Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics

J. Elis HOFFMANN; Alfred KRÖNER; Ernst HEGNER; Sebastian VIEHMANN; Hangqian XIE; Linda M. IACCHERI; Kathrin P. SCHNEIDER; Axel HOFMANN; Jean WONG; Hongyan GENG; Jinhui YANG

doi:10.1016/j.precamres.2016.01.026

Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics

J. Elis HOFFMANN^*, Alfred KRÖNER, Ernst HEGNER, Sebastian VIEHMANN, Hangqian XIE, Linda M. IACCHERI, Kathrin P. SCHNEIDER, Axel HOFMANN, Jean WONG, Hongyan GENG, Jinhui YANG

^*Corresponding author for this work

Research output: Journal Publications › Journal Article (refereed) › peer-review

57 Citations (Scopus)

Abstract

The ca. 3480-3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200-3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis.In contrast to the widespread view that Archaean crust is mainly composed of TTG igneous suites that formed from juvenile sources, the geochemical and isotopic compositions of the TG indicate that these rocks represent a calc-alkaline plutonic suite which possibly formed by magma mixing processes involving juvenile, mantle-derived tholeiitic melts as well as partial melts of the older Ngwane gneiss. Alternatively, the TG may represent a magmatic suite that formed by fractional crystallization of a hydrous intermediate magma. These results contrast with field evidence of a relatively uniform and homogeneous composition. Our geochronological and isotopic data show that the TG intruded the NG during a time span of at least 50 Ma without any significant compositional change of the source. The predominant influence of fractional crystallization of a tholeiitic mafic magma, as well as assimilation-fractional-crystallization processes (AFC) can be excluded for the TG from major and trace element modelling. The magma processes proposed here suggest efficient mixing of approximately equal amounts of TG magmas with those derived from the NG basement and is supported by the largely homogeneous Hf-Nd isotopic compositions of the whole-rock samples.We propose that melting and mixing occurred in the lower crust that mainly consisted of >3.50 Ga NG and was possibly triggered by plume-related underplated and intraplated tholeiitic magmas in sills and/or laccoliths. This model is supported by geochemical evidence for a mafic end member lacking a negative Nb anomaly and implying that subduction processes were not involved in the formation of the TG.

Original language	English
Pages (from-to)	43-66
Number of pages	24
Journal	Precambrian Research
Volume	276
Early online date	1 Feb 2016
DOIs	https://doi.org/10.1016/j.precamres.2016.01.026
Publication status	Published - May 2016
Externally published	Yes

Bibliographical note

JEH thanks Jonas Tusch, Sebastian Kommescher and Andreas Wittke for help during sample preparation and laboratory assistance. S.V. acknowledges Jacobs University Bremen for a PhD scholarship. Almut Katzemich is acknowledged for XRF analyses in Cologne. Guangshen Ni and Baoying Zheng of the Beijing SHRIMP Centre prepared the zircon concentrates, Liqin Zhou and Xiao-Chao Che provided the zircon CL images, Chun Yang prepared perfect zircon mounts, and Jianhui Liu and Zhiqing Yang made sure that SHRIMP II in Beijing was in excellent operating conditions. Jing-Yuan Chen and Yang Yue-Heng are thanked for help during Hf isotope analyses of zircons in the Institute of Geology and Geophysics, Chinese Academy of Science, Beijing. We thank Kris Szilas for comments on a draft version of the manuscript. This is a contribution to IGCP-SIDA project 599.

Funding

We thank Guochun Zhao for editorial handling and Roberto Dall’Agnol and Armin Zeh for helpful and constructive reviews. This research was supported by grants HO 4697/1-1 , HO 4697/1-2 and KR-590/94-1 of the German Science Foundation (DFG) to JEH and AK, grants from the German Academic Exchange Service (DAAD, PPP Program Germany-Hong Kong) and the Hong Kong Research Council to AK and Min Sun as well as National Natural Science Foundation of China Project No. 41221002 to J.-H. Yang. AH and EH also acknowledge support from the German Ministry for Education and Research (BMWF), grant SUA 08/038.

