四合堂剪切带活动时代及其对燕山运动B幕时间的限定   总被引：4，自引：0，他引：4  

陈印  朱光  姜大志  张必龙 《地质学报》2013,87(3):295-310

翁文灏以燕山为标准地区创名的中生代"燕山运动",现今人们将其分为A幕与B幕,各自对应着区域性角度不整合,但发生的准确时间一直无法确定。燕山构造带中段的云蒙山地区,发育了著名的四合堂逆冲型韧性剪切带,是燕山运动B幕的产物。该韧性剪切带出现在早白垩世初云蒙山复式岩体的北部边缘,上盘向南南西运动,周边的变质基底、中—新元古代盖层及晚侏罗世与早白垩世初期岩体一同卷入了变形。剪切带内及周边发育了大量同构造岩脉,可区分出早、中、晚3个阶段,对应着剪切带活动早、中、晚阶段。本次工作中分别从早、中、晚3阶段同构造岩脉中获得了锆石LA-ICP-MSU-Pb年龄,分别为143.0±2.1Ma、140.8±1.4Ma和137.5±2.4Ma。这可靠地指示了四合堂韧性剪切带的活动时间为143～138Ma。这也表明,以逆冲活动为特征的燕山运动B幕(尤其是燕山造山带中段)发生的时间就是143～138Ma。这一结果与近年来该B幕事件角度不整合之上、下地层中所获得火山岩锆石年龄相吻合。  相似文献   

Geochemistry and geochronology of the Rathjen Gneiss: Implications for the early tectonic evolution of the Delamerian Orogen     

J. Foden  M. Sandiford  J. Dougherty-Page  I. Williams 《Australian Journal of Earth Sciences》2013,60(3):377-389

The Rathjen Gneiss is the oldest and structurally most complex of the granitic intrusives in the southern Adelaide Fold‐Thrust Belt and therefore provides an important constraint on the timing of the Delamerian Orogen. Zircons in the Rathjen Gneiss show a complex growth history, reflecting inheritance, magmatic crystallisation and metamorphism. Both single zircon evaporation (‘Kober’ technique) and SHRIMP analysis yield best estimates of igneous crystallisation of 514 ± 5 Ma, substantially older than other known felsic intrusive ages in the southern Adelaide Fold‐Thrust Belt. This age places an older limit on the start of the Delamerian metamorphism and is compatible with known stratigraphic constraints suggesting the Early Cambrian Kanmantoo Group was deposited, buried and heated in less than 20 million years. High‐U overgrowths on zircons were formed during subsequent metamorphism and yield a ²⁰⁶Pb/²³⁸U age of 503 ± 7 Ma. The Delamerian Orogeny lasted no more than 35 million years. The emplacement of the Rathjen Gneiss as a pre‐ or early syntectonic granite is emphasised by its geochemical characteristics, which show affiliations with within‐plate or anorogenic granites. In contrast, younger syntectonic granites in the southern Adelaide Fold‐Thrust Belt have geochemical characteristics more typical of granites in convergent orogens. The Early Ordovician post‐tectonic granites then mark a return to anorogenic compositions. The sensitivity of granite chemistry to changes in tectonic processes is remarkable and clearly reflects changes in the contribution of crust and mantle sources.  相似文献   

Nearshore to offshore facies and depositional history of the Ordovician Daylesford Limestone New South Wales     

V. Semeniuk 《Australian Journal of Earth Sciences》2013,60(4):449-463

The Daylesford Limestone is the basal formation of the Ordovician Bowan Park Group of central western New South Wales. The formation contains four main limestone types and minor intercalated terrigenous beds. Limestones are: (1) grain‐stone, (2) grey skeletal wackestone and packstone, (3) dark grey burrowed wackestone and packstone, and (4) dark grey burrowed lime mudstone. Grainstone and grey skeletal wackstone and packstone are dominant in eastern sections; they are laterally equivalent to, and interfinger with, dark grey muddy limestones that dominate western sections. Lithoclasts are abundant in the grainstone but are absent from muddy sections to the west except in thin beds above disconformities. The rock types of the Daylesford Limestone also tend to occur sequentially above some disconformities; the full sequence is: grainstone (or grey skeletal wackestone and packstone) grading up into dark grey burrowed wackestone and packstone and thence into dark grey burrowed lime mudstone. Each sequence is probably trans‐gressive and reflects deepening water.

