The Experts below are selected from a list of 1986 Experts worldwide ranked by ideXlab platform
Wentao Huang - One of the best experts on this subject based on the ideXlab platform.
-
paleomagnetic tests of tectonic reconstructions of the india asia collision zone
Geophysical Research Letters, 2015Co-Authors: Douwe J.j. Van Hinsbergen, Wentao Huang, Zhaojie Guo, Peter C Lippert, Guillaume DupontnivetAbstract:Several solutions have been proposed to explain the long-standing kinematic observation that postcollisional upper crustal shortening within the Himalaya and Asia is much less than the magnitude of India-Asia convergence. Here we implement these hypotheses in global plate reconstructions and test Paleolatitudes predicted by the global apparent polar wander path against independent, and the most robust paleomagnetic data. Our tests demonstrate that (1) reconstructed 600–750 km postcollisional intra-Asian shortening is a minimum value; (2) a 52 Ma collision age is only consistent with paleomagnetic data if intra-Asian shortening was ~900 km; a ~56–58 Ma collision age requires greater intra-Asian shortening; (3) collision ages of 34 or 65 Ma incorrectly predict Late Cretaceous and Paleogene Paleolatitudes of the Tibetan Himalaya (TH); and (4) Cretaceous counterclockwise rotation of India cannot explain the paleolatitudinal divergence between the TH and India. All hypotheses, regardless of collision age, require major Cretaceous extension within Greater India.
-
Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc: Evidence from paleomagnetism, sediment provenance, and stratigraphy
Earth and Planetary Science Letters, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Devon Orme, Marco Maffione, Guillaume Dupont-nivet, Elias Tawil AlAbstract:The India–Asia suture zone of southern Tibet exposes Lower Cretaceous Xigaze ophiolites and radiolarian cherts, and time-equivalent Asian-derived clastic forearc sedimentary rocks (Xigaze Group). These ophiolites have been interpreted to have formed in the forearc of the north-dipping subduction zone below Tibet that produced the Gangdese magmatic arc around 15–20◦N, or in the forearc of a sub-equatorial intra-oceanic subduction zone. To better constrain the latitude of the ophiolites, we carried out an integrated paleomagnetic, geochronologic and stratigraphical study on epi-ophiolitic radiolarites (Chongdui and Bainang sections), and Xigaze Group turbiditic sandstones unconformably overlying the ophiolite’s mantle units (Sangsang section). Detrital zircon U–Pb geochronology of tuffaceous layers from the Chongdui section and sandstones of the Xigaze Group at the Sangsang sectionprovides maximum depositional ages of 116.5 ±3.1Maand128.8 ±3.4Ma, respectively,for the Chongdui sectionand an Asian provenance signature for the Xigaze Group. Paleomagnetic analyses, integrated with rock magnetic experiments, indicate significant compaction-related inclination ‘shallowing’ of the remanence within the studied rocks. Two independent methods are applied for the inclination shallowing correction of the paleomagnetic directions from the Sangsang section, yielding consistent mean Paleolatitudes of 16.2◦N [13◦N, 20.9◦N] and 16.8◦N [11.1◦N, 23.3◦N], respectively. These results are indistinguishable from recent Paleolatitude estimates for the Gangdese arc in southern Tibet. Radiolarites from the Chongdui and Bainang sections yield low paleomagnetic inclinations that would suggest a sub-equatorial Paleolatitude, but the distribution of the paleomagnetic directions in these rocksstrongly suggests a low inclination bias by compaction. Our data indicate that spreading of the Xigaze ophiolite occurred in the Gangdese forearc, and formed the basement of the forearc strata.
-
What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou Basin, Tibet)
Tectonics, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Morgan Ganerod, Xiaochun Liu, Zhaojie Guo, Paul KappAbstract:The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou Basin. The lower and upper parts of the section previously yielded particularly conflicting ages and Paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of ~52 Ma for the upper Linzizong, and 40Ar/39Ar dates (~51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent Paleolatitude of ~5°N, compared to the upper part (~20°N) and to underlying Cretaceous strata (~20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by ~52 Ma at ~20°N.
-
Can a primary remanence be retrieved from partially remagnetized Eocence volcanic rocks in the Nanmulin Basin (southern Tibet) to date the India-Asia collision?
