U-Pb zircon geochronology of late Neoproterozoic–Early Cambrian granitoids in Iran: Implications for paleogeography, magmatism, and exhumation history of Iranian basement     

Jamshid Hassanzadeh  Daniel F. Stockli  Brian K. Horton  Gary J. Axen  Lisa D. Stockli  Marty Grove  Axel K. Schmitt  J. Douglas Walker 《Tectonophysics》2008,451(1-4):71-96

Eurasia has largely grown to its present enormous size through episodic addition of crustal blocks by recurring birth and demise of oceans such as Paleotethys and Neotethys. Excluding the Kopet Dagh Mountains in the northeast, crystalline basement rocks of various dimensions are exposed in all continental tectonic zones of Iran. These rocks have traditionally been viewed as continental fragments with Gondwanan affinity and summarily been assigned Precambrian or younger ages, despite the fact that evidence from isotopic dating has largely been lacking. This study presents new ion microprobe and thermal-ionization zircon U-Pb geochronological data from granitoids and orthogneisses from several locations in central Iran and the Sanandaj–Sirjan structural zones to determine crystallization ages and investigate the origin and continental affinity of these various crustal fragments. The resulting U-Pb crystallization ages for the granites and orthogneisses range from late Neoproterozoic to Early Cambrian, matching the mostly juvenile Arabian–Nubian shield and Peri-Gondwanan terranes constructed after the main phase of Pan-African orogenesis. TIMS analyses of zircons with inherited cores from western Iran suggest that the Neoproterozoic crust of Iran might not be entirely juvenile, pointing to the potential presence of inherited older Proterozoic components as is common in the eastern Arabian shield. More importantly, the new zircon U-Pb crystallization ages unequivocally demonstrate that crystalline basement underlying the Sanandaj–Sirjan zone, central Iran, and the Alborz Mountains is composed of continental fragments with Gondwanan affiliation, characterized by wide spread late Neoproterozoic subduction-related magmatism. The exposure of these late Neoproterozoic–Early Cambrian basement rocks in the Iranian regions north of the Zagros is structurally controlled and linked to both large-scale crustal extension and exhumation during Mesozoic and Tertiary time as well as Tertiary collisional tectonics associated with the closure of Neotethys.  相似文献   

Sedimentary facies of a glacially influenced continental succession in the Pennsylvanian Jericho Formation, Galilee Basin, Australia     

ANDREW T. JONES  CHRISTOPHER R. FIELDING 《Sedimentology》2008,55(3):531-556

Recent work on the Late Palaeozoic Ice Age in eastern Australia has shown the Joe Joe Group in the eastern Galilee Basin, Queensland, to be of critical importance as it is one of few records of Pennsylvanian glacial activity outside South America. This paper presents detailed sedimentological data, from which the Late Palaeozoic environment of the region is reconstructed and which, consequently, allows for robust comment on the broader Gondwanan glaciation. The Jericho Formation, in the lower Joe Joe Group, was deposited in an active extensional basin in lacustrine to fluvial environments, during the mid‐Namurian to early Stephanian. The region experienced a cool climate during this time, and polythermal mountain or valley‐type glaciers periodically advanced into the area from highlands to the north‐east. The Jericho Formation preserves a suite of proglacial to terminal glacial facies that is characterized by massive and stratified diamictites deposited from debris flows, massive and horizontally laminated conglomerates and sandstones deposited from hyperconcentrated density flows, laminated siltstones with outsized clasts and interlaminated siltstone/conglomerate deposited through ice‐rafting into lakes, and sedimentary dykes and breccias deposited through overpressurization of groundwater beneath permafrost. Non‐glacial facies are dominated by fluvial sandstones and lacustrine/overbank siltstones. The glacigenic rocks of the Jericho Formation are confined to discrete packages, recording three separate glacial advances during the latest Namurian to late Westphalian. This arrangement is consistent with the temporal distribution of glacigenic rocks from around the remainder of Australia and Gondwana, which supports the theory that glacial deposits occurred in discrete intervals. The Joe Joe Group is a key succession in the world in this context as, at this time, eastern Australia provides the only unequivocal evidence of a Namurian/Westphalian glaciation outside South America. The continuous record of sedimentation through the Pennsylvanian and Early Permian is indicative of significant warming between glacial intervals, which is difficult to reconcile with the development of long‐lived, cold‐based ice sheets across the supercontinent.  相似文献   

Age and kinematics of ductile deformation in the Cerro Durazno area, NW Argentina: Significance for orogenic processes operating at the western margin of Gondwana during Ordovician – Silurian times     

Maja I. Wegmann  Ulrich Riller  Fernando D. Hongn  Johannes Glodny  Onno Oncken 《Journal of South American Earth Sciences》2008,26(1):78-90

