The Genesis of Serpentinite and Nephrite in the Fault Zone of Fengtien, Hualiann

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Project title

Code/計畫編號

MOST109-2116-M019-006

Translated Name/計畫中文名

花蓮豐田斷層帶蛇紋岩與閃玉之成因研究(之二)

Project Coordinator/計畫主持人

Huei-Fen Chen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Institute of Earth Sciences

Website

https://www.grb.gov.tw/search/planDetail?id=13539846

Year

2020

Start date/計畫起

01-08-2020

Expected Completion/計畫迄

31-10-2021

Bugetid/研究經費

1786千元

ResearchField/研究領域

地球科學

綠色閃玉目前發現皆與海洋板塊隱沒過程之增積岩體有關，主要由蛇紋岩經過含鈣之熱液換質形成，換質溫度約320℃至420℃左右。閃玉接觸帶的黑色蛇岩經常出現斷層擦痕構造，而片岩出現塑性變形與斷層角礫岩構造，似乎說明斷層裂隙是熱水通道的主要原因。根據花蓮豐田地區閃玉的熱液換質帶、觀察岩石構造與礦物特徵，發現片岩經換質作用後形成斜黝簾石的出現，斜黝簾石岩和蛇紋岩接觸帶形成閃玉與透輝石脈，閃玉和透輝石中含翠綠色的含鉻鈣鋁榴石的形成，及黑色磁鐵礦消失僅殘留鉻鐵礦和含鉻尖晶石，且反應後鉻鐵礦的外圈Mn、Zn、Ti含量異常增高。我們可以推測此熱液系統成份的演變。透輝石形成之後，明顯有方解石和石英脈切穿透輝石與斜黝簾石岩。透過觀察礦物生長順序，進一步分析礦物化學成分和全岩化學組成的變化，以及熱液脈沉澱之透輝石、方解石或石英之液包體溫度，了解形成此系統之熱液溫度與化學演化。此外也將完成碳酸鹽脈之叢同位素分析、U-Th 定年分析，結合構造位態研究以探討蛇紋岩和閃玉變形問題，更進一步了解此地區是否為更新世晚期的構造活動與熱水入侵造成特殊的礦物相產出。 Formation of green nephrite is regarded to the accretionary prism of subduction oceanic plate. The nephrite is derived from the hydrothermal metasomatism of serpentinite between 320℃to 420℃. Near the contact zone of nephrite, the surface of black serpetinite often has slickenside texture and schist reveals faulting breccia texture with plastic deformation. It seems to interpret the fracture zone is the pass way for hydrothermal fluid. According to hydrothermal metasomatism in Fengtien nephrite and observation of rock structure and mineral characters, we found that schist was altered to clinozoisite rock through metasomatism, and nephrite and diopside veins form between clinozoisite and serpeinite in the hydrothermal alteration zone. The new forming Cr-grossular appears in diopside and nephrite, but magnetite disappears. Only rich Mn, Zn and Ti in the reaction rim of chromite and Cr-spinel phase are residual in diopside and nephrite. We can speculate the chemical variation of the hydrothermal system. After the formation of diopside, calcite and quartz vein penetrates diopside and clinozoisite rock. We will observe the order of mineral growth, and then analyze variations of the mineral and rock compositions. Furthermore, we will analyze the fluid inclusions of diopside, calcite and quartz to understand the hydrothermal temperature and chemical variations. Clumping isotope and U-Th dating will be used in carbonate veins. Combining the structure to discuss the deformation of serpentinite and nephrite in the fault zone for interpreting the tectonic activity in late Pleistocene and the occurrence of characteristic minerals during hydrothermal intrusion.

Keyword(s)

閃玉
透輝石
熱液換質
化學
同位素
nephrite
diopside
hydrothermal matasomatism
chemical
isotope

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The Genesis of Serpentinite and Nephrite in the Fault Zone of Fengtien, Hualiann

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