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1.
U‐series ages from thermal ionisation mass spectrometry are reported here for the raised coral reefs of Futuna Island, which lies adjacent to the eastern margin of the backarc Futuna Trough in south Vanuatu, southwest Pacific. U‐series ages from coral from the lowest raised reef indicate that its upper part is most likely to be ca 210 ka, whereas the most elevated raised reef has a likely age of ca 520 ka (range 600–440 ka). The inferred Pliocene‐Quaternary history for Futuna Island and the adjacent Futuna Trough is: (i) formation of the Pliocene—Early Quaternary basaltic‐andesite cone in a southeast part of the Vanuatu Island Arc; (ii) inception of the Futuna Trough (adjacent to the west margin of Futuna Island) since 1.8 Ma; (iii) subsequent uplift of the volcanic cone above sea‐level caused ～500 m of its upper part to be removed by marine erosion; (iv) the island then subsided and at least 160 m of limestone was deposited on the truncated cone; and (v) during the period 520 ka to ca 210 ka seven fringing reefs formed at the margin of the cone as the island was uplifted. Since ca 210 ka Futuna further subsided and, as a result, the post ca 210 ka history of the island is obscure.  相似文献   

2.
Lake George contains the longest continuous sedimentary record of any Australian lake basin, but previous age models are equivocal, particularly for the oldest (pre-Quaternary) part of the record. We have applied a combination of cosmogenic nuclide burial dating, magnetostratigraphy and biostratigraphy to determine the age of the basal (fluvial) unit in the basin, the Gearys Gap Formation. Within the differing resolutions achievable by the three dating techniques, our results show that (i) the Gearys Gap Formation, began accumulating at ca 4 Ma, in the early Pliocene (Zanclean), and (ii) deposition had ceased by ca 3 Ma, in the mid late Pliocene (Piacenzian). Whether the same age control provides an early Pliocene (Zanclean) age for the formation of the lake basin is uncertain. During the Piacenzian, the vegetation at the core site was a wetland community dominated by members of the coral fern family Gleicheniaceae, while the surrounding dryland vegetation was a mix of sclerophyll and temperate rainforest communities, with the latter including trees and shrubs now endemic to New Guinea–New Caledonia and Tasmania. Mean annual rainfall and temperatures are inferred to have been ～2000–3000 mm, although probably not uniformly distributed throughout the year, and within the mesotherm range (>14°C <20°C), respectively. Unresolved issues are: (1) Does the basal gravel unit predate uplift of the Lake George Range and therefore provide evidence that one of the proposed paleo-spillways of Lake George, that above Geary's Gap, has been elevated up to 100–200 m by neotectonic activity over the past 4 million years? (2) Did a shallow to deepwater lake exist elsewhere in the lake basin during the Pliocene?  相似文献   

3.
Detrital zircons from Holocene beach sand and igneous zircons from the Cretaceous syenite forming Cape Sines (Western Iberian margin) were dated using laser ablation – inductively coupled plasma – mass spectrometry. The U–Pb ages obtained were used for comparison with previous radiometric data from Carboniferous greywacke, Pliocene–Pleistocene sand and Cretaceous syenite forming the sea cliff at Cape Sines and the contiguous coast. New U–Pb dating of igneous morphologically simple and complex zircons from the syenite of the Sines pluton suggests that the history of zircon crystallization was more extensive (ca 87 to 74 Ma), in contrast to the findings of previous geochronology studies (ca 76 to 74 Ma). The U–Pb ages obtained in Holocene sand revealed a wide interval, ranging from the Cretaceous to the Archean, with predominance of Cretaceous (37%), Palaeozoic (35%) and Neoproterozoic (19%) detrital‐zircon ages. The paucity of round to sub‐rounded grains seems to indicate a short transportation history for most of the Cretaceous zircons (ca 95 to 73 Ma) which are more abundant in the beach sand that was sampled south of Cape Sines. Comparative analysis using the Kolmogorov–Smirnov statistical method, analysing sub‐populations separately, suggests that the zircon populations of the Carboniferous and Cretaceous rocks forming the sea cliff were reproduced faithfully in Quaternary sand, indicating sediment recycling. The similarity of the pre‐Cretaceous ages (>ca 280 Ma) of detrital zircons found in Holocene sand, as compared with Carboniferous greywacke and Pliocene–Pleistocene sand, provides support for the hypothesis that detritus was reworked into the beach from older sedimentary rocks exposed along the sea cliff. The largest percentage of Cretaceous zircons (<ca 95 Ma) found in Holocene sand, as compared with Pliocene–Pleistocene sand (secondary recycled source), suggests that the Sines pluton was the one of the primary sources that became progressively more exposed to erosion during Quaternary uplift. This work highlights the application of the Kolmogorov–Smirnov method in comparison of zircon age populations used to identify provenance and sediment recycling in modern and ancient detrital sedimentary sequences.  相似文献   

