Three-dimensional structure along the inverted Palaeoproterozoic Fiery Creek Fault System, Mount Isa terrane, Australia

The NW-dipping Fiery Creek Fault System, located in the northern Mount Isa terrane, comprises numerous sub-parallel faults that record multiple episodes of Palaeo- to Mesoproterozoic movement. Hanging wall wedge-shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension (Mount Isa Rift Event; ca. 1710–1655 Ma). Reactivation of the fault system during regional shortening and basin inversion associated with the Mesoproterozoic Isan Orogeny (ca. 1590–1500 Ma) resulted in complex three-dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system. This has resulted in the development of discrete hanging wall deformation compartments, that are characterised by different structural styles. High strain compartments are characterised by relatively intense folding and the development of break-back thrusts, whereas low strain compartments are only weakly folded. Variations in hanging wall strain are attributed to selective reactivation of normal fault segments, controlled by the pre-inversion fault dip and lithological contrasts across the faults. Variation of the pre-inversion fault dip is interpreted to have been caused by episodic tilt-block rotation during crustal extension. Moderately dipping faults active early in the Mount Isa Rift Event show the greatest degree of reactivation, whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall.     

The Acadian thermal history of western Maine

ABSTRACT Following the Middle Devonian Acadian deformation an extensive belt of high grade metamorphism was formed in New England. In south-western Maine, at the northern end of this belt, there occurs a transition along the strike from regional low-pressure/high-temperature metamorphism to contact metamorphism in low-grade rocks. Petrological studies indicate that this transition occurs along a surface plunging to the north-east at about 3.5°, with respect to the Middle-to-Late Devonian erosion surface. In addition, detailed petrological mapping has defined a history of temporally separate, localized metamorphic events associated with plutonism and occurring at increasingly deeper levels to the south-west. Geochronological studies constrain ambient temperatures in the transition zone at the time of metamorphism to be less than 300° C in the north-east and between 350° C and 500° C in the south-west. They also establish a pattern of diachronous cooling due to differential uplift and erosion, with cooling occurring later and most rapidly to the south-west. Geophysical evidence suggests that along with this spatial variation in metamorphic style the shapes of the plutons in Maine undergo a transition from laterally extensive sheet-like bodies in the high grade terrane to more equant-shaped bodies in the low-grade terrane. Using the results of these petrological, geochronological and geophysical studies, as well as those of stratigraphical and structural studies we construct a thermal model for the transition zone. The model suggests that the Acadian metamorphism in south-western Maine is a result of deep-level contact metamorphism near laterally extensive granitic sills dipping to the north-east with respect to the present erosion surface. The plutons themselves are interpreted to be a result of lower crustal melting in response to crustal thickening in the presence of normal or slightly augmented mantle heat flux.     

The geodynamic evolution of the Internal Zone of the Betic Cordilleras (south-east Spain): a model based on structural analysis and geothermobarometry

ABSTRACT The Internal Zone of the Betic Cordilleras consists of several superimposed major thrust sheets with different P-T-t evolutions. On the basis of an integrated field, microscopic and laboratory study, the tectono-metamorphic history of the Mulhacen Complex and Almanzora Unit has been reconstructed in detail. The Mulhacen Complex has been affected by at least five phases of penetrative deformation, which have been labelled D_x-1, D_x, D_x+1, D_x+2 and D_x+3. D_x-1, and D_x are related to continent-continent collision, which is indicated by high pressure-low temperature (HP/LT) and subsequent intermediate P/T metamorphic conditions. D_x+1 is related to crustal thinning and heterogeneous extension. During this event the Almanzora Unit was juxtaposed against the Mulhacen Complex. This phase was succeeded by the establishment of low pressure-high temperature (LP/HT) conditions and at least two phases of folding and overthrusting. The Almanzora Unit shows a comparable tectono-metamorphic evolution post D_x+1. However, the P/T conditions prior to D_x+1 indicate a higher crustal position with respect to the Mulhacen Complex during the collisional event.     

据40Ar/39Ar快中子年龄新资料讨论震旦系底界年龄

作者对相当于晋宁运动岩浆活动产物的湖北峡东黄陵岩体和江西九岭岩体分别进行了⁴⁰Ar/³⁹Ar快中子定年。对采自宜昌莲沱地区的黑云母斜长花岗岩体和黄陵庙黑云母花岗闪长岩体的样品测得两条年龄谱,HH-01黑云母的高温坪年龄为893.7±6.7Ma,HH-05角闪石坪年龄为886.4±4.6Ma。对采自江西宜丰黄岗口的九岭岩体中黑云母测得的高温坪年龄为937.1±6.4Ma。从上述三个年龄值,并综合以前测定的晋宁期侵入体的年龄值以及不整合面上覆盖层和基底最上部沉积层的一些年龄值认为,以900Ma作为震旦系底界年龄是合适的。     

Contrasting styles of Taconian, Eastern Acadian and Western Acadian metamorphism, central and western New England

