中國東南地區是世界上重要的火成岩體產地之一，對於此地區晚中生代的構造岩漿演化之成因探討，至今仍有許多學者提出不同的隱沒模式，嘗試解釋此區域廣泛分布火成岩之成因，然而，在區域地球動力學的角度上，仍建立在古太平洋板塊隱沒形成的主動大陸邊緣。近年來，有許多研究利用中國東南地區的基性火成岩去探討地函源區特徵，而在過去研究中，基性岩相關地化資料顯示，多數基性岩具有地殼訊號，且多數學者認為地殼物質訊號應為隱沒作用帶入源區屬於源區混染(Source contamination)，而很少學者探討地殼混染(Crustal contamination)的可能性。因此本研究將針對地殼與源區作用關係進行探討，並希望可以了解中國東南地區岩漿與地殼物質交互作用的構造演化關係。
本研究樣本多取自於福建地區，成分以輝綠岩為主，並利用其主要元素、微量元素及Sr-Nd同位素的分析結果進行探討。主要元素中， SiO2含量介於48.9─55.6%，全鹼值(Total alkalis, Na2O+K2O)含量為3.02- 6.32%、CaO含量為6.24- 9.77%，由於樣本之燒失率(LOI)介於1.58-3.67%(正常玄武岩為0.05%)，代表樣本受到蝕變作用影響，因此我們無法以主要元素將樣本分類。首先，樣本依據微量元素分群，在整體不相容元素分布圖中，樣本具有Rb、Ba富集，而Nb、Ta負異常之現象者為group 1，而不具Nb、Ta和Ti負異常者為group 2樣本。然而本研究缺乏定年資料，因此以微量元素訊號及Sr-Nd同位素之特徵與中生代和新生代玄武岩的特徵比較，結果顯示樣本屬於中生代基性岩。Zr/TiO2- Nb/Y圖中，樣本屬於玄武岩及玄武岩質安山岩，而在Th- Co圖中樣本屬於鈣鹼性及高鉀鈣鹼性岩漿。在上述資訊中，微量元素之Nb、Ta負異常及鈣鹼性和高鉀鈣鹼性岩漿等地化特徵顯示樣本成分受到地殼物質加入影響，加上Nb/Y- Rb/Y圖中，group 1樣本之Nb/Rb值小於2，亦暗示樣本成分受到地殼物質影響。
在兩端元混合模式討論中，樣本分別受到地殼和源區混染作用影響，且地殼與地函之交互作用於角閃岩相的深度區間。在源區混染之混合模式中，變質泥岩經低於20%的部份熔融，以10-30%的比例混入虧損地函中；地殼混染之混合模式，其N-MORB和E-MORB岩漿分別與變質泥岩產生之岩漿混合的兩模式皆可解釋樣本之地殼訊號來源，經歷低於20%的部份熔融，以10-20%的比例混入地函源岩漿中，由此現象推論，樣本之地函源岩漿成份介於N-MORB和E-MORB岩漿之間。
整合所有結果，推測本研究區域應處於拉張的環境，隨構造由聚合轉為拉張，具有EM II訊號之地函發生部份熔融，並在岩漿上升的過程中受到地殼混染，因而同時具有源區混染及地殼混染之訊號。此外，地殼混染的成因也與輝綠岩之演化機制相符，因為岩漿庫在地殼中冷卻過程中，與圍岩產生交互作用，使地殼物質混入岩漿庫為必然現象，故所分析輝綠岩之Nb、Ta負異常和鈣鹼質岩漿之訊號並非單由島弧隱沒造成，而同時亦是地殼混染產生的現象，但仍無法排除源區混染之可能性。

SUMMARY
The Cretaceous basaltic dikes in southeast China are characterized by Nb-Ta-Ti depletions relative to elements of similar compatibilities during mantle melting. Both source and crustal contaminations have been proposed to be responsible for these crustal signatures, however, without supports from model calculations. In this study, five basaltic dike samples were analyzed for major and trace element compositions as well as Sr and Nd isotopic ratios. These data were compared to the results from model calculations simulating source contamination and crustal contamination to address the roles of these two processes in generating the crustal signatures in the samples.
The samples are composed of subordinate amounts of plagioclase, clinopyroxene and chlorite with minor amounts of calcite. They have SiO2, Al2O3, CaO, MgO, and Na2O content in the ranges of 48.9–55.6%, 13.6–17.9%, 6.24–9.77%, 3.8–8.17% and 2.56–3.72%, respectively. In the primitive mantle normalized trace element abundance plot, nine of the fourteen samples show prominent depletions in Nb, Ta, and Ti concentrations, reflecting the involvement of crustal component. Based on the mixing model plots, the data can explained with generation from a depleted mantle that were metasomatized by melt derived from subducted metapelite by 10-30% partial melting. Alternatively, mixtures containing 80-90% mantle-derived melts (N-MORB or E-MORB) and 10–20% metapelite-derived melt are also characterized by Nb, Th, Zr and La concentrations comparable to the samples. Similar results were obtained from 87Sr/86Sr–143Nd/144Nd simulation. It, therefore, appears that these Cretaceous mafic dikes were generated from a metasomatized mantle and experienced crustal contamination.
Key words: Southeast China, mafic dikes, crustal contamination, source contamination.

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