中國金宝搏入口188在古俯沖帶地球動力學過程研究取得重要進展
俯沖(chong)(chong)(chong)帶(dai)(dai)是殼幔(man)物質循(xun)環(huan)和(he)能(neng)量交換(huan)的(de)關鍵場所(suo)，為弧巖漿活(huo)(huo)動和(he)大(da)陸(lu)地(di)(di)殼形(xing)成提(ti)供了(le)有利條件。弧巖漿的(de)時空分布特征(zheng)(zheng)為理解俯沖(chong)(chong)(chong)帶(dai)(dai)地(di)(di)球(qiu)動力(li)學(xue)(xue)過(guo)程提(ti)供了(le)重要線索。研究表明，弧巖漿活(huo)(huo)動主要受控(kong)于(yu)兩大(da)因素：一(yi)是俯沖(chong)(chong)(chong)板(ban)塊(kuai)動力(li)學(xue)(xue)和(he)幾(ji)何形(xing)態的(de)變(bian)(bian)化，包括海(hai)溝前進/后退、板(ban)片窗形(xing)成、俯沖(chong)(chong)(chong)角度(du)與匯聚速率(lv)的(de)改變(bian)(bian)；二(er)是上覆板(ban)塊(kuai)狀態的(de)改變(bian)(bian)，如俯沖(chong)(chong)(chong)侵(qin)蝕/增(zeng)生、板(ban)塊(kuai)厚度(du)變(bian)(bian)化以及構造(zao)控(kong)制的(de)巖漿上升(sheng)和(he)侵(qin)位。這(zhe)些因素共同調(diao)控(kong)著地(di)(di)幔(man)楔的(de)熔融條件、巖漿上升(sheng)路徑和(he)滯(zhi)留(liu)時間，從而(er)直(zhi)接控(kong)制巖漿的(de)形(xing)成與分布特征(zheng)(zheng)。雖然現代(dai)活(huo)(huo)動大(da)陸(lu)邊緣(yuan)為研究這(zhe)些地(di)(di)球(qiu)動力(li)學(xue)(xue)過(guo)程提(ti)供了(le)豐(feng)富資料，但(dan)古(gu)老(lao)造(zao)山帶(dai)(dai)中保存的(de)長(chang)期巖漿記錄為揭示古(gu)俯沖(chong)(chong)(chong)帶(dai)(dai)動力(li)學(xue)(xue)演化提(ti)供了(le)獨特窗口，這(zhe)一(yi)領域仍存在諸(zhu)多未(wei)解之謎。
188bet足球地(di)(di)球(qiu)(qiu)和(he)空(kong)(kong)間科學(xue)(xue)學(xue)(xue)院、巖(yan)(yan)(yan)石圈演化和(he)環境演變(bian)全國重點實驗室鄭永飛院士研(yan)(yan)究團隊戴立群教(jiao)授研(yan)(yan)究組(zu)以(yi)中國西北天(tian)山為研(yan)(yan)究靶區，系統(tong)梳(shu)理了(le)該區域的古(gu)生代(dai)(dai)(dai)火成(cheng)巖(yan)(yan)(yan)、蛇(she)綠巖(yan)(yan)(yan)和(he)碎屑鋯石的空(kong)(kong)間分布、年(nian)代(dai)(dai)(dai)學(xue)(xue)與地(di)(di)球(qiu)(qiu)化學(xue)(xue)數據。結果顯示(shi)，古(gu)生代(dai)(dai)(dai)巖(yan)(yan)(yan)漿活動存在(zai)明顯的時空(kong)(kong)演化規律，巖(yan)(yan)(yan)漿巖(yan)(yan)(yan)與碎屑鋯石隨(sui)時間演化均顯示(shi)逐漸虧(kui)損Nd-Hf同(tong)位素特征(圖1)，并伴隨(sui)有同(tong)時期富Nb玄武巖(yan)(yan)(yan)-高鎂(mei)安山巖(yan)(yan)(yan)-埃達克巖(yan)(yan)(yan)組(zu)合以(yi)及Cu-Au礦床的形成(cheng)，指(zhi)示(shi)了(le)洋脊-轉換斷層交錯俯沖導致的板片窗間歇(xie)性打(da)開對弧巖(yan)(yan)(yan)漿的控制作用(yong)。相關研(yan)(yan)究成(cheng)果以(yi)“Magmatic record reveals an ancient slab window linked to paleo-oceanic subduction”為題，5月23日(ri)發表(biao)在(zai)Nature Index收錄的國際地(di)(di)質學(xue)(xue)知(zhi)名期刊《Geology》上。
圖(tu)1. 弧巖(yan)漿作用時空演化(hua)(A-B) 與巖(yan)漿巖(yan)和(he)碎屑鋯石Nd-Hf同位素變化(hua)(C-D)
