediments up to 110 °C, suggesting sedimentation of about 3 km of, now eroded, Upper Triassic to Jurassic. The period of greatest erosion occurred in the Pliocene and Quaternary and affected almost the entire Sierra de Guadarrama. It was preceded by a Middle-Miocene cooling event that correlates with the beginning of the neo-tectonic setting of central Spain. The greatest Tertiary rock uplift occurred in the central part of the Sierra de Guadarrama: 5.9 ± 11.6 km. The Pliocene to recent event constitutes most of the Tertiary denudation. It is accommodated by active NE-SW trending reverse faults, and attended by about 3.2 km of denudation. These data fit as far-field effects in the plate tectonic setting of ongoing NW-SE oriented convergence between the European and African plate. 相似文献
5.
Thermal Evolution of the Tanlu Fault Zone on the Eastern Margin of the Dabie Mountains and Its Tectonic Implications 总被引：7，自引：3，他引：4
ZHU Guang HOU Minjin WANG Yongsheng LIU Guosheng NIU Manlan School of Resource Environment Engineering Hefei University of Technology Hefei Anhui Geological Survey of Anhui Hefei Anhui 《《地质学报》英文版》2004,78(4):940-953
Five samples of muscovite from mylonites of the earlier Tanlu ductile shear zone on the eastern margin of the Dabie Mountains yield 40Ar/39Ar ages ranging from 178 Ma to 196 Ma. Three of them have reliable plateau ages of 188.7±0.7 Ma, 189.7±0.6 Ma and 192.5±0.7 Ma respectively, which indicates a syn-orogenic, sinistral strike-slip thermal event. This displacement movement derived from the continent-continent collision of the North and South China blocks took place in the Early Jurassic and after uplifting of high-pressure to ultrahigh-pressure slabs to the mid-crust. It is suggested that during the collision the Tanlu fault zone was an intracontinental transform fault caused by differential subduction speeds. The 40Ar/39Ar ages of mylonite whole-rock and muscovite from the later Tanlu ductile shear zone suggest another sinistral strike-slip cooling event at 128 Ma. During this strike-slip faulting, large-scale intrusion and doming uplift occurred in the eastern part of the Dabie orogenic belt. Data o 相似文献
6.
Paleo-uplift and cooling rates from various orogenic belts of India, as revealed by radiometric ages
The significant discordance of the radiometric (Rb-Sr, Pb-U, K-Ar and fission track) ages from various orogenic cycles of the Dharwar, Satpura, Aravalli and Himalayan orogenic belts in India, coupled with their corresponding blocking temperatures for various radiometric clocks in whole rocks and minerals, has been used to evaluate the cooling and the uplift histories of the respective orogenic belts. The blocking temperatures used in the present study of various Rb-Sr (isotopic homogenization at 600°C, muscovite at 500°C and biotite at 300°C), Pb-U (monazite at 530°C), K-Ar (muscovite at 350°C and biotite at 300°C) and fission-track clock (zircon at 350°C, sphene at 300°C, garnet at 280°C, muscovite at 130°C, hornblende at 120°C and apatite at 100°C for the cooling rate l°C/Ma) have been found suitable to explain the differences in mineral ages by different radiometric techniques. The nature of the cooling curves drawn using the temperature versus age data for various orogenic cycles in India has also been discussed. The cooling and the uplift patterns determined for various orogenic cycles of India, suggest comparatively slow cooling (5.0–0.2°C/Ma) and uplift (180–2 m/Ma) for the Peninsular regions and rapid cooling (25.0–1.0° C/Ma) and fast uplift (800–30 m/Ma) during the Himalayan Orogenic Cycle (Upper Cretaceous—Tertiary) in the Extra-Peninsular region. 相似文献
7.