Keywords

Continental crust
Hf-Nd
Magma mixing
Swaziland
Tonalite
TTG

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10.1016/j.precamres.2016.01.026

Cite this

HOFFMANN, J. E., KRÖNER, A., HEGNER, E., VIEHMANN, S., XIE, H., IACCHERI, L. M., SCHNEIDER, K. P., HOFMANN, A., WONG, J., GENG, H., & YANG, J. (2016). Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics. Precambrian Research, 276, 43-66. https://doi.org/10.1016/j.precamres.2016.01.026

@article{0c3b0f40793e49289394b749afd4ab9c,

title = "Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics",

abstract = "The ca. 3480-3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200-3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis.In contrast to the widespread view that Archaean crust is mainly composed of TTG igneous suites that formed from juvenile sources, the geochemical and isotopic compositions of the TG indicate that these rocks represent a calc-alkaline plutonic suite which possibly formed by magma mixing processes involving juvenile, mantle-derived tholeiitic melts as well as partial melts of the older Ngwane gneiss. Alternatively, the TG may represent a magmatic suite that formed by fractional crystallization of a hydrous intermediate magma. These results contrast with field evidence of a relatively uniform and homogeneous composition. Our geochronological and isotopic data show that the TG intruded the NG during a time span of at least 50 Ma without any significant compositional change of the source. The predominant influence of fractional crystallization of a tholeiitic mafic magma, as well as assimilation-fractional-crystallization processes (AFC) can be excluded for the TG from major and trace element modelling. The magma processes proposed here suggest efficient mixing of approximately equal amounts of TG magmas with those derived from the NG basement and is supported by the largely homogeneous Hf-Nd isotopic compositions of the whole-rock samples.We propose that melting and mixing occurred in the lower crust that mainly consisted of >3.50 Ga NG and was possibly triggered by plume-related underplated and intraplated tholeiitic magmas in sills and/or laccoliths. This model is supported by geochemical evidence for a mafic end member lacking a negative Nb anomaly and implying that subduction processes were not involved in the formation of the TG.",

keywords = "Continental crust, Hf-Nd, Magma mixing, Swaziland, Tonalite, TTG",

author = "HOFFMANN, {J. Elis} and Alfred KR{\"O}NER and Ernst HEGNER and Sebastian VIEHMANN and Hangqian XIE and IACCHERI, {Linda M.} and SCHNEIDER, {Kathrin P.} and Axel HOFMANN and Jean WONG and Hongyan GENG and Jinhui YANG",

note = "JEH thanks Jonas Tusch, Sebastian Kommescher and Andreas Wittke for help during sample preparation and laboratory assistance. S.V. acknowledges Jacobs University Bremen for a PhD scholarship. Almut Katzemich is acknowledged for XRF analyses in Cologne. Guangshen Ni and Baoying Zheng of the Beijing SHRIMP Centre prepared the zircon concentrates, Liqin Zhou and Xiao-Chao Che provided the zircon CL images, Chun Yang prepared perfect zircon mounts, and Jianhui Liu and Zhiqing Yang made sure that SHRIMP II in Beijing was in excellent operating conditions. Jing-Yuan Chen and Yang Yue-Heng are thanked for help during Hf isotope analyses of zircons in the Institute of Geology and Geophysics, Chinese Academy of Science, Beijing. We thank Kris Szilas for comments on a draft version of the manuscript. This is a contribution to IGCP-SIDA project 599.",

year = "2016",

month = may,

doi = "10.1016/j.precamres.2016.01.026",

language = "English",

volume = "276",

pages = "43--66",

journal = "Precambrian Research",

issn = "0301-9268",

publisher = "Elsevier B.V.",

}

HOFFMANN, JE, KRÖNER, A, HEGNER, E, VIEHMANN, S, XIE, H, IACCHERI, LM, SCHNEIDER, KP, HOFMANN, A, WONG, J, GENG, H & YANG, J 2016, 'Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics', Precambrian Research, vol. 276, pp. 43-66. https://doi.org/10.1016/j.precamres.2016.01.026

Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics. / HOFFMANN, J. Elis; KRÖNER, Alfred; HEGNER, Ernst et al.
In: Precambrian Research, Vol. 276, 05.2016, p. 43-66.

Research output: Journal Publications › Journal Article (refereed) › peer-review

TY - JOUR

T1 - Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics

AU - HOFFMANN, J. Elis

AU - KRÖNER, Alfred

AU - HEGNER, Ernst

AU - VIEHMANN, Sebastian

AU - XIE, Hangqian

AU - IACCHERI, Linda M.

AU - SCHNEIDER, Kathrin P.

AU - HOFMANN, Axel

AU - WONG, Jean

AU - GENG, Hongyan

AU - YANG, Jinhui

N1 - JEH thanks Jonas Tusch, Sebastian Kommescher and Andreas Wittke for help during sample preparation and laboratory assistance. S.V. acknowledges Jacobs University Bremen for a PhD scholarship. Almut Katzemich is acknowledged for XRF analyses in Cologne. Guangshen Ni and Baoying Zheng of the Beijing SHRIMP Centre prepared the zircon concentrates, Liqin Zhou and Xiao-Chao Che provided the zircon CL images, Chun Yang prepared perfect zircon mounts, and Jianhui Liu and Zhiqing Yang made sure that SHRIMP II in Beijing was in excellent operating conditions. Jing-Yuan Chen and Yang Yue-Heng are thanked for help during Hf isotope analyses of zircons in the Institute of Geology and Geophysics, Chinese Academy of Science, Beijing. We thank Kris Szilas for comments on a draft version of the manuscript. This is a contribution to IGCP-SIDA project 599.

