From fishing to farming: Shellfish aquaculture expansion and the complexities of ocean space on Canada's west coast     

《Applied geography (Sevenoaks, England)》2014

Ocean spaces are social and political, and just as with terrestrial governance, oceans governance is prone to ambiguity, contradiction, and contestation. The validity and dynamics of these claims will be demonstrated through a study of discourse and structured agreements employed to involve coastal First Nations in the expansion of the shellfish aquaculture sector in British Columbia. Analysis focuses on the West Coast of Vancouver Island, a region identified as having good biophysical potential for shellfish aquaculture and much of which is territorial home of the Nuu-chah-nulth First Nations. Through community interviews and document and discourse analysis, the article highlights that: seafood, including shellfish, is intimately connected with Nuu-chah-nulth identity; many Nuu-chah-nulth have long-engaged in subsistence and commercial harvests of wild-growing shellfish; and, there are important prospective differences between longer-standing shellfish harvests and shellfish aquaculture. Findings and discussion offer perspective on the sorts of choices that First Nations might encounter in the pursuit of shellfish aquaculture, as well as raise bigger questions about whether or how Nations might tradeoff territorial authority and collective harvest opportunities against leasing state-sanctioned private marine tenures.  相似文献   

扬子地台西南缘古元古代末的裂解事件——来自武定地区辉绿岩锆石U Pb年龄和地球化学证据   总被引：7，自引：0，他引：7  

郭阳  王生伟  孙晓明  王子正  杨斌  廖震文  周邦国  蒋小芳  侯林  杨波 《地质学报》2014,88(9):1651-1665

云南省武定地区广泛出露元古宙辉绿岩体,本文报道了武定地区海孜辉绿岩的地球化学特征及锆石的LA-ICP-MS U-Pb年龄,结果为1767±15Ma(MSWD=0.19,n=17),表明本区广泛出露的辉绿岩群侵位时代为古元古代晚期。辉绿岩岩石化学表现为低SiO2、MgO以及高TiO2(3.24%~4.02%)、碱(K2O+Na2O)和P2O5含量(0.32%~0.45%),具有偏碱性的拉斑质玄武岩的岩石化学特征。辉绿岩的大离子半径元素如K、Rb、Ba等富集,高场强元素如Ta、Nb和Zr、Hf没有明显的亏损,其地球化学参数也多与夏威夷碱性洋岛玄武岩相近。辉绿岩的微量、稀土元素的配分模式与典型的OIB和峨眉山高Ti玄武岩具有高度一致性。海孜辉绿岩原始岩浆形成于相对较富集的过渡型地幔的部分熔融,其源区为尖晶石橄榄岩相,演化过程中,有少量下地壳物质的加入。海孜辉绿岩与扬子地台西南缘广泛出露古元古代晚期的岩浆岩一致,形成于全球性Columbia超级大陆裂解的大地构造背景。海孜辉绿岩OIB的地球化学属性,为古元古代晚期全球性Columbia超级大陆裂解的地幔柱活动提供了最重要的地球化学证据。  相似文献   

Petrogenesis of the crater-facies Tokapal kimberlite pipe,Indrvati Basin,Central India     

N.V. Chalapathi Rao  B. Lehmann  B.K. Panwar  Alok Kumar  D. Mainkar 《地学前缘(英文版)》2014,5(6)