Journal of Geophysical Research, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Zhaojie Guo, Xiaoran Zhang, Dongdong Liu, Paul KappAbstract:Paleomagnetic dating of the India-Asia collision hinges on determining the Paleogene latitude of the Lhasa terrane (southern Tibet). Reported latitudes range from 5°N to 30°N, however, leading to contrasting paleogeographic interpretations. Here we report new data from the Eocene Linzizong volcanic rocks in the Nanmulin Basin, which previously yielded data suggesting a low Paleolatitude (~10°N). New zircon U-Pb dates indicate an age of ~52 Ma. Negative fold tests, however, demonstrate that the isolated characteristic remanent magnetizations, with notably varying inclinations, are not primary. Rock magnetic analyses, end-member modeling of isothermal remanent magnetization acquisition curves, and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low-temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously. Previously reported paleomagnetic data from the Nanmulin Basin implying low Paleolatitude should thus not be used to estimate the time and latitude of the India-Asia collision. We show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization. We tentatively propose a new method to recover a primary remanence with inclination of 38.1° (35.7°, 40.5°) (95% significance) and a secondary remanence with inclination of 42.9° (41.5°,44.4°) (95% significance). The Paleolatitude defined by the modeled primary remanence—21°N (19.8°N, 23.1°N)—is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper Linzizong Group corrected for inclination shallowing. The start of the Tibetan Himalaya-Asia collision was situated at ~20°N and took place by ~50 Ma.
Douwe J.j. Van Hinsbergen - One of the best experts on this subject based on the ideXlab platform.
-
a Paleolatitude calculator for paleoclimate studies
PLOS ONE, 2015Co-Authors: Douwe J.j. Van Hinsbergen, Lennart V De Groot, Sebastiaan J Van Schaik, Wim Spakman, Peter K Bijl, Appy Sluijs, C G Langereis, Henk BrinkhuisAbstract:Realistic appraisal of paleoclimatic information obtained from a particular location requires accurate knowledge of its Paleolatitude defined relative to the Earth’s spin-axis. This is crucial to, among others, correctly assess the amount of solar energy received at a location at the moment of sediment deposition. The Paleolatitude of an arbitrary location can in principle be reconstructed from tectonic plate reconstructions that (1) restore the relative motions between plates based on (marine) magnetic anomalies, and (2) reconstruct all plates relative to the spin axis using a paleomagnetic reference frame based on a global apparent polar wander path. Whereas many studies do employ high-quality relative plate reconstructions, the necessity of using a paleomagnetic reference frame for climate studies rather than a mantle reference frame appears under-appreciated. In this paper, we briefly summarize the theory of plate tectonic reconstructions and their reference frames tailored towards applications of paleoclimate reconstruction, and show that using a mantle reference frame, which defines plate positions relative to the mantle, instead of a paleomagnetic reference frame may introduce errors in Paleolatitude of more than 15° (>1500 km). This is because mantle reference frames cannot constrain, or are specifically corrected for the effects of true polar wander. We used the latest, state-of-the-art plate reconstructions to build a global plate circuit, and developed an online, user-friendly Paleolatitude calculator for the last 200 million years by placing this plate circuit in three widely used global apparent polar wander paths. As a novelty, this calculator adds error bars to Paleolatitude estimates that can be incorporated in climate modeling. The calculator is available at www.Paleolatitude.org. We illustrate the use of the Paleolatitude calculator by showing how an apparent wide spread in Eocene sea surface temperatures of southern high latitudes may be in part explained by a much wider paleolatitudinal distribution of sites than previously assumed.
-
paleomagnetic tests of tectonic reconstructions of the india asia collision zone
Geophysical Research Letters, 2015Co-Authors: Douwe J.j. Van Hinsbergen, Wentao Huang, Zhaojie Guo, Peter C Lippert, Guillaume DupontnivetAbstract:Several solutions have been proposed to explain the long-standing kinematic observation that postcollisional upper crustal shortening within the Himalaya and Asia is much less than the magnitude of India-Asia convergence. Here we implement these hypotheses in global plate reconstructions and test Paleolatitudes predicted by the global apparent polar wander path against independent, and the most robust paleomagnetic data. Our tests demonstrate that (1) reconstructed 600–750 km postcollisional intra-Asian shortening is a minimum value; (2) a 52 Ma collision age is only consistent with paleomagnetic data if intra-Asian shortening was ~900 km; a ~56–58 Ma collision age requires greater intra-Asian shortening; (3) collision ages of 34 or 65 Ma incorrectly predict Late Cretaceous and Paleogene Paleolatitudes of the Tibetan Himalaya (TH); and (4) Cretaceous counterclockwise rotation of India cannot explain the paleolatitudinal divergence between the TH and India. All hypotheses, regardless of collision age, require major Cretaceous extension within Greater India.