During deposition of the Daylesford Limestone, an area to the east was uplifted, providing lithoclasts to be reworked into the neighbouring depositional basin. Uplift also produced numerous regressions and subaerial disconformities. Facies patterns were essentially similar throughout the history of the formation. Grainstone accumulated in high‐energy nearshore environments adjacent to the uplifted area, and grey skeletal wackestone and packstone in low‐energy nearshore environments. Dark grey lime mudstone formed in offshore low‐energy environments to the west of the uplifted area; and dark grey wackestone and packstone in intermediate environments. In parts, burrowing organisms kept pace with sedimentation and locally mixed interbedded grainstone and muddy limestone.  相似文献   

Dating of Neoproterozoic and Cambrian orogenies in Tasmania*     

N. J. Turner  L. P. Black  M. Kamperman 《Australian Journal of Earth Sciences》2013,60(5):789-806

A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole‐rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high‐level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low‐angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high‐level emplacement of ultramafic‐bearing allochthons and deep‐seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep‐seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions.  相似文献   

Geochemical Features, Age, and Tectonic Significance of the Kekekete Mafic-ultramafic Rocks, East Kunlun Orogen, China   总被引：3，自引：0，他引：3  

LI Ruibao  PEI Xianzhi  LI Zuochen  SUN Yu  FENG Jianyong  PEI Lei  CHEN Guochao  LIU Chengjun  CHEN Youxin 《《地质学报》英文版》2013,87(5):1319-1333

The Kekekete mafic-ultramafic rocks are exposed in the Kekesha-Kekekete-Dawate area,which are in the eastern part of the East Kunlun Orogenic Belt.It outcrops as tectonic slices intruding tectonically in the Paleoproterozoic Baishahe Group and the Paleozoic Nachitai Group.The Kekekete mafic and ultramafic rocks is located near the central fault in East Kunlun and lithologically mainly consists of serpentinite,augite peridotite,and gabbro.The LA-ICP-MS zircon U-Pb age of the gabbro is 501±7 Ma,indicating that Kekekete mafic-ultramafic rocks formed in the Middle Cambrian.This rock assemblage is relatively poor in SiO2 and(Na2 O+K2 O) but rich in MgO and SFeO.The chondrite-normalized REE patterns of the gabbro dip slightly to the right;the primitive mantle and MORBnormalized spidergrams of trace elements show enrichment of large-ion lithophile elements(Cs,Rb,Ba,etc.) and no differentiation of high field strength elements.The general dominance of E-MORB features and the geochemical characteristics of OIB suggest that the Kekekete mafic-ultramafic rocks formed in an initial oceanic basin with slightly enriched mantle being featured by varying degrees of mixing of N-MORB depleted mantle and a similar-OIB-type source.From a comprehensive study of the previous data,the author believes that the tectonic history of the East Kunlun region was controlled by a geodynamic system of rifting and extension in the late stages of the Neoproterozoic to early stages of the Early Paleozoic and this formed the paleo-oceanic basin or rift system now represented by the ophiolites along the central fault in East Kunlun,the Kekekete mafic-ultramafic rocks and Delisitan ophiolite.  相似文献   

Provenance and deformation history of the Eastern Thomson Orogen and implications for the Paleozoic evolution of the Tasmanides (Eastern Australia)     

R. Abdullah  U. Shaanan  K. Lynn  G. Rosenbaum 《Australian Journal of Earth Sciences》2020,67(2):153-173

Abstract

Cambrian deformation associated with the Delamerian Orogeny is most evident in the Delamerian Orogen (southwestern Tasmanides) but has also been documented in the Thomson Orogen (northern Tasmanides). The tectonic evolution of the Thomson Orogen in the context of the Delamerian Orogeny is poorly understood. In particular, tectonostratigraphic relationships between the different parts of the Thomson Orogen (Anakie Inlier, Nebine Ridge, and southern Thomson Orogen) are still unclear. New detrital zircon data from the Nebine Ridge revealed an age spectrum that is consistent with published geochronological data from the Anakie Inlier. These results, in conjunction with petrographic observations and the interpretation of geophysical data, suggest that along the eastern part of the Thomson Orogen, the?～?NNE-trending Nebine Ridge represents the southward continuation of the?～?N–S-trending Anakie Inlier. New detrital zircon geochronological data are also presented for metasedimentary rocks from both sides of the Thomson–Lachlan boundary. The results constrain the maximum age of deposition (Ordovician–Devonian), and show that both sides of the Thomson–Lachlan boundary received detritus from a similar provenance. This might suggest that the Thomson–Lachlan boundary did not play a major role as a crustal-scale boundary prior to the Devonian. We speculate that transpressional deformation along this?～?E–W boundary, during the Early Devonian, was responsible for disrupting the original belt that connected the Delamerian Orogen (Koonenberry Belt) with the eastern Thomson Orogen (Nebine Ridge and Anakie Inlier).

1. Highlights

2. The Nebine Ridge is the southward continuation of the Anakie Inlier.

3. The Anakie Inlier and Nebine Ridge represent a northern segment of the Cambrian Delamerian–Thomson Belt.

4. ～E–W-trending crustal-scale structures at the southern Thomson Orogen were active during Devonian.