New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic Indr avati Basin are presented.The kimberlite has been subjected to extensive and pervasive low-temperature alteration.Spinel is the only primary phase identifiable,while olivine macrocrysts and juvenile lapilli are largely pseudomorphed(talc-serpentinecarbonate alteration).However,with the exception of the alkalies,major element oxides display systematic fractionation trends; likewise,HFSE patterns are well correlated and allow petrogenetic interpretation.Various crustal contamination indices such as(SiO2+Al2O3+Na2O)/(MgO+ K2O) and Si/Mg are close to those of uncontaminated kimberlites.Similar La/Yb(79-109) of the Tokapal samples with those from the kimberlites of Wajrakarur(73-145) and Narayanpet(72-156),Eastern Dharwar craton,southern India implies a similarity in their genesis.In the discriminant plots involving HFSE the Tokapal samples display strong affinities to Group II kimberlites from southern Africa and central India as well as to ‘transitional kimberlites' from the Eastern Dharwar craton,southern India,and those from the Prieska and Kuruman provinces of southern Africa.There is a striking similarity in the depleted-mantle(TDM) Nd model ages of the Tokapal kimberlite system,Bastar craton,the kimberlites from NKF and WKF,Eastern Dharwar craton,and the Majhgawan diatreme,Bundelkhand craton,with the emplacement age of some of the lamproites from within and around the Palaeo-Mesoproterozoic Cuddapah basin,southern India.These similar ages imply a major tectonomagmatic event,possibly related to the breakup of the supercontinent of Columbia,at 1.3-1.5 Ga across the three cratons.The ‘transitional'geochemical features displayed by many of the Mesoproterozoic potassic-ultrapotassic rocks,across these Indian cratons are inferred to be memories of the metasomatising fluids/melts imprinted on their source regions during this widespread event.  相似文献   

Petrogenesis of the crater-facies Tokapal kimberlite pipe,Indravati Basin,Central India     

N.V. Chalapathi Rao  ;B. Lehmann  ;B.K. Panwar  ;Alok Kumar  ;D. Mainkar 《地学前缘(英文版)》2014,5(6):781-790

New geochemical data of the crater-facies Tokapal kimberlite system sandwiched between the lower and upper stratigraphic horizons of the Mesoproterozoic lndravati Basin a：：e presented. The kimberlite has been subjected to extensive and pervasive low-temperature alteration. Spinel is the only primary phase identifiable, while olivine macrocrysts and juvenile lapilli are largely pseudomorphed （talc-serpentine- carbonate alteration）. However, with the exception of the alkalies, major element oxides display systematic fractionation trends; likewise, HFSE patterns are well correlated and allow petrogenetic interpretation. Various crustal contamination indices such as （SiO2 ＋ AI：：O3 ~ Na20）]（MgO ~ K20） and Si] Mg are close to those of uncontaminated kimberlites. Similar La]Yb （＇79-109） of the Tokapal samples with those from the kimberlites of Wajrakarur （73-145） and Narayanpet （72-156）, Eastern Dharwar craton, southern India implies a similarity in their genesis. In the discriminant plots involving HFSE the Tokapal samples display strong affinities to Group 1I kimberlites from southern Africa and central India as well as to ＇transitional kimberlites＇ from the Eastern Dharwar craton, southern India, and those from the Prieska and Kuruman provinces of southern Africa. There is a striking ~;imilarity in the depleted-mantle （TOM） Nd model ages of the Tokapal kimberlite system, Bastar craton, th~ kimberlites from NKF and WKE Eastern Dharwar craton, and the Majhgawan diatreme, Bundelkhand craton, with the emplacement age of some of the lamproites from within and around the Palaeo~Mesoproterozoic Cuddapah basin, southern India. These similar ages imply a major tectonomagmatic event, possibly related to the break- up of the supercontinent of Columbia, at 1.3-1.5 Ga across the l：hree cratons. The ＇transitional＇ geochemical features displayed by many of the Mesoproterozoic po~：assic-ultrapotassic rocks, across these Indian cratons are inferred to be memories of the metasomatisi  相似文献   

Geochemistry of black shales from the Mesoproterozoic Srisailam Formation,Cuddapah basin,India: Implications for provenance,palaeoweathering, tectonics,and timing of Columbia breakup     