4.
基于TM遥感图像解译和野外调研，分析了攀西地区大渡河、安宁河深切河谷地貌特征和断裂带构造变形特征，建立了安宁河断裂带晚新生代5阶段变形历史。研究表明，中新世晚期—上新世早期，安宁河断裂以挤压走滑活动为主；上新世晚期至早更新世时期，断裂以斜张走滑活动为主，活动强度较弱；早中更新世之间发生的元谋运动使昔格达组湖相地层褶皱变形；中晚更新世时期发生断陷作用，形成安宁河两堑夹—垒的构造格局；晚更新世—全新世时期又以左旋走滑活动为主。综合安宁河、大渡河河谷地貌和晚新生代地层记录和变形特征，提出了攀西高原晚新生代4阶段隆升模式：中新世早中期(12Ma之前)以缓慢隆升与区域夷平化作用为主，中新世晚期—上新世早期(12～3．4Ma)是高原快速隆升与河流强烈下切的时期，上新世晚期—早更新世(3．4～1.1Ma)为昔格达湖盆发育时期，中晚更新世—全新世(1．1Ma以来)是高原快速隆升与河谷阶地发育时期。最后指出，至上新世晚期(3．4Ma以前)，攀西高原海拔高度可能超过了3000m。  相似文献   

5.
The Waratah Fault is a northeast trending, high angle, reverse fault in the Late Paleozoic Lachlan Fold Belt at Cape Liptrap on the Southeastern Australian Coast. It is susceptible to reactivation in the modern intraplate stress field in Southeast Australia and exhibits Late Pliocene to Late Pleistocene reactivation. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) dating of marine terraces on Cape Liptrap are used to constrain rates of displacement across the reactivated Waratah Fault. Six marine terraces, numbered Qt6–Tt1 (youngest to oldest), are well developed at Cape Liptrap with altitudes ranging from ～1.5 m to ～170 m amsl, respectively. On the lowest terrace, Qt6, barnacles in wave-cut notches ～1.5 m amsl, yielded a radiocarbon age of 6090–5880 Cal BP, and reflect the local mid-Holocene sea level highstand. Qt5 yielded four OSL ages from scattered locations around the cape ranging from ～80 ka to ～130 ka. It formed during the Last Interglacial sea level highstand (MIS 5e) at ～125 ka. Inner edge elevations (approximate paleo high tide line) for Qt5 occur at distinctly different elevations on opposite sides of the Waratah Fault. Offsets of the inner edges across the fault range from 1.3 m to 5.1 m with displacement rates ranging from 0.01 mm/a to 0.04 mm/a. The most extensive terrace, Tt4, yielded four Early Pleistocene cosmogenic radionuclide (CRN) ages: two apparent burial ages of 0.858 Ma ± 0.16 Ma and 1.25 Ma ± 0.265 Ma, and two apparent exposure ages of 1.071 Ma ± 0.071 Ma (10Be) and 0.798 Ma ± 0.066 Ma (26Al). Allowing for muonic production effects from insufficient burial depths, the depth corrected CRN burial ages are 1.8 Ma ± 0.56 Ma and 2.52 Ma ± 0.88 Ma, or Late Pliocene. A Late Pliocene age is our preferred age. Offsets of Tt4 across the Waratah Fault range from a minimum of ～20 m for terrace surface treads to a maximum of ～70 m for terrace bedrock straths. Calculated displacement rates for Tt4 range from 0.01 mm/a to 0.04 mm/a (using a Late Pliocene age, ～2 Ma), identical to the rates calculated for the Last Interglacial terrace, Qt5. This indicates that deformation at Cape Liptrap has been ongoing at similar time-averaged rates at least since the Late Pliocene. The upper terraces in the sequence, Tt3 (～110 m amsl), Tt2 (～140 m) and Tt1 (～180 m) are undated, but most likely correlate to sea level highstands in the Neogene. Terraces Tt1–Tt4 show an increasing northward tilt with age.The Waratah Fault forms a prominent structural boundary in the Lachlan Fold Belt discernible from airborne magnetic and bouger gravity anomalies. Seismicity and deformation are episodic. Episodic movement on the Waratah Fault may be coincident with sea level highstands since the Late Pliocene, possibly from increased loading and elevated pore pressure within the fault zone. This suggests that intervals between major seismic events could be on the order of 100 ka.  相似文献   