Dissected remnants of a high elevation low relief surface (HELRS) are encountered all along the Pyrenean range. All authors agree that the HELRS was shaped during the post‐shortening evolution of the belt, but doubt remains on its original elevation. Notably, whether a post‐shortening uplift event occurred after the generation of the Pyrenean planation surface is still debated. Based on a geomorphological study of the entrenchment of the Aspe River in the North‐Western Pyrenees, we describe a post‐Oligocene multi‐stage dissection of the HELRS linked to a regional post‐shortening uplift. Each incision stage is recorded by erosional triangular facets and associated stepped remnants of former smooth topographies. Compared analysis of patterns of incision in the Axial Zone and its northern border allows to evidence differential vertical motions. We discuss the forcing mechanism(s) that controlled this morphological evolution. 相似文献
8.
We reconstruct the history of denudation and landscape evolution of the northern East- Brazilian continental margin using apatite fission-track thermochronology and thermal history modeling. This part of the Brazilian Atlantic margin is morphologically characterized by inland and coastal plateaus surrounding a wide low-lying inland region, the Sertaneja Depression. The apatite fission track ages and mean track lengths vary from 39 ± 4 to 350 ± 57 Ma and from 10.0 ± 0.3 to 14.2 ± 0.2 μm, respectively, implying a protracted history of spatially variable denudation since the Permian at relatively low rates (<50 m My−1). The Sertaneja Depression and inland plateaus record Permian-Early Jurassic (300–180 Ma) denudation that precedes rifting of the margin by > 60 Myrs. In contrast, the coastal regions record up to 2.5 km of Late Jurassic-Early Cretaceous (150–120 Ma) denudation, coeval with rifting of the margin. The samples from elevated coastal regions, the Borborema Plateau and the Mantiqueira Range, record cooling from temperatures above 120 °C since the Late Cretaceous extending to the Cenozoic. We interpret this denudation as related to post-rift uplift of these parts of the margin, possibly resulting from compressional stresses transmitted from the Andes and/or magmatism at that time. Several samples from these areas also record accelerated Neogene (<30 Ma) cooling, which may record landscape response to a change from a tropical to a more erosive semi-arid climate during this time. The inferred denudation history is consistent with the offshore sedimentary record, but not with evolutionary scenarios inferred from the recognition of “planation surfaces” on the margin. The denudation history of the northeastern Brazilian margin implies a control of pre-, syn- and post-rift tectonic and climatic events on landscape evolution. 相似文献
9.
10.
Knowledge of the thermal history of the onshore Dongpu Sag (DPS), Bohai Bay Basin is important for understanding its tectonic development within a broader regional context and for elucidating its poorly studied source‐rock maturation history. To unravel DPS time‐temperature development, apatite fission‐track data were acquired from eight sandstone samples in three deep wells. Thermal history modelling indicates continuous heating during the rifting stage (early Eocene to late Oligocene), followed by cooling attributed to tectonic uplift between ~27 and ~16 Ma, which resulted in the removal of ~1,400 to 1,800 m of section. Reheating occurred during the subsidence stage from middle Miocene until present. Unlike typical passive continental margin basins, the DPS experienced accelerated post‐rifting subsidence from ~5.8 Ma, which was especially marked since ~2.6 Ma. This phase was probably triggered by normal fault reactivation, in combination with a variation in the deep heat flow pattern. 相似文献
11.
The Polopos E–W- to ESE–WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE–SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene. 相似文献
12.
Low‐temperature thermochronology (LTT) is commonly used to investigate onshore records of continental rifting and geomorphic evolution of passive continental margins. The SE Australian passive margin, like many others, has an elevated plateau separated from the coastal plain by an erosional escarpment, presumed to originate through Cretaceous rifting prior to Tasman Sea seafloor spreading. Previous LTT studies have focused on reconciling thermal histories with development of the present‐day topography. New apatite LTT data along an escarpment‐to‐coast transect define a classic “boomerang” (mean track length vs. fission‐track age), indicating variable overprinting of late‐Palaeozoic cooling ages by a younger, mid‐Cretaceous cooling event. Regionally, however, the boomerang trend diverges NNW away from the coast and crosses the escarpment, implying the underlying thermal history pre‐dates escarpment formation and is largely independent from post‐breakup landscape evolution. We suggest that Cretaceous cooling might relate to erosion of Permo‐Triassic sedimentary cover from a formerly more extensive Sydney Basin. 相似文献
13.