《Chemie der Erde / Geochemistry》2017,77(4):596-613

The Mesoproterozoic Srisailam Formation, exposed along the northern part of the Cuddapah basin, India, comprises mainly medium- to fine-grained siliciclastics, and is devoid of any carbonate sediment. Preliminary sedimentological studies helped in recognizing fifteen distinct facies (five facies associations) in Chitrial outlier of the Srisailam Formation deposited in continental half-graben basin(s). Black shales (sensu lato) are minor components of the Srisailam Formation, and inferred to have deposited in deep lacustrine and prodelta facies of the half-graben(s). The black shales show restricted thickness (up to 29.0 m), and are characterized by overall high ‘black shale' to ‘total shale' ratio (>0.51). Their geochemical characteristics were studied to constrain provenance, palaeoclimate, and tectonic setting of deposition of the Srisailam Formation. Further, an attempt has been made to use the Srisailam black shales as proxy for constraining the timing of breakup of the supercontinent Columbia.The Srisailam black shales are geochemically quite distinct. At similar SiO₂ contents they are considerably different from PAAS. They are characterized by considerably lower ΣREE (Av. 136.0 ± 50.4 ppm) but a more conspicuous negative Eu-anomaly (Av. 0.34 ± 0.09) than PAAS. Al₂O₃/TiO₂ and TiO₂/Zr ratios coupled with Eu/Eu*, Gd_CN/Yb_CN, La/Sc, Th/Sc, and Th/Cr ratios suggest their derivation from granite and granodiorite. The CIA values (65–90, Av. 72 ± 9) as a whole indicate moderate chemical weathering under semiarid climate. Discriminating geochemical parameters indicate passive margin depositional setting. The combined sedimentological and geochemical characteristics reveal deposition of the Srisailam sediments in continental rift basin(s).Thick succession of black shales (with high CIA values) that deposited with shelf carbonates proxy for mantle superplume and supercontinent breakup events. The sedimentological characteristics and geochemical data of the Srisailam black shales plausibly exclude any large-scale breakup of Columbia during the interval (1400–1327 Ma) of deposition of the Srisailam Formation.  相似文献   

Volcanological and environmental controls on the Snowdon mineralization,North Wales,UK: A failed volcanogenic massive sulfide system in the Avalon Zone of the British Caledonides     

《Ore Geology Reviews》2017

The Snowdon caldera of North Wales is host to base metal sulfide-bearing veins and stockworks, mineralized breccias, disseminated sulfides, and localized zones of semi-massive to massive sulfide, with subordinate magnetite-rich veins. The late Ordovician host volcanic sequence accumulated in a shallow marine, back-arc environment in the Welsh Basin, which forms part of the Avalon Zone of the British and Irish Caledonides. New field evidence, sulfur isotopes, and U-Pb dating indicate that the Snowdon mineralization is genetically and temporally related to Late Ordovician magmatism and caldera formation. It is interpreted to represent volcanogenic pipe-style sulfide mineralization, resulting from focused hydrothermal fluids moving along caldera-related faults and simultaneous dispersal of fluids through the volcaniclastic pile. Sulfur isotope data suggest that, whilst a limited contribution of magmatic S cannot be ruled out, thermochemical reduction of contemporaneous Ordovician seawater sulfate was the dominant mechanism for sulfide production in the Snowdon system, resulting in a mean value of about 12‰ in both the host volcanic strata and the mineralized veins. Despite the tectonic setting being prospective for VMS deposits, strata-bound sulfide accumulations are absent in the caldera. This is attributed to the shallow water depths, which promoted boiling and the formation of sub-seafloor vein-type mineralization. Furthermore, the tectonic instability of the caldera and the high energy, shallow marine environment would have limited preservation of any seafloor deposits. The new U-Pb dates for the base (454.26 ± 0.35 Ma) and top (454.42 ± 0.45 Ma) of the host volcanic rocks, indicate that the Snowdon magmatic activity was short lived, which is likely to have limited the duration and areal extent of the ore-forming system. The absence of massive sulfide mineralization is consistent with the general paucity of economic VMS deposits in the Avalon Zone. Despite the highly prospective geological setting this study further illustrates the importance of volcanic facies mapping and associated paleo-environmental interpretations in VMS exploration.  相似文献   

