Content uploaded by Joachim Jacobs
Author content
All content in this area was uploaded by Joachim Jacobs on Apr 29, 2014
Content may be subject to copyright.
A preview of the PDF is not available
Apatite fission track evidence for contrasting thermal and uplift histories of metamorphic basement blocks in western Dronning Maud Land
... Trace elements and fluid inclusions in quartz from the megacrystic coarse-grained two mica granite within the Land's End granitic complex [1] of southwest England have been studied in order to link chemical evolution of quartz and the coexisting fluid to the P-T-X history [2] [3] of the intrusion. Two main stages of quartz growth are observed: Up to 1 cm large phenocrysts with weak oscillatory cathodoluminescence zoning, sometimes with a lower luminescent core, and fine grained, mostly < 1 mm, quartz with strong normal cathodoluminescence zoning. ...
... j.oregeorev.2005.05.002. [2] Charoy, B. 1982: in Mineralization Associated with Acid Magmatism (ed A. M. Evans) 63-70 (John Wiley). [3] Pownall, J. M., Waters, D. J., Searle, M. P., Shail, R. K. & Robb, L. J. 2012: Shallow laccolithic emplacement of the Land's End and Tregonning granites, Cornwall, UK: Evidence from aureole field relations and P-T modeling of cordieriteanthophyllite hornfels. ...
... The Varanger glaciogenic deposits in northern Norway remain only roughly constrained to ca. 630 to 560 Ma. Our earlier imprecise Re-Os age of ~560 Ma for the Biri Shale, below the Moelv tillite in south Norway suggested correlation with the Gaskier [2]. Further study shows that the upper part of the shale section was disturbed by a redox front during the Caledonian orogeny. ...
Carboniferous rift basin architecture in the SW Barents Sea
Mahajan, A.*, Faleide, J.I. & Gabrielsen, R.H.
Department of Geosciences, University of Oslo
*aatisha.mahajan@geo.uio.no
The geological background for the regional orientation of the Late Paleozoic basins in the SW Barents Sea is a topic of recent debate. Two models have been suggested. The first suggests that the positions and orientations of the basins are dominated by a NE-SW
trending grain. The other model is based on evidence from recent high-quality magnetic data suggesting a NNW-SSE-strike for these Late Paleozoic basins. With the recent acquisition of long-offset reflection seismic data, imaging of the Late Palaeozoic structures
is much clearer and the seismic coverage has also become denser. We are using this dataset to map the Carboniferous basin structures. From our interpretation, we observe a fan-shaped basin architecture with three main branches i) an ENE oriented branch to the south of the Nordkapp Basin ii) a NE-SW-oriented branch between the Nordkapp and Ottar basins and, iii) a NNESSW-oriented branch associated with the Hoop Fault Complex and Maud Basin. This basin architecture forms graben units with inter- and intra-basinal highs. From the orientation of the Carboniferous rift structures, the predominant stress regime is assumed to have been predominnantly oriented WNW-ESE. This basin configuration also had an impact on later Permian depositional system and facies distribution.
Thus, we suggest that the NNW-SSE trending basins as reflected by the magnetic data likely represents thick Devonian basin configurations related to the collapse of
Caledonian Orogen in the SW Barents Sea, rather than younger Carboniferous structures which cross-cut the older grain.
... Most of the types of studies described above remain to be applied for the continental margin of Dronning Maud Land, Antarctica. Low temperature geochronology data from both ends of the escarpment reveal periods of cooling that can be related to denudation shortly after continental breakup (Jacobs et al., 1992(Jacobs et al., , 1995Näslund, 2001;Krohne, 2017). As elsewhere in the world, however, the spatial and depth resolutions of these data are not sufficient to unequivocally support the idea of escarpment retreat by erosional backwearing. ...
... As at many other margins worldwide, the distribution of mineral cooling data from Dronning Maud Land means such interpretations are not unequivocal (Braun and van der Beek, 2004). Näslund's (2001) interpretation of post-breakup denudation in western Dronning Maud Land (Jacobs et al., 1992(Jacobs et al., , 1995 in terms of erosional retreat of an originally-tectonic fault scarp thus remains be tested using complementary approaches. ...
