Subduction,fluids, and accessory minerals: a celebration of the career of Sorena S. Sorensen     

W. G. Ernst  Barbara L. Dutrow  Virginia Sisson  Sarah Penniston-Dorland 《International Geology Review》2017,59(5-6):523-525

ABSTRACT

This is a preface to the topical issue entitled ‘Subduction, Fluids, and Accessory Minerals: A Celebration of the Career of Sorena S. Sorensen’  相似文献   

The contribution of the young Cretaceous Caribbean Oceanic Plateau to the genesis of late Cretaceous arc magmatism in the Cordillera Occidental of Ecuador     

J. Allibon  P. Monjoie  H. Lapierre  E. Jaillard  F. Bussy  D. Bosch  F. Senebier 《Journal of South American Earth Sciences》2008,26(4):355-368

The eastern part of the Cordillera Occidental of Ecuador comprises thick buoyant oceanic plateaus associated with island-arc tholeiites and subduction-related calc-alkaline series, accreted to the Ecuadorian Continental Margin from Late Cretaceous to Eocene times. One of these plateau sequences, the Guaranda Oceanic Plateau is considered as remnant of the Caribbean–Colombian Oceanic Province (CCOP) accreted to the Ecuadorian Margin in the Maastrichtien.Samples studied in this paper were taken from four cross-sections through two arc-sequences in the northern part of the Cordillera Occidental of Ecuador, dated as (Río Cala) or ascribed to (Macuchi) the Late Cretaceous and one arc-like sequence in the Chogòn-Colonche Cordillera (Las Orquídeas). These three island-arcs can clearly be identified and rest conformably on the CCOP.In all four localities, basalts with abundant large clinopyroxene phenocrysts can be found, mimicking a picritic or ankaramitic facies. This mineralogical particularity, although not uncommon in island arc lavas, hints at a contribution of the CCOP in the genesis of these island arc rocks.The complete petrological and geochemical study of these rocks reveals that some have a primitive island-arc nature (MgO values range from 6 to 11 wt.%). Studied samples display marked Nb, Ta and Ti negative anomalies relative to the adjacent elements in the spidergrams characteristic of subduction-related magmatism. These rocks are LREE-enriched and their clinopyroxenes show a tholeiitic affinity (FeO_T–TiO₂ enrichment and CaO depletion from core to rim within a single crystal).The four sampled cross-sections through the island-arc sequences display homogeneous initial Nd, and Pb isotope ratios that suggest a unique mantellic source for these rocks resulting from the mixing of three components: an East-Pacific MORB end-member, an enriched pelagic sediment component, and a HIMU component carried by the CCOP. Indeed, the ankaramite and Mg-basalt sequences that form part of the Caribbean-Colombian Oceanic Plateau are radiogenically enriched in ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb and contain a HIMU component similar to that observed in the Gorgona basalts and Galápagos lavas. The subduction zone that generated the Late Cretaceous arcs occurred far from the continental margin, in an oceanic environment. This implies that no terrigenous detrital sediments interacted with the source at this period. Thus, the enriched component can only result from the melting of subducted pelagic sediments.We have thus defined the East-Pacific MORB, enriched (cherts, pelagic sediments) and HIMU components in an attempt to constrain and model the genesis of the studied island-arc magmatism, using a compilation of carefully selected isotopic data from literature according to rock age and paleogeographic location at the time of arc edification.Tripolar mixing models reveal that proportions of 12–15 wt.% of the HIMU component, 7–15 wt.% of the pelagic sediment end-member and 70–75 wt.% of an East-pacific MORB end-member are needed to explain the measured isotope ratios. These surprisingly high proportions of the HIMU/CCOP component could be explained by the young age of the oceanic plateau (5–15 Ma) during the Late Cretaceous arc emplacement. The CCOP, basement of these arc sequences, was probably still hot and easily assimilated at the island-arc lava source.  相似文献   

The Berridale Wrench fault: A major structure in the Snowy Mountains of New South Wales     