This study presents the first suite of apatite fission‐track (AFT) ages from the SE part of the Western Sudetes. AFT cooling ages from the Orlica‐?nie?nik Dome and the Upper Nysa K?odzka Graben range from Late Cretaceous (84 Ma) to Early Palaeocene–Middle Eocene (64–45 Ma). The first stage of basin evolution (~100–90 Ma) was marked by the formation of a local extensional depocentre and disruption of the Mesozoic planation surface. Subsequent far‐field convergence of European microplates resulted in Coniacian–Santonian (~89–83 Ma) thrust faulting. AFT data from both metamorphic basement and Mesozoic sedimentary cover indicate homogenous Late Cretaceous burial of the entire Western Sudetes. Thermal history modeling suggests that the onset of cooling could be constrained between 89 and 63 Ma with a climax during the Palaeocene–Middle Eocene basin inversion phase. 相似文献
14.
Arne P. Willner Stuart N. Thomson Johannes Glodny Hans‐Joachim Massonne Rolf L. Romer Cees R. van Staal Alexandre Zagorevski 《地学学报》2019,31(1):1-10
Following Appalachian orogenesis, metamorphic rocks in central Newfoundland were exhumed and reburied under Tournaisian strata. New zircon fission‐track (ZFT) ages of metamorphic rocks below the Tournaisian unconformity yield post‐depositionally reset ages of 212–235 Ma indicating regional fluid‐absent reheating to at least ≥220°C. Post‐Tournaisian sedimentary thicknesses in surrounding basins show that burial alone cannot explain such temperatures, thus requiring that palaeo‐geothermal gradients increased to ≥30–40°C/km before final late Triassic accelerated cooling. We attribute these elevated palaeo‐geothermal gradients to localized thermal blanketing by insulating sediments overlying radiogenic high‐heat‐producing granitoids. Late Triassic rifting and magmatism before break up of Pangaea likely also contributed to elevated heat flow, as well as uplift, triggering late Triassic accelerated cooling and exhumation. Thermochronological ages of 240–200 Ma are seen throughout Atlantic Canada, and record rifting and basaltic magmatism on the conjugate margins of the Central Atlantic Ocean preceding the onset of oceanic spreading at ~190 Ma. 相似文献
15.
Climate evolution associated with the uplift in Gyirong, southern margin of the Tibetan plateau, was investigated based on
the clay mineralogy of the Gyirong sediments, using X-ray diffraction and scanning electron microscopy methods. The (chlorite + illite)/(kaolinite + smectite)
ratio and the illite crystallinity index suggest the trend of paleoclimate evolution in Gyirong basin during ~7–1.7 Ma BP,
with a warm and humid climate in ~7.0–5.8 Ma, a relative cool and dry climate in ~5.8–5.5 Ma, a relative warm and humid climate
in ~5.5–2.5 Ma, and a much warmer climate in ~2.5–1.7 Ma, respectively. The fluctuating kaolinite/smectite index and calcite
content and the frequent occurrence of gypsum in the episode of ~6.7–5.5 Ma suggest intense climatic fluctuations between
humid and more seasonal humid conditions. Five peaks exhibit at 5.8, 4.9, 4.3, 3.6, and 2.5 Ma in the curves of illite and
chlorite content and illite crystallinity. The intense uplift and tectonic-forced cooling at ~5.8 and 4.3 Ma were indicated
by the high-illite crystallinity index and illite and chlorite content. A remarkable increase in illite and chlorite content
associated with only little increase in illite crystallinity at ~3.6 Ma indicates a rapid uplift, but no significant climate
change. And a sharp increase in illite crystallinity, while small change in illite and chlorite content at ~2.5 Ma suggests
that no remarkable relief was produced by the uplift, which may take place in the whole south Tibet plateau, while cooling
at 4.9 Ma is probably a record of the global climate cooling. 相似文献
16.
