Metamorphism and exhumation of basement gneiss domes in the Quadrilátero Ferrífero:Two stage dome-and-keel evolution?     

Kathryn Cutts  Cristiano Lana  Fernando Alkmim  Federico Farin  Hugo Moreira  Viviane Coelho 《地学前缘(英文版)》2019,10(5):1765-1787

The presence of dome-and-keel provinces in Archean cratons has been connected with the initiation of plate tectonics on Earth as these features are most commonly observed in Archean rocks.The Quadrilátero Ferrífero in Brazil has been identified as a Paleoproterozoic dome-and-keel province for more than three decades.The prevailing model suggests that it formed during the Rhyacian Transamazonian orogeny,making it unique among dome-and-keel provinces.However,a lack of appropriate lithologies,datable minerals and the metamorphic overprint of later orogenesis has resulted in a cryptic metamorphic record for the formation of this dome-and-keel province.A clinopyroxene-bearing migmatite from the core of the Ba??o dome has peak P-T conditions of 5-7 kbar and 700-750 ℃ and a published age of ca.2730 Ma based on U-Pb ages of zircon from leucosomes,suggesting that this age represents the migmatisation event.A fine-grained epidote-albite-titanite assemblage overprints the coarse-grained clinopyroxene and amphibole,giving P-7 conditions of 8-9 kbar and 550 ℃ with an associated titanite age of ca.2050 Ma.A garnet-bearing amphibolite sample also from the core of the dome has peak P-T conditions of 7-8 kbar and 650-700 ℃,and texturally late titanite from this sample produces an age of ca.2060 Ma.Three additional samples were collected from the edges of the dome.A garnet-gedrite bearing felsic schist produces peak P-T conditions of 8-9 kbar and 650-700℃ on a clockwise P-T evolution.This sample has a U-Pb zircon age of ca.2775 Ma,which could date metamorphism or be the age of its volcaniclastic protolith.Texturally unconstrained titanite from the sample gives an age of ca.2040 Ma.A garnet-bearing amphibolite that occurs as a boudin within the felsic schist gives both zircon and titanite ages of ca.2050 Ma and has peak P-T conditions of 5-6 kbar and 650-700 ℃ on a near isobaric P-T path.An amphibolite dike,observed to cross-cut the felsic schist produces a zircon U-Pb age of ca.2760 Ma.Altogether this data suggests that the samples were metamorphosed in the Archean(ca.2775-2730 Ma)and again during the Transamazonian event.The most plausible explanation for this data is that dome-and-keel formation occurred in the Archean with migmatisation and high-temperature metamorphism occurring at this time.The Paleoproterozoic event is interpreted as a reactivation of the dome-and-keel formation structures,with Paleoproterozoic keels crosscutting Archean keels and producing metamorphic aureoles.The high radiogenic heat production and the presence of dense sedimentary successions in Archean terranes make dome-and-keel provinces a uniquely Archean feature,but they are susceptible to reworking,resulting in an enigmatic record of formation.  相似文献   

Zircon U-Pb and Lu-Hf isotope constraints on Archean crustal evolution in Southeastern Guyana Shield     

Joao Marinho Milhomem Neto  Jean-Michel Lafon 《地学前缘(英文版)》2019,10(4):1477-1506

The southeastern Guyana Shield,northeast Amazonian Craton,in the north of Brazil,is part of a widespread orogenic belt developed during the Transamazonian orogenic cycle(2.26-1.95 Ga)that includes a large Archean continental landmass strongly reworked during the Transamazonian orogeny,named Amapa Block.It consists mainly of a high-grade metamorphic granulitic-migmatitic-gneiss complex,of Meso-to Neoarchean age and Rhyacian granitoids and supracrustal sequences.For the first time,coupled U-Pb and Lu-Hf isotope data were obtained on zircon by LA-ICP-MS from five tectono-stratigraphic units of the Archean basement and one Paleoproterozoic intrusive rock,in order to investigate the main episodes of crustal growth and reworking.Whole-rock Sm-Nd isotope data were compared to the zircon Lu-Hf data.Three main magmatic episodes were defined by U-Pb zircon dating,two in the Mesoarchean(~3.19 Ga and 2.85 Ga)and one in the Neoarchean(~2.69-2.65 Ga).SubchondriticεHf(t)values obtained for almost all investigated units indicate that crustal reworking processes were predominant during the formation of rocks that today make up the Amapa Block.Hf-TDMC model ages,ranging from2.99 Ga to 3.97 Ga,indicate that at least two important periods of mantle extraction and continental crust formation occurred during the Archean in southeastern Guyana Shield,an older one in the Eoarchean(~4.0 Ga)and a younger one in the Mesoarchean(~3.0-3.1 Ga).The latter is recognized as an important period of crustal accretion worldwide.The recognition of an Eoarchean episode to the southeastern most part of the Guyana Shield is unprecedented and was not recorded by whole-rock Sm-Nd data,which were restricted to the Meso-Paleoarchean(2.83 Ga to 3.51 Ga).This finding reveals t hat continental crust generation in the Amazonian Craton began at least 500 Ma earlier than previously suggested by the SmNd systematics.  相似文献   