盡管俯沖(chong)上(shang)盤和(he)(he)下(xia)盤均(jun)可影響弧(hu)(hu)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)的(de)(de)形成(cheng)(cheng)(cheng)(cheng)和(he)(he)演化(hua)，但是西(xi)北天山古(gu)生代(dai)弧(hu)(hu)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)活動(dong)與蛇綠巖(yan)(yan)(yan)(yan)在(zai)時(shi)空分布上(shang)同(tong)(tong)步變(bian)化(hua)，表(biao)明弧(hu)(hu)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)作用與蛇綠巖(yan)(yan)(yan)(yan)侵位(wei)具有(you)成(cheng)(cheng)(cheng)(cheng)因(yin)(yin)聯(lian)系，因(yin)(yin)此俯沖(chong)板(ban)(ban)塊的(de)(de)行(xing)為是控(kong)制(zhi)弧(hu)(hu)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)演化(hua)的(de)(de)主導(dao)因(yin)(yin)素(su)。此外(wai)(wai)，傳(chuan)統(tong)的(de)(de)機制(zhi)，如海溝(gou)前(qian)進/后退、俯沖(chong)角度(du)與匯聚速率改(gai)變(bian)、板(ban)(ban)片(pian)斷離及(ji)巖(yan)(yan)(yan)(yan)石圈(quan)拆沉(chen)，都難以解(jie)釋(shi)平行(xing)于海溝(gou)的(de)(de)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)活動(dong)轉移(yi)和(he)(he)同(tong)(tong)位(wei)素(su)組(zu)成(cheng)(cheng)(cheng)(cheng)的(de)(de)逐(zhu)(zhu)漸(jian)虧(kui)損。綜(zong)合各(ge)項(xiang)地質(zhi)證(zheng)據表(biao)明，洋(yang)(yang)脊(ji)-轉換斷層交錯俯沖(chong)引起的(de)(de)板(ban)(ban)片(pian)窗最有(you)可能解(jie)釋(shi)這些特征(圖2)。當北天山洋(yang)(yang)的(de)(de)洋(yang)(yang)中脊(ji)與伊犁-中天山板(ban)(ban)塊北緣以小(xiao)角度(du)交匯，板(ban)(ban)片(pian)窗間歇(xie)性打開，促使巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)弧(hu)(hu)從西(xi)北向東南方向逐(zhu)(zhu)漸(jian)轉移(yi)并造(zao)(zao)成(cheng)(cheng)(cheng)(cheng)周期性巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)作用 (圖1和(he)(he)2A-C)，同(tong)(tong)時(shi)伴隨高溫變(bian)質(zhi)作用，富Nb玄武巖(yan)(yan)(yan)(yan)-高鎂(mei)安(an)山巖(yan)(yan)(yan)(yan)-埃達克巖(yan)(yan)(yan)(yan)組(zu)合、Cu-Au礦床(chuang)和(he)(he)A型花崗巖(yan)(yan)(yan)(yan)的(de)(de)形成(cheng)(cheng)(cheng)(cheng)。當北天山洋(yang)(yang)閉合，洋(yang)(yang)脊(ji)俯沖(chong)到大陸之下(xia)，最終在(zai)大陸邊緣產生廣泛的(de)(de)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)作用(圖2D)。此外(wai)(wai)，板(ban)(ban)片(pian)窗的(de)(de)打開導(dao)致虧(kui)損的(de)(de)軟流圈(quan)地幔物(wu)質(zhi)上(shang)涌，造(zao)(zao)成(cheng)(cheng)(cheng)(cheng)Nd-Hf同(tong)(tong)位(wei)素(su)系統(tong)性虧(kui)損。因(yin)(yin)此，洋(yang)(yang)脊(ji)-轉換斷層交錯俯沖(chong)不僅(jin)控(kong)制(zhi)了(le)弧(hu)(hu)巖(yan)(yan)(yan)(yan)漿(jiang)(jiang)(jiang)(jiang)(jiang)活動(dong)的(de)(de)時(shi)空分布和(he)(he)地球化(hua)學特征，同(tong)(tong)時(shi)也塑造(zao)(zao)了(le)古(gu)俯沖(chong)帶獨特的(de)(de)構造(zao)(zao)演化(hua)格局(ju)。
圖2.洋脊(ji)-轉換斷層(ceng)交錯(cuo)俯沖對弧巖漿演化(hua)的(de)影響
馬利(li)濤特任副研(yan)究員為論文的第一作者，戴(dai)立群教(jiao)授(shou)為通(tong)訊作者。該項研(yan)究工作得(de)到了國家自然科學基金(42488101和42303044)資(zi)助。
文章鏈接：//pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53112.1/654561/Magmatic-record-reveals-an-ancient-slab-window.
（地(di)球(qiu)和空間(jian)科學(xue)學(xue)院、科研部）