We report SHRIMP U–Th–Pb monazite, conventional U–Pb titanite, Sm–Nd garnet and Rb–Sr muscovite and biotite ages for metamorphic rocks from the Danba Domal Metamorphic Terrane in the eastern Songpan‐Garzê Orogenic Belt (eastern Tibet Plateau). These ages are used to determine the timing of polyphase metamorphic events and the subsequent cooling history. The oldest U–Th–Pb monazite and Sm–Nd garnet ages constrain an early Barrovian metamorphism (M1) in the interval c. 204–190 Ma, coincident with extensive Indosinian granitic magmatism throughout the Songpan‐Garzê Orogenic Belt. A second, higher‐grade sillimanite‐grade metamorphic event (M2), recorded only in the northern part of the Danba terrane, was dated at c. 168–158 Ma by a combination of U–Th–Pb monazite and titanite and Sm–Nd garnet ages. It is suggested that M1 was a thermal event that affected the entire orogenic belt while M2 may represent a local thermal perturbation. Rb–Sr muscovite ages range from c. 138–100 Ma, whereas Rb–Sr biotite ages cluster at c. 34–24 Ma. These ages document regional cooling at rates of c. 2–3 °C Myr?1 following the M1 peak for most of the terrane. However, those parts of the terrane affected by the higher‐temperature M2 event (e.g. the migmatite zone) experienced initially more rapid (c. 8 °C Myr?1) cooling after peak M2 before joining the regional slow cooling path defined by the rest of the terrane at c. 138 Ma. Regional slow cooling between c. 138 and c. 30 Ma is thought to be the result of post‐tectonic isostatic uplift after extensive crustal thickening caused by collision of the South and North China Blocks. The clustering of biotite Rb–Sr ages marks the onset of rapid uplift across the entire terrane commencing at c. 30–20 Ma. This cooling history is shared with many other regions of the Tibet Plateau, suggesting that uplift of the Tibet Plateau (including the Songpan‐Garzê Orogenic Belt) occurred predominantly in the last c. 30 Myr as a response to the continuing northwards collision of India with Eurasia. 相似文献
17.
Guillermo Booth-Rea José Miguel Azañón Bruno Goffé Olivier Vidal José Miguel Martı́nez-Martı́nez 《Comptes Rendus Geoscience》2002,334(11):857-865
We present the first occurrences of high-pressure, low-temperature ferro-magnesiocarpholite-bearing mineral assemblages associated to quartz segregations in the Alpujarride units of southeastern Betics (Sierra de Almagro, Sierra de los Pinos and Sierra Cabrera). Thermobarometric results show that the carpholite-bearing rocks underwent the same P–T conditions in the three outcrops, i.e. 8–10 kbar, 350–400 °C. Metamorphic and structural data allow us to conclude that these rocks belong to the same Alpujarride unit. In the Sierra de Almagro, tectonic units with carpholite-bearing rocks overlie low-pressure, low-temperature Alpujarride units, then forming a stack with an inverted tectono-metamorphic sequence, as observed in the central and western part of the Alpujarride complex. The preservation of carpholite-bearing assemblages in these rocks implies that no significant temperature increase occurred during the exhumation history. To cite this article: G. Booth-Rea et al., C. R. Geoscience 334 (2002) 857–865. 相似文献
18.
