Marble-hosted ruby deposits from Central and Southeast Asia: Towards a new genetic model     

Virginie Garnier  Gaston Giuliani  Daniel Ohnenstetter  Anthony E. Fallick  Jean Dubessy  David Banks  Hong Quang Vinh  Thrse Lhomme  Henri Maluski  Arnaud Pêcher  Kausar Allah Bakhsh  Pham Van Long  Phan Trong Trinh  Dietmar Schwarz 《Ore Geology Reviews》2008,34(1-2):169

Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO₂ released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO₂–H₂S–COS–S₈–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO₂ released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO₄). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby.  相似文献   

Evidence for excess argon during high pressure metamorphism in the dora maira massif (Western Alps,Italy), using an ultra-violet laser ablation microprobe 40Ar-39Ar technique     

N. O. Arnaud  S. P. Kelley 《Contributions to Mineralogy and Petrology》1995,121(1):1-11

 Ultra-high pressure eclogite/amphibolite grade metamorphism of the Dora Maira Massif in the western Alps is a well established and intensively studied event. However, the age of peak metamorphism and early cooling remains controversial. The ⁴⁰Ar-³⁹Ar step-heating and laser spot ages from high pressure phengites yield plateau ages as old as 110 Ma which have been interpreted as the time of early cooling after the high pressure event. Recent U/Pb and Sm/Nd results challenge this assertion, indicating a much younger age for the event, around 45 Ma, and hence a radically different timing for the tectonic evolution of the western Alps. In a new approach to the problem, samples from the undeformed Hercynian metagranite, Brossasco, were studied using an ultra-violet laser ablation microprobe technique for ⁴⁰Ar-³⁹Ar dating. The new technique allowed selective in situ analysis, at a spatial resolution of 50 μm, of quartz, phengite, biotite and K-feldspar. The results demonstrate the frequent occurrence of excess argon with high ⁴⁰Ar-³⁶Ar ratios (1000–10000) and a strong relationship between apparent ages and metamorphic textures. The highest excess argon ratios are always associated with high closure temperature minerals or large diffusion domains within single mineral phases. The best interpretation of this relationship seems to be that excess argon was incorporated in all phases during the high pressure event, then mixed with an atmospheric component during rapid cooling and retrogression, producing a wide range of argon concentrations and ⁴⁰Ar/³⁶Ar ratios. Step-heating analysis of minerals with this mixture would produce linear arrays on a ³⁶Ar/⁴⁰Ar versus ³⁹Ar/⁴⁰Ar correlation diagram, leading to geologically meaningless plateau ages, older than the true closure age. In the present case, some ages in the range 60–110 Ma could be explained by the presence of excess argon incorporated around 40–50 Ma ago. Similar results found in other high pressure terrains in the Alps may reconcile the argon geochronometer with other systems such as Rb/Sr, U/Pb or Sm/Nd. This study therefore calls for an increasing use of high resolution in situ sampling techniques to clarify the meaning of ⁴⁰Ar/³⁹Ar ages in many high pressure terrains. Received: 6 January 1994/Accepted: 4 April 1995  相似文献   

Survival of eclogite xenolith in a Cretaceous granite intruding the Central Dabieshan migmatite gneiss dome (Eastern China) and its tectonic implications   总被引：3，自引：0，他引：3  

Wei Lin  Masaki Enami  Michel Faure  Urs Schärer  Nicolas Arnaud 《International Journal of Earth Sciences》2007,96(4):707-724

Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new ⁴⁰Ar/³⁹Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.  相似文献   

UPb emplacement and 40Ar/39Ar cooling ages of the eastern Mont-Louis granite massif (Eastern Pyrenees,France)     

Olivier Maurel  Jean-Patrick Respaut  Patrick Monié  Nicolas Arnaud  Maurice Brunel 《Comptes Rendus Geoscience》2004,336(12):1091-1098

Zircon UPb dating by SIMS of the Mont-Louis granite yields an age of 305±5 Ma, intrepreted to reflect the igneous emplacement age of the massif. It is in agreement with the Hercynian syntectonic character of Pyrenees granite. ⁴⁰Ar/³⁹Ar on hornblende, biotite and K-feldspar permit, to estimate the massif cooling. A rapid temperature decrease (≈30 °C/Ma) is revealed from Westphalian to Late Stephanian, coeval with the emplacement of a laccolithe in the upper crust. Then, the cooling rate decreases to ≈1 °C/Ma. This would be consistent with a long time residence for the pluton from the Late Palaeozoic to the Early Cainozoic at 6–8 km depth. To cite this article: O. Maurel et al., C. R. Geoscience 336 (2004).  相似文献   

Experimental soft‐sediment deformation caused by fluidization and intrusive ice melt in sand     

Pascal Bertran  Marianne Font  Arnaud Giret  Kevin Manchuel  Deborah Sicilia 《Sedimentology》2019,66(3):1102-1117

Identifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work has failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in a permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates.  相似文献   

Landscape Evolution Modelling of naturally dammed rivers          下载免费PDF全文

Wouter van Gorp  Arnaud J.A.M. Temme  Jantiene E.M. Baartman  Jeroen M. Schoorl 《地球表面变化过程与地形》2014,39(12):1587-1600

