地質(zhì)學(xué)

地質(zhì)學(xué)

來(lái)源出版物：Science China: Earth Sciences, 2015, 58(9): 1523-1537聯(lián)系郵箱：ZHU Ri-xiang, rxzhu@mail.iggcas.ac.cn

板塊構(gòu)造對(duì)海相鉀鹽礦床分布與成礦模式的控制

劉成林，趙艷軍，方小敏，等

表生鉀鹽礦床主要沉積于陸殼板塊上的陸表海盆地中，其沉積受制于全球板塊運(yùn)動(dòng)，具體影響表現(xiàn)在板塊的規(guī)模、邊界特征、漂移歷史與古緯度、古氣候等的控制作用。在巨型穩(wěn)定克拉通上，出現(xiàn)巨型陸表海盆，沉積分布廣、厚度大的巨型鉀鹽礦床或礦集區(qū)，礦床沉積類型屬于化學(xué)巖型即碳酸鹽巖型鉀鹽礦；板塊匯聚區(qū)域，如特提斯造山帶，出現(xiàn)較多的小陸塊并形成較小規(guī)模的海相及海陸交互相盆地，也形成了一些厚度大的巨型-超大型鉀鹽礦床或礦床群，沉積類型有化學(xué)巖型及碎屑巖型鉀礦兩類；而大陸板塊邊緣及其內(nèi)部，出現(xiàn)裂谷盆地成鉀，沉積環(huán)境可以從海相到非海相及過(guò)渡類型，鉀鹽沉積規(guī)模不等，也可出現(xiàn)超大型礦床，基本屬于碎屑巖型鉀礦；最后，在大陸板塊內(nèi)部出現(xiàn)典型陸相鉀鹽沉積。從時(shí)代上看，穩(wěn)定巨型克拉通板塊成鉀，主要出現(xiàn)于古生代；而板塊匯聚時(shí)期成鉀，主要發(fā)生在中生代；裂谷成鉀則主要出現(xiàn)在新生代，典型陸相鉀鹽礦床則出現(xiàn)在第四紀(jì)。由此可見(jiàn)，從古生代到新生代，地球表生成鉀模式發(fā)生了重大轉(zhuǎn)換。從成鉀物質(zhì)來(lái)源看，穩(wěn)定克拉通海盆主要以海水補(bǔ)給為主，特提斯小陸塊的海相盆地成鉀物質(zhì)，以海水補(bǔ)給為主，可能存在非海相（以火山活動(dòng)帶來(lái)深部物質(zhì)等）的補(bǔ)給；而裂谷成鉀物質(zhì)補(bǔ)給，則是海相與非海相混合型，甚至一些盆地以非海相物質(zhì)補(bǔ)給為主。從古生代到中生代，再到新生代，成鉀盆地規(guī)模快速變?。凰纬傻拟淃}資源量也呈相應(yīng)遞減變化規(guī)律。中國(guó)小陸塊的漂移演化歷史受控于全球主要板塊的構(gòu)造演化，其海相盆地成鉀作用也應(yīng)符合世界主要鉀鹽成礦的基本規(guī)律，因此，掌握全球板塊對(duì)鉀鹽成礦基本約束規(guī)律，有助于研究中國(guó)小陸塊海相成鉀規(guī)律，指導(dǎo)中國(guó)海相找鉀勘查突破。

板塊運(yùn)動(dòng)；小陸塊；海相；鉀鹽礦床；成礦模式

來(lái)源出版物：地質(zhì)學(xué)報(bào), 2015, 89(11): 1893-1907聯(lián)系郵箱：劉成林，liuchengl@263.net

Decratonic gold deposits

ZHU Ri-xiang, FAN Hong-rui, LI Jian-wei, et al.

The North China Craton (NCC) hosts numerous gold deposits and is known as the most gold-productive region of China. The gold deposits were mostly formed within a few million years in the Early Cretaceous (130-120 Ma), coeval with widespread occurrences of bimodal magmatism, rift basins and metamorphic core complexes that marked the peak of lithospheric thinning and destruction of the NCC. Stable isotope data and geological evidence indicate that ore-forming fluids and other components were largely exsolved from cooling magma and/or derived from mantle degassing during the period of lithospheric extension. Gold mineralization in the NCC contrasts strikingly with that of other cratons where gold ore-forming fluids were sourced mostly from metamorphic devolatization in compressional or transpressional regimes. In this paper, we present a summary and discussion on time-space distribution and ore genesis of gold deposits in the NCC in the context of the timing, spatial variation, and decratonic processes. Compared with orogenic gold deposits in other cratonic blocks, the Early Cretaceous gold deposits in the NCC are quite distinct in that they were deposited from magma-derived fluids under extensional settings and associated closely with destruction of cratonic lithosphere. We argue that Early Cretaceous gold deposits in the NCC cannot be classified as orogenic gold deposits as previously suggested, rather, they are a new type of gold deposits, termed as “decratonic gold deposits” in this study. The westward subduction of the paleo-West Pacific plate (the Izanagi plate) beneath the eastern China continent gave rise to an optimal tectonic setting for large-scale gold mineralization in the Early Cretaceous. Dehydration of the subducted and stagnant slab in the mantle transition zone led to continuous hydration and considerable metasomatism of the mantle wedge beneath the NCC. As a consequence, the refractory mantle became oxidized and highly enriched in large ion lithophile elements and chalcophile elements (e.g., Cu, Au, Ag and Te). Partial melting of such a mantle would have produced voluminous hydrous, Au-and S-bearing basaltic magma, which, together with crust-derived melts induced by underplating of basaltic magma, served as an important source for ore-forming fluids. It is suggested that the Eocene Carlin-type gold deposits in Nevada, occurring geologically in the deformed western margin of the North America Craton, are comparable with the Early Cretaceous gold depo-sits of the NCC because they share similar tectonic settings and auriferous fluids. The NCC gold deposits are characterized by gold-bearing quartz veins in the Archean amphibolite facies rocks, whereas the Nevada gold deposits are featured by fine-grained sulfide dissemination in Paleozoic marine sedimentary rocks. Their main differences in gold mineralization are the different host rocks, ore-controlling structures, and ore-forming depth. The similar tectonic setting and ore-forming fluid source, however, indicate that the Carlin-type gold deposits in Nevada are actually analogous to decratonic gold deposits in the NCC. Gold deposits in both the NCC and Nevada were formed in a relatively short time interval (＜10 Myr) and become progressively younger toward the subduction zone. Younging of gold mineralization toward subductionzone might have been attributed to retreat of subduction zone and rollback of subducted slab. According to the ages of gold deposits on inland and marginal zones, the retreat rates of the Izanagi plate in the western Pacific in the Early Cretaceous and the Farallon plate of the eastern Pacific in the Eocene are estimated at 8.8 cm/yr and 3.3 cm/yr, respectively.

Early Cretaceous; craton destruction; decratonic gold deposit; ore deposit model