Buoyancy-driven, rapid exhumation of ultrahigh-pressure metamorphosed continental crust

被引:246
作者
Ernst, WG
Maruyama, S
Wallis, S
机构
[1] TOKYO INST TECHNOL,DEPT EARTH & PLANETARY SCI,MEGURO KU,TOKYO 152,JAPAN
[2] KYOTO UNIV,FAC SCI,DEPT GEOL & MINERAL,SAKYO KU,KYOTO 60601,JAPAN
关键词
D O I
10.1073/pnas.94.18.9532
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Preservation of ultrahigh-pressure (UHP) minerals formed at depths of 90-125 km require unusual conditions. Our subduction model involves underflow of a salient (250 +/- 150 km wide, 90-125 km long) of continental crust embedded in cold, largely oceanic crust-capped lithosphere; loss of leading portions of the high-density oceanic lithosphere by slab break-off, as increasing volumes of microcontinental material enter the subduction zone; buoyancy-driven return toward midcrustal levels of a thin (2-15 km thick), low-density slice; finally, uplift, backfolding, normal faulting, and exposure of the UHP terrane. Sustained over approximate to 20 million years, rapid (approximate to 5 mm/year) exhumation of the thin-aspect ratio UHP sialic sheet caught between cooler hanging-wall plate and refrigerating, downgoing lithosphere allows withdrawal of heat along both its upper and lower surfaces. The intracratonal position of most UHP complexes reflects consumption of an intervening ocean basin and introduction of a sialic promontory into the subduction zone. UHP metamorphic terranes consist chiefly of transformed, yet relatively low-density continental crust compared with displaced mantle material-otherwise such complexes could not return to shallow depths. Relatively rare metabasaltic, metagabbroic, and metacherty lithologies retain traces of phases characteristic of UHP conditions because they are massive, virtually impervious to fluids, and nearly anhydrous. In contrast, H2O-rich quartzofeldspathic, gneissose/schistose, more permeable metasedimentary and metagranitic units have backreacted thoroughly, so coesite and other UHP silicates are exceedingly rare. Because of the initial presence of biogenic carbon, and its especially sluggish transformation rate, UHP paragneisses contain the most abundantly preserved crustal diamonds.
引用
收藏
页码:9532 / 9537
页数:6
相关论文
共 84 条
[1]   THE GRANULITE ECLOGITE FACIES TRANSITION - A COMPARISON OF EXPERIMENTAL WORK AND A NATURAL OCCURRENCE IN THE BERGEN ARCS, WESTERN NORWAY [J].
AUSTRHEIM, H .
LITHOS, 1990, 25 (1-3) :163-169
[2]  
BALLY AW, 1981, GEOL SOC LOND SPEC P, V9, P13
[3]  
BEANE RJ, 1996, GEOL SOC AM ABSTR, V28, P170
[4]  
Beaumont C, 1996, GEOLOGY, V24, P675, DOI 10.1130/0091-7613(1996)024<0675:MMFSCT>2.3.CO
[5]  
2
[6]  
BIINO GG, 1992, SCHWEIZ MINER PETROG, V72, P347
[7]  
BURCHFIEL BC, 1985, GEOLOGY, V13, P679, DOI 10.1130/0091-7613(1985)13<679:NEWTCH>2.0.CO
[8]  
2
[9]   DEFORMATION OF LEUCOGRANITES OF THE CRYSTALLINE MAIN CENTRAL SHEET IN SOUTHERN TIBET (CHINA) [J].
BURG, JP ;
BRUNEL, M ;
GAPAIS, D ;
CHEN, GM ;
LIU, GH .
JOURNAL OF STRUCTURAL GEOLOGY, 1984, 6 (05) :535-&
[10]  
CHARLTON TR, 1991, GEOLOGY, V19, P28, DOI 10.1130/0091-7613(1991)019<0028:PEIACC>2.3.CO