PY - 2016/5

Y1 - 2016/5

N2 - The ca. 3480-3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200-3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis.In contrast to the widespread view that Archaean crust is mainly composed of TTG igneous suites that formed from juvenile sources, the geochemical and isotopic compositions of the TG indicate that these rocks represent a calc-alkaline plutonic suite which possibly formed by magma mixing processes involving juvenile, mantle-derived tholeiitic melts as well as partial melts of the older Ngwane gneiss. Alternatively, the TG may represent a magmatic suite that formed by fractional crystallization of a hydrous intermediate magma. These results contrast with field evidence of a relatively uniform and homogeneous composition. Our geochronological and isotopic data show that the TG intruded the NG during a time span of at least 50 Ma without any significant compositional change of the source. The predominant influence of fractional crystallization of a tholeiitic mafic magma, as well as assimilation-fractional-crystallization processes (AFC) can be excluded for the TG from major and trace element modelling. The magma processes proposed here suggest efficient mixing of approximately equal amounts of TG magmas with those derived from the NG basement and is supported by the largely homogeneous Hf-Nd isotopic compositions of the whole-rock samples.We propose that melting and mixing occurred in the lower crust that mainly consisted of >3.50 Ga NG and was possibly triggered by plume-related underplated and intraplated tholeiitic magmas in sills and/or laccoliths. This model is supported by geochemical evidence for a mafic end member lacking a negative Nb anomaly and implying that subduction processes were not involved in the formation of the TG.

AB - The ca. 3480-3430 Ma Tsawela Gneiss (TG) is a well-preserved coarse-grained diorite to tonalite suite within the Ancient Gneiss Complex of Swaziland, eastern Kaapvaal craton. These gneisses are texturally and compositionally distinct from the hosting oldest components of the ca. 3200-3660 Ma TTG-type Ngwane Gneisses (NG). Major and trace elements, in combination with whole-rock hafnium-neodymium isotopic data, were analyzed in the TG and in three samples of ca. 3450 Ma grey NG to constrain sources and magmatic processes. High-field-strength element data (HFSE) were combined with U-Pb SHRIMP II ages and Hf-in-zircon data for key samples to constrain their ages and petrogenesis.In contrast to the widespread view that Archaean crust is mainly composed of TTG igneous suites that formed from juvenile sources, the geochemical and isotopic compositions of the TG indicate that these rocks represent a calc-alkaline plutonic suite which possibly formed by magma mixing processes involving juvenile, mantle-derived tholeiitic melts as well as partial melts of the older Ngwane gneiss. Alternatively, the TG may represent a magmatic suite that formed by fractional crystallization of a hydrous intermediate magma. These results contrast with field evidence of a relatively uniform and homogeneous composition. Our geochronological and isotopic data show that the TG intruded the NG during a time span of at least 50 Ma without any significant compositional change of the source. The predominant influence of fractional crystallization of a tholeiitic mafic magma, as well as assimilation-fractional-crystallization processes (AFC) can be excluded for the TG from major and trace element modelling. The magma processes proposed here suggest efficient mixing of approximately equal amounts of TG magmas with those derived from the NG basement and is supported by the largely homogeneous Hf-Nd isotopic compositions of the whole-rock samples.We propose that melting and mixing occurred in the lower crust that mainly consisted of >3.50 Ga NG and was possibly triggered by plume-related underplated and intraplated tholeiitic magmas in sills and/or laccoliths. This model is supported by geochemical evidence for a mafic end member lacking a negative Nb anomaly and implying that subduction processes were not involved in the formation of the TG.

KW - Continental crust

KW - Hf-Nd

KW - Magma mixing

KW - Swaziland

KW - Tonalite

KW - TTG

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U2 - 10.1016/j.precamres.2016.01.026

DO - 10.1016/j.precamres.2016.01.026

M3 - Journal Article (refereed)

AN - SCOPUS:84958170851

SN - 0301-9268

VL - 276

SP - 43

EP - 66

JO - Precambrian Research

JF - Precambrian Research

ER -

Source composition, fractional crystallization and magma mixing processes in the 3.48-3.43 Ga Tsawela tonalite suite (Ancient Gneiss Complex, Swaziland) - Implications for Palaeoarchaean geodynamics

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