阿尔泰南缘阿舍勒盆地泥盆纪火山岩中古老锆石的U-Pb年龄、Hf同位素和稀土元素特征及其地质意义   总被引：5，自引：3，他引：5  

宋国学  秦克章  刘铁兵  李光明  申萍 《岩石学报》2010,26(10):2946-2958

阿尔泰造山带南缘发育有NW向斜列的四个泥盆纪海相火山岩沉积盆地,位于北西端的阿舍勒盆地产有阿舍勒大型铜锌矿床,前人对该矿床开展了大量研究,但其容矿火山岩的年龄尚未明确厘定。本文应用LA-ICP-MS锆石U-Pb定年和锆石Hf同位素、微量元素,对阿舍勒铜锌矿区内出露的泥盆纪火山岩进行了研究。由锆石U-Pb定年获得了一组火山岩老锆石谐和年龄为1985±8.9Ma,加权年龄为2005±30Ma,代表了阿尔泰地区前寒武纪结晶基底的形成时代,其Th/U值在0.25～0.90之间,εHf(t)为-1.4～8.5,平均值为3.3;另外一组新锆石年龄为408±8Ma,其εHf(t)为9.3,Th/U值为0.49,具有典型岩浆锆石特征,代表了早泥盆世岩浆活动高峰期一次火山活动时代。老锆石∑REE从最低的1015×10-6变化到最高的3486×10-6,表现为轻稀土亏损,重稀土富集特征;本组锆石不同于正常岩浆锆石的显著特征是部分出现Ce元素负异常。锆石U-Pb年龄、Hf同位素及稀土元素Ce负异常特征综合显示,阿尔泰前寒武纪结晶基底可能形成于Columbia超大陆拼合聚集背景下,其物源来自强还原性地幔物质与氧化性地壳物质的不均匀混合。  相似文献   

Alluvial architecture of mid-channel fluvial–tidal barforms: The mesotidal Lower Columbia River,Oregon/Washington,USA     

Eric W. Prokocki  James L. Best  Philip J. Ashworth  Gregory H. Sambrook Smith  Andrew P. Nicholas  Daniel R. Parsons  Christopher J. Simpson 《Sedimentology》2020,67(7):3533-3566

Barforms of mesotidal to macrotidal fluvial–tidal transitions, regardless of fluvial-discharge, are currently thought to display a sedimentary architecture dominated by tidal signatures. Due to the scarcity of observations from modern mesotidal fluvial–tidal transitions, especially those of multi-channelled large-rivers (mean annual discharge ≥7000 m³ s⁻¹ and peak discharges ≥15 000 m³ s⁻¹) with mid-channel bars, this concept remains unproven. The present study analyses data produced by a combination of high-resolution ground penetrating radar and coupled shallow vibracores (<5 m depth), collected from modern fluvial–tidal mid-channel bars of the mesotidal multi-channelled Lower Columbia River, Washington/Oregon, USA, which can experience peak discharges ≥18 000 m³ s⁻¹. These data were used alongside time-sequenced aerial imagery to characterize the spatio-temporal sedimentological evolution of these barforms in singular flows or combined flows consisting of river, tidal and/or wind-wave oscillatory, current components operating in unique fluvial–tidal transition regimes. Results indicate that ca 75% of the Lower Columbia River fluvial–tidal transition produces braid-bars with basal to bar-top sedimentological architectures that are indistinguishable from fluvial-only braid-bars recorded in the literature. Barform stratal characteristics within the fluvial–tidal transitions of mesotidal large-rivers are therefore more likely to be dominated by downstream-oriented currents. Furthermore, a new style of low-angle (<5°) inclined heterolithic stratification found in bar-top accretion-sets within upper-mixed tidal–fluvial regime braid-bars is observed. This common stratification is created by combined-flows characterized by intrabasinal wind-wave oscillatory-currents and bidirectional tidal-currents. This inclined heterolithic stratification marks the initial downstream fluvial–tidal crossover point from Lower Columbia River up-dip fully-fluvial braid-bar architectures, to those possessing bar-top facies produced by the hydraulic-sedimentation response of combined intrabasinal wind-wave and tidal influence. When preserved, this form of mid-channel bar inclined heterolithic stratification provides a unique sedimentological signature of multi-channelled fluvial–tidal transitions that possess an open-water lower basin with intrabasinal wind-waves.  相似文献   