The two major Early to Middle Palaeozoic tectonic/metamorphic events in the northern Appalachians were the Taconian (Middle to Late Ordovician) in central to western areas and the Acadian (Late Silurian to early Middle Devonian) in eastern to west-central areas. This paper presents a model for the Acadian orogenic event which separates the Acadian metamorphic realm into eastern and western belts based on distinctively different styles. We propose that the Acadian metamorphism in the east was the delayed consequence of Taconian back-arc lithospheric modification. East of the Taconian island arc, thick accumulations of Late Ordovician and Silurian sediments, coupled with plutons rising along a magmatic arc, produced crustal thermal conditions appropriate for anomalously high-T, low-P metamorphism accompanied by major crustal anatexis. In this zone, upward melt migration was coupled with subsequent E-W crustal shortening (possibly due to outboard collision with the Avalon terrane) to produce mechanical conditions that favoured formation of fold and thrust nappes and resultant tectonic thickening to the west (and probably to the east as well). The basis for the distinction between the Eastern and Western Acadian events lies in the contrasting styles of metamorphism accompanying each. Evidence for contrasting metamorphic styles consists of (1) estimated metamorphic field gradients (MFGs) based on thermobarometric studies, and (2) petrological evidence for contrasting P–T trajectories. West of the Acadian metamorphic front, the Taconian zone has an MFG in which peak temperatures of 400-600° C were reached at pressures of about 4–6 kbar, with both P and T increasing to the east. Near its western edge, the Western Acadian metamorphic overprint has a similar MFG to the Taconian, and is mainly discriminated by ⁴⁰Ar/³⁹Ar dating and microtextural evidence. East of this narrow zone, the Western Acadian overprint is characterized by progressively higher temperatures (600–725° C) and pressures (6.5–10 kbar, or more) to the east, yielding an overall MFG that lies along, or slightly above, the kyanite–sillimanite boundary on a P–T diagram. There is little or no plutonism accompanying Western Acadian metamorphism. In contrast, thermobarometry in the Eastern Acadian, east of the Bronson Hill Belt, yields high-T, intermediate-P conditions for the highest grade rocks known in New England: T= 650–750° C, P= 4.5–6.5 kbar for granulite facies assemblages which apparently formed along an ‘anticlockwise’P–T path. The Bronson Hill Belt lies geographically between the Eastern and Western Acadian zones and shows transitional petrological behaviour: anomalously high temperatures at intermediate pressures, but a ‘clockwise’ path with decompression cooling. Radiometric dating indicates peak Taconian conditions may have been achieved as early as 475 Ma in the Taconian hinterland and as late as 445 Ma in the Taconian foreland (including the Taconic allochthons). Eastern Acadian magmatism may have started as early as 425 Ma, and most nappe-stage deformation and metamorphism in the Eastern Acadian zone appears to have ended by about 410 Ma. Tectonic thickening in the Western Acadian (including the western counterparts of the nappe-stage deformation documented in the Eastern Acadian) must pre-date attainment of peak metamorphic conditions dated at 395–385 Ma. Dome-stage deformation clearly post-dates peak metamorphism and deforms metamorphic isograds. The end of Western Acadian deformation is well constrained by 370-375 Ma radiometric ages of late pegmatites and granitoids which cross-cut all structures.     

阿尔泰造山带的构造运动

变形式样、建造类型及同位素年代学数据研究表明,阿尔泰造山带依次经历了5期构造运动,即:喀纳斯运动,形成白哈巴组(O_3)与哈巴河群(Z—O_2)间的角度不整合;大桥运动(S_3—D_(1—2)),形成海西早期类拗拉谷拉张陆壳区;阿尔泰运动(海西中晚期)导致陆内斜向碰撞并形成大型剪切弧型推覆构造系,为强烈造山阶段;泛阿尔泰运动(海西末至印支期)导致山脉整体隆起及剥蚀;喜马拉雅运动,导致新生代以来造山带各断裂系的复活及断块隆起。     

关于大别运动的新认识

本文依据红安群（宿松群）和大别山杂岩在岩石建造和变形、变质改造等方面的重大差异以及其间残存的角度不整合面，进一步肯定了大别运动的存在。大别运动主要发生时间为２５００Ｍａ左右，区域上大致可与华北地台阜平运动对比，是大别山地区原始硅铝质陆壳形成和韧性再造的变革运动。初步将大别旋回划分出早期伸展、中期挤压和晚期走滑剪切３个变形幕。指出了大别运动界面是大别山上部地壳极其重要的滑脱界面和层圈构造，沿袭这一古老构造薄弱面曾先后发生了韧性滑覆、脆－韧性逆冲推覆和脆性剥离等变形事件。     

The Orogeny in the Altaides1

Abstract Studies of the deformation styles, formation types and isotopic age data indicate that the Altaides has successively experienced 5 stages of orogeny: (1) the Kanas orogeny forming the angular unconformity between the Baihaba Formation (O₃) and the Habahe Group (Z-O₂); (2) the Daqiao orogeny (S₃-D_1-2) giving rise to the early Hercynian quasi-aulacogen extensional continental crust of the area; (3) the Altay orogeny (middle- late Hercynian) leading to the oblique intracontinental collision and the formation of large shear arc-shaped thrust system and representing a strong orogeny stage; (4) the pan-Altay orogeny (latest Hercynian-Indosinian) resulting in the uplifting and erosion of the mountains as a whole; (5) the Himalayan movement causing the rejuvenation of fault systems and block uplift of the Altaides since the Cenozoic.     

大别山印支运动的同位素年代学证据

本文根据Sm-Nd同位素年代学成果论证了大别山印支运动的表现。主要依据:(1)阿尔卑斯型橄榄岩的侵入(244±11Ma);(2)辉石岩类超基性岩浆岩的侵入(231±61Ma);(3)高压低温变质岩(如C型榴辉岩)的生成(221±20-224±5Ma)。它们都发生在印支早期,并从而证明了华北陆块、大别山微型陆块、扬子陆块三者是在早三叠世拼接在一起的。在此之前,华北陆块和扬子陆块之间存在一古特提斯洋。