A new cache of Eoarchaean detrital zircons from the Singhbhum craton,eastern India and constraints on early Earth geodynamics     

Bulusu Sreenivas  Sukanta Dey  Y.J.Bhaskar Rao  T.Vijaya Kumar  E.V.S.S.K.Babu  Ian S.Williams 《地学前缘(英文版)》2019,10(4):1359-1370

The dominant geodynamic processes that underpin the formation and evolution of Earth’s early crust remain enigmatic calling for new information from less studied ancient cratonic nuclei.Here,we present U-Pb ages and Hf isotopic compositions of detrital zircon grains from^2.9 Ga old quartzites and magmatic zircon from a 3.505 Ga old dacite from the Iron Ore Group of the Singhbhum craton,eastern India.The detrital zircon grains range in age between 3.95 Ga and 2.91 Ga.Together with the recently reported Hadean,Eoarchean xenocrystic(up to 4.24 Ga)and modem detritus zircon grains from the Singhbhum craton,our results suggest that the Eoarchean detrital zircons represent crust generated by recycling of Hadean felsic crust formed at^4.3-4.2 Ga and^3.95 Ga.We observe a prominent shift in Hf isotope compositions at^3.6-3.5 Ga towards super-chondritic values,which signify an increased role for depleted mantle and the relevance of plate tectonics.The Paleo-,Mesoarchean zircon Hf isotopic record in the craton indicates crust generation involving the role of both depleted and enriched mantle sources.We infer a short-lived suprasubduction setting around^3.6-3.5 Ga followed by mantle plume activity during the Paleo-,Mesoarchean crust formation in the Singhbhum craton.The Singhbhum craton provides an additional repository for Earth’s oldest materials.  相似文献   

Petrology,geochemistry, and zircon U-Pb geochronology of the Zambezi Belt in Zimbabwe: Implications for terrane assembly in southern Africa     

Yusuke Kuribara  Toshiaki Tsunogae  Yusuke Takamura  Yukiyasu Tsutsumi 《地学前缘(英文版)》2019,10(6):2021-2044

The Zambezi Belt in southern Africa has been regarded as a part of the 570-530 Ma Kuunga Orogen formed by a series of collision of Archean cratons and Proterozoic orogenic belts.Here,we report new petrological,geochemical,and zircon U-Pb geochronological data of various metamorphic rocks(felsic to mafic orthogneiss,pelitic schist,and felsic paragneiss) from the Zambezi Belt in northeastern Zimbabwe,and evaluate the timing and P-T conditions of the collisional event as well as protolith formation.Geochemical data of felsic orthogneiss indicate within-plate granite signature,whereas those of mafic orthogneiss suggest MORB,ocean-island,or within-plate affinities.Metamorphic P-Testimates for orthogneisses indicate significant P-T variation within the study area(700-780 C/6.7-7.2 kbar to 800-875 C/10-11 kbar) suggesting that the Zambezi Belt might correspond to a suture zone with several discrete crustal blocks.Zircon cores from felsic orthogneisses yielded two magmatic ages:2655±21 Ma and 813士5 Ma,which suggests Neoarchean and Early Neoproterozoic crustal growth related to within-plate magmatism.Detrital zircons from metasediments display various ages from Neoarchean to Neoproterozoic(ca.2700-750 Ma).The Neoarchean(ca.2700-2630 Ma) and Paleoproterozoic(ca.2200-1700 Ma) zircons could have been derived from the adjacent Kalahari Craton and the Magondi Belt in Zimbabwe,respectively.The Choma-Kalomo Block and the Lufilian Belt in Zambia might be proximal sources of the Meso-to Neoproterozoic(ca.1500-950 Ma) and early Neoproterozoic(ca.900-750 Ma) detrital zircons,respectively.Such detrital zircons from adjacent terranes possibly deposited during late Neoproterozoic(744-670 Ma),and subsequently underwent highgrade metamorphism at 557-555 Ma possibly related to the collision of the Congo and Kalahari Cratons during the latest Neoproterozoic to Cambrian.In contrast,670-627 Ma metamorphic ages obtained from metasediments are slightly older than previous reports,but consistent with~680-650 Ma metamorphic ages reported from different parts of the Kuunga Orogen,suggesting Cryogenian thermal events before the final collision.  相似文献   