Modelling-, rock cooling-, sedimentation- and exposure-based interpretations of the mechanisms by which topography evolves at extended continental margins vary widely. Observations from the margin of Dronning Maud Land, Antarctica, have until now not strongly contributed to these interpretations. Here, we present new airborne gravity and radar data describing the eastern part of this margin. Inland of a tall (2.5 km) great escarpment, a plateau topped by a branching network of valleys suggests preservation of a fluvial landscape with SW-directed drainage beneath a cold-based ice sheet. The valley floor slopes show that this landscape was modified during a period of alpine-style glaciation prior to the onset of the current cold-based phase around 34 Ma. The volume of sediments in basins offshore in the Riiser-Larsen Sea balances with the volume of rock estimated to have been eroded and transported by north-directed drainage from between the escarpment and the continental shelf break. The stratigraphy of these basins shows that most of the erosion occurred during the ~40 Myr following late Jurassic continental breakup. This erosion is unlikely to have been dominated by backwearing because the required rate of escarpment retreat to its present location is faster than numerical models of landscape evolution suggest to be possible. We suggest an additional component of erosion by downwearing seawards of a pre-existing inland drainage divide. The eastern termination of the great escarpment and inland plateau is at the West Ragnhild trough, a 300 km long, 15-20 km wide and up to 1.6 km deep subglacial valley hosting the West Ragnhild glacier. Numerous overdeepened (by >300 m) segments of the valley floor testify to its experience of significant glacial erosion. Thick late Jurassic and early Cretaceous sediments fanning out from the trough’s mouth into the eastern Riiser-Larsen Sea betray an earlier history as a river valley. The lack of late Jurassic relief-forming processes in this river’s catchment in the interior of East Antarctica suggests this erosion was related to regional climatic change.
... Low-temperature thermochronological data are available from eight studies in western and central DML [14][15][16]25,[37][38][39][40] . The data that have been published so far include 203 apatite fission-track (AFT) analyses, 71 apatite (U-Th)/He (AHe) analyses, 14 zircon fission-track analyses, 11 zircon (U-Th)/ He analyses and 22 titanite fission-track analyses. ...
The coast-parallel Dronning Maud Land (DML) mountains represent a key nucleation site for the protracted glaciation of Antarctica. Their evolution is therefore of special interest for understanding the formation and development of the Antarctic ice sheet. Extensive glacial erosion has clearly altered the landscape over the past 34 Myr. Yet, the total erosion still remains to be properly constrained. Here, we investigate the power of low-temperature thermochronology in quantifying glacial erosion in-situ. Our data document the differential erosion along the DML escarpment, with up to c. 1.5 and 2.4 km of erosion in western and central DML, respectively. Substantial erosion at the escarpment foothills, and limited erosion at high elevations and close to drainage divides, is consistent with an escarpment retreat model. Such differential erosion suggests major alterations of the landscape during 34 Myr of glaciation and should be implemented in future ice sheet models. The topography of the Dronning Maud Land Mountains, Antarctica, has become more pronounced and rugged since preglacial times due to higher glacial erosion at low elevations and lower erosion at high elevations, according to low-temperature thermochronology
... The Jutulstraumen Graben represents a deep topographic depression which cuts through the otherwise continuous DML mountains extending for 1500 km from 15 W to 30 E (Jacobs, 1991;Jacobs et al., 1992). This mountain chain includes the Borgmassivet and Sverdrupfjella, which form the flanks of the Jutulstraumen Graben, and the Kirwanveggen separating the western Jutul-Penck Graben from the main Jutulstraumen Graben (Riedel et al., 2012;Steinhage et al., 1999) in the east (Figure 1c). ...
The landscape of Antarctica, hidden beneath kilometre‐thick ice in most places, has been shaped by the interactions between tectonic and erosional processes. The flow dynamics of the thick ice cover deepened pre‐formed topographic depressions by glacial erosion, but also preserved the subglacial landscapes in regions with moderate to slow ice flow. Mapping the spatial variability of these structures provides the basis for reconstruction of the evolution of subglacial morphology. This study focuses on the Jutulstraumen Glacier drainage system in Dronning Maud Land, East Antarctica. The Jutulstraumen Glacier reaches the ocean via the Jutulstraumen Graben, which is the only significant passage for draining the East Antarctic Ice Sheet through the western part of the Dronning Maud Land mountain chain. We acquired new bed topography data during an airborne radar campaign in the region upstream of the Jutulstraumen Graben to characterise the source area of the glacier. The new data show a deep relief to be generally under‐represented in available bed topography compilations. Our analysis of the bed topography, valley characteristics and bed roughness leads to the conclusion that much more of the alpine landscape that would have formed prior to the Antarctic Ice Sheet is preserved than previously anticipated. We identify an active and deeply eroded U‐shaped valley network next to largely preserved passive fluvial and glacial modified landscapes. Based on the landscape classification, we reconstruct the temporal sequence by which ice flow modified the topography since the beginning of the glaciation of Antarctica.
