马达加斯加Antanisoa石墨矿床成因分析

马达加斯加是世界优质大鳞片石墨矿重要产地之一,随着大鳞片石墨在诸多新兴领域发挥着越来越大的作用,对马达加斯加石墨矿床的研究显得越来越重要。矿床成因研究对石墨矿床的找矿勘查具有指导作用,然而目前关于马达加斯加石墨矿床的研究程度较低,人们普遍认为马达加斯加的石墨矿床是沉积变质成因。文章将Antanisoa石墨矿床作为研究对象,通过对矿区内石墨片岩的岩相学研究以及矿物化学特征研究,发现沉积变质成因的说法并不妥当。野外地质调查和岩相学研究显示出较多与流体充填有关的现象,矿物化学特征表明石墨片岩中与石墨共生的云母为金云母,浅色电气石为镁电气石。结合前人对马达加斯加岛地质背景研究结果与认识,认为马达加斯加Antanisoa石墨矿床更有可能与幔源流体充填有关,有待进一步研究。     

Toward institutions for community-based management of inshore marine resources in the Western Indian Ocean

This paper examines the frameworks being developed to co-manage coral reefs in Kenya and Madagascar. The historical and social context, flexibility of rule-making, monitoring and enforcement, and how community-based organizations are nested within other organizations is described. A comparison of the degree to which these two frameworks contain 10 key design principles thought to be important for successful commons institutions is presented. Finally, recommendations are made for improving co-management in these countries. A principal finding is that both co-management frameworks were developed for other systems (terrestrial and lakes), which creates misfits for how marine systems can be managed.     

钒钛磁铁矿床的透岩浆流体成矿模型——来自马达加斯加扎卡岩体的证据

目前,国内外学术界对赋存于镁铁-超镁铁杂岩体中的钒钛磁铁矿床的成因存在多种不同的解释,在一定程度上对这类矿床的资源勘查造成了困惑。因此,阐明镁铁-超镁铁侵入体中成矿物质大规模聚集的机理依然是矿床学界和勘查学界面临的重要科学前缘问题。马达加斯加中北部Alaotra湖地区的扎卡岩体是一个赋存有超大型钒钛磁铁矿床的典型镁铁质层状侵入体,已探明铁矿石远景资源量8亿t(含333),伴生钛6000万t,伴生钒230万t,为阐明钒钛磁铁矿床的成因提供了良好的条件。本文报道了扎卡岩体的地质学、矿体地质学、岩相学、矿相学和岩石地球化学特征,主要得出以下认识:(1)扎卡岩体发育韵律性火成层理,为一个典型的镁铁质层状岩体,但伟晶岩可构成独立的侵入单元;(2)矿体主要赋存在层状岩体中,可划分为整合型、不整合型和伟晶岩型等3种不同的类型;(3)辉长岩具有橄榄石→斜长石→单斜辉石或橄榄石→斜长石+单斜辉石的结晶顺序,暗示扎卡岩体为一浅成层状岩体,岩浆侵位深度约3 km;(4)矿石矿物与硅酸盐矿物呈热力学不平衡关系,且与含水暗色矿物平衡共生,暗示成矿作用发生在岩浆演化晚期的富含挥发分环境;(5)致密块状铁矿石的REE四分组效应也表明成矿过程伴随着富F、Cl等组分的流体活动。据此,本文提出扎卡岩体中钒钛磁铁矿床的形成与透岩浆流体过程有关。     

马达加斯加蓝色蓝宝石的颜色特征

为了了解马达加斯加蓝色蓝宝石的颜色特征,采用GemDialogue颜色系统对其进行了描述与分级。对比世界上主要产地（澳大利亚、斯里兰卡、柬埔塞、缅甸）蓝宝石的颜色特征发现,马达加斯加蓝色蓝宝石样品的黑色罩过高,使得其最终的颜色等级大多在1～4范围内,属于“商业级”。为了进一步确定马达加斯加蓝色蓝宝石样品的颜色特征及其与全Fe,Ti质量分数的关系,采用紫外一可见光分光光度计和电子探针测试了样品。结果显示,随着全Fe与Ti质量分数的增加,样品的蓝色加深;当蓝宝石样品中全Fe的质量分数为0．02％～0．75％、Ti的质量分数为0．006%～O．040％且其全Fe与Ti质量分数比值为10～30时,蓝宝石样品的颜色为纯正蓝色;当超出此范围时,蓝宝石样品通常含有绿色或紫色色调。     

Structural reworking and heat transfer related to the late-Panafrican Angavo shear zone of Madagascar

The basement of central Madagascar displays two contrasted structural patterns. The first one (D1) is characterized by north-striking foliations that are gently dipping to the west and carry W- to WSW-plunging lineations, whereas the second one (D2) is characterized by steeper foliations that are striking to the NNE and lineations that are either subhorizontal or gently plunging to the SSW. The younger pattern is related to late-Panafrican tectonics along the major Angavo shear zone that is about 1000 km in length and 40 km in width with apparently little offset. Deformation in the Angavo zone induced interference folding on both sides. The D2 event is characterized by low pressures (ca 400 MPa) and high temperatures (up to 790 °C) responsible for prograde granulite facies conditions, that resulted from heat transfer due to magma and fluid advection in the Angavo shear zone. The D2 event is pinned at 550 ± 11 Ma by a new monazite age from a reoriented Andringitrean granite near Ankaramena. A new suite of amphibole and biotite Ar–Ar geochronological data enables to retrace the thermochronogical evolution inside and outside the Angavo shear zone. Combined with new structural results from the western interference zone, these ages yield a better understanding of the late-Panafrican history of central Madagascar. No diachronism is observed along the strike of the Angavo shear zone. Conversely, amphibole and especially biotite ages decrease from West to East, i.e. towards the shear zone. These new ages range from 511 to 469 Ma. A 1-D conductive model constrains the thermal effect in relation with the Angavo shear zone to be restricted to a lateral distance of ca 60 km (in map view) for a maximum heating duration of 20 Myr. This is in agreement with the Ar–Ar data and with the width of the observed interference zone. Following this episode of deformation and heat transfer, the estimated cooling rates of the Angavo shear zone range from to 15 to 6 °C/Myr, respectively before and after 515 Ma. A post-collision intracontinental setting is suggested for the Angavo shear zone, which is regarded as a remote effect of the Kuunga Orogeny between India and Antarctica.     

