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題名 | Thermal Modeling and Chronological Constraints of Granitic Plutonism in Zhangzhou Igneous Complex, SE China=漳州複式岩體花崗岩侵位之數值熱模擬研究 |
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作者 | 呂學諭; 田蓉禮; 羅清華; 陳正宏; | 書刊名 | 中國地質學會會刊 |
卷期 | 42:4 1999.11[民88.11] |
頁次 | 頁521-541 |
分類號 | 358.43 |
關鍵詞 | 冝Ar/効Ar dating thermochronology; 數值熱模擬; 漳州複式岩體; 氬氬定年; 淺侵位岩漿活動; Numerical thermal modeling; Zhangzhou igneous complex; High-level plutonism; |
語文 | 英文(English) |
中文摘要 | 位於中國大陸東南沿海的漳州複式岩體由八個主要的深成岩體組成,其成份由基 性到酸性兼而有之,本研究旨在利用數值熱模式模擬漳州複式岩體之熱歷史。因其體積之故 ,祖地、長泰、古農三個岩體在數值熱模擬中,遠比其他岩體重要,故本研究僅模擬上述三 個岩體侵位的冷卻史。 由前人研究已知長泰及古農岩體在高溫階段 (873 ∼ 673K) 的冷卻 速率分別為 >300 ° K/m.y.,及 40 ° k/m.y.。而數值熱模擬的結果顯示,在正常的地溫 梯度下 (31.0 ° K/km),深度 6 公里的淺位侵入花崗岩之冷卻速率遠大於 800 ° K/m.y. 。因此,唯有在地溫梯度 46.7 ° K/km 下,才能模擬出長泰岩體的冷卻速率。若將模式中 的理論地表熱流值 (>105mWm-2) 和現今重測的地表熱流值相比較, 長泰岩拉侵位時應處於 模式。因此,除了張裂的地體構造環境外,仍需額外的熱源才能將古農岩體之冷卻速率降至 40 ° K/m.y.。這個熱源可能來自於後續深成岩體的侵位,但仍不能排除其他熱運動的影響 。在所有的出露岩體中,若前岩體最可能大幅降低古農岩體的冷卻速率。若岩前岩體在古農 岩體之後五百萬年侵入古農岩體之下,即可成功地在不影響祖地、長泰岩體下,將古農岩體 之冷卻速率降至 40 ° K/m. y. 左右。但這樣的變化,僅止於局部而無關區域之熱事件。 |
英文摘要 | Zhangzhou Igneous Complex (ZIC) located in the coastal area of southeastern China is composed of eight plutons with geochemical compositions ranging from basic to acidic. Zudi, Changtai and Kunon plutons are thermodynamically more significant than the others due to their larger volumes. With utilizing thermochronological data and other geological constraints, a numerical thermal model is constructed to simulate the temperature-time (T-t) paths for the plutons. According to previous studies, the emplacement depths of these plutons and thickness of crust are estimated at around 6km and 30 km, respectively. In order to obtain the T-t path of the Changtai pluton under geological constraints, a high geothermalgradient of 46.7 ° K/km in the uppermost 1-km crust is needed.The modeled surface heat flow is also greater than 105 mWm-2. It is not too surprising to see such a high heat flow and geothermal gradient for the regime since the ZIC is a product of a lateMesozoic extensional tectonism. Although the Kunon plutonemplaced almost immediately after the Changtai pluton, thecooling rate (40 ° K/m.y.) is surprisingly much lower than that ofthe Changtai pluton from the data of 40Ar/39Ar dating. According to the result of numerical thermal modeling, the latent heat simply released from the preceding plutonisms is not sufficient to causesuch a low cooling rate. It needs a thermal pulse and/or a plutonism,which occurred after the emplacement of the Kunon pluton to reset the K-Ar isotopic systematics in biotite witin the Kunonpluton. The Yanchian pluton would be the candidate if it intrudedabout 5.0 Ma after the Kunon plutonism. |
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