... Similar cooling phases have previously been described in western and central Dronning Maud Land (e.g. Jacobs et al., 1992;Jacobs et al., 1995;Jacobs and Lisker, 1999;Meier, 1999;Meier et al., 2004;Emmel et al., 2009) and in southern Africa (e.g. Brown et al., 1990;Brown et al., 2002;Wildman et al., 2015;Wildman et al., 2016;Wildman et al., 2017) where it has been attributed to different phases of Gondwana rifting and the subsequent opening of the Atlantic. ...
The Dronning Maud Land Mountains form a c. 1500 km long, coast-parallel escarpment that possibly formed by flexural uplift during Jurassic rifting between East and West Gondwana. Contemporaneous to the rifting, considerable amounts of continental flood basalts, associated with the Karoo mantle plume, were emplaced at c. 183 Ma. The basalts are still widespread in South Africa, making up elevated topography, but are only preserved as smaller remnants in western Dronning Maud Land. By investigating the paleo-thermal effect of the basalts, we aim to constrain the extent and original thickness, as well as the subsequent erosion history of the Jurassic continental flood basalts. Thus, we have applied low-temperature thermochronological methods to 40 samples from western Dronning Maud Land. This has resulted in 34 new apatite fission track ages, ranging from c. 310 to 90 Ma, 31 apatite (U–Th)/He ages spanning from c. 400 to 50 Ma and, and 9 zircon (U–Th)/He ages between c. 650 and 200 Ma.
Thermal modelling of 26 samples indicates variable thickness of the Jurassic basaltic cover. The greatest basaltic thicknesses are recorded in Heimefrontfjella and H.U. Sverdrupfjella, where up to c. 2 km are estimated. Thicknesses at Kirwanveggen, Hochlinfjellet, Midbresrabben and Ahlmannryggen range from c. 100 m to 600 m. Thickness variations are attributed to the proximity to the emplacement zone, possible pre-existing topography and syn-volcanic rift flank uplift.
Since the continental flood basalt emplacement, two phases of enhanced cooling have been documented: 1) A Jurassic-Cretaceous cooling phase is attributed to reactivation of the Jutulstraumen–Penckgraben rift, the initial rifting and opening of the South Atlantic and enhanced chemical weathering and deep erosion due to a Jurassic temperate–subtropical climate. 2) Late Paleogene cooling is attributed to the transition from green house to ice-house conditions and ice-sheet initiation at the Eocene-Oligocene boundary. Post-Jurassic denudation of at least 2 km is suggested.
... B3 v e r f a l t e t S2: (JACOBS et al. 1992). ...
... Since the area was probably a peneplain in Permian times, the mountain range must have undergone a strong post-Permian geomorphic evolution. Apatite fission-track analyses across the mountain range indicate that the entire area was probably covered with ã 2000 m thick lava pile during Jurassic times (~170 Ma), relics of which are still exposed at Bjørnnutane (JACOBS et al. 1992, JACOBS & LISKER 1999. The lavas are related to the Bouvet mantle plume that probably led to dynamic uplift of the mountain range in Jurassic times. ...
The Sivorg Terrane is the largest crustal block of the Heimefrontfjella. It consists of a thick supracrustal sequence of metavolcanic and metasedimentary rocks that are intruded by a wide range of predominantly granitic plutonic rocks. The protolith ages of the metavolcanic rocks have been dated at ∼1170-1140 Ma and the granitoid intrusions at ∼1110-1050 Ma. The best estimate for Grenville-age metamorphism in the Sivorg Terrane is 1090-1060 Ma. Unlike the other two terranes in the Heimefrontfjella, the Sivorg Terrane records intense reworking of Mesoproterozoic rocks during the Late Neoproterozoic-Cambrian East African - Antarctic Orogeny. U-Pb detrital zircon provenance analyses from two samples indicate that at least two age-groups of different supracrustal sequences crop out in the Sivorg Terrane. The older, preorogenic sequence gave youngest detrital ages of ∼1140 Ma, which are interpreted as dating the maximum deposition age of the original sediment. These rocks also provide evidence of a Palaeoproterozoic to Archaean foreland. The second sample is dominated by Mesoproterozoic to late Neoproterozoic detrital zircons, with a significant proportion of ages ranging from 1100 to 980 Ma. The youngest ages significantly postdate the Grenville-age metamorphism, so the sediments must have been deposited after or during the Late Mesoproterozoic orogenesis and, as such, might represent remnants of a molasse deposit of the orogen.
ResearchGate has not been able to resolve any references for this publication.