Natural damming of upland river systems, such as landslide or lava damming, occurs worldwide. Many dams fail shortly after their creation, while other dams are long‐lived and therefore have a long‐term impact on fluvial and landscape evolution. This long‐term impact is still poorly understood and landscape evolution modelling (LEM) can increase our understanding of different aspects of this response. Our objective was to simulate fluvial response to damming, by monitoring sediment redistribution and river profile evolution for a range of geomorphic settings. We used LEM LAPSUS, which calculates runoff erosion and deposition and can deal with non‐spurious sinks, such as dam‐impounded areas. Because fluvial dynamics under detachment‐limited and transport‐limited conditions are different, we mimicked these conditions using low and high erodibility settings, respectively. To compare the relative impact of different dam types, we evaluated five scenarios for each landscape condition: one scenario without a dam and four scenarios with dams of increasing erodibility. Results showed that dam‐related sediment storage persisted at least until 15 000 years for all dam scenarios. Incision and knickpoint retreat occurred faster in the detachment‐limited landscape than in the transport‐limited landscape. Furthermore, in the transport‐limited landscape, knickpoint persistence decreased with increasing dam erodibility. Stream capture occurred only in the transport‐limited landscape due to a persisting floodplain behind the dam and headward erosion of adjacent channels. Changes in sediment yield variation due to stream captures did occur but cannot be distinguished from other changes in variation of sediment yield. Comparison of the model results with field examples indicates that the model reproduces several key phenomena of damming response in both transport‐limited and detachment‐limited landscapes. We conclude that a damming event which occurred 15 000 years ago can influence present‐day sediment yield, profile evolution and stream patterns. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Complexity and non‐linearity in earth surface processes – concepts,methods and applications          下载免费PDF全文

Arnaud J.A.M. Temme  Margreth Keiler  Derek Karssenberg  Andreas Lang 《地球表面变化过程与地形》2015,40(9):1270-1274

Complexity has long been recognized and is increasingly becoming mainstream in geomorphology. However, the relative novelty of various concepts and techniques associated to it means that ambiguity continues to surround complexity. In this commentary, we present and discuss a variety of recent contributions that have the potential to help clarify issues and advance the use of complexity in geomorphology. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Why is there net surface heating over the Antarctic Circumpolar Current?     

Arnaud Czaja  John Marshall 《Ocean Dynamics》2015,65(5):751-760

  相似文献   

Catchment response to lava damming: integrating field observation,geochronology and landscape evolution modelling          下载免费PDF全文

Wouter van Gorp  Jeroen M. Schoorl  Arnaud J. A. M. Temme  Tony Reimann  Jan R. Wijbrans  Darrel Maddy  Tuncer Demir  Tom Veldkamp 《地球表面变化过程与地形》2016,41(11):1629-1644

Combining field reconstruction and landscape evolution modelling can be useful to investigate the relative role of different drivers on catchment response. The Geren Catchment (~45 km²) in western Turkey is suitable for such a study, as it has been influenced by uplift, climate change and lava damming. Four Middle Pleistocene lava flows (⁴⁰Ar/³⁹Ar‐ dated from 310 to 175 ka) filled and dammed the Gediz River at the Gediz–Geren confluence, resulting in base‐level fluctuations of the otherwise uplift‐driven incising river. Field reconstruction and luminescence dating suggest fluvial terraces in the Geren Catchment are capped by Middle Pleistocene aggradational fills. This showed that incision of the Geren trunk stream has been delayed until the end of MIS 5. Subsequently, the catchment has responded to base‐level lowering since MIS 4 by 30 m of stepped net incision. Field reconstruction left us with uncertainty on the main drivers of terrace formation. Therefore, we used landscape evolution modelling to investigate catchment response to three scenarios of base‐level change: (i) uplift with climate change (rainfall and vegetation based on arboreal pollen); (ii) uplift, climate change and short‐lived damming events; (iii) uplift, climate and long‐lived damming events. Outputs were evaluated for erosion–aggradation evolution in trunk streams at two different distances from the catchment outlet. Climate influences erosion–aggradation activity in the catchment, although internal feedbacks influence timing and magnitude. Furthermore, lava damming events partly control if and where these climate‐driven aggradations occur. Damming thus leaves a legacy on current landscape evolution. Catchment response to long‐duration damming events corresponds best with field reconstruction and dating. The combination of climate and base level explains a significant part of the landscape evolution history of the Geren Catchment. By combining model results with fieldwork, additional conclusions on landscape evolution could be drawn. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Protracted,coeval crust and mantle melting during Variscan late-orogenic evolution: U–Pb dating in the eastern French Massif Central     

Laurent  Oscar  Couzinié  Simon  Zeh  Armin  Vanderhaeghe  Olivier  Moyen  Jean-François  Villaros  Arnaud  Gardien  Véronique  Chelle-Michou  Cyril 《International Journal of Earth Sciences》2017,106(2):421-451

International Journal of Earth Sciences - The late stages of the Variscan orogeny are characterized by middle to lower crustal melting and intrusion of voluminous granitoids throughout the belt,...  相似文献