Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation
<p>A nonconformity refers to a hiatal surface located between metamorphic or igneous rocks and overlying sedimentary or volcanic rocks. These surfaces are key features with respect to understanding the relations among climate, lithosphere and tectonic movements during ancient times. In this st...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-05-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/12/1165/2021/se-12-1165-2021.pdf |
| _version_ | 1818952396697501696 |
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| author | F. Liang J. Niu J. Niu A. Linsel M. Hinderer D. Scheuvens R. Petschick |
| author_facet | F. Liang J. Niu J. Niu A. Linsel M. Hinderer D. Scheuvens R. Petschick |
| author_sort | F. Liang |
| collection | DOAJ |
| description | <p>A nonconformity refers to a hiatal surface located
between metamorphic or igneous rocks and overlying sedimentary or volcanic
rocks. These surfaces are key features with respect to understanding the relations among
climate, lithosphere and tectonic movements during ancient times. In this
study, the petrological, mineralogical and geochemical characteristics of
Variscan basement rock as well as its overlying Permian volcano-sedimentary
succession from a drill core in the Sprendlinger Horst, Germany, are analyzed
by means of polarization microscopy, and environmental scanning electron
microscope, X-Ray diffraction, X-ray fluorescence and inductively coupled
plasma mass spectrometry analyses. In the gabbroic diorite of the basement,
the intensity of micro- and macro-fractures increases towards the top,
indicating an intense physical weathering. The overlying Permian volcanic
rock is a basaltic andesite that shows less intense physical weathering
compared with the gabbroic diorite. In both segments, secondary minerals are
dominated by illite and a mixed-layer phase of illite and smectite (I–S). The
corrected chemical index of alteration (CIA) and the plagioclase index of
alteration (PIA) indicate an intermediate to unweathered degree in the
gabbroic diorite and an extreme to unweathered degree in the basaltic
andesite. The <span class="inline-formula"><i>τ</i></span> values for both basaltic andesite and gabbroic diorite
indicate an abnormal enrichment of K, Rb and Cs that cannot be observed in
the overlying Permian sedimentary rocks. Accompanying minerals such as
adularia suggest subsequent overprint by (K-rich) fluids during burial
diagenesis which promoted the conversion from smectite to illite. The
overall order of element depletion in both basaltic andesite and gabbroic
diorite during the weathering process is as follows: large-ion lithophile
elements (LILEs) <span class="inline-formula"><i>></i></span> rare earth elements (REEs) <span class="inline-formula"><i>></i></span> high-field-strength elements (HFSEs). Concerning the REEs, heavy rare earth elements
(HREEs) are less depleted than light rare earth elements (LREEs). Our study
shows that features of supergene physical and chemical paleo-weathering are
well conserved at the post-Variscan nonconformity despite hypogene
alteration. Both can be distinguished by characteristic minerals and
geochemical indices. Based on these results, a new workflow to eliminate
distractions for paleoclimate evaluation and evolution is developed.</p> |
| first_indexed | 2024-12-20T09:49:43Z |
| format | Article |
| id | doaj.art-20f8b04ccf524552b57fa6090034ca34 |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-20T09:49:43Z |
| publishDate | 2021-05-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-20f8b04ccf524552b57fa6090034ca342022-12-21T19:44:38ZengCopernicus PublicationsSolid Earth1869-95101869-95292021-05-01121165118410.5194/se-12-1165-2021Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluationF. Liang0J. Niu1J. Niu2A. Linsel3M. Hinderer4D. Scheuvens5R. Petschick6Material and Geosciences, Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt 64287, GermanyMaterial and Geosciences, Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt 64287, GermanyFaculty of Petroleum, China University of Petroleum-Beijing, Karamay Campus, Karamay 834000, ChinaMaterial and Geosciences, Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt 64287, GermanyMaterial and Geosciences, Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt 64287, GermanyMaterial and Geosciences, Institute of Applied Geosciences, Technical University of Darmstadt, Darmstadt 64287, GermanyFaculty of Geosciences and Geography, Goethe University Frankfurt, Frankfurt 60438, Germany<p>A nonconformity refers to a hiatal surface located between metamorphic or igneous rocks and overlying sedimentary or volcanic rocks. These surfaces are key features with respect to understanding the relations among climate, lithosphere and tectonic movements during ancient times. In this study, the petrological, mineralogical and geochemical characteristics of Variscan basement rock as well as its overlying Permian volcano-sedimentary succession from a drill core in the Sprendlinger Horst, Germany, are analyzed by means of polarization microscopy, and environmental scanning electron microscope, X-Ray diffraction, X-ray fluorescence and inductively coupled plasma mass spectrometry analyses. In the gabbroic diorite of the basement, the intensity of micro- and macro-fractures increases towards the top, indicating an intense physical weathering. The overlying Permian volcanic rock is a basaltic andesite that shows less intense physical weathering compared with the gabbroic diorite. In both segments, secondary minerals are dominated by illite and a mixed-layer phase of illite and smectite (I–S). The corrected chemical index of alteration (CIA) and the plagioclase index of alteration (PIA) indicate an intermediate to unweathered degree in the gabbroic diorite and an extreme to unweathered degree in the basaltic andesite. The <span class="inline-formula"><i>τ</i></span> values for both basaltic andesite and gabbroic diorite indicate an abnormal enrichment of K, Rb and Cs that cannot be observed in the overlying Permian sedimentary rocks. Accompanying minerals such as adularia suggest subsequent overprint by (K-rich) fluids during burial diagenesis which promoted the conversion from smectite to illite. The overall order of element depletion in both basaltic andesite and gabbroic diorite during the weathering process is as follows: large-ion lithophile elements (LILEs) <span class="inline-formula"><i>></i></span> rare earth elements (REEs) <span class="inline-formula"><i>></i></span> high-field-strength elements (HFSEs). Concerning the REEs, heavy rare earth elements (HREEs) are less depleted than light rare earth elements (LREEs). Our study shows that features of supergene physical and chemical paleo-weathering are well conserved at the post-Variscan nonconformity despite hypogene alteration. Both can be distinguished by characteristic minerals and geochemical indices. Based on these results, a new workflow to eliminate distractions for paleoclimate evaluation and evolution is developed.</p>https://se.copernicus.org/articles/12/1165/2021/se-12-1165-2021.pdf |
| spellingShingle | F. Liang J. Niu J. Niu A. Linsel M. Hinderer D. Scheuvens R. Petschick Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation Solid Earth |
| title | Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| title_full | Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| title_fullStr | Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| title_full_unstemmed | Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| title_short | Rock alteration at the post-Variscan nonconformity: implications for Carboniferous–Permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| title_sort | rock alteration at the post variscan nonconformity implications for carboniferous permian surface weathering versus burial diagenesis and paleoclimate evaluation |
| url | https://se.copernicus.org/articles/12/1165/2021/se-12-1165-2021.pdf |
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