  相似文献   

Toward a stepwise Kwangsian Orogeny   总被引：2，自引：0，他引：2  

Xu Chen  JunXuan Fan  Qing Chen  Lan Tang  XuDong Hou 《中国科学:地球科学(英文版)》2014,57(3):379-387

The Kwangsian Orogeny originated along the southeast coast of China and stepwise developed in a northwest direction. It includes two stages, a long locally varying uplift from the Late Ordovician to the early Silurian and a finally tectonic movement near the Silurian and Devonian transition. The Kwangsian uplift event shows a stepwise delay northwestwards from the southeastern coast area in Nemagraptus gracilis Biozone (Sa1) to the south side of the Xuefeng Mountains in or later than Cystograptus vesiculosus Biozone (R3) to Coronograptus cyphus Biozone (R4). In the southern of Yangtze Platform, the Yichang Uplift was droved by the Kwangsian Orogeny forming a diachronous stratigraphical break through Rhuddanian and Aeronian. The distribution of the early Telychian lower marine red beds indicates a northwestward increase of the Cathaysian Oldland. Stratigraphical evidence may explain why the Kwangsian movement was marked by an angular disconformity during the Pridoli to earliest Devonian interval.  相似文献   

Fold-interference patterns in the Bowen Basin,northeastern Australia   总被引：1，自引：1，他引：0  

M. J. Campbell  U. Shaanan  C. Verdel 《Australian Journal of Earth Sciences》2017,64(5):577-585

Deformation patterns of Paleozoic and Mesozoic strata in eastern Australia are evidence of a structural and tectonic history that included multiple periods of deformation with variable strain intensities and orientations. Detailed analysis of structural data from the Bowen Basin in northeastern Australia reveals previously undescribed, north–south elongate, Type-1 fold-interference patterns. The Bowen Basin structures have similar orientations to previously described interference patterns of equivalent scale in upper Paleozoic strata of the New England Orogen and Sydney Basin of eastern Australia. The east Australian folds with north–south-trending axes most likely formed during late stages of the Permian–Triassic Hunter–Bowen Orogeny, and they were subsequently refolded around east–west axes during post 30 Ma collision of the Indo-Australian plate with the Eurasian and Pacific plates. The younger, east–west-trending folds have orientations that are well aligned with the present-day horizontal stress field of much of eastern Australia, raising the possibility that they are active structures.  相似文献   

Episodic gold mineralisation correlated with discrete structural events at Ballarat East,southeast Australia     

《Ore Geology Reviews》2017

New ⁴⁰Ar/³⁹Ar geochronological data suggest orogenic gold mineralisation at the Ballarat East deposit, southeast Australia, occurred in three main episodes at ca. 445–435 Ma, ca. 420–415 Ma and ca. 380–370 Ma. The gold mineralisation is localised in muscovite-bearing quartz and quartz-carbonate veins hosted in the steep faults (70–90°), on limbs of tight and isoclinal folds in an Ordovician turbidite sequence, and within west-dipping (≤45°) faults, historically known as leather jacket lodes. Initiation of the ≤45° faults that are confined to fold culminations, begins at ca. 445 Ma, with peak metamorphic conditions at 440 Ma. The earliest vein sets (V₁), were emplaced on limb thrusts at ca. 445–435 Ma and are characterised by arsenopyrite-dominated quartz veins. These V₁ veins parallel arsenopyrite-rich shale units, historically referred to as ‘indicator beds’. Both the steep and ≤45° faults were reactivated during fold amplification with deposition of the V₂ auriferous veins at ca. 420–415 Ma. A later set of auriferous veins (V₃–V₄) with ages of 380–370 Ma, dominated by pyrite-sphalerite-galena-white-mica quartz-(V₃) or carbonate-rich (V₄) veins are predominantly associated with reactivation of the ≤45° west-dipping faults. This new geochronological data constrains the local kinematic history of the Ballarat East deposit and has regional implications. The V₁–V₂ vein development appears to be synchronous across the entire western section of the Lachlan Orogen, where previous studies have suggested that initial gold mineralisation was linked to orogenesis at ∼440 Ma, as a result of metamorphic devolatilisation reactions in the lower crust. In contrast, a close spatial and temporal relationship exists between the felsic dykes and the mineralisation recognised in the V₃–V₄ veins. The deformation that accompanies V₃–V₄ vein development is attributed to small, localised events during east-west shortening, utilising pre-existing fold and fault structures. The origin of the fluids producing the V₃–V₄ veins may be metamorphic devolatilisation associated with widespread felsic magmatism that occurred at this time across central Victoria.  相似文献   

华南陆域内古特提斯形迹、二叠纪造山作用和互换构造域的东延   总被引：24，自引：2，他引：24       下载免费PDF全文

马文璞 《地质科学》1996,31(2):105-113

华南大陆由扬子克拉通和华夏陆块拼合而成,后者具有滇缅泰马(Sibumasu)、印支等互换构造域内诸地块共同的特点。古特提斯洋的一个分支从两广-浙闽东部通过,沟通了以西越南黑水河(SongDa)带和以东环太平洋晚古生代大洋亲缘诸地体。这个分支始于华南中泥盆世的陆内裂陷作用,古生代末扩展成广海。晚二叠世的龙潭组含煤地层和钦防地区的放射虫硅质岩分别代表浅水台地和远海盆地两个不同地形台阶的沉积,中间隔着一个向南倾斜的大陆斜坡。东吴运动在两广交界地区产生磨拉石、混杂堆积,并伴生六万大山等S型花岗岩基,代表云开地块向北的拼贴。类似事件在闽浙东部可能一直持续到晚中生代。  相似文献