-
Lower Cretaceous Xigaze ophiolites formed in the Gangdese forearc: Evidence from paleomagnetism, sediment provenance, and stratigraphy
Earth and Planetary Science Letters, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Devon Orme, Marco Maffione, Guillaume Dupont-nivet, Elias Tawil AlAbstract:The India–Asia suture zone of southern Tibet exposes Lower Cretaceous Xigaze ophiolites and radiolarian cherts, and time-equivalent Asian-derived clastic forearc sedimentary rocks (Xigaze Group). These ophiolites have been interpreted to have formed in the forearc of the north-dipping subduction zone below Tibet that produced the Gangdese magmatic arc around 15–20◦N, or in the forearc of a sub-equatorial intra-oceanic subduction zone. To better constrain the latitude of the ophiolites, we carried out an integrated paleomagnetic, geochronologic and stratigraphical study on epi-ophiolitic radiolarites (Chongdui and Bainang sections), and Xigaze Group turbiditic sandstones unconformably overlying the ophiolite’s mantle units (Sangsang section). Detrital zircon U–Pb geochronology of tuffaceous layers from the Chongdui section and sandstones of the Xigaze Group at the Sangsang sectionprovides maximum depositional ages of 116.5 ±3.1Maand128.8 ±3.4Ma, respectively,for the Chongdui sectionand an Asian provenance signature for the Xigaze Group. Paleomagnetic analyses, integrated with rock magnetic experiments, indicate significant compaction-related inclination ‘shallowing’ of the remanence within the studied rocks. Two independent methods are applied for the inclination shallowing correction of the paleomagnetic directions from the Sangsang section, yielding consistent mean Paleolatitudes of 16.2◦N [13◦N, 20.9◦N] and 16.8◦N [11.1◦N, 23.3◦N], respectively. These results are indistinguishable from recent Paleolatitude estimates for the Gangdese arc in southern Tibet. Radiolarites from the Chongdui and Bainang sections yield low paleomagnetic inclinations that would suggest a sub-equatorial Paleolatitude, but the distribution of the paleomagnetic directions in these rocksstrongly suggests a low inclination bias by compaction. Our data indicate that spreading of the Xigaze ophiolite occurred in the Gangdese forearc, and formed the basement of the forearc strata.
-
What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou Basin, Tibet)
Tectonics, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Morgan Ganerod, Xiaochun Liu, Zhaojie Guo, Paul KappAbstract:The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou Basin. The lower and upper parts of the section previously yielded particularly conflicting ages and Paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of ~52 Ma for the upper Linzizong, and 40Ar/39Ar dates (~51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent Paleolatitude of ~5°N, compared to the upper part (~20°N) and to underlying Cretaceous strata (~20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by ~52 Ma at ~20°N.
-
Can a primary remanence be retrieved from partially remagnetized Eocence volcanic rocks in the Nanmulin Basin (southern Tibet) to date the India-Asia collision?
Journal of Geophysical Research, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Zhaojie Guo, Xiaoran Zhang, Dongdong Liu, Paul KappAbstract:Paleomagnetic dating of the India-Asia collision hinges on determining the Paleogene latitude of the Lhasa terrane (southern Tibet). Reported latitudes range from 5°N to 30°N, however, leading to contrasting paleogeographic interpretations. Here we report new data from the Eocene Linzizong volcanic rocks in the Nanmulin Basin, which previously yielded data suggesting a low Paleolatitude (~10°N). New zircon U-Pb dates indicate an age of ~52 Ma. Negative fold tests, however, demonstrate that the isolated characteristic remanent magnetizations, with notably varying inclinations, are not primary. Rock magnetic analyses, end-member modeling of isothermal remanent magnetization acquisition curves, and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low-temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously. Previously reported paleomagnetic data from the Nanmulin Basin implying low Paleolatitude should thus not be used to estimate the time and latitude of the India-Asia collision. We show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization. We tentatively propose a new method to recover a primary remanence with inclination of 38.1° (35.7°, 40.5°) (95% significance) and a secondary remanence with inclination of 42.9° (41.5°,44.4°) (95% significance). The Paleolatitude defined by the modeled primary remanence—21°N (19.8°N, 23.1°N)—is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper Linzizong Group corrected for inclination shallowing. The start of the Tibetan Himalaya-Asia collision was situated at ~20°N and took place by ~50 Ma.