W. J. Collins  B. E. Hobbs 《Australian Journal of Earth Sciences》2013,60(1):25-41

One of the most significant, but poorly understood, tectonic events in the east Lachlan Fold Belt is that which caused the shift from mafic, mantle‐derived calc‐alkaline/shoshonitic volcanism in the Late Ordovician to silicic (S‐type) plutonism and volcanism in the late Early Silurian. We suggest that this chemical/isotopic shift required major changes in crustal architecture, but not tectonic setting, and simply involved ongoing subduction‐related magmatism following burial of the pre‐existing, active intraoceanic arc by overthrusting Ordovician sediments during Late Ordovician — Early Silurian (pre‐Benambran) deformation, associated with regional northeast‐southwest shortening. A review of ‘type’ Benambran deformation from the type area (central Lachlan Fold Belt) shows that it is constrained to a north‐northwest‐trending belt at ca 430 Ma (late Early Silurian), associated with high‐grade metamorphism and S‐type granite generation. Similar features were associated with ca 430 Ma deformation in east Lachlan Fold Belt, highlighted by the Cooma Complex, and formed within a separate north‐trending belt that included the S‐type Kosciuszko, Murrumbidgee, Young and Wyangala Batholiths. As Ordovician turbidites were partially melted at ca 430 Ma, they must have been buried already to ～20 km before the ‘type’ Benambran deformation. We suggest that this burial occurred during earlier northeast‐southwest shortening associated with regional oblique folds and thrusts, loosely referred to previously as latitudinal or east‐west structures. This event also caused the earliest Silurian uplift in the central Lachlan Fold Belt (Benambran highlands), which pre‐dated the ‘type’ Benambran deformation and is constrained as latest Ordovician — earliest Silurian (ca 450–440 Ma) in age. The south‐ to southwest‐verging, earliest Silurian folds and thrusts in the Tabberabbera Zone are considered to be associated with these early oblique structures, although similar deformation in that zone probably continued into the Devonian. We term these ‘pre’‐ and ‘type’‐Benambran events as ‘early’ and ‘late’ for historical reasons, although we do not consider that they are necessarily related. Heat‐flow modelling suggests that burial of ‘average’ Ordovician turbidites during early Benambran deformation at 450–440 Ma, to form a 30 km‐thick crustal pile, cannot provide sufficient heat to induce mid‐crustal melting at ca 430 Ma by internal heat generation alone. An external, mantle heat source is required, best illustrated by the mafic ca 430 Ma, Micalong Swamp Igneous Complex in the S‐type Young Batholith. Modern heat‐flow constraints also indicate that the lower crust cannot be felsic and, along with petrological evidence, appears to preclude older continental ‘basement terranes’ as sources for the S‐type granites. Restriction of the S‐type batholiths into two discrete, oblique, linear belts in the central and east Lachlan Fold Belt supports a model of separate magmatic arc/subduction zone complexes, consistent with the existence of adjacent, structurally imbricated turbidite zones with opposite tectonic vergence, inferred by other workers to be independent accretionary prisms. Arc magmas associated with this ‘double convergent’ subduction system in the east Lachlan Fold Belt were heavily contaminated by Ordovician sediment, recently buried during the early Benambran deformation, causing the shift from mafic to silicic (S‐type) magmatism. In contrast, the central Lachlan Fold Belt magmatic arc, represented by the Wagga‐Omeo Zone, only began in the Early Silurian in response to subduction associated with the early Benambran northeast‐southwest shortening. The model requires that the S‐type and subsequent I‐type (Late Silurian — Devonian) granites of the Lachlan Fold Belt were associated with ongoing, subduction‐related tectonic activity.  相似文献   

The ‘orogenic andesite’ puzzle of C. E. Tilley: 1—Is the volatile phase the missing piece?     

