Post-collisional exhumation and geotherm pattern in northern Tananao Complex, northeastern Taiwan
Post-collisional exhumation and geotherm pattern in northern Tananao Complex, northeastern Taiwan
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台湾东北部塔那尾杂岩北部碰撞后折返和地热模式
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发表时间：
2020
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影响因子：
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通讯作者：
Chenguang Wu
中科院分区：
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作者：
Tzu;Tsungkwei Liu;Shao;P. Hsieh;Chenguang Wu
台湾东北部地区经历了由碰撞后造山带琉球俯冲系统引起的挤压碰撞向伸展的应力转换过程。为了弄清伸展阶段何时开始以及冷却折返历史如何随构造应力的变化而变化，采集了塔南澳杂岩北部花岗片麻岩的磷灰石和锆石裂变径迹年龄。利用已有的黑云母40Ar-39Ar年龄估算4.1~3.0 Ma以来的折返速率约为4mmyr-1，并假定地温梯度均匀。在1.5-0.2 Ma期间，折返速率保持在2.3-1.6 mm yr-1，在年龄-海拔关系(AER)中，磷灰石和锆石的斜率相似。在3.0~1.5 Ma之间，折返作用的减弱被解释为从琉球俯冲带向台湾东北部伸展侵袭的开始。在约0.2 Ma后，磷灰石AER的截获表明，山脉的折返速度加快到~5 mm yr-1，而谷底的折返速度保持稳定。垂直剖面的年龄偏移量支持地壳浅层的正断层活动。1.5~0.2 Ma的加速降温和稳定折返反映了古地温梯度随时间的增加。1.5 Ma以后，古地温梯度估计在100℃Km-1以上，表明希望区具有复杂构造构造形成的热源。但现代地温较低，可能受近地表水循环的影响。
The northeast region of Taiwan has experienced a stress transition from the compressive collision to the extension induced from the Ryukyu subduction system in a post-collisional orogenic belt. In order to clarify when the extensional stage began and how the cooling and exhumation history varied with the transition of tectonic stress, apatite and zircon fission-track ages on the granitic gneiss in northern Tananao Complex were collected from a ~2700 m high sub-vertical profile. The exhumation rate was estimated as ~4 mm yr -1 since 4.1 - 3.0 Ma using previous biotite 40 Ar- 39 Ar ages with an assumed uniform geothermal gradient. During the period of 1.5 - 0.2 Ma, the exhumation rate remained at 2.3 - 1.6 mm yr -1 , evidenced by the similar slopes for apatite and zircon in the age-elevation relationship (AER). The decrease in exhumation occurred in between 3.0 and 1.5 Ma is interpreted as the onset of the extensional im-pact into NE Taiwan from the Ryukyu subduction zone. After ~0.2 Ma, the intercepts of apatite AER suggest that exhumation accelerated to ~5 mm yr -1 at the mountain range but was steady at the valley bottom. The offset in ages of the vertical profile is supportive of the normal faulting at the shallow crust. The accelerating cooling with the steady exhumation from 1.5 - 0.2 Ma implies the increase in paleogeothermal gradient with time. The paleogeothermal gradients are estimated to be over 100°C km -1 after 1.5 Ma, suggesting that the Hoping area possesses heat sources induced from the complex tectonic configuration. However, the modern geotherm is relatively low and may be influenced by the water circulation near surface.