Annelise Santoni - One of the best experts on this subject based on the ideXlab platform.
-
diagenetic and environmental control of the clay mineralogy organic matter and stable isotopes c o of jurassic pliensbachian lowermost toarcian sediments of the rodiles section asturian basin northern spain
Marine and Petroleum Geology, 2020Co-Authors: Jean-françois Deconinck, Pierre Pellenard, Ludovic Bruneau, Théophile Cocquerez, Juan J. Gómez, Francois Baudin, Hugo Biscay, Olivier Mathieu, Annelise SantoniAbstract:Abstract Clay mineralogical and geochemical analyses (δ18Ocarb, and paired carbonate and organic matter carbon isotope), completed by the characterization of organic matter, have been performed on the Pliensbachian sediments exposed on the Rodiles section (Asturian Basin, Northern Spain). The objectives were to precise the Pliensbachian climate evolution at a relatively low Paleolatitude of the Tethyan domain by comparison with previously published high-resolution clay mineralogical and geochemical data from the NW Tethyan domain (e.g. Paris Basin and Cardigan Bay Basin, West Wales). The clay mineral assemblages are dominantly composed of illite and illite-smectite mixed-layers (I–S) associated with minor proportions of chlorite and kaolinite. Smectites are not identified what may result either to their absence at the time of sedimentation or to their progressive illitization due to the burial diagenesis. Rock-Eval data show that organic matter reaching more than 5% in black-shale horizons is thermally mature with Tmax comprised between 444 and 454 °C indicating that the section is in the oil window and that the burial temperature reached or exceeded 80–90 °C. The low δ18Obulk values comprised between −3 and −6‰ clearly results from a diagenetic influence (thermal effect due to burial) but their fluctuations compared with δ18O measured on well-preserved belemnites guards show that the overall trend is however preserved. By comparison with higher latitude sedimentary basins, the most striking feature is the very small proportions of kaolinite (generally less than 5% while the proportions of this mineral reach 40% at higher Paleolatitudes), except at the Pliensbachian/Toarcian transition, where the proportion of kaolinite increases significantly. Clay minerals likely originated from the erosion of the Iberian Massif located to the South of the Asturian Basin in a semi-arid climatic belt. This may explain the scarcity of kaolinite by comparison with sedimentary basins located at higher latitude influenced by more humid climate. The increasing proportions of kaolinite by the end of the Pliensbachian suggest southward expansion of the humid belt as a consequence of cooler temperatures and the establishment of steeper latitudinal gradients of temperature likely resulting from the formation of restricted polar ice cap. The main δ13C (on both 13Cinorg and 13Corg) Pliensbachian excursions including the negative excursion of the Sinemurian/Pliensbachian Boundary Event (SPBE) and the Late Pliensbachian positive excursion are well recognized.
S T Reid - One of the best experts on this subject based on the ideXlab platform.
-
the effect of strawn desmoinesian paleogeography and Paleolatitude on the distribution of carbonate facies in the byrant g field midland basin texas
AAPG Bulletin, 1992Co-Authors: D Mobil Exploration A Walker, Mobil Exploration J Golonka, Andy Reid, S T ReidAbstract:Paleogeography and Paleolatitude reconstructions assisted in locating Strawn Formation grainstone shoals that form a stratigraphic trap on the eastern edge of the Byrant G field. Previous to this study, Strawn production was thought to be limited to fractured mudstoens found predominantly in the northwestern parts of the field. The grainstones were tested by a recompletion adding prolific new pay in the Strawn. The Desmoinesian Paleolatitude and paleogeography of the basin influenced carbonate sedimentation at the Byrant G field by controlling the direction of regional prevailing winds and ocean currents. Wind directions change in relation to latitude. When within 10{degree} north or south of the equator, prevailing winds generally are northeast or southeast, respectively. Because the Midland basin was very near the equator during the Desmoinesian, sedimentation at the Byrant G field would have been influenced by winds and currents from a southeasterly or northeasterly direction, depending on Paleolatitude. Grain dominated sediments were predicted to accumulate on east-facing edges of structural highs because the Desmoinesian prevailing winds and ocean currents generally were easterly. Indeed, grainstones were located on the eastern or windward edges of structures in the field. They probably were deposited as beaches or marine shoals oriented slightly northeast-southwest. Furthermore » to the west, gray mudstones, representing leeward deposits, accumulated in what probably was a lagoonal environment. These facies changes indicate an environmental transition from high to low energy in an east to west direction across the field.« less
