Petrogenesis of a similar to 900 Ma mafic sill from Xuzhou, North China: Implications for the genesis of Fe-Ti-rich rocks

doi:10.1016/j.lithos.2018.08.023

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	Petrogenesis of a similar to 900 Ma mafic sill from Xuzhou, North China: Implications for the genesis of Fe-Ti-rich rocks
	Su, Xiangdong 1,2; Peng, Peng 1,2; Wang, Chong 1,2; Sun, Fengbo 1,2; Zhang, Zhiyue 1,2; Zhou, Xiaotong 1,2
刊名	LITHOS
	2018-10-01
卷号	318 页码:357-375
关键词	Fe-Ti-rich gabbro Sill complex Fractional crystallisation Titanite Neoproterozoic North China Craton
ISSN号	0024-4937
DOI	10.1016/j.lithos.2018.08.023
英文摘要	The Niutishan sill, one of the similar to 900 Ma mafic sills in Xuzhou (Jiangsu province, North China), has a thickness of similar to 30 m. We have identified chemical parameters that define three differentiated interlayers from thirty-eight samples in a similar to 22 m profile. The sill reveals a succession consisting of an upper border zone of fine-grained dolerite (UZ), a middle zone of quartz-bearing gabbro (MZ), a coarse-grained apatite-enriched gabbro (LZc), a layer of Fe-Ti oxide-enriched gabbro (LZb) and a deeper medium-grained massive gabbro (LZa) at the bottom of the lower zone, capped by an uppermost chilled margin (CM) of plagioclase-clinopyroxene-porphyritic dolerite. Its significantly differentiated interlayers offer an opportunity to investigate the petrogenesis of high-Fe-Ti gabbro. The chilled margin composition suggests a highly evolved ferro-basaltic parental magma (whole-rock Mg#: 39, with similar to 2.9 wt% TiO2 and similar to 14.2 wt% FeOt), which likely represents a residual magma derived from a deep-seated magma chamber after significant removal of olivine. The internal compositional variation was controlled by fractional crystallisation with successive presence of plagioclase and Fe-poor clinopyroxene, followed by Fe-Ti oxides plus Fe-rich clinopyroxene, and finally apatite and albite-oligoclase. This sequence is consistent with the result of thermodynamic modelling of MELTS at a low H2O content of similar to-0.2 wt% and in a temperature range from 1200 to 780 degrees C and at a pressure of 70 MPa. The saturation of clinopyroxene before Fe-Ti oxides in liquids is interpreted to imply low-fO(2) and water-unsaturated conditions, which led the residual magma to an Fe-Ti-enriched trend. After the saturation and mechanical settling of clinopyroxene primocrysts from the parental magma, large amounts of Fe-Ti oxides crystallised from the evolved Fe-Ti-rich melt. Further crystallisation and solidification of the crystal mush led to the formation of the major Fe-Ti oxide-rich layer and expelled interstitial melt upward to mix with the more evolved residual melts, leading to the saturation of apatite. Meanwhile, the residual melts gradually tended to Si enrichment, which matches the observed compositions (enriched incompatible elements) of naturally occurring quartz- gabbro in the MZ. As a result, viscosity would increase, trapping highly evolved melts and impeding liquid separation, as exhibited by the silicic mesostasis of graphic intergrowths of quartz and alkali feldspar, and occasionally calcite. This sill is also characterized by considerable amounts of titanite at the bottoms of the UZ and LZ, which was likely formed during the late evolutionary stages as products of reaction between the primary Ti-rich minerals and a late igneous fluid/melt at temperature near 584 degrees C. The F-rich and Cl-poor apatite (X-F > 0.95) and Ti-rich magnetite (7.2-9.7 wt% Ti) from Fe-Ti (P)-rich layers indicate a magmatic origin from high-temperature Fe-Ti-rich melts. It is thus concluded that the significantly differentiated Niutishan sill was formed by the combined processes of fractionation, accumulation and compaction under water-unsaturated and low-fO(2) conditions, which most likely occurred in an intra-continental rather than a subduction-related environment. Further synthetic analysis suggests conclusion that this magmatism may record a break-up event. (C) 2018 Elsevier B.V. All rights reserved.
资助项目	NFSC Project[41772192] ; Advanced Science Key Research Project of CAS[QYZDB-SSW-DQC04281712250]
WOS关键词	SILICATE LIQUID IMMISCIBILITY ; ILES LAYERED INTRUSION ; SKAERGAARD INTRUSION ; PHASE-RELATIONS ; THOLEIITIC MAGMAS ; U-PB ; FRACTIONAL CRYSTALLIZATION ; BASALT PETROGENESIS ; LIAODONG PENINSULA ; IGNEOUS COMPLEX
WOS研究方向	Geochemistry & Geophysics ; Mineralogy
语种	英语
出版者	ELSEVIER SCIENCE BV
WOS记录号	WOS:000449141300024
资助机构	NFSC Project ; NFSC Project ; Advanced Science Key Research Project of CAS ; Advanced Science Key Research Project of CAS ; NFSC Project ; NFSC Project ; Advanced Science Key Research Project of CAS ; Advanced Science Key Research Project of CAS ; NFSC Project ; NFSC Project ; Advanced Science Key Research Project of CAS ; Advanced Science Key Research Project of CAS ; NFSC Project ; NFSC Project ; Advanced Science Key Research Project of CAS ; Advanced Science Key Research Project of CAS
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/89442]
专题	地质与地球物理研究所_岩石圈演化国家重点实验室
通讯作者	Peng, Peng
作者单位	1.Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, POB 9825, Beijing 100029, Peoples R China 2.Univ Chinese Acad Sci, Beijing 100049, Peoples R China
推荐引用方式 GB/T 7714	Su, Xiangdong,Peng, Peng,Wang, Chong,et al. Petrogenesis of a similar to 900 Ma mafic sill from Xuzhou, North China: Implications for the genesis of Fe-Ti-rich rocks[J]. LITHOS,2018,318:357-375.
APA	Su, Xiangdong,Peng, Peng,Wang, Chong,Sun, Fengbo,Zhang, Zhiyue,&Zhou, Xiaotong.(2018).Petrogenesis of a similar to 900 Ma mafic sill from Xuzhou, North China: Implications for the genesis of Fe-Ti-rich rocks.LITHOS,318,357-375.
MLA	Su, Xiangdong,et al."Petrogenesis of a similar to 900 Ma mafic sill from Xuzhou, North China: Implications for the genesis of Fe-Ti-rich rocks".LITHOS 318(2018):357-375.