青藏高原地热资源与地幔柱构造的关系——地幔热柱多级演化导致岩浆上侵成为浅部热源

Relationship between Geothermal Resources and Mantle Plume Structure in the Qinghai-Xizang Plateau-Multi-stage Evolution of Mantle Heat Plumes Resulting in Magma Intrusion into Shallow Heat Source

青藏高原丰产高温地热资源己闻名于世。1977年,中国在西藏羊八井地热田建设了24兆瓦中高温地热发电站。经多年地质调研,证实拉萨地体是一条巨型构造-岩浆带,自西向东为:西部构造结—SN向平行的“裂谷”群(含羊八井地热田)—南迦巴瓦构造结—柬延至走滑逃逸构造的腾冲地体(腾冲高温地热田),组成了复杂地质背景构造格局,并分布有剧烈的中、新生代火山-岩浆活动,其成因是与印度板片撕裂、分段碰撞俯冲和地幔热柱上隆构造密切相关。羊八井地热田与新生代侵入岩有关,腾冲地热田与新生代火山岩有关,两者具有时空关联,均属新生代高温地热田。据地震层析资料,以及拉萨附近蛇绿岩型铬铁矿中发现金刚石和高温柯石英,足以阐明区内的矿产和两个高温地热田均属地幔热柱活动的产物,据此热源可能是来自深部的地幔楔,但在热流运移过程中,地壳熔融参与成分两地有所差异,这可从氦和锶同位素数据获得佐证。

The Tibetan Plateau is famous for its abundant high-temperature geothermal resources.In 1977,China successfully built a 24 MW medium-high temperature geothermal power station in the Yangbajing geothermal field in Tibet.After years of geological survey,it has been confirmed that the Lhasa Terrain is a giant tectonicmagma belt from the west to the east.The complex geological background tectonic framework is composed of the western syntaxis-“rift valley”group parallel to the South and North(including the Yangbajing geothermal field)-Namjagbarwa syntaxis-extending eastward to Tengchong Terrain with strike-slip and escape structure(Tengchong high-temperature geothermal field),where there are intense Mesozoic and Cenozoic volcanic-magmatic activities,which are caused by tearing of India plates,the sectional collision-subduction and the uplift structure of mantle plume in India.The Yangbajing geothermal field is related to Cenozoic granite intrusion,while the Tengchong geothermal field is closely related to Cenozoic volcano rock.Both of them have temporal and spatial associations and belong to the Cenozoic high-temperature geothermal fields.According to seismic tomography data and the discovery of diamond and high-temperature coesite in the ophiolite-type chromite ore near Lhasa,it is sufficient to clarify that the minerals and two high-temperature geothermal fields in the area are the products of the mantle plume activities.This heat source may be derived from the deep mantle wedge.However,during the process of heat flow migration,there are differences in the composition of crustal melting in the two places,which can be supported by helium and strontium isotope data.