Pre‐Tabberabberan deformation in eastern Tasmania: A southern extension of the Benambran Orogeny     

A. R. Reed 《Australian Journal of Earth Sciences》2013,60(6):785-796

Recumbent folding in eastern Tasmania affected turbidites containing Lower to Middle Ordovician (Bendigonian Be1 to Darriwilian Da3) fossils, but not stratigraphically overlying turbidites containing Silurian (Ludlow) graptolites, and is of a timing consistent with Ordovician to Silurian Benambran orogenesis on the Australian mainland. Two subsequent phases of upright folding post‐date deposition of turbidites containing Devonian plant fossils but pre‐date intrusion of Middle Devonian granitoids, and are of Tabberabberan age. A closely spaced disjunctive cleavage (S₂), associated with the first phase of Tabberabberan folding, everywhere cuts a slaty cleavage (S₁) associated with the earlier formed recumbent folds. However, refolding associated with development of S₂ is not always clear in outcrop and it is proposed that coincident tectonic vergence between the two events has resulted in reactivation of recumbent D₁ structures during the D₂ event. The transition to rocks not affected by recumbent folding coincides with a marked change in sedimentology from shale‐ to sand‐dominated successions. This contact does not outcrop but, from seismic data, appears to dip moderately to the east, and can only be explained as an unconformity. The current grouping of all pre‐Middle Devonian turbidites in eastern Tasmania into the one Mathinna Group is misleading in that the turbidite sequence can be subdivided into two distinct sedimentary packages separated by an orogenic event. It is proposed that the Mathinna Group be given supergroup status and existing formations placed into two new groups: an older Early to Middle Ordovician Tippogoree Group and a younger Silurian to Devonian Panama Group.  相似文献   

eo-Variscan (Devonian?) melting in the High Grade Metamorphic Complex of the NE Sardinia Belt (Italy)     

《Geodinamica Acta》2013,26(3-4):155-164

New structural data pointed out the presence of an older scattered migmatization event (Devonian?, M1) overcome by the well known Variscan migmatization event (Lower-Middle Carboniferous, M2) related to the Late extensional tectonic that affected the High Grade Metamorphic Complex (HGMC) in the Variscan Belt of Sardinia (Italy). The M1 event is only recognizable in the kyanite – amphibole bearing migmatitic gneiss. Both migmatization events (M1 and M2) are characterized by a syn-tectonic non coaxial deformations (D1 and D2 deformational events). D1 shows a top to NW sense of shear while the D2 event a top to NE/SE sense of shear (the shear senses are considered at the present Sardinia – Corsica block position in the Mediterranean sea). The M2+D2 is characterized by a complicate, composite normal shear network; the M1+D1 by inverse shear zones. The M2+D2 is transposed by the late D3 strike slip shear event: the D3 is characterized by strike slip shear zones syn-kinematic to the emplacement of Late Carboniferous granitoids (320 Ma – 300 Ma). Despite the absence of geochronological data about the M1+D1 event, the field relationships suggest, for first time, an older migmatization process (Devonian?) syn-tectonic with the late stage of thickness of the Sardinia Variscan Belt. Similar evolutions are recognized in different segments of the Variscan Belt such as the Massif Central (France) or in the eastern mid-European Variscides.  相似文献   

Contemporaneous assembly of Western Gondwana and final Rodinia break-up: Implications for the supercontinent cycle   总被引：2，自引：0，他引：2  

Sebastián Oriolo  Pedro Oyhantçabal  Klaus Wemmer  Siegfried Siegesmund 《地学前缘(英文版)》2017,8(6):1431-1445