Fiddling while Madagascar burns. Deforestation discourses and highland history

Madagascar has been highlighted as a hotspot for biodiversity because of its unique natural history and a high level of endemism. This heritage of biodiversity is believed to be at serious risk, due to deforestation caused by local people. This paper concerns the landscape of the Madagascar highlands, and how interpretations of them have changed the past century. A social constructivist approach reveals two opposing views about the vegetation cover and seeks to unfold which specific scientific paradigms, narratives or received wisdom they are based on. Most important are changing paradigms in ecology, from classic equilibrium ecology to non‐equilibrium ecology, and changes in social sciences from a structural to an interactionist approach. Another important aspect addressed in the paper is the impact of the re‐interpretations on environmental policy and management. The Ambohitantely Special Reserve is used as a case to illustrate how interpretations of forest history are influenced by the hegemonic discourse.     

Re-mining the collections: From bioprospecting to biodiversity offsetting in Madagascar

Madagascar has always held a special place on the bioprospecting map. Designated as one of the world’s “hottest” biodiversity hotspots, scientists believe the extremely high flora and faunal endemism contain unique potential for the commercialisation of natural products. Years of collections by bioprospectors in Madagascar are beginning to pay off, not necessarily from drug discovery, but through the biodata from their botanical collections. In the paper, we highlight the links between labour and value over time to illustrate the historical process of collecting inventories of biodata and calculating biodiversity metrics. As we demonstrate, biodata originally used for the purposes of drug discovery and scientific exploration are now being repurposed in biodiversity offsetting programs for multinational mining operations in Madagascar. This project of “re-mining” biodata has reinforced the power of select research institutions which now service their expertise for biodiversity offsetting initiatives. In sum, botanical agencies are far from apolitical actors in these new iterations of market-conservation but active participants in a new age of green grabbing.     

U–Pb zircon geochronology and geochemistry of Neoproterozoic granitoids of the Maevatanana area,Madagascar: implications for Neoproterozoic crustal extension of the Imorona–Itsindro Suite and subsequent lithospheric subduction

Voluminous Neoproterozoic granitoid sheets of the Imorona–Itsindro Suite are important components of exposed basement in west-central Madagascar. Here, we report precise new zircon U–Pb ages and whole-rock geochemistry for granitoids within the Maevatanana area of Madagascar. The new laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating undertaken during this study indicates that Antanimbary granitoid and Antasakoamamy granitoid were emplaced at 747 ± 9 Ma and 729 ± 9–727 ± 8 Ma, respectively. Geochemically, the Antanimbary granitoids show poor Nb, Ta anomalies, pronounced positive Zr anomalies, and are K-rich (K₂O/Na₂O > 1), but the Antasakoamamy granitoids are relatively depleted in Nb, Ta, show slightly negative Zr anomalies, and are Na-rich (Na₂O/K₂O > 1). Both suites contain zircons with strongly negative εHf(t), indicating participation of much older (Palaeoproterozoic and Archaean) crust. Their geochemical characteristics, along with the use of various discrimination diagrams, reveals that crustal delamination and asthenospheric upwelling resulted in crustal extension of the region before ~747 Ma, with subsequent lithospheric subduction and arc magmatism after 729–727 Ma.     

Néotectonique en distension et morphologies karstiques de zone intertropicale : exemple de Madagascar

Résumé

A Madagascar, les morphologies karstiques et leur activité dépendent de l’interaction entre les facteurs climatiques, lithologi-ques et structuraux, en particulier de l’histoire tectonique récente à actuelle. Le rôle des différents facteurs est analysé et quatre cas-types d’activité karstique sont dégagés en fonction de l’importance, variable dans l’espace et dans le temps, des facteurs tectoniques (fracturation et mouvements verticaux) et climatiques (excédent ou déficit pluviométri-que).     

A social contract with the ancestors—Culture and ecosystem services in southern Madagascar

We investigate the role of culture in sustaining essential ecosystem services in the arid and erratic climate of an agropastoral landscape in southern Madagascar. Our fieldwork and interviews in Ambovombe subprefecture in Androy addressed land use, agropastoralism, livelihood, institutions and their moral basis. Our analysis points to the interdependence of cultural practices and ecosystem services: sacred forests, crop pollination, subsistence farming, cattle economy and societal transition and purification rituals. We posit a social-ancestral contract that works as a moral attractor structuring and sustaining the agropastoral ecosystem services system. The contract between living and nonliving clan members underpins the cultural practices and rituals that regulate the vulnerable agropastoral system. We conclude that the well-being values of the inhabitants of the south of Madagascar depend upon moralities that lend legitimacy and stability to the management of the social–ecological processes that precondition ecosystem services production. Neither ecosystem nor culture delivers ecosystem services to society. Ecosystem services are generated by an interdependent social–ecological system in which knowledge, practice, and beliefs coevolve: culture is a key factor in their generation and persistence. The study suggests these are significant interdependences to consider in dynamic analyses of ecosystem service production.