山西云岗石窟侏罗系地震液化砂岩柱的发现及其大地构造意义   总被引：1，自引：0，他引：1  

苏德辰  杨战兵  孙爱萍  乔秀夫 《地质学报》2019,93(8):1814-1830

本文主要报道在华北克拉通北缘云岗石窟景区内侏罗系地层中发现的20余个由地震液化形成的砂岩柱。地震导致的砂土液化是非常普遍的自然现象,地震波的震动使埋藏在地下未固结的饱和砂质沉积物迅速变为流体并在巨大压力下喷涌至地表,形成砂火山或泥火山。2008年汶川8. 0级大地震和2012年新西兰6. 2级地震都产生了严重的液化现象,在对地表造成严重破坏的同时,分别在地表形成了一系列的溢出丘和形态完好的砂火山。古地震之后,液化砂质沉积物往往在上涌的通道内固结成岩,形成穿层的岩柱或岩管。近年来,美国科罗拉多大峡谷相继发现很多地震液化形成的中生代巨型碎屑岩柱。2018年,本文作者在云岗石窟景区内的侏罗系云岗组中发现了20多条直径15~20cm左右、高可达2m以上穿层“侵入”的砂岩柱,有的在纵向上呈串珠状排列,有的呈不规则的树枝状自下向上伸展,膨大狭缩、分支复合现象非常明显,砂岩柱内部结构均一,不见任何层理。砂岩柱顶端的泥质围岩石中有明显向上牵引、拖拽的痕迹。这些砂岩柱没有任何硅化木的特征,也不是普通成岩作用形成的结核,与暴雨、泥石流、重力滑塌等作用均无任何关系,是古地震液化作用在地层内保存的遗迹,故称为液化砂岩柱。地震液化砂岩柱发育的层位位于李振宏等人(2014)在宁武—静乐盆地侏罗系云岗组顶部的凝灰质泥晶碳酸盐层位(160 Ma)之下约40m处,初步判定形成这些液化砂岩柱的古地震发生于160. 75 Ma~160 Ma之间的晚侏罗世。古地震的形成过程与燕山运动引起的地壳运动有直接的关联,是华北克拉通内与燕山运动伴生的古地震在地层中留下的最直接证据。  相似文献   

Large geographic and temporal extensions of the Río de la Plata Craton,South America,and its metacratonic eastern margin   总被引：1，自引：0，他引：1  

João O.S. Santos  Carlos J. Chernicoff  Eduardo O. Zappettini  Neal J. McNaughton  Léo A. Hartmann 《International Geology Review》2019,61(1):56-85

Integration of existing isotopic and geological data allows a reconsideration of the distribution and age of the Río de la Plata Craton within South America. The reinterpretation increases the area of the craton to about 2,400,000 km² with implications for the tectonic map of South America and for global reconstruction of palaeocontinents. Four areas previously considered as separate cratons (Luís Alves, Curitiba, Tebicuary, and Paranapanema) are interpreted as part of the same Río de la Plata Craton. The craton is organized into six provinces and domains: Buenos Aires–Piedra Alta, Taquarembó, Tebicuary, Luís Alves, Encantadas, and Nico Pérez. The term ‘Transplatense’ is proposed to replace ‘Trans-Amazonian’ for Rhyacian events that occurred within the Río de la Plata Craton. The craton is formed not only by dominant Rhyacian rocks and local Archaean rocks, but also by Statherian and Mesoproterozoic rocks. The domains are all partially to totally covered by Phanerozoic basins (Paraná, Chacoparanense, Claromecó, Salado, Balcarce, and Colorado) which makes their investigation difficult. The Ediacaran–Cambrian collisions of the Brasilian orogen generated tectonic mixtures of orogenic and cratonic zones. This is more evident in the eastern margin of the craton, which behaved as a metacraton.  相似文献   

Archean-Paleoproterozoic Lithospheric Mantle at the Northern Margin of the North China Craton Represented by Tectonically Exhumed Peridotites     

TIAN Wei  WANG Shuangyue  LIU Fenglin  CHU Zhuyin  WANG Bin  CHEN Mimi  Jennifer PRICHARD 《《地质学报》英文版》2017,91(6):2041-2057

