Finding of Ca. 1.6 Ga Detrital Zircons from the Mesoproterozoic Dagushi Group, Northern Margin of the Yangtze Block
4
Citation
88
Reference
10
Related Paper
Citation Trend
Abstract:
The middle Mesoproterozoic is a crucial time period for understanding the Precambrian tectonic evolutionary history of the northern Yangtze Block and its relationship with the supercontinent Columbia. The Dagushi Group (Gp) is one of the Mesoproterozoic strata rarely found at the northern margin of the Yangtze Block. U–Pb geochronology and Lu–Hf isotopic analyses of detrital zircons were analyzed for three metamorphic quartz sandstone samples collected from the Luohanling and Dangpuling formations of the Dagushi Gp. These metasandstones yielded major zircon populations at ~2.65 Ga and ~1.60 Ga, respectively. The ~1.60 Ga ages first discovered yield a narrow range of ɛHf(t) values from −1.8 to +1.8, which lie above the old crust evolutionary line of the Yangtze Block, suggesting the addition of mantle material. Trace element data indicate that ~1.60 Ga detrital zircons share a basic provenance, whereby they have low Hf/Th and high Nb/Yb ratios. Zircon discrimination diagrams suggest that the ~1.60 Ga detrital zircon source rocks formed in an intra-plate rifting environment. Dagushi Gp provenance studies indicate that the ~1.60 Ga detrital zircon was most likely sourced from the interior Yangtze Block. Thus, we suggest that the late Paleoproterozoic to early Mesoproterozoic continental break-up occurred at the northern margin of the Yangtze Block.Keywords:
Supercontinent
Rodinia
Passive margin
Geochronology
Continental Margin
The north-central Appalachians lie just southwest of the boundary between the central/southern and northern Appalachians, occupying a critical position within the 3000+ km-long Appalachian orogen. The history of tectonic activity in the north-central Appalachians spans more than one billion years, from the assembly and breakup of a Neoproterozoic supercontinent, through active orogenesis during Laurentia9s Paleozoic northward journey off the western margin of West Gondwana, to the Mesozoic transformation of the active orogen into a passive margin during Pangea9s disassembly. The major tectonic events include five compressional orogenies and two extensional episodes: 1. The late Mesoproterozoic Grenville orogeny assembled several continental masses into the Neoproterozoic supercontinent, Rodinia. It was the most widespread but now least exposed tectonism, and rocks involved in this event underlie as basement most of the exposed north-central Appalachians. Large fragments of Laurentian Grenville rock were subsequently broken off and incorporated in later Appalachian orogenesis. 2. Crustal extension and rifting late in the Neoproterozoic and into the earliest Cambrian separated Laurentia from West Gondwana, thereby forming the intervening Theic ocean and two continental rifts on Laurentia9s eastern margin, the Catoctin rift and, later in the Middle? to Late Cambrian, the so-called Rome trough. The initial siliciclastic sedimentation on the margin migrated westward through time onto the craton, supplanted by a thick and increasingly wide carbonate shelf on Laurentia9s eastern margin. Two microcontinents of Grenville-age, non-Laurentian(?) continental rock became positioned east of Laurentia, thereby creating the Octoraro sea as an arm of Theia. 3. In Theia, east of the two microcontinents, magmatic arcs developed over a subduction zone late in the Cambrian. Convergence within Theia caused the Potomac orogeny, which obduced the arcs (Wilmington Complex, Cecil Amalgamate) over the microcontinents and associated Theic deposits (including accretionary wedge sediments). 4. Continued westward convergence collapsed the Octoraro sea, producing the Middle to Late Ordovician Taconic orogeny in which the Potomac-deformed magmatic arcs and associated Theic elements were obduced onto the Laurentian continental margin. This obduction: drowned the carbonate shelf with siliciclastic sediments (Martinsburg Formation); drove continental rise and basinal deposits over the carbonate shelf on the Martic thrust; slid the Hamburg klippe onto the shelf; and accreted the Potomac package of microcontinent/arc/basinal-sediments onto the Laurentian margin. This orogeny transformed the broad Early Paleozoic carbonate shelf into the Appalachian basin that persisted throughout the Middle and Late Paleozoic. 5. The Middle Devonian Acadian orogeny ended the largely paralic environment that dominated the Appalachian basin during the Late Silurian. Active orogenesis in New England probably extended southward to the north-central Appalachians, because a vast amount of terrigenous sediment was introduced into the Appalachian basin to form the Catskill delta; however, evidence of actual Acadian deformation and metamorphism is lacking at this latitude. These presumed internal Acadides have yet to be found. 6. The convergence of West Gondwana and Laurentia during the Late Carboniferous and earliest Permian produced the Permian Alleghany orogeny in the north-central Appalachians. This widespread decollement tectonism directly affected a larger area of the presently exposed central and southern Appalachians than any earlier Paleozoic tectonic event. An early layer-parallel shortening phase gave way to a fold-thrust development above a basal decollement. This Alleghany fold-and-thrust tectonism created long, arcuate folds in the Appalachian basin. Late in the Alleghany orogeny, rock thrust northward over the Carboniferous rocks in the Anthracite region of northeastern Pennsylvania caused anthracitization of the underlying coals. The internal Alleghanides are not presently exposed. 7. Crustal extension in the Late Triassic and Early Jurassic produced numerous local, closed basins along eastern North America. Igneous intrusions and effusions marked the beginning of the Jurassic. By the end of the Early Jurassic, horizontal crustal rebound in response to opening of the Atlantic Ocean rotated the basins by crustal inversion, which folded some within-basin rocks and produced a prominent topographic ridge along the Piedmont, up-dip of the basins. Subsequent erosion of this Piedmont ridge and other parts of the Appalachian orogen fed large volumes of sediment to offshore basins during the remainder of the Mesozoic and throughout the Cenozoic. Each of these orogenies affected most of the Appalachian orogen. The tectonic expression of each orogeny varied along and across the orogen. The elements and structural bodies involved in each also varied along strike. However, many common elements persist from one part of the orogen to another; only a few features are singular in time and space. The tectonic boundary between the central and northern Appalachians is one of these singular features-it is solely an Alleghanian artifact.
