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標題: | 土耳其東部造山帶岩漿活動之年代與地球化學研究 Age and Geochemical Constraints on the Collision Zone Magmatism in Eastern Turkey |
作者: | Yu-Chin Lin 林俞青 |
指導教授: | 鍾孫霖(Sun-Lin Chung) |
關鍵字: | 新特提斯洋,阿拉伯?歐亞大陸碰撞帶,碰撞帶岩漿活動,地球化學,放射性定年, Neotethys,Arabia?Eurasia?collision?zone,collision?zone?magmatism,geochemistry,radiometric?dating, |
出版年 : | 2020 |
學位: | 博士 |
摘要: | 阿拉伯與歐亞大陸板塊碰撞造山帶包含了一系列新特提斯洋的關閉、微陸塊的加積與最終的大陸碰撞,這個過程造成了高加索-伊朗-安納托利亞高原地區(簡稱CIA地區)廣泛分布自白堊紀以降的碰撞帶岩漿活動,其形成機制多所爭議。本研究針對土耳其東部之(1)埃拉澤地區晚白堊紀火成岩及(2)新近紀至第四紀火山岩,分析鋯石鈾-鉛年齡、鋯石鉿同位素組成、全岩氬-氬年齡、全岩地球化學及鍶-釹-鉿同位素組成,以討論其時空分布與岩石成因,進而對CIA地區之地體構造演化提供新的制約。
土耳其東南部埃拉澤晚白堊紀火成岩於83 Ma至73 Ma形成,這些樣本的地球化學性質隨著時間系統性的變化,岩性從矽質、鈣鹼質、演化為鉀玄岩質,並且在蛛網圖中都展現了鉭-鈮-鈦的虧損現象,而這些樣本隨時間演化的趨勢亦展現於輕稀土元素相對於重稀土元素的富集[如(La/Yb)N自0.5-6至12-24]、大離子半徑元素的富集、以及全岩釹-鉿同位素的降低[如εNd(T)自+7.1至-4.4、εHf(T)自+16至-2]等地球化學特性上。混染模擬結果顯示這個隨時間的變化是由於島弧岩漿活動的源區、地函楔隨著時間有越來越高比例由阿拉伯陸塊所提供的古老大陸地殼物質加入所造成,代表阿拉伯陸塊向海溝靠近的結果,並導致了Bitlis-Puturge地塊於79 Ma至74 Ma的高壓低溫變質作用與新特提斯洋南支的關閉及蛇綠岩套的侵位。因此本研究認為這套白堊紀島弧(83-73 Ma)與新特提斯洋蛇綠岩套(92-83 Ma)可能形成於一洋內島弧系統、隨著阿拉伯陸塊的靠近而弧陸碰撞、島弧岩漿活動停止。由於阿拉伯陸塊提供的沉積物在島弧岩漿活動初期即開始加入地函楔中,本研究認為此短生命週期的島弧形成於新特提斯洋中一靠近阿拉伯陸塊的弧溝回捲系統,並且代表了阿拉伯陸塊北緣的新特提斯洋蛇綠岩套系統中的”消失的島弧”。 整個CIA地區廣泛分佈碰撞後岩漿活動所造成的新近紀至第四紀火山岩,本研究根據定年及地球化學分析結果,認為東安納托利亞地區碰撞後岩漿活動可分為初期(17-5 Ma)與後期(<6.5 Ma)兩階段。初期岩漿活動在CIA地區呈現由東南安納托利亞(~17 Ma)向西北伊朗(~11 Ma)、向東北安納托利亞(~9 Ma)的不等時開始,並造成明顯鍶-釹同位素差異、由基性岩(SiO2 = 48-52 wt%; εNd = +6至+3)與酸性岩(SiO2 = 58-71 wt%; εNd = +4 to -5)所組成的雙峰式火山岩,指示其主要的岩漿源區包含了地函及古老大陸地殼。後期火山岩則在CIA地區造成廣泛分布的鈣鹼性與鹼性岩序列,同位素組成顯示除了凡湖地區有明顯地殼混染(εNd = +1至-4)外,其餘地區多繼承地函的特性(εNd = +7至+1)。此外,本研究發現東安納托利亞部分初期岩漿活動的酸性岩具有埃達克岩的性質(17-5 Ma),並且在小高加索(4-3 Ma)以及西北伊朗(<10 Ma)地區皆有埃達克岩的出露,其地球化學特徵及同位素組成空間的變化(εNd於北帶為+4至0,南帶為-2至-5)指示這些埃達克岩可能為至少兩種不同的增厚基性下地殼部分熔融而來。由於CIA地區的基盤為多個微陸塊拼貼而成,從碰撞後火山岩的地球化學特性及時空變化,本研究認為初期岩漿活動是由多個縫合帶中各個隱沒的海洋岩石圈不等時的拆離、軟流圈上湧使岩石圈地函與含水基性下部地殼熔融所造成;而後期岩漿活動複雜的地球化學組成則指示了多重的岩漿源區,可能是持續的碰撞使得增厚的岩石圈發生了大規模的拆沉活動所造成的大型熱事件。此外,自兩百萬年來,此碰撞帶的碰撞後岩漿活動呈現一個由東安納托利亞高原向西北伊朗、東南伊朗演化的趨勢,可能源自於阿拉伯與歐亞大陸斜向碰撞。 The continental collision between Arabia and Eurasia, following the closure of the Neotethys and accretion of the micron-continent, gave rise to the Caucasus-Iran-Anatolia (CIA) province and resulted in widespread collision zone magmatism of Cretaceous to Quaternary ages. Several petrogenetic issues remain to be resolved. In this thesis, zircon U-Pb ages, zircon Hf isotopes, whole-rock Ar-Ar ages, and whole-rock geochemical and Sr-Nd-Hf isotopic data are reported from (1) Late Cretaceous Elazig magmatic rocks from SE Turkey, and (2) Neogene-Quaternary volcanic rocks from Eastern Turkey, to provide constraints on the temporal-spatial distribution and petrogenetic history of this region. The Elazıg magmatic rocks that formed within 83 to 73 Ma are characterized by significant geochemical variations over time, from low-K tholeiitic to calc-alkaline, and then shoshonitic suites, associated with progressive enrichment in LREE and LILE, and change in isotopic ratios such as whole-rock εHf(T) values that range from +16 to -2. Such variations are interpreted as changing magma source