R. L. Stanton 《Australian Journal of Earth Sciences》2013,60(5):625-641

Some 65 years ago, C. E. Tilley, in his 1950 Presidential Address to the Geological Society of London, brought into sharp focus the then perhaps-not-fully-recognised problem of the origin of what he termed the ‘orogenic andesites’—and, in particular, their commonly constituent calc-alkaline lineage of lavas and pyroclastic materials. In spite of much investigation and progress since, the problem remains not fully resolved. The two most conspicuous features of such orogenic—i.e. island arc—volcanism are its copious, explosive, degassing and, as Tilley noted, its copious development of andesites and their more felsic associates. If these rock types were derived from basalt, the principal relevant changes in major element composition are reductions in Fe, Ca and Mg, and increases in Si, Al and (Na + K). Four principal mechanisms for inducing these changes have been proposed: (1) magmatic differentiation induced by fractional crystallisation, (2) magma mixing, (3) partial melting of an ultramafic-derived basaltic parent, and (4) crustal contamination. A fifth postulate—long recognised but only occasionally seriously considered—is that loss in the volatile phase during eruption and later degassing may make a significant contribution to the overall process. On the basis that Tilley's (and others’) orogenic basalt–andesite–dacite–rhyolite series constitutes a linear arrangement on the conventional FeO_t–MgO–(Na₂O + K₂O) diagram it is shown on numerical grounds that fractional crystallisation alone cannot account for the observed compositional trend—that, while accumulates are neither uncommon nor insubstantial in amount in modern arcs, they are olivine-rich, not magnetite-rich, and that numerical, petrological and field evidence indicates that the high oxidation/magnetite subtraction hypothesis of orogenic andesite genesis can no longer be seriously entertained. The partial melting hypothesis encounters contrary numerical evidence, closely analogous with that adduced for fractional crystallisation. Magma mixing eventually encounters the difficulty of the nature of the felsic material required for rhyolite formation, and assimilation of the preservation of primitive isotope ratios as lava evolution progresses. A fifth mechanism—volatile loss—may make a significant contribution to the relevant compositional change, perhaps in combination with one or more of the other proposed processes. Geochemical, petrological and field evidence pertaining to this is reviewed and examined, and it is postulated that indeed a combination of fractional crystallisation as the principal mechanism, volatile loss as a contributing factor, provides a plausible process. A case is made for an exploratory experimental investigation of the possibility of significant loss in a gas/vapour phase.  相似文献   

Phase-space volume of regions of trapped motion: multiple ring components and arcs     

Luis Benet  Olivier Merlo 《Celestial Mechanics and Dynamical Astronomy》2009,103(3):209-225

The phase-space volume of regions of regular or trapped motion, for bounded or scattering systems with two degrees of freedom respectively, displays universal properties. In particular, sudden reductions in the phase-space volume or gaps are observed at specific values of the parameter which tunes the dynamics; these locations are approximated by the stability resonances. The latter are defined by a resonant condition on the stability exponents of a central linearly stable periodic orbit. We show that, for more than two degrees of freedom, these resonances can be excited opening up gaps, which effectively separate and reduce the regions of trapped motion in phase space. Using the scattering approach to narrow rings and a billiard system as example, we demonstrate that this mechanism yields rings with two or more components. Arcs are also obtained, specifically when an additional (mean-motion) resonance condition is met. We obtain a complete representation of the phase-space volume occupied by the regions of trapped motion.  相似文献   

Contribution of slab-fluid in arc magmas beneath the Japan arcs   总被引：5，自引：0，他引：5  

Hitomi Nakamura  Hikaru Iwamori 《Gondwana Research》2009,16(3-4):431-445

Identifying the amount and composition of slab-derived fluid and its spatial variation is key to quantifying fluid processes in subduction zones. Based on the isotopic systematics of arc lavas, we found regional variations over the Japan arcs in terms of the amount and composition of slab-derived fluid added to the melting source region. The average amounts of slab-derived fluid differ among the arcs: 2.6 wt.% for Central Japan, 0.69 wt.% for Ryukyu, 0.17 wt.% for NE Japan, and 0.12 wt.% for both Kurile and Izu–Bonin. These differences may be attributed to the arc setting (oceanic or continental) and the geometry of the slabs. Contribution of sediment involved in the slab-derived fluid is dominant in NE Japan compared to the Izu–Bonin and Central Japan arcs. This could be attributed to mechanical features such as fractures near the subducting plate surface, in addition to the arc setting and the slab geometry. Therefore, the amount and composition of slab-derived fluid are thought to be controlled not only by the thermal conditions, but also by the tectonic and mechanical features around the subduction zone. On top of the variability of slab-derived fluid, the mantle wedge shows the regional variation in terms of proportion of the Pacific-type and Indian-type MORB-source mantle components, which also contributes to the compositional variations of arc magmas.  相似文献   

Izu-Bonin arc subduction under the Honshu island, Japan: Evidence from geological and seismological aspect   总被引：1，自引：1，他引：0  

Shinji Yamamoto  Junichi Nakajima  Akira Hasegawa  Shigenori Maruyama 《Gondwana Research》2009,16(3-4):572-580

The Izu-Bonin intra-oceanic arc with 20–35 km thick continental crust is being subducted under the Honshu, presumably since 17 Ma. Tomographic image clearly demonstrates that the whole Izu-Bonin arc is subducting under the Honshu arc. Geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 Ma.  相似文献   

