Details
| Original language | English |
|---|---|
| Pages (from-to) | 164-182 |
| Number of pages | 19 |
| Journal | Chemical geology |
| Volume | 478 |
| Early online date | 30 Sept 2017 |
| Publication status | Published - 5 Feb 2018 |
Abstract
Spatially associated A- and I- type granites and mafic dyke rocks from the Jiuhuashan region (South China) have been geochemically studied with a special emphasis on their halogen (F, Cl, Br, I) contents to better understand the role of halogens during their genesis. The A-type granites and mafic dyke rocks (125–130 Ma) intruded later than the I-type rocks (140–143 Ma) and whole-rock Nb/Ta ratios increase from I-type granites (12–14) via A-type granites (14–18) to mafic dykes (19–20). The εNd(t) values for the two rock series are indistinguishable (about − 4 to − 8), whereas mafic dykes reach εNd(t) values of up to + 2. We suggest that I- and A-type granites generate from a common source dominated by lower crust, whereas the associated mafic dykes representing mantle-derived magma. We propose that the I-type rocks were emplaced during subduction of the paleo-Pacific slab, whereas subsequent tectonic extension triggered upwelling of mantle-derived magmas that provided sufficient heat to re-melt the residual lower crust, and crystallized to the A-type granites. Relative to I-type granites, the A-type rocks are F-rich (mean of 1230 ppm vs. 540 ppm) but poor in Cl (mean of 25 ppm vs. 50 ppm) and Br (mean of 130 ppb vs. 200 ppb), with indistinguishable I contents (from < 1 to 30 ppb). Apatite and biotite from the two rock series show very similar relationships in terms of their F and Cl contents. A potential role of F for the genesis of A-type rocks is indicated by positive correlations with whole-rock HFSE and HREE contents and many other trace elements (e.g., Ga, Tl, Rb, Be). Calculated F and Cl abundances for primary melts are much higher than the respective whole-rock F and Cl contents, supporting late-stage volatile release during magma evolution. We suggest that the elevated F contents in A-type granites may initially originate from a F-rich melt and further elevated during prolonged magma differentiation.
Keywords
- A-type granite, Fluorine, Halogens, Jiuhuashan region, Prolonged differentiation, South China
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Geology
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
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In: Chemical geology, Vol. 478, 05.02.2018, p. 164-182.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Halogen geochemistry of I- and A-type granites from Jiuhuashan region (South China)
T2 - Insights into the elevated fluorine in A-type granite
AU - Wang, Lian Xun
AU - Ma, Chang Qian
AU - Zhang, Chao
AU - Zhu, Yu Xiang
AU - Marks, Michael A.W.
PY - 2018/2/5
Y1 - 2018/2/5
N2 - Spatially associated A- and I- type granites and mafic dyke rocks from the Jiuhuashan region (South China) have been geochemically studied with a special emphasis on their halogen (F, Cl, Br, I) contents to better understand the role of halogens during their genesis. The A-type granites and mafic dyke rocks (125–130 Ma) intruded later than the I-type rocks (140–143 Ma) and whole-rock Nb/Ta ratios increase from I-type granites (12–14) via A-type granites (14–18) to mafic dykes (19–20). The εNd(t) values for the two rock series are indistinguishable (about − 4 to − 8), whereas mafic dykes reach εNd(t) values of up to + 2. We suggest that I- and A-type granites generate from a common source dominated by lower crust, whereas the associated mafic dykes representing mantle-derived magma. We propose that the I-type rocks were emplaced during subduction of the paleo-Pacific slab, whereas subsequent tectonic extension triggered upwelling of mantle-derived magmas that provided sufficient heat to re-melt the residual lower crust, and crystallized to the A-type granites. Relative to I-type granites, the A-type rocks are F-rich (mean of 1230 ppm vs. 540 ppm) but poor in Cl (mean of 25 ppm vs. 50 ppm) and Br (mean of 130 ppb vs. 200 ppb), with indistinguishable I contents (from < 1 to 30 ppb). Apatite and biotite from the two rock series show very similar relationships in terms of their F and Cl contents. A potential role of F for the genesis of A-type rocks is indicated by positive correlations with whole-rock HFSE and HREE contents and many other trace elements (e.g., Ga, Tl, Rb, Be). Calculated F and Cl abundances for primary melts are much higher than the respective whole-rock F and Cl contents, supporting late-stage volatile release during magma evolution. We suggest that the elevated F contents in A-type granites may initially originate from a F-rich melt and further elevated during prolonged magma differentiation.
AB - Spatially associated A- and I- type granites and mafic dyke rocks from the Jiuhuashan region (South China) have been geochemically studied with a special emphasis on their halogen (F, Cl, Br, I) contents to better understand the role of halogens during their genesis. The A-type granites and mafic dyke rocks (125–130 Ma) intruded later than the I-type rocks (140–143 Ma) and whole-rock Nb/Ta ratios increase from I-type granites (12–14) via A-type granites (14–18) to mafic dykes (19–20). The εNd(t) values for the two rock series are indistinguishable (about − 4 to − 8), whereas mafic dykes reach εNd(t) values of up to + 2. We suggest that I- and A-type granites generate from a common source dominated by lower crust, whereas the associated mafic dykes representing mantle-derived magma. We propose that the I-type rocks were emplaced during subduction of the paleo-Pacific slab, whereas subsequent tectonic extension triggered upwelling of mantle-derived magmas that provided sufficient heat to re-melt the residual lower crust, and crystallized to the A-type granites. Relative to I-type granites, the A-type rocks are F-rich (mean of 1230 ppm vs. 540 ppm) but poor in Cl (mean of 25 ppm vs. 50 ppm) and Br (mean of 130 ppb vs. 200 ppb), with indistinguishable I contents (from < 1 to 30 ppb). Apatite and biotite from the two rock series show very similar relationships in terms of their F and Cl contents. A potential role of F for the genesis of A-type rocks is indicated by positive correlations with whole-rock HFSE and HREE contents and many other trace elements (e.g., Ga, Tl, Rb, Be). Calculated F and Cl abundances for primary melts are much higher than the respective whole-rock F and Cl contents, supporting late-stage volatile release during magma evolution. We suggest that the elevated F contents in A-type granites may initially originate from a F-rich melt and further elevated during prolonged magma differentiation.
KW - A-type granite
KW - Fluorine
KW - Halogens
KW - Jiuhuashan region
KW - Prolonged differentiation
KW - South China
UR - http://www.scopus.com/inward/record.url?scp=85030715611&partnerID=8YFLogxK
U2 - 10.1016/j.chemgeo.2017.09.033
DO - 10.1016/j.chemgeo.2017.09.033
M3 - Article
AN - SCOPUS:85030715611
VL - 478
SP - 164
EP - 182
JO - Chemical geology
JF - Chemical geology
SN - 0009-2541
ER -