6.
The low-relief summit plateaus (high plains) of the Southeastern Highlands are remnants of a widespread peneplain that was initially uplifted in the mid-Cretaceous and reached its current elevation in the Miocene–Pliocene. There are two mutually exclusive scenarios for the origin of the high plains: an uplifted peneplain originally formed by long-term denudation through the Mesozoic and late Paleozoic, contrasting with creation by ～1.5 km of erosion following the mid-Cretaceous uplift (based on fission track data). The hypothesis of a Mesozoic peneplain is consistent with the low relief of the high plains, the ca 200 Ma available to form the peneplain, and the pre-late Mesozoic oxygen-isotope composition of secondary kaolinites in weathering profiles on the high plains. If the ca 30 Ma cooling event recorded by the fission track data is due to ～1.5 km of denudation, then the high plains peneplain formed in the Late Cretaceous–early Paleogene, close to sea-level, and was uplifted in the early Paleogene, because evidence from basalts and fossil floras shows that the high plains surface was moderately elevated in the Eocene. This scenario is difficult to reconcile with the long-term erosion necessary to form such an extensive peneplain, the lack of sedimentary evidence for early Paleogene uplift, and the relatively small reduction in elevation (～250 m) that would have resulted from ～1.5 km of erosion (because the crust in this area is in isostatic equilibrium). Furthermore, extensive Cretaceous–early Paleogene denudation should have removed the pre-late Mesozoic secondary kaolinites present in weathering profiles in the highlands. There is no evidence that the Mesozoic peneplain was buried by kilometres of sediment and then exhumed in the Cretaceous–early Paleogene. I therefore conclude that the high plains of the Southeastern Highlands are the remnants of a Mesozoic peneplain uplifted in the mid-Cretaceous and again in the Miocene–Pliocene.  相似文献   

7.
Apatite fission track thermochronology reveals that uplift and erosion occurred during the mid‐Cretaceous within the Bathurst Batholith region of the eastern highlands, New South Wales. Apatite fission track ages from samples from the eastern flank of the highlands range between ca 73 and 139 Ma. The mean lengths of confined fission tracks for these samples are > 13 μm with standard deviations of the track length distributions between 1 and 2 μm. These data suggest that rocks exposed along the eastern flank of the highlands were nearly reset as the result of being subjected to palaeotemperatures in the range of approximately 100–110°C, prior to being cooled relatively quickly through to temperatures < 50°C in the mid‐Cretaceous at ca 90 Ma. In contrast, samples from the western flank of the highlands yield apparent apatite ages as old as 235 Ma and mean track lengths < 12.5 μm, with standard deviations between 1.8 and 3 μm. These old apatite ages and relatively short track lengths suggest that the rocks were exposed to maximum palaeotemperatures between approximately 80° and 100°C prior to the regional cooling episode. This cooling is interpreted to be the result of kilometre‐scale uplift and erosion of the eastern highlands in the mid‐Cretaceous, and the similarity in timing of uplift and erosion within the highlands and initial extension along the eastern Australian passive margin prior to breakup (ca 95 Ma) strongly suggests these two occurrences are related.  相似文献   