Geological, geochronological and isotopic data are integrated in order to present a revised model for the Neoproterozoic evolution of Western Gondwana. Although the classical geodynamic scenario assumed for the period 800–700 Ma is related to Rodinia break-up and the consequent opening of major oceanic basins, a significantly different tectonic evolution can be inferred for most Western Gondwana cratons. These cratons occupied a marginal position in the southern hemisphere with respect to Rodinia and recorded subduction with back-arc extension, island arc development and limited formation of oceanic crust in internal oceans. This period was thus characterized by increased crustal growth in Western Gondwana, resulting from addition of juvenile continental crust along convergent margins. In contrast, crustal reworking and metacratonization were dominant during the subsequent assembly of Gondwana. The Río de la Plata, Congo-São Francisco, West African and Amazonian cratons collided at ca. 630–600 Ma along the West Gondwana Orogen. These events overlap in time with the onset of the opening of the Iapetus Ocean at ca. 610–600 Ma, which gave rise to the separation of Baltica, Laurentia and Amazonia and resulted from the final Rodinia break-up. The East African/Antarctic Orogen recorded the subsequent amalgamation of Western and Eastern Gondwana after ca. 580 Ma, contemporaneously with the beginning of subduction in the Terra Australis Orogen along the southern Gondwana margin. However, the Kalahari Craton was lately incorporated during the Late Ediacaran–Early Cambrian. The proposed Gondwana evolution rules out the existence of Pannotia, as the final Gondwana amalgamation postdates latest connections between Laurentia and Amazonia. Additionally, a combination of introversion and extroversion is proposed for the assembly of Gondwana. The contemporaneous record of final Rodinia break-up and Gondwana assembly has major implications for the supercontinent cycle, as supercontinent amalgamation and break-up do not necessarily represent alternating episodic processes but overlap in time.  相似文献   

From mountains to basins - Insights from orogenic collapse in southern Ryukyu and northern Taiwan     

Louis S. TENG 《地球学报》2009,30(Z1):81-81

Along the Eurasian continental margin, fragments of island arcs and continents affiliated with Gond-wanaland have continually been accreted as suspect terraines through the processes of accretionary orogeny and ensuing orogenic collapse. These proc-esses can be vividly perceived in the present Western Pacific area, where southern Ryukyu and northern Taiwan serve as the youngest and most dynamic ex-ample of tectonic transformation from a rising moun-tain belt to a deepening marine basin.  相似文献   

Imposition of a Proterozoic salient on a Palaeozoic orogen at the eastern margin of Gondwana     

H.A. Williams  J.R. Stewart  P.G. Betts 《Gondwana Research》2009,16(3-4):669-686

Regional analysis of the distribution of metamorphic fabrics and shear zones in the Palaeo-Mesoproterozoic Curnamona Province has enabled the deconstruction of a Cambrian fold arc that defines part of the eastern margin of Gondwana. We suggest a tectonic model whereby the arc formed at ca. 500 Ma, during accretion of Phanerozoic terranes to the eastern margin of Precambrian Australia. The regional fold arc is interpreted to have formed along an irregular plate margin comprising a SE-convex rigid promontory of Precambrian basement during initial accretion of the Phanerozoic terranes during the Cambrian. An early phase of dextral oblique-slip along shear zones in the south and west of the province indicates an initial WNW transport direction. As the arc was folded, a slightly later phase of sinistral oblique-slip shearing was initiated along shear zones in the east, in response to deflection of the arc around the rigid promontory.  相似文献   

Anatomy of a Cambrian suture in Gondwana: Pacific-type orogeny in southern India?   总被引：7，自引：4，他引：3  