《Chemie der Erde / Geochemistry》2016,76(3):391-404
The quartz veins and pegmatites of the Sierra de Comechingones (Sierras de Córdoba, NE Argentina) belong to the Comechingones Pegmatite field (CPF). For the quartz veins and the zoned pegmatites related parental granites are missing. The country rock of the quartz veins are mylonitic augengneisses in granulite to upper amphibolite facies. Field relations, microscopy, cathodoluminescence, radiometric age data, fluid inclusion, chemical and isotopic composition and literature define the quartz veins as synorogenic formed during the high-temperature phase of the Famatinian (480–460 Ma) event. During the Famatinian up to the Achalian (382–366 Ma) event the synorogenic quartz veins were subjected to high temperature ductile deformation documented by folding, boudinage and finally brittle shearing. K-Ar ages of illite from the shear zones of about 166 Ma document the final cooling of the Sierras Pampeanas below 100 °C. The long lasting thermal and deformational history of the study area is reflected by very different populations of fluid inclusions in vein quartz with remarkably high contents of thermogenic hydrocarbons in the early-formed fluid inclusions. LA–ICP–MS analysis reveals very low lattice-bound trace element contents, i.e. high purity quartz. 相似文献
19.
龙门山前陆盆地晚三叠世沉积通量与造山带的隆升和剥蚀 总被引：2，自引：0，他引：2
根据钻井资料、地层剖面资料,利用Surfer8.0软件编制出晚三叠世前陆盆地各组段的残留地层等厚图,得出各组段残留地层的沉积总量,并计算出各阶段沉积通量:21.4 t/(m2·Ma)、184.2 t/(m2·Ma)、278.0 t/(m2·Ma)、147.6 t/(m2·Ma)、703.5 t/(m2·Ma)、272.0 t/(m2·Ma)。然后,利用物质平衡法将沉积物回剥至龙门山造山带并进行脱压校正,计算出晚三叠世龙门山造山带剥蚀总厚度为2 514 m,各阶段造山带剥蚀速率分别为:0.009 mm/a、0.114 mm/a、0.133 mm/a、0.094 mm/a、0.423 mm/a和0.133 mm/a。最终,重塑了龙门山造山带晚三叠世的隆升历史:在距今228.0~199.6 Ma的时间内龙门山造山带地壳隆升了约4.3~4.6 km,地表隆升了1.8~2.1 km;并且隆升过程具有明显的阶段性,可划分为初始隆升(228.0~216.5 Ma)、加速隆升(216.5~211.0 Ma)、缓慢隆升(211.0~203.6 Ma)、急剧隆升(203.6~202.7 Ma)和缓慢隆升(202.7~199.6 Ma)五个阶段。 相似文献
20.
The Cretaceous and Cenozoic fill of the continental margins of southern Africa (South‐East Atlantic and Agulhas Margins) contains a continuous record of sediment supplied from the South African Plateau (SAP) for the past 134 million years. Estimates of solid sediment volumes deposited offshore were calculated from isopach maps and extrapolated vertical cross‐sections derived from a large amount of industrial geophysical data. Solid phase volumes and accumulation rates were calculated for six epochs: Lower Cretaceous (134–113 Ma), Mid Cretaceous (113–93.5 Ma), Upper Cretaceous (93.5–81 and 81–66 Ma), Palaeogene (66–25 Ma), Neogene (25–0 Ma). Our new compilation demonstrates the existence of two periods of elevated flux. The most important one occurs in the late Cretaceous (93.5–66 Ma) and was synchronous with an acceleration of onshore denudation as shown by thermochronometric data. After a period of extremely low accumulation rate, the second phase of elevated flux started in the Oligocene (~30–25 Ma) until present‐day. From these observations we suggest that the main phase of uplift of the SAP took place during the Upper Cretaceous. Two mechanisms, namely uplift caused by lithospheric delamination or by dynamic topography caused by the continent moving over the African Superplume, are viable explanations for our observations. The more recent and lower amplitude episode of enhanced accumulation rates is likely to correspond to a second period of uplift, potentially associated with the onset of uplift and extension along the East African Rift System. 相似文献