Supercontinent
Rodinia
Laurentia
Orogeny
Passive margin
Continental Margin
Siliciclastic
Cite
Citations (99)
Supercontinent
Rodinia
Hadean
Cite
Citations (253)
Supercontinent
Rodinia
Continental Margin
Cite
Citations (84)
Rodinia
Supercontinent
Cite
Citations (15)
Abstract Petrographical and geochemical data from the Togo structural unit (TSU), also referred to as the Atacora structural unit, are presented together with the existing dataset; geochemical and age data from the sedimentary and metasedimentary rocks from the passive margin sequences of the Dahomeyide belt in Ghana to infer their provenance and depositional setting and expand the discussion on the Rodina–Gondwana supercontinent assembly during the Pan-African orogeny. The metasedimentary rocks of the TSU are quartzites and phyllites. The framework grains of the quartzites consisting dominantly of quartz and small amounts of feldspar grains and relict lithic fragments classify them as quartz arenite, subarkose and sublitharenite. Generally, the studied rocks show similar rare-earth element and multi-element patterns, which imply derivation from similar sources. Elemental ratios, including (La/Lu) N , Th/Sc and La/Sc, suggest sediments sourced from intermediate to felsic rocks. Provenance and depositional setting indicators of the TSU suggest deposition in a passive margin setting, with the West African and Amazonian cratons’ granitoids and granitic gneisses as possible provenance, akin to siliciclastic rocks of the Buem structural unit and the Voltaian Supergroup of the Volta Basin. The deformational history of the TSU is similar to those of the Buem structural unit and the eastern margin of the Voltaian Supergroup, indicating the effect of the Pan-African orogeny on the passive margin of the Dahomeyide belt. We, therefore, propose the formation and evolution of a Neoproterozoic passive margin unit, which was tectonically deformed during the Rodinia–Gondwana supercontinent cycle.
Rodinia
Supercontinent
Margin (machine learning)
Passive margin
Cite
Citations (0)
Supercontinent
Rodinia
Continental arc
Continental Margin
Cite
Citations (1)
The aim of this paper is to discuss the Late Precambrian rock complexes in the southern margin of the Siberian Craton, associated with the extension. The analysis of the data available suggests two episodes of intracontinental breakup which resulted in the opening of oceanic spaces (1300-900 and 850-550 million years). The time sequence of volcanogenic terrigenous of rifting origin ! basic dike swarms ! carbonate- terrigenous rock sequences ! ophiolites and island-arc rocks reflects the consecutive change of geodynamic environments in the marginal part of the craton. The stage of intracontinental rifting was replaced by the stage of advanced rifting, which preceded the continental breakup and the formation of the oceanic crust. Next followed two stages of oceanic crust evolution: the passive stage (sedimentary complexes of the passive margins) and the active stage (island arcs, backarc seas, and the like). Dierent versions are discussed for the manifestation of extension processes in the southwestern and southeastern segments of the Siberian Craton in connection with the breakup of the Rodinia supercontinent.
Supercontinent
Rodinia
Terrigenous sediment
Passive margin
Cite
Citations (3)
Abstract Between 1300 and 500 Ma the Neoproterozoic supercontinent Rodinia aggregated (1300–950 Ma), broke up (850–600 Ma) and a new supercontinent, Pannotia-Gondwana, formed (680–550 Ma). Only c. 11% of the preserved continental crust was produced during this 800 Ma time interval and most of this crust formed as arcs, chiefly continental margin arcs. At least 50% of juvenile continental crust produced between 750 and 550 Ma is in the Arabian-Nubian Shield and in other terranes that formed along the northern border of Amazonia and West Africa. An additional 20% occurs in Pan-African orogens within Amazonia, and c. 16% in the Adamastor and West African orogens. The growth rate of continental crust between 1350 and 500 Ma was similar or less than the average rate of continental growth during the Phanerozoic of 1 km 3 /a, and this low rate characterizes both formation and breakup stages of the supercontinents. The low rates of continental growth during the Neoproterozoic may be due to the absence of a superplume event associated with either Rodinia or Pannotia-Gondwana. If supercontinent breakup is required to produce a superplume event, perhaps by initiating catastrophic collapse of lithospheric slabs at the 660 km seismic discontinuity, the absence of a Meso-proterozoic-Neoproterozoic superplume event may mean that a Palaeoproterozoic supercontinent did not fully breakup prior to aggregation of Rodinia.
Geologic record
Cite
Citations (82)