M. Santosh  Shigenori Maruyama  Kei Sato 《Gondwana Research》2009,16(2):321

Southern India occupies a central position in the Late Neoproterozoic–Cambrian Gondwana supercontinent assembly. The Proterozoic mosaic of southern India comprises a collage of crustal blocks dissected by Late Neoproterozoic–Cambrian crust-scale shear/suture zones. Among these, the Palghat–Cauvery Suture Zone (PCSZ) has been identified as the trace of the Cambrian suture representing Mozambique Ocean closure during the final phase of amalgamation of the Gondwana supercontinent. Here we propose a model involving Pacific-type orogeny to explain the Neoproterozoic evolution of southern India and its final amalgamation within the Gondwana assembly. Our model envisages an early rifting stage which gave birth to the Mozambique Ocean, followed by the initiation of southward subduction of the oceanic plate beneath a thick tectosphere-bearing Archean Dharwar Craton. Slices of the ocean floor carrying dunite–pyroxenite–gabbro sequence intruded by mafic dykes representing a probable ophiolite suite and invaded by plagiogranite are exposed at Manamedu along the southern part the PCSZ. Evidence for the southward subduction and subsequent northward extrusion are preserved in the PCSZ where the orogenic core carries high-pressure and ultrahigh-temperature metamorphic assemblages with ages corresponding to the Cambrian collisional orogeny. Typical eclogites facies rocks with garnet + omphacite + quartz and diagnostic ultrahigh-temperature assemblages with sapphirine + quartz, spinel + quartz and high alumina orthopyroxene + sillimanite + quartz indicate extreme metamorphism during the subduction–collision process. Eclogites and UHT granulites in the orogenic core define P–T maxima of 1000 °C and up to 20 kbar. The close association of eclogites with ultramafic rocks having abyssal signatures together with linear belts of iron formation and metachert in several localities within the PCSZ probably represents subduction–accretion setting. Fragments of the mantle wedge were brought up through extrusion tectonics within the orogenic core, which now occur as suprasubduction zone/arc assemblages including chromitites, highly depleted dunites, and pyroxene bearing ultramafic assemblages around Salem. Extensive CO₂ metasomatism of the ultramafic units generated magnesite deposits such as those around Salem. High temperature ocean floor hydrothermal alteration is also indicated by the occurrence of diopsidite dykes with calcite veining. Thermal metamorphism from the top resulted in the dehydration of the passive margin sediments trapped beneath the orogenic core, releasing copious hydrous fluids which moved upward and caused widespread hydration, as commonly preserved in the Barrovian amphibolite facies units in the PCSZ. The crustal flower structure mapped from PCSZ supports the extrusion model, and the large scale north verging thrusts towards the north of the orogenic core may represent a fold-thrust belt. Towards the south of the PCSZ is the Madurai Block where evidence for extensive magmatism occurs, represented by a number of granitic plutons and igneous charnockite massifs of possible tonalite–trondhjemite–granodiorite (TTG) setting, with ages ranging from ca. 750–560 Ma suggesting a long-lived Neoproterozoic magmatic arc within a > 200 km wide belt. All these magmatic units were subsequently metamorphosed, when the Pacific-type orogeny switched over to collision-type in the Cambrian during the final phase of assembly of the Gondwana supercontinent. One of the most notable aspects is the occurrence of arc magmatic rocks together with high P/T rocks, representing the deeply eroded zone of subduction. The juxtaposition of these contrasting rock units may suggest the root of an evolved Andean-type margin, as in many arc environments the roots of the arc comprise ultramafic/mafic cumulates and the felsic rocks represent the core of the arc. The final phase of the orogeny witnessed the closure of an extensive ocean — the Mozambique Ocean — and the collisional assembly of continental fragments within the Gondwana supercontinent amalgam. The tectonic history of southern India represents a progressive sequence from Pacific-type to collision-type orogeny which finally gave rise to a Himalayan-type Cambrian orogen with characteristic magmatic, metasomatic and metamorphic factories operating in subduction–collision setting.  相似文献   

Pre‐Variscan metagabbro from NW Sardinia,Italy: evidence of an enriched asthenospheric mantle source for continental alkali basalts     

Marcello Franceschelli  Gabriele Cruciani  Mariano Puxeddu  Daniela Utzeri 《Geological Journal》2003,38(2):145-159

Small metagabbro bodies are enclosed in the metasedimentary sequence of NW Sardinia. The metagabbros represent the last magmatic episode before the continent–continent collision that built up the Variscan chain of north Sardinia. The metagabbros are composed of variable proportions of plagioclase and pyroxene igneous relics and metamorphic minerals. Major and trace element data, specifically high TiO₂ and P₂O₅ and low K and Rb contents, as well as light rare‐earth elements, Nb and Ta enrichment, suggest an alkaline affinity for the gabbro and emplacement in a within‐plate tectonic setting. The gabbro was derived from an ocean island alkali basalt‐like asthenospheric mantle source enriched with incompatible elements and uncontaminated by crustal or subducted materials. Non‐modal modelling indicates a 5–7% partial melting of the asthenospheric mantle. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Geochemistry,zircon U–PB ages and HF isotopes of the Muong Luan granitoid pluton,Northwest Vietnam and its petrogenetic significance     

