Model Study Of Early Cretaceous Thermal Structure Of Lithosphere From Songliao Basin, NE China

As to the magma affair of Songliao Basin in the early Cretaceous, there exists one thing in common: the lithosphere did thin, no matter the delamination or basaltic magma intrusion. There is still some query about the delamination or basaltic magma intrusion in the Cretaceous period. The controversy is focus on thinning process of the lithosphere and extension of the Songliao basin. It is difficult to distinguish the two process. Today most of researchers use Ro to reckon the palaeo-heat flow, but limit in the sediment lay about 5 km because of the flaw of this method. If delamination or basaltic magma intrusion did exists, why Songliao Basin did not upheave just like the Tibet tableland, instead of the sedimentation from the Houshiling period to Yingcheng period. Moreover, Songliao Basin is always a high heat flow basin. All this lead to the fact that Songliao basin extends greatly in the early Cretaceous. Only because of this extension can keep the Songliao basin low altitude.In order to study the early Cretaceous thermal structure of lithosphere from Songliao Basin, I have to figure out the thickness of lithosphere in the early Cretaceous or the Jurassic. Lots granite of high Sr/Y shows that Da Hinggan Mountain and Songliao Basin were plateau. But in the early Cretaceous, there were thick sediment layer and alkaline granite in Songliao Basin implying extend environment. The intermediate-felsic volcanic rocks (Yingcheng period) origin at about 30km in the low crust basing on geothermobarometer but the basalt (Houshiling period) was come from more than 40-60km. The melt layer in the low crust made Songliao Basin very hot and soft,inclining to flow. That the thick of the melt layer is 5 km is considered to be rational.In the thesis, first I learn that there is not crust melt lay in the crust from the physical geography. Second is the lithosphere of thickness in early Cretaceous, which provide geologic boundary constriction for later model study. Then comes the ground temperature grads of Songliao basin, from the earth's surface to low lithosphere, which is figure out of both nowadays and the Cretaceous period basing on Ro. The heat flow we know today of the Cretaceous mostly comes from Ro. But not all the Ro can be owed to crust radioactive elements and mantle flow, especially in Northeast China. The melt layer of down crust may has great contribution to Ro. That is the reason of why the heat conduction equation is built and used to weigh up the heat flow of different thickness of melt layers. The result shows that: Houshiling period and Yingcheng period are born in different setting of lithosphere thickness. Most of Houshiling formation is basaltic, contrasting to granitic rock of Yingcheng period. In Houshiling period, the lithosphere was more than 60-70km of thickness and more than 45-50km crust thickness with 70 heat flow. But in Yingcheng period the lithosphere mantle thickness was 2-15km and the crust was 28km. If there is a 5-kilometre-thick intermediate-felsic melt magma layer, the ground temperature grads of Cretaceous would be 42-45 of upper crust, and down crust about 37, upper lithosphere mantle about 26. The Ro would mostly be 0.7-1.5, and heat flow is about 128, observably higher than today of 31 of ground temperature grads and 69 of heat flow. Last but not least, we make out the rough strength of lithosphere, it shows that the heat lithosphere is in dominant in the Cretaceous period and it is the two layer extension that keep surface of Songliao Basin low. 2/mmWkmC/0kmC/0kmC/0/mmWkmC/02/mmWIV...