The Cerro Durazno Pluton belongs to a suite of Paleozoic granitoid intrusions in NW-Argentina, that are central for understanding the tectonic setting of the western margin of Gondwana in Ordovician and Silurian times. The pluton and its host rocks were tectonically overprinted by metamorphic mineral shape fabrics formed under middle greenschist-facies metamorphic conditions and associated with the nearby Agua Rosada Shear Zone. Kinematic analysis of the shear zone based on the geometric relationship between individual segments of the shear plane and principal axes of mineral fabric ellipsoids indicates reverse-sense of shear with a minor component of left-lateral displacement. This is compatible with the kinematics of other ductile deformation zones in this area, collectively forming a network, which accomplished orogen-parallel extension in addition to vertical thickening. Using the Rb–Sr isotopic system, an undeformed pegmatite dike of the Cerro Durazno Pluton was dated at 455.8 ± 3.6 Ma and mineral fabrics of the Agua Rosada Shear Zone formed at middle greenschist-facies metamorphism gave deformation ages of 437.0 ± 3.8 Ma and 428.4 ± 4.5 Ma. Thus, tectonic overprint at low metamorphic grade occurred about 20–30 Ma after terminal magmatism in the Cerro Durazno area. Our data from the Cerro Durazno area and regional considerations suggest that the western margin of Gondwana was characterized by orogen-parallel extension in addition to crustal thickening as well as episodes of magmatism and ductile deformation that varied greatly in time and space.  相似文献   

冈瓦纳大陆北缘早期的洋壳信息──来自青藏高原羌塘中部早古生代蛇绿岩的依据     

李才  翟庆国  董永胜  蒋光武  王明  解超明  吴彦旺 《地质通报》2008,27(10)

冈瓦纳大陆北缘裂解普遍认为发生在泥盆纪,形成了古特提斯洋并持续演化到晚三叠世。最近在羌塘中部的桃形湖—果干加年山一带发现了完整的蛇绿岩组合,蛇绿岩中的堆晶辉长岩具有洋中脊玄武岩的地球化学特征,在堆晶辉长岩中获得467 Ma～431Ma的锆石SHRIMP U-Pb年龄,这是龙木错-双湖缝合带首次发现早古生代蛇绿岩,应记录了冈瓦纳北缘早期的洋壳演化信息,冈瓦纳大陆北缘的裂解可能发生于早古生代。  相似文献   

Petrology and CHIME geochronology of Pan-African high K and Sr/Y granitoids in the Nkambe area, Cameroon   总被引：1，自引：1，他引：0  

Samuel Tetsopgang  Kazuhiro Suzuki  Emmanuel Njonfang 《Gondwana Research》2008,14(4):686

The Central African Belt in the Nkambe area, northwestern Cameroon represents a collisional zone between the Saharan metacraton and the Congo craton during the Pan-African orogeny, and exposes a variety of granitoids including foliated and massive biotite monzogranites in syn- and post-kinematic settings. Foliated and massive biotite monzogranites have almost identical high-K calc-alkaline compositions, with 73–67 wt.% SiO₂, 17–13 wt.% Al₂O₃, 2.1–0.9 wt.% CaO, 4.4–2.7 wt.% Na₂O and 6.3–4.4 wt.% K₂O. High concentrations of Rb (264–96 ppm), Sr (976–117 ppm), Ba (3680–490 ppm) and Zr (494–99 ppm), with low concentrations of Y (mostly< 20 ppm with a range 54–6) and Nb (up to 24 ppm) suggest that the monzogranites intruded in collisional and post-collisional settings. The Sr/Y ratio ranges from 25 to 89. K, Rb and Ba resided in a single major phase such as K-feldspar in the source. Garnet was present in the source and remained as restite at the site of magma generation. This high K₂O and Sr/Y granitic magma was generated by partial melting of a granitic protolith under high-pressure and H₂O undersaturated conditions where garnet coexists with K-feldspar, albitic plagioclase. CHIME (chemical Th–U-total Pb isochron method) dating of zircon yields ages of 569 ± 12–558 ± 24 Ma for the foliated biotite monzogranite and 533 ± 12–524 ± 28 Ma for the massive biotite monzogranite indicating that the collision forming the Central African Belt continued in to Ediacaran (ca 560 Ma).  相似文献   

The Neoproterozoic assembly of Gondwana and its relationship to the Ediacaran–Cambrian radiation   总被引：16，自引：15，他引：1  

Joseph G.  Bruce S.   《Gondwana Research》2008,14(1-2):5

The assembly of the Gondwana supercontinent during the waning stages of the Proterozoic provides a tectonic backdrop for the myriad biological, climatological, tectonic and geochemical changes leading up to, and including, the Cambrian radiation. A polyphase assembly of Gondwana during the East Africa, Brasiliano, Kuungan and Damaran orogenies resulted in an extensive mountain chain which delivered nutrients into a shifting oceanic realm. An analysis of key evolutionary events during this time period reveals the following (a) several fauna show well established endemism that may be rooted in a cryptic evolutionary pulse (c). 580 Ma (b) the margins of the Mirovian and Mawson Oceans formed the locus of radiation for the Ediacaran fauna (c) the margins of the Iapetan and Mirovian oceans form the olenellid trilobite realm (d) the margins of the Mawson and Paleo-Asian oceans are the birthplace of the so-called Gondwana Province fauna (e) evolutionary events associated with the Cambrian radiation were likely driven by internal (biological) changes, but radiation was enhanced and ecosystems became more complex because of the geochemical, ecological and tectonic changes occurring during Ediacaran–Cambrian periods.  相似文献   