8.
Fifty‐five new SHRIMP U–Pb zircon ages from samples of northern Australian ‘basement’ and its overlying Proterozoic successions are used to refine and, in places, significantly change previous lithostratigraphic correlations. In conjunction with sequence‐stratigraphic studies, the 1800–1580 Ma rock record between Mt Isa and the Roper River is now classified into three superbasin phases—the Leichhardt, Calvert and Isa. These three major depositional episodes are separated by ～20 million years gaps. The Isa Superbasin can be further subdivided into seven supersequences each 10–15 million years in duration. Gaps in the geological record between these supersequences are variable; they approach several million years in basin‐margin positions, but are much smaller in the depocentres. Arguments based on field setting, petrography, zircon morphology, and U–Pb systematics are used to interpret these U–Pb zircon ages and in most cases to demonstrate that the ages obtained are depositional. In some instances, zircon crystals are reworked and give maximum depositional ages. These give useful provenance information as they fingerprint the source(s) of basin fill. Six new ‘Barramundi’ basement ages (around 1850 Ma) were obtained from crystalline units in the Murphy Inlier (Nicholson Granite and Cliffdale Volcanics), the Urapunga Tectonic Ridge (‘Mt Reid Volcanics’ and ‘Urapunga Granite’), and the central McArthur Basin (Scrutton Volcanics). New ages were also obtained from units assigned to the Calvert Superbasin (ca 1740–1690 Ma). SHRIMP results show that the Wollogorang Formation is not one continuous unit, but two different sequences, one deposited around 1730 Ma and a younger unit deposited around 1722 Ma. Further documentation is given of a regional 1725 Ma felsic event adjacent to the Murphy Inlier (Peters Creek Volcanics and Packsaddle Microgranite) and in the Carrara Range. A younger ca 1710 Ma felsic event is indicated in the southwestern McArthur Basin (Tanumbirini Rhyolite and overlying Nyanantu Formation). Four of the seven supersequences in the Isa Superbasin (ca 1670–1580 Ma) are reasonably well‐constrained by the new SHRIMP results: the Gun Supersequence (ca 1670–1655 Ma) by Paradise Creek Formation, Moondarra Siltstone, Breakaway Shale and Urquhart Shale ages grouped between 1668 and 1652 Ma; the Loretta Supersequence (ca 1655–1645 Ma) by results from the Lady Loretta Formation, Walford Dolomite, the upper part of the Mallapunyah Formation and the Tatoola Sandstone between ca 1653 and 1647 Ma; the River Supersequence (ca 1645–1630 Ma) by ages from the Teena Dolomite, Mt Les and Riversleigh Siltstones, and Barney Creek, Lynott, St Vidgeon and Nagi Formations clustering around 1640 Ma; and the Term Supersequence (ca 1630–1615 Ma) by ages from the Stretton Sandstone, lower Doomadgee Formation and lower part of the Lawn Hill Formation, mostly around 1630–1620 Ma. The next two younger supersequences are less well‐constrained geochronologically, but comprise the Lawn Supersequence (ca 1615–1600 Ma) with ages from the lower Balbirini Dolomite, and lower Doomadgee, Amos and middle Lawn Hill Formations, clustered around 1615–1610 Ma; and the Wide Supersequence (ca 1600–1585 Ma) with only two ages around 1590 Ma, one from the upper Balbirini Dolomite and the other from the upper Lawn Hill Formation. The Doom Supersequence (<1585 Ma) at the top of the Isa Superbasin is essentially unconstrained. The integration of high‐precision SHRIMP dating from continuously analysed stratigraphic sections, within a sequence stratigraphic context, provides an enhanced chronostratigraphic framework leading to more reliable interpretations of basin architecture and evolution.  相似文献   

9.
The Late Cenozoic basins in the Weihe–Shanxi Graben, North China Craton are delineated by northeast-striking faults. The faults have, since a long time, been related to the progressive uplift and northeastward expansion of the Tibetan Plateau. To show the relation between the basins and faults, two Pliocene–Pleistocene stratigraphic sections(Chengqiang and Hongyanangou) in the southern part of the Nihewan Basin at the northernmost parts of the graben are studied herein. Based on the sedimentary sequences and facies, the sections are divided into three evolutionary stages, such as alluvial fan-eolian red clay, fan delta, and fluvial, with boundaries at ~2.8 and ~1.8 Ma. Paleocurrent indicators, the composition of coarse clastics, heavy minerals, and the geochemistry of moderate–fine clastics are used to establish the temporal and spatial variations in the source areas. Based on features from the middlenorthern basin, we infer that the Nihewan Basin comprises an old NE–SW elongate geotectogene and a young NW–SE elongate subgeotectogene. The main geotectogene in the mid-north is a half-graben bounded by northeast-striking and northwest-dipping normal faults(e.g., Liulengshan Fault). This group of faults was mainly affected by the Pliocene(before ~2.8–2.6 Ma) NW–SE extension and controlled the deposition of sediments. In contrast, the subgeotectogene in the south was affected by northwest-striking normal faults(e.g., Huliuhe Fault) that were controlled by the subsequent weak NE–SW extension in the Pleistocene. The remarkable change in the sedimentary facies and provenance since ~1.8 Ma is possibly a signal of either weak or strong NE–SW extension. This result implies that the main tectonic transition ages of ~2.8–2.6 Ma and ~1.8 Ma in the Weihe–Shanxi Graben are affected by the Tibetan Plateau in Pliocene–Pleistocene.  相似文献   