秦祁结合部清水-张家川基性岩形成时代和构造归属探讨   总被引：1，自引：1，他引：0  

付长垒  闫臻  王秉璋 《岩石学报》2019,35(10):3141-3160

中央造山系北缘发育完整的早古生代"弧-盆"体系,而其洋内弧盆体系还是陆缘弧盆体系属性的确定,可为原特提斯域古板块构造格局和中央造山系早期造山过程的恢复提供依据。秦岭-祁连结合部清水-张家川地区出露的与原特提斯洋俯冲作用相关的基性岩形成时代和构造归属的探究,是解决中央造山系早古生代洋-陆转换过程以及东西链接等科学问题的重要内容之一。清水-张家川地区主要出露块状、枕状玄武岩以及少量辉绿岩墙和硅质岩夹层,玄武岩和辉绿岩明显富集Th、LREE,亏损Nb、Ta、Zr、Hf和Ti元素,而Th/Nb比值则分为1. 09～2. 04和0. 18～0. 73两组,分别与岛弧和弧后裂谷熔岩相一致。另外,这些基性岩具较高的Th/Yb和εNd(t)(+4. 4～+4. 8)值,显示岩浆来自受洋壳沉积物混染的亏损地幔源区。最新LA-ICP-MS锆石U-Pb测年结果显示辉绿岩墙形成于500±3Ma。结合区域岩石地层资料,综合分析表明清水-张家川地区基性岩形成于寒武纪,早于晚奥陶世酸性火山岩和侵入岩。它们与其东、西侧北秦岭和北祁连构造带内的寒武纪-早奥陶世洋内弧和弧后盆地岩浆岩共同构成了原特提斯洋北缘早古生代洋内弧-盆体系。  相似文献   

内蒙古贺根山蛇绿岩中方辉橄榄岩岩石地球化学特征及构造环境分析     

王成  任利民  余国飞  张晓军  方磊 《新疆地质》2019,(2):156-166

贺根山蛇绿岩块位于二连浩特-贺根山缝合带中段,其橄榄岩端元主体为方辉橄榄岩,少量纯橄榄岩,均发生了较强的蛇纹石化。对方辉橄榄岩进行岩石学和岩石地球化学分析研究,结果显示:方辉橄榄岩中主要造岩矿物橄榄石为镁橄榄石(Fo=90.6~90.7),斜方辉石为顽火辉石(En=88.9~90.0),单斜辉石为透辉石,以低铝(1.82%~2.13%)和高镁(Mg^#=94.2~94.7)为特征。橄榄岩主量元素表现出高Mg(MgO=34.98%~40.86%)、高Cr(Cr2O3=0.18%~0.27%)、高Ni(NiO=0.27%~0.35%)、低Si(SiO2=36.10%~41.41%)、贫Al(Al2O3=0.89%~1.58%)、低Fe(FeOT=7.58%~9.63%)特征,Mg^#=91.59~92.36,m/f=9.16~10.13,属典型镁质超基性岩。稀土元素总含量较低,ΣREE为1.42×10^-6~2.94×10^-6,球粒陨石标准化稀土元素分布模式为轻稀土富集的弱右倾型,其(La/Yb)N=2.15~10.47,Eu异常不明显,Ce显示负异常。富集Ba,U,Pb,Sr,亏损Nb,Ta,Ti。贺根山地幔橄榄岩属变质橄榄岩,为SSZ型蛇绿岩底部组成单元,形成于俯冲带环境中洋内弧后盆地环境。  相似文献   

亚暴期间高纬黄昏-子夜扇区极光弧增亮与衰减及其与IMF的关系   总被引：3，自引：0，他引：3  

洪明华  汤克云  胡红桥  刘瑞源 《地球物理学报》2001,44(1):12-23

利用南极中山站极光全天空摄相、地磁、地磁脉动数据和Wind卫星的行星际磁场IMF观测数据，分析了7个亚暴期间高纬黄昏-子夜扇区极光弧的短暂增亮现象.极光弧特征是，短暂增亮随后很快衰减，历时10-20min，基本沿着日-地方向，有明显黄昏方向运动.这些事件大都发生在IMFB_z南转之后，亚暴增长相或膨胀相期间，极光浪涌到达之前10-73min消失.相应的IMFB_x＞0，IMFB_y＜0.这种极光弧和亚暴极光不同，它们与地磁活动及Pi2脉动不相关.这7个极光弧的形态和IMF特征表明，极光弧的增亮很可能由尾瓣重联产生，很快衰减归因于IMFB_z南向条件，而黄昏方向运动受IMFB_y控制.  相似文献