-
late paleozoic Paleolatitude and paleogeography of the midland basin texas
AAPG Bulletin, 1992Co-Authors: D Mobil Exploration A Walker, Mobil Exploration J Golonka, Andy Reid, S T ReidAbstract:During the Late Pennsylvanian through Early Permian, the Midland basin was located in the low latitudes. In the Desmoinesian (Strawn), the basin was astride the equator; during the Missourian (Canyon), the center of the basin had migrated northward so it was located at 1-2N latitude. In the Virgilian (Cisco), the basin center was located around 2-4N latitude, and by the Wolfcampian, it was positioned at around 4-6N latitude. From the Desmoinesian (312 Ma) through the Missourian (306 Ma), the relative motion of the basin was 63NE. Later during the Virgilian (298 Ma) to Wolfcampian (280 Ma), the direction of motion was 24NE. This change in motion reflects a major tectonic event, occurring between the Missourian and Virgilian, that greatly modifed the movement of the Laurentian (North American) plate. At that time, Laurentia had collided with Gondwana and become part of the supercontinent Pangea. Throughout the late Paleozoic, Laurentia was rotated so the Midland basin was oriented 43{degree} northeast from its current setting. Late Paleozoic paleogeography and Paleolatitude controlled the direction of prevailing winds and ocean currents, thereby influencing the distribution of carbonate facies in the Midland basin. Present prevailing winds and ocean currents have been shown to have a majormore » impact on modern carbonate sedimentation and facies distribution in Belize, the Bahamas and Turks, and Caicos. A clearer understanding of how late Paleozoic latitude and geography affected sedimentation helps explain and predict the distribution of carbonates throughout the Midland basin.« less
Paul Kapp - One of the best experts on this subject based on the ideXlab platform.
-
What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou Basin, Tibet)
Tectonics, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Morgan Ganerod, Xiaochun Liu, Zhaojie Guo, Paul KappAbstract:The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou Basin. The lower and upper parts of the section previously yielded particularly conflicting ages and Paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of ~52 Ma for the upper Linzizong, and 40Ar/39Ar dates (~51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent Paleolatitude of ~5°N, compared to the upper part (~20°N) and to underlying Cretaceous strata (~20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by ~52 Ma at ~20°N.
-
Can a primary remanence be retrieved from partially remagnetized Eocence volcanic rocks in the Nanmulin Basin (southern Tibet) to date the India-Asia collision?
Journal of Geophysical Research, 2015Co-Authors: Wentao Huang, Douwe J.j. Van Hinsbergen, Guillaume Dupont-nivet, Peter Lippert, Mark Dekkers, Ross Waldrip, Zhaojie Guo, Xiaoran Zhang, Dongdong Liu, Paul KappAbstract:Paleomagnetic dating of the India-Asia collision hinges on determining the Paleogene latitude of the Lhasa terrane (southern Tibet). Reported latitudes range from 5°N to 30°N, however, leading to contrasting paleogeographic interpretations. Here we report new data from the Eocene Linzizong volcanic rocks in the Nanmulin Basin, which previously yielded data suggesting a low Paleolatitude (~10°N). New zircon U-Pb dates indicate an age of ~52 Ma. Negative fold tests, however, demonstrate that the isolated characteristic remanent magnetizations, with notably varying inclinations, are not primary. Rock magnetic analyses, end-member modeling of isothermal remanent magnetization acquisition curves, and petrographic observations are consistent with variable degrees of posttilting remagnetization due to low-temperature alteration of primary magmatic titanomagnetite and the formation of secondary pigmentary hematite that unblock simultaneously. Previously reported paleomagnetic data from the Nanmulin Basin implying low Paleolatitude should thus not be used to estimate the time and latitude of the India-Asia collision. We show that the paleomagnetic inclinations vary linearly with the contribution of secondary hematite to saturation isothermal remanent magnetization. We tentatively propose a new method to recover a primary remanence with inclination of 38.1° (35.7°, 40.5°) (95% significance) and a secondary remanence with inclination of 42.9° (41.5°,44.4°) (95% significance). The Paleolatitude defined by the modeled primary remanence—21°N (19.8°N, 23.1°N)—is consistent with the regional compilation of published results from pristine volcanic rocks and sedimentary rocks of the upper Linzizong Group corrected for inclination shallowing. The start of the Tibetan Himalaya-Asia collision was situated at ~20°N and took place by ~50 Ma.