10.
One of the most significant, but poorly understood, tectonic events in the east Lachlan Fold Belt is that which caused the shift from mafic, mantle‐derived calc‐alkaline/shoshonitic volcanism in the Late Ordovician to silicic (S‐type) plutonism and volcanism in the late Early Silurian. We suggest that this chemical/isotopic shift required major changes in crustal architecture, but not tectonic setting, and simply involved ongoing subduction‐related magmatism following burial of the pre‐existing, active intraoceanic arc by overthrusting Ordovician sediments during Late Ordovician — Early Silurian (pre‐Benambran) deformation, associated with regional northeast‐southwest shortening. A review of ‘type’ Benambran deformation from the type area (central Lachlan Fold Belt) shows that it is constrained to a north‐northwest‐trending belt at ca 430 Ma (late Early Silurian), associated with high‐grade metamorphism and S‐type granite generation. Similar features were associated with ca 430 Ma deformation in east Lachlan Fold Belt, highlighted by the Cooma Complex, and formed within a separate north‐trending belt that included the S‐type Kosciuszko, Murrumbidgee, Young and Wyangala Batholiths. As Ordovician turbidites were partially melted at ca 430 Ma, they must have been buried already to ～20 km before the ‘type’ Benambran deformation. We suggest that this burial occurred during earlier northeast‐southwest shortening associated with regional oblique folds and thrusts, loosely referred to previously as latitudinal or east‐west structures. This event also caused the earliest Silurian uplift in the central Lachlan Fold Belt (Benambran highlands), which pre‐dated the ‘type’ Benambran deformation and is constrained as latest Ordovician — earliest Silurian (ca 450–440 Ma) in age. The south‐ to southwest‐verging, earliest Silurian folds and thrusts in the Tabberabbera Zone are considered to be associated with these early oblique structures, although similar deformation in that zone probably continued into the Devonian. We term these ‘pre’‐ and ‘type’‐Benambran events as ‘early’ and ‘late’ for historical reasons, although we do not consider that they are necessarily related. Heat‐flow modelling suggests that burial of ‘average’ Ordovician turbidites during early Benambran deformation at 450–440 Ma, to form a 30 km‐thick crustal pile, cannot provide sufficient heat to induce mid‐crustal melting at ca 430 Ma by internal heat generation alone. An external, mantle heat source is required, best illustrated by the mafic ca 430 Ma, Micalong Swamp Igneous Complex in the S‐type Young Batholith. Modern heat‐flow constraints also indicate that the lower crust cannot be felsic and, along with petrological evidence, appears to preclude older continental ‘basement terranes’ as sources for the S‐type granites. Restriction of the S‐type batholiths into two discrete, oblique, linear belts in the central and east Lachlan Fold Belt supports a model of separate magmatic arc/subduction zone complexes, consistent with the existence of adjacent, structurally imbricated turbidite zones with opposite tectonic vergence, inferred by other workers to be independent accretionary prisms. Arc magmas associated with this ‘double convergent’ subduction system in the east Lachlan Fold Belt were heavily contaminated by Ordovician sediment, recently buried during the early Benambran deformation, causing the shift from mafic to silicic (S‐type) magmatism. In contrast, the central Lachlan Fold Belt magmatic arc, represented by the Wagga‐Omeo Zone, only began in the Early Silurian in response to subduction associated with the early Benambran northeast‐southwest shortening. The model requires that the S‐type and subsequent I‐type (Late Silurian — Devonian) granites of the Lachlan Fold Belt were associated with ongoing, subduction‐related tectonic activity.  相似文献   

11.
Devonian strata near Fowlers Gap and Nundooka Stations, northern Barrier Ranges comprise ～2.7 km of sparsely fossiliferous, fluvially deposited sandstones (Mulga Downs Group). These strata are subdivided into the Coco Range Sandstone (oldest, Emsian‐Eifelian) found west of the north‐trending Nundooka Creek Fault, and the Nundooka Sandstone (youngest, ?Frasnian‐Famennian found east of the fault). Eleven stratigraphic units are mapped and two of these in the Coco Range Sandstone are formally named as The Valley Tank Arenite and Copi Dam Arenite Members. The Coco Range Sandstone and Nundooka Sandstone are tentatively correlated with strata in the Bancannia Trough. Deposition of the Coco Range Sandstone and Nundooka Sandstone was, however, separate from that of the Bancannia Trough, probably due to topographic highs which occurred east of the Western Boundary Fault.