Pham T. Hieu  Nong T. Q. Anh  Pham Minh  Nguyen T. B. Thuy 《Island Arc》2020,29(1)

The Indosinian Orogeny plays a significant role in tectonic background and magmatic evolution in Indochina and surrounding regions. Being a part product of the Indosinian magmatism in northwest Vietnam during late Permian–middle Triassic period, Muong Luan granitoid pluton dominantly consists of granodiorite, less diorite and granite. This pluton is located in the Song Ma suture and assigned to the Dien Bien complex. Geochemically, the Muong Luan granitoid rocks are characterized by a wide range of SiO₂ contents (59.9–75.1 wt%) and high K₂O contents. They display typical features of I‐type granites. The presence of hornblende and no muscovite and cordierite in the rocks further supports for I‐type character of granitoids. The emplacement age of the Muong Luan pluton obtained by LA–ICP–MS U–Pb zircon is at 242–235 Ma, corresponding to Indosinian time. Zircon ε_Hf values of –5.6 to –10.4, in combination with moderate Mg values of 34–45 suggested that the Muong Luan granitoid was derived from partial melting of mafic crustal source rocks, which are probably Paleoproterozoic in age as revealed by Hf model ages (T_DM2 = 1624–1923 Ma).  相似文献   

下扬子独立地块与中生代改造型残留盆地   总被引：21，自引：7，他引：14       下载免费PDF全文

叶舟  马力  梁兴  吴根耀  徐克定  张廷山 《地质科学》2006,41(1):81-101

下扬子地块在古纬度、火山岩和花岗岩时空发育、区域成矿专属性、沉积建造和构造变形等方面具独特性,与扬子地块有显著差异,是一个晚古生代——中生代早期的独立地块。受燕山期苏鲁板间造山作用影响,下扬子地块直至燕山中期才“楔入”在印支期已拼合的扬子与华北地块,从而演化成独特的下扬子改造型残留叠合盆地。这种改造型叠合盆地的基本特点是:晚印支-早燕山同造山期前陆盆地沉积层和上叠的中燕山期陆相沉积层遭受大量剥蚀,并与古生-中生界海相沉积层一起被卷入强烈的多期次的燕山造山运动,晚白垩世——古近纪又强烈反转成为断陷盆地,形成鲜明的上部地壳的双层结构。这是造成下扬子地区海相古生-中生界油气地质勘探高复杂性、高难度性和高风险性的根本原因,也造就了下扬子区海相烃源岩的二次生烃和晚期成藏的优势。  相似文献   

Structural control on gold mineralization at Walhalla,Victoria     

K. M. Tomlinson  C. J. L. Wilson  R. Hazeldene  E. M. Lohe 《Australian Journal of Earth Sciences》2013,60(4):421-444

Gold mineralization associated with quartz reefs is related to the structural history of the Early Devonian, Walhalla Group. These reefs are situated in the Walhalla Synclinorium, developed during the Middle to Late Devonian Tabberabberan Orogeny. A pervasive north‐south‐trending axial planar cleavage and two styles of folding were produced during regional east‐west compression. The first are upright, open to close folds with sub‐horizontal fold axes. The second are plunging inclined, close to tight folds with fold axes that plunge steeply to the north and south. An extensional event is associated with the emplacement of the Woods Point Dyke swarm and a set of normal faults that offset all earlier structures. High‐angle reverse faults, which post‐date the folding and the emplacement of the dykes, were utilized as conduits for hydrothermal fluids and preferentially localize mineralization to laminated quartz veins. En echelon vein arrays formed during initial stages of reverse faulting became deformed during prolonged shearing to produce ptygmatic veins. Laminated quartz veins within high‐angle reverse faults contain arsenopyrite and pyrite in vein margins and gold in fractures that cross‐cut continuous quartz crystals. Gold, galena, chalcopyrite and sphalerite may also be deposited adjacent to and within fractured arsenopyrite and pyrite. Late‐stage, cross faults developed in a regime of north‐south compression and post‐date the laminated quartz veins and mineralization.  相似文献