安徽宿松上石炭统碳酸盐岩台地沉积物定量分析与海平面变化          下载免费PDF全文

芦艳琳  李双应  赵大千  王冰  稽在飞 《古地理学报》2014,16(5):735-746

安徽宿松地区上石炭统碳酸盐岩发育,厚约100m,化石丰富,属于比较典型的浅海碳酸盐岩台地沉积。定量分析显示,研究区岩石类型主要为颗粒灰岩和泥粒灰岩,颗粒平均含量分别为81.2％和69.6％,以浅海生物碎屑为主;其次为粒泥灰岩和泥晶灰岩,颗粒平均含量分别为26.4％和4.1％。依据岩石学特征,研究区主要发育开阔台地相和潮坪相,并可进一步划分出5种沉积亚相,分别是台内滩、台内盆、台内坪、潮间坪和潮上坪。在研究区上石炭统中共识别出3个长期的海进—海退旋回,其表现出在海平面变化总体呈下降趋势的背景之上叠加了短期的高频海平面波动的特征。这3个旋回与扬子板块其他地区及欧美板块同时代地层中的长期海进—海退旋回相当,表明海平面的变化可能受到晚古生代冈瓦纳大陆冰川的冰期和间冰期交替活动的影响。  相似文献   

滇西保山、泰国西部和南部及澳大利亚悉尼盆地的冈瓦纳相二叠系对比     

王小娟  王向东  李文忠  沈树忠  石光荣 《地层学杂志》2004,28(4):336-343

对滇西保山地块、泰国西部和南部及澳大利亚悉尼盆地的冈瓦纳相二叠纪地层进行了对比。前两者的二叠纪地层岩性和所含生物群面貌基本可以对比 ,皆反映出由冈瓦纳相向特提斯相的转变 ,后者是典型的冈瓦纳相 ,仅早二叠世地层的岩性和所含化石与前两者相似。  相似文献   

Ruby Mineralization in Southwest Madagascar   总被引：2，自引：0，他引：2  

A. Mercier  M. Rakotondrazafy  B. Ravolomiandrinarivo 《Gondwana Research》1999,2(3):433

Gem-variety of red corundum (i.e. ruby) is produced in the Ejeda-Fotadrevo area, in southwestern Madagascar. The primary ruby deposits are closely associated with basic/ultrabasic complexes within the high grade metamorphic terranes of the Precambrian Vohibory unit. Ruby is recovered from amphibolite and anorthosite veins within these complexes. Petrographic data and P-T estimates indicate that the ruby-bearing rocks crystallized under granulites facies conditions of 750–850°C and 9–11.5kbar, in accordance with the conditions recorded from the surrounding granulites. The Malagasy ruby deposits present numerous similarities with East African deposits, especially Tanzanian, indicating similar geological context of ruby mineralization and suggesting that ruby formation in both these areas resulted from a same mineralizing event when Madagascar was still adjacent to East Africa (Kenya, Tanzania) in the Gondwanaland assembly at the end of Proterozoic times.  相似文献   

In search of Gondwana heritage in the Outer Melanesian Arc: no pre-upper Eocene detrital zircons in Viti Levu river sands (Fiji Islands)     

D. Cluzel  S. Meffre 《Australian Journal of Earth Sciences》2019,66(2):265-277

Volcanic arcs of the Southwest Pacific, collectively referred to as the Outer Melanesian Arc, are generally thought to result from subduction of the Pacific Plate since the Late Cretaceous. Meanwhile, it is largely accepted that eastward roll-back of the old and dense oceanic plate allowed opening of marginal basins, which isolated large blocks of the former Gondwana margin. Incidentally, some ‘intra-oceanic’ volcanic arcs may have been nucleated on small continental fragments. Detrital zircons collected from sand banks in the mid-reaches of rivers from Viti Levu Island have been analysed for U–Pb geochronology and geochemistry, in order to search for a possible ancient continental arc basement, remnants of a Late Cretaceous arc, and determine the timing and evolution of Fiji arc magmatism. In contrast with some other places of the Outer Melanesian Arc (Solomon, Vanuatu), no pre-upper Eocene zircons have been found. Thus, Gondwana-derived fragments or Late Cretaceous–Paleocene arc remnants are unlikely to form the basement of Viti Levu. Zircon geochemistry confirms the purely intra-oceanic character of volcanic-arc magmatism as well. Variations in some trace-element ratios closely reflect the evolution of Viti Levu Arc from upper Eocene inception to upper Miocene climax and finally Pliocene intra-arc rifting and abandonment.  相似文献