The Coco Range Sandstone is cut by northeast‐trending faults splaying from the Nundooka Creek Fault. These faults have vertical planes and are thought to predate deposition of the Nundooka Sandstone. In the Late Cretaceous the Nundooka Creek and Western Boundary Faults became active and areas west of these faults were uplifted to form Coco Range and Bald Hill. This fossil landscape was progressively buried by deposition of the Palaeocene‐Eocene Eyre Formation until it was half covered by strata. During the Oligocene silcrete of the Cordillo Surface formed and was overlain conformably by the sandy Doonbara Formation (Miocene). Since the Miocene, much of the Eyre Formation has been removed by erosion to exhume a Late Cretaceous landscape. Subsequently in the ?Pliocene there was some faulting along the Nundooka Creek and Western Boundary Faults because locally the Cordillo Surface and the Doonbara Formation dip toward the faults at 30–72°. At three localities there is evidence of probable Quaternary activity on the Nundooka Creek and the Western Boundary Faults (downthrow to the east) suggesting a different style of tectonics from that in the Miocene.  相似文献   

12.
The Bogong High Plains of eastern Victoria occur as plateau remnants in a highly dissected region of the Australian Alps. Results from apatite fission track analyses indicate that the Bogong region experienced multiple episodes of rapid low‐temperature cooling, most of which can be tentatively linked to a tectonic cause. Early episodes of cooling occurred during the Middle to Late Devonian (ca 400–370 Ma) and Late Carboniferous to Early Permian (ca 310–290 Ma), presumably during different stages of deformation associated with the development of the Lachlan Fold Belt and glacial erosion. Rapid cooling occurred during the Late Permian to Early Triassic (ca 260–240 Ma), presumably in response to the Hunter‐Bowen orogenic event along the eastern Australian continental margin. Since the Triassic, two major episodes of fault reactivation have further displaced fission track ages between sample groups on different structural blocks. The first episode occurred during the middle Cretaceous at ca 110–90 Ma, probably in response to initial extension and denudation along the eastern Australian passive margin prior to breakup. Subsequently during the Early to mid‐Tertiary at ca 65–45 Ma, large‐scale fault reactivation occurred along the Kiewa Fault, possibly in response to changes in intraplate stresses which occurred during the middle Tertiary.  相似文献   

13.
The thick, Eocene to Pliocene, sedimentary sequence in Qaidam Basin at the northern margin of the Tibetan Plateau records the surface uplift history of the northeastern Tibetan plateau. In this study, we present detailed geochemistry, heavy mineral, and clay mineralogy data of the well preserved sedimentary record in the Dahongou section in the northeast of the Qaidam Basin. The results suggest that the sedimentary sequence recorded a 30 Ma young uplift/unroofing event in the northern edge of the Qaidam Basin, which is characterized by high ZTR index value and chlorite content, and low CIW`. The results are consistent with previous sedimentological studies of the Qaidam Basin, which indicated rapid increase of the accumulation rates around 30 Ma. Based on past thermochronological data from the mountains around the Qaidam Basin and the accumulation rates of the Cenozoic basins in the northeastern Tibetan Plateau, we infer a regional uplift and denudation event along the northeastern Tibetan Plateau during early Oligocene (～30 Ma), indicating that the Tibetan Plateau had expanded north-eastward of the study area at that time.  相似文献   

14.
Detrital zircon from two basement blocks (Kubor and Bena Bena) in the central Highlands of Papua New Guinea has an age signature that strongly suggests a northern Australian provenance. Samples of the Omung Metamorphics, southeastern Kubor Block, together yield principal zircon populations with ages of ca 1.8 Ga (～10% of the total), ca 1.55 Ga (～10%), 470–440 Ma (～15%), ca 340 Ma (～10%) and 290–260 Ma (～40%).Two tonalite stocks of the Kubor Intrusive Complex, which intrude the Omung Metamorphics, yield indistinguishable ages of 244.8 ± 4.9 Ma and 239.1 ± 4.2 Ma.Therefore, the deposition and subsequent deformation of the Omung Metamorphics is Late Permian to Early Triassic. A sample of Goroka Formation (Bena Bena Block) contains detrital zircon of similar ages to the Omung Metamorphics, ca 1.8 Ga (5%), ca 1.55 Ga (～45%), ca 430 Ma (～5%) and ca 310 Ma (～40%), suggesting that the Goroka Formation has a similar provenance and might be correlative. In contrast, a metapsammite from the Bena Bena Formation yielded only ages of 290–280 Ma (85%) and ca 240 Ma (15%). A tuff interbedded in the Bena Bena Formation yielded only igneous zircon with a Late Triassic age of 221 ± 3 Ma. Contrary to previous interpretations, the Bena Bena Formation is probably younger than the Goroka Formation. Ages of New Guinea detrital zircon closely match those of igneous and detrital zircon from the Coen Inlier, northeastern Queensland, but contrast with the ages of zircon from terranes further south, east and west. The Kubor and Bena Bena Blocks are not suspect terranes, but rather form part of the Australian craton. The craton margin, modified by rifting during the Mesozoic, was re‐inverted during Cenozoic compression. The Australian craton, in the eastern Highlands of Papua New Guinea, extends at least as far north as the Markham Valley, the northern edge of the Bena Bena terrane.  相似文献   