Tectonically emplaced peridotites from North Hebei Province, North China Craton, have retained an original harzburgite mineral assemblage of olivine(54%–58%) + orthopyroxene(40%–46%)+minor clinopyroxene(1%)+spinel. Samples with boninite-like chemical compositions also coexist with these peridotites. The spinels within the peridotites have high-Al end-members with Al_2O_3 content of 30 wt % –50 wt %, typical of mantle spinels. When compared with experimentally determined melt extraction trajectories, the harzburgites display a high degree of melting and enrichment of SiO_2, which is typical of cratonic mantle peridotites. The peridotites display variably enriched light rare earth elements(REEs), relatively depleted middle REEs and weakly fractionated heavy REEs, which suggest a melt extraction of over 25% in the spinel stability field. The occurrence of arc-and SSZ-type chromian spinels in the peridotites suggests that melt extraction and metasomatism occurred mostly in a subduction-related setting. This is also supported by the geochemical data of the coexisting boninite-like samples. The peridotites have ~(187)Os/~(188)Os ratios ranging from 0.113–0.122, which is typical of cratonic lithospheric mantle. These ~(187)Os/~(188)Os ratios yield model melt extraction ages(TRD) ranging from 981 Ma to 2054 Ma, which may represent the minimum estimation of the melt extraction age. The Al_2O_3-~(187)Os/~(188)Os-proxy isochron ages of 2.4 Ga–2.7 Ga suggest a mantle melt depletion age between the Late Achaean and Early Paleoproterozoic. Both the peridotites and boninite-like rocks are therefore interpreted as tectonically exhumed continental lithospheric mantle of the North China Craton, which has experienced mantle melt depletion and subduction-related mantle metasomatism during the Neoarchean-Paleoproterozoic.  相似文献   

Meso—Cenozoic lithospheric thermal structure in the Bohai Bay Basin,eastern North China Craton     

Zongxing Li  Yinhui Zuo  Nansheng Qiu  Jun Gao 《地学前缘(英文版)》2017,8(5):977-987

The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.  相似文献   

Devonian alkaline magmatism in the northern North China Craton: Geochemistry,SHRIMP zircon U-Pb geochronology and Sr-Nd-Hf isotopes     

Dingling Huang  Qingye Hou 《地学前缘(英文版)》2017,8(1):171-181

The Wulanhada pluton is among the rare suite of Devonian alkaline plutons occurring along the northern margin of the North China Craton(NCC).The intrusion is mainly composed of quartz-monzonite.Here we report zircon SHRIMP U-Pb data from this intrusion which shows emplacement age of ca.381.5 Ma.The rock is metaluminous with high(Na_2O + K_2O) values ranging from 8.46 to 9.66 wt.%.The REE patterns of the rocks do not show any Eu anomaly whereas the primitive-mantle-normalized spider diagram shows strong positive Sr and Ba anomalies.The Wulanhada rocks exhibit high initial values of(~(87)Sr/~(86)Sr)_t = 0.70762-0.70809,low ε_(Nd)(t) =-12.76 to-12.15 values and negative values of ε_(Hf)(t) =-23.49 to-17.02 with small variations in(~(176)Hf/~(177)Hf),(0.281873-0.282049).These geochemical features and quantitative isotopic modeling results suggest that the rocks might have been formed through the partial melting of Neoarchean basic rocks in the lower crust of the NCC.The Wulanhada rocks,together with the Devonian alkaline rocks and mafic-ultramafic complex from neighboring regions,constitute a post-collisional magmatic belt along the northern NCC.  相似文献   

Structural patterns of the late Mesozoic crustal detachment system in the Raoyang Sag,Bohai Bay Basin,eastern China: New insights from 3D seismic data     

《Marine and Petroleum Geology》2017

Understanding the late Mesozoic tectonic origin and structural patterns of the Bohai Bay Basin (BBB) is of growing importance for its buried-hill petroleum exploration. This study revealed, based on 3D seismic and borehole data, that the Raoyang Sag in the Jizhong Depression, western BBB, was dominated by a crustal detachment system during the late Jurassic to the early Cretaceous. It was characterized by the WNW-dipping low-angle detachment fault F₀ (namely Cangxi Fault), the structural dome cored by Archean Basement rocks at the footwall and supradetachment basins on the hanging wall. We suggested the late Mesozoic volcanic materials and coarse deposits accumulated in the supradetachment basins had locally diminished the petroleum prospect, but the syndetachment deformation and denudation had contributed to it by means of promoting petroleum migration from source rocks to reservoirs and improving porosity and permeability of the reservoir rocks by karstification and structural fracturing.  相似文献