region by addition of continental crust materials back into the mantle wedge during the arc magmatism. This process can be attributed to the approaching Arabian continent that also led to the HP-LT metamorphism (79-74 Ma) in the Bitlis-Puturge Massif, closure of the southern branch of Neotethys, and emplacement of the Neotethyan ophiolites. This short-lived arc magmatism, as well as the Neotethyan ophiolites (92-83 Ma), can be best explained by a rapid tectonic switching from intra-oceanic subduction to continental collision. This subduction zone may have developed in an arc–trench rollback system near the Arabian continent so that the Arabian sediments can be evolved into the arc magmatism within a short period, and this arc was the “missing arc” of the Neotethyan ophiolites bordering the northern margin of the Arabian continent. Based on the new age and geochemical data, the post-collisional magmatism in Eastern Anatolia can be divided into two stages: an initial stage (17-5 Ma) and a younger stage (<6.5 Ma). The age data indicate a diachronous onset of volcanism that began ~17 Ma in SE Anatolia and propagated northward from ~11 to 9 Ma toward NE Anatolia and NW Iran. The rocks are characteristically bimodal with significant isotopic variations that include dominantly basic (SiO2= 48-52 wt%; εNd = +6 to +3) and silicic (SiO2= 58-71 wt%; εNd = +4 to -5) rocks. These rocks may be derived from two principal magma sources: (1) a juvenile mantle-derived component and (2) an older continental crust component. Subsequent volcanism that began from ~6.5 Ma resulted in a wide spectrum of calc-alkaline and alkaline rocks, with mafic to felsic lithologies in the entire province. Most rocks were dominated by mantle-like isotopic compositions (εNd = +7 to +1), except rocks from the Van area that were affected by crustal contamination (εNd = +1 to -4). The thickened crust-derived adakitic rocks are identified from not only the silicic rocks of the initial stage in Eastern Anatolia (17-5 Ma) but also Lesser Caucasus (4-3 Ma) and NW Iran (<10 Ma). Their Nd isotopic compositions allow this study to subdivide these rocks into the northern-middle (εNd = +4 to 0) and the southern zone (εNd = -2 to -5), indicating two crustal components in the CIA province. This thesis attributes the volcanic initiation to a migrating post-collisional extension locus caused by the successive breakoff of subducted Neo-Tethyan slabs. Subsequent, more extensive and heterogeneous volcanism is explained by “wholesale” lithospheric delamination as a consequence of collision and lithospheric thickening. From ~2 Ma, volcanism ceased in the western CIA province and subsequently propagated eastward and southeastward to SE Iran, consistent with the notion of an oblique continental collision between Arabia and Eurasia. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/62972 |
DOI: | 10.6342/NTU201704221 |
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顯示於系所單位: | 地質科學系 |
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