15.
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16.
嘉黎断裂带两侧晚新生代差异隆升的磷灰石裂变径迹纪录   总被引：5，自引：0，他引：5  
对嘉黎断裂带两侧的磷灰石裂变径迹年代学测试表明,断裂带北侧的磷灰石裂变径迹年龄在5.6~11.7Ma之间,属中新世晚期;断裂带南侧的磷灰石裂变径迹年龄明显较小,6个样品中有5个样品的磷灰石裂变径迹年龄在4.0~5.9Ma之间,属上新世早期.嘉黎断裂带北侧5.6~11.7Ma期间的隆升速率为0.07~0.09mm/a.5.8Ma以来平均剥露速率为0.50mm/a,平均隆升速率1.33mm/a.断裂带南侧4.7Ma以来平均剥露速率为0.62mm/a,平均隆升速率1.68mm/a.两侧样品都反映上新世以来有较强烈的隆升作用,并且南侧比北侧隆升作用更强烈.  相似文献   

17.
This study provides an integrated interpretation for the Mesozoic-Cenozoic tectonothermal evolutionary history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin. Apatite fission-track and apatite/zircon(U-Th)/He thermochronometry, bitumen reflectance, thermal conductivity of rocks, paleotemperature recovery, and basin modeling were used to restore the Meso-Cenozoic tectonothermal history of the Permian Strata. The Triassic AFT data have a pooled age of ～180±7 Ma with one age peak and P(χ2)=86%. The average value of corrected apatite(U-Th)/He age of two Permian sandstones is ～168±4 Ma and a zircon(U-Th)/He age from the Cambrian strata is ～231±14 Ma. Bitumen reflectance and maximum paleotemperature of two Ordovician mudstones are 1.81%, 1.57% and ～210°C, ～196°C respectively. After undergoing a rapid subsidence and increasing temperature in Triassic influenced by intrusive rocks in some areas, the Permian strata experienced four cooling-uplift stages after the time when the maximum paleotemperature reached in late Jurassic:(1) A cooling stage(～163 Ma to ～140 Ma) with temperatures ranging from ～132°C to ～53°C and a cooling rate of ～3°C/Ma, an erosion thickness of ～1900 m and an uplift rate of ～82 m/Ma;(2) A cooling stage(～140 Ma to ～52 Ma) with temperatures ranging from ～53°C to ～47°C and a cooling rate less than ～0.1°C/Ma, an erosion thickness of ～300 m and an uplift rate of ～3 m/Ma;(3)(～52 Ma to ～8 Ma) with ～47°C to ～43°C and ～0.1°C/Ma, an erosion thickness of ～500 m and an uplift rate of ～11 m/Ma;(3)(～8 Ma to present) with ～43°C to ～20°C and ～3°C/Ma, an erosion thickness of ～650 m and an uplift rate of ～81 m/Ma. The tectonothermal evolutionary history of the Qishan area in Triassic was influenced by the interaction of the Qinling Orogeny and the Weibei Uplift, and the south Qishan area had the earliest uplift-cooling time compared to other parts within the Weibei Uplift. The early Eocene at ～52 Ma and the late Miocene at ～8 Ma, as two significant turning points after which both the rate of uplift and the rate of temperature changed rapidly, were two key time for the uplift-cooling history of the Permian strata in the Qishan area of the southwestern Weibei Uplift, Ordos Basin.  相似文献   