Ca. 1.7 Ga Magmatism on Southwestern Margin of the Yangtze Block: Response to the Breakup of Columbia     

GENG Yuansheng  DU Lilin  KUANG Hongwei  LIU Yongqing 《《地质学报》英文版》2020,94(6):2031-2052

This paper presents some data of the Jiaopingdu gabbro and Caiyuanzi granite at the southwestern margin of the Yangtze Block, on the geochemical compositions, zircon LA–ICP–MS U–Pb ages and Hf isotopic data. The Jiaopingdu gabbro gives the age of 1721 ± 5 Ma, the Caiyuanzi granite 1732 ± 6 Ma and 1735 ± 4 Ma, and the Wenjiacun porphyry granite 1713 ± 4 Ma, suggesting nearly contemporaneous formation time of the gabbro and granite. The bimodal feature is demonstrated by the gabbro SiO2 content of 44.64–46.87 wt% and granite 73.81–77.03 wt%. In addition, the granite has high content of SiO2 and Na2O + K2O, low content of Al2O3 and CaO, enriched in REEs (except Eu) and Zr, Nb, Ga and Y, depleted in Sr, implying it belongs to A-type granite geochemistry and origin of within-plate environment. The zircon εHf(t) of the granite and gabbro is at the range of 2–6, which is near the 2.0 Ga evolution line of the crust, implying the parent magma of the gabbro being derived from the depleted mantle and a small amount of crustal material, and the parent magma of the granite from partial melting of the juvenile crust and some ancient crustal material at the same time. Compared with 1.8–1.7 Ga magmatism during breakup of other cratons in the world, we can deduce that the Columbia has initially broken since ca. 1.8 Ga, and some continental marginal or intra-continental rifts occurred at ca. 1.73 Ga.  相似文献   

内蒙古固阳地区白云常合山A型花岗岩:年代学、地球化学、Hf同位素研究及其对Columbia超大陆裂解的响应   总被引：1，自引：1，他引：0  

康健丽  王惠初  任云伟  肖志斌  相振群  曾乐 《岩石学报》2020,36(8):2431-2446

在对固阳白云常合山花岗岩详细的野外地质调查基础上,对其岩相学、地球化学、锆石U-Pb年代学及Lu-Hf同位素特征进行了综合研究。白云常合山花岗岩的地球化学特征显示其具有高SiO2(70.68%～77.21%)、富碱(7.88%～9.21%)、高Fe2O3T/MgO (12.60～90.38)和10000×Ga/Al (3.63～6.17)值,低Al2O3(11.70%～13.23%)、MgO (0.06%～0.24%)、CaO (0.23%～1.20%)的特征;微量元素富集Rb、Th、K等,亏损Ba、Sr、Eu、Ti、P;稀土元素总量较高,轻稀土富集,重稀土亏损,呈现典型的右倾"海鸥型"分布模式,具有明显的Eu负异常。通过锆石饱和温度的计算,得到白云常合山花岗岩的结晶温度为824～957℃,平均值为903℃,表明其形成于高温环境。这些特征与A型花岗岩相一致。锆石LA-ICP-MS年龄测试结果显示,白云常合山花岗岩形成于～1720Ma;锆石εHf(t)=-1.84～+6.08,以正值为主,单阶段模式年龄和二阶段模式年龄分别为1.9～2.2Ga和2.5～3.2Ga,岩浆源区主要是新太古代新生地壳,在上升过程中可能受到古老地壳物质的混染。构造环境判别图解显示其为A1型花岗岩,且有板内岩浆的特点,因此白云常合山花岗岩应该是大陆裂谷岩浆活动的产物。结合区域上与裂解事件有关地质体的同位素年代学资料,认为白云常合山花岗岩应该是固阳地区年龄可靠的最早响应哥伦比亚超大陆裂解的岩体。  相似文献