18.
Apatite fission track thermochronology from Early Palaeozoic granitoids centred around the Kosciuszko massif of the Snowy Mountains, records a denudation history that was episodic and highly variable. The form of the apatite fission track age profile assembled from vertical sections and hydroelectric tunnels traversing the mountains, together with numerical forward modelling, provide strong evidence for two episodes of accelerated denudation, commencing in Late Permian—Early Triassic (ca 270–250 Ma) and mid‐Cretaceous (ca 110–100 Ma) times, and a possible third episode in the Cenozoic. Denudation commencing in the Late Permian—Early Triassic was widespread in the eastern and central Snowy Mountains area, continued through much of the Triassic, and amounted to at least ～2.0–2.4 km. This episode was probably the geomorphic response to the Hunter‐Bowen Orogeny. Post‐Triassic denudation to the present in these areas amounted to ～2.0–2.2 km. Unambiguous evidence for mid‐Cretaceous cooling and possible later cooling is confined to a north‐south‐trending sinuous belt, up to ～15 km wide by at least 35 km long, of major reactivated Palaeozoic faults on the western side of the mountains. This zone is the most deeply exposed area of the Kosciuszko block. Denudation accompanying these later events totalled up to ～1.8–2.0 km and ～2.0–2.25 km respectively. Mid‐Cretaceous denudation marks the onset of renewed tectonic activity in the southeastern highlands following a period of relative quiescence since the Late Triassic, and establishes a temporal link with the onset of extension related to the opening of the Tasman Sea. Much of the present day relief of the mountains resulted from surface uplift which disrupted the post‐mid‐Cretaceous apatite fission track profile by variable offsets on faults.  相似文献   

19.
The Willyama Supergroup of the Broken Hill region in southern Australia consists of supracrustal sedimentary and magmatic rocks, formed between 1810 and 1600 Ma. A statistical analysis of nearly 2000 SHRIMP U–Pb zircon spot ages, compiled from published and unpublished sources, provides evidence for three distinct tectonostratigraphic successions and four magmatic events during this interval. Succession 1 includes Redan Geophysical Zone gneisses and the lower part of the Thackaringa Group (Cues Formation). These rocks were deposited after 1810 Ma and host granite sills of the first magmatic event (1710–1700 Ma). Succession 2 includes the upper Thackaringa Group (Himalaya Formation), the Broken Hill Group and the Sundown Group and was deposited between 1710 and 1660 Ma. These rocks all contain detrital zircons from the first magmatic event (1710–1700 Ma) and in some cases from the second magmatic event (1690–1680 Ma). The second magmatic event (1690–1680 Ma) was bimodal, resulted from crustal extension, and was coeval with deposition of the Broken Hill Group and deepening of the basin. With this event a mafic sill swarm focused in the Broken Hill Domain. Mafic sills lack any trace of inheritance, unlike the granitoids that commonly contain inherited zircons typical of the supracrustal sediments. Succession 3, the Paragon Group and equivalents were deposited after 1660 Ma, but before a regional metamorphic event at 1600 Ma. Metamorphism was closely followed by inversion of the succession into a fold‐and‐thrust belt, accompanied by a fourth late to post‐orogenic magmatic event (ca 1580 Ma) characterised by granite intrusion and regional acid volcanism (the local equivalents of the Gawler Range Volcanics in South Australia).  相似文献   

20.
Tuffaceous mudrocks are common in the banded iron‐formations (BIF) of the Brockman Iron Formation. These tuffaceous mudrocks are either stilpnomelane‐rich or siliceous. Their compositions reflect bimodal volcanic activity in the vicinity of the Hamersley BIF depositional site. They also contain complex zircon populations that record resedimentation, syndepositional volcanism and post‐depositional isotopic disturbance. The best estimates of depositional age are obtained from siliceous tuffaceous mudrocks in the Joffre Member that contain 2459 ± 3 Ma and 2454 ± 3 Ma zircon populations most likely derived from felsic volcanism coeval with BIF deposition. These dates constrain the sedimentation rates for the ～370 m‐thick Joffre Member BIF to >15 m per million years. Siliceous tuffaceous mudrocks are not present in the underlying ～120 m‐thick Dales Gorge Member and it is uncertain whether previously reported ages of ca 2479–2470 Ma for this unit reflect detrital/xenocrystic or syndepositional zircon populations in resedimented stilpnomelane‐rich tuffaceous mudrocks. The increased abundance of tuffaceous mudrocks in the Joffre Member suggests that a pulse of enhanced igneous and hydrothermal activity accompanied deposition of the bulk of the Brockman Iron Formation BIF after ca 2460 Ma. This preceded and culminated in the emplacement of the 2449 ± 3 Ma large igneous province represented by BIF and igneous rocks of the Weeli Wolli Formation